[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 3588

AAA Working Group                                         Pat R. Calhoun
Internet-Draft                                      Black Storm Networks
Category: Standards Track                                  John Loughney
<draft-ietf-aaa-diameter-15.txt>                                   Nokia
                                                            Erik Guttman
                                                  Sun Microsystems, Inc.
                                                               Glen Zorn
                                                     Cisco Systems, Inc.
                                                              Jari Arkko
                                                                Ericsson
                                                            October 2002



                         Diameter Base Protocol



Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   Distribution of this memo is unlimited.

   Copyright   (C) The Internet Society 2002.  All Rights Reserved.









Calhoun et al.             expires April 2003                   [Page 1]


Internet-Draft                                              October 2002


Abstract

   The Diameter base protocol is intended to provide an AAA framework
   for applications such as network access or IP mobility. Diameter is
   also intended to work in both local AAA and roaming situations. This
   draft specifies the message format, transport, error reporting,
   accounting and security services to be used by all Diameter
   applications. The Diameter base application MUST be supported by all
   Diameter implementations.

Table of Contents

      1     Introduction
            1.1   Diameter Protocol
                  1.1.1 Description of the Document Set
            1.2   Approach to Extensibility
                  1.2.1 Defining New AVP Values
                  1.2.2 Creating New AVPs
                  1.2.3 Creating New Authentication Applications
                  1.2.4 Creating New Accounting Applications
                  1.2.5 Application Authentication Procedures
            1.3   Requirements Language
            1.4   Terminology

      2     Protocol Overview
            2.1   Transport
                  2.1.1 SCTP Guidelines
            2.2   Securing Diameter Messages
            2.3   Diameter Application Compliance
            2.4   Application Identifiers
            2.5   Connections vs. Sessions
            2.6   Peer Table
            2.7   Realm-Based Routing Table
            2.8   Role of Diameter Agents
                  2.8.1 Relay Agents
                  2.8.2 Proxy Agents
                  2.8.3 Redirect Agents
                  2.8.4 Translation Agents
            2.9   End-to-End Security Framework

      3     Diameter Header
            3.1   Command Codes
            3.2   Command Code ABNF specification
            3.3   Diameter Command Naming Conventions

      4     Diameter AVPs
            4.1   AVP Header
            4.2   Optional Header Elements



Calhoun et al.             expires April 2003                   [Page 2]


Internet-Draft                                              October 2002


            4.3   Basic AVP Data Formats
            4.4   Derived AVP Data Formats
            4.5   Grouped AVP Values
                  4.5.1 Example AVP with a Grouped Data Type
            4.6   Diameter Base Protocol AVPs

      5     Diameter Peers
            5.1   Peer Connections
            5.2   Diameter Peer Discovery
            5.3   Capabilities Exchange
                  5.3.1 Capabilities-Exchange-Request
                  5.3.2 Capabilities-Exchange-Answer
                  5.3.3 Vendor-Id AVP
                  5.3.4 Firmware-Revision AVP
                  5.3.5 Host-IP-Address AVP
                  5.3.6 Supported-Vendor-Id AVP
                  5.3.7 Product-Name AVP
            5.4   Disconnecting Peer Connections
                  5.4.1 Disconnect-Peer-Request
                  5.4.2 Disconnect-Peer-Answer
                  5.4.3 Disconnect-Cause AVP
            5.5   Transport Failure Detection
                  5.5.1 Device-Watchdog-Request
                  5.5.2 Device-Watchdog-Answer
                  5.5.3 Transport Failure Algorithm
                  5.5.4 Failover and Failback Procedures
            5.6   Peer State Machine
                  5.6.1 Incoming connections
                  5.6.2 Events
                  5.6.3 Actions
                  5.6.4 The Election Process

      6     Diameter Message Processing
            6.1   Diameter Request Routing Overview
                  6.1.1 Originating a Request
                  6.1.2 Sending a Request
                  6.1.3 Receiving Requests
                  6.1.4 Processing Local Requests
                  6.1.5 Request Forwarding
                  6.1.6 Request Routing
                  6.1.7 Redirecting Requests
                  6.1.8 Relaying and Proxying Requests
            6.2   Diameter Answer Processing
                  6.2.1 Processing Received Answers
                  6.2.2 Relaying and Proxying Answers
            6.3   Origin-Host AVP
            6.4   Origin-Realm AVP
            6.5   Destination-Host AVP



Calhoun et al.             expires April 2003                   [Page 3]


Internet-Draft                                              October 2002


            6.6   Destination-Realm AVP
            6.7   Routing AVPs
                  6.7.1 Route-Record AVP
                  6.7.2 Proxy-Info AVP
                  6.7.3 Proxy-Host AVP
                  6.7.4 Proxy-State AVP
            6.8   Auth-Application-Id AVP
            6.9   Acct-Application-Id AVP
                  6.10  Inband-Security-Id AVP
                  6.11  Vendor-Specific-Application-Id AVP
                  6.12  Redirect-Host AVP
                  6.13  Redirect-Host-Usage AVP
                  6.14  Redirect-Max-Cache-Time AVP
                  6.15  E2E-Sequence AVP

      7     Error Handling
            7.1   Result-Code AVP
                  7.1.1 Informational
                  7.1.2 Success
                  7.1.3 Protocol Errors
                  7.1.4 Transient Failures
                  7.1.5 Permanent Failures
            7.2   Error Bit
            7.3   Error-Message AVP
            7.4   Error-Reporting-Host AVP
            7.5   Failed-AVP AVP
            7.6   Experimental-Result AVP
            7.7   Experimental-Result-Code AVP

      8     Diameter User Sessions
            8.1   Authorization Session State Machine
            8.2   Accounting Session State Machine
            8.3   Server-Initiated Re-Auth
                  8.3.1 Re-Auth-Request
                  8.3.2 Re-Auth-Answer
            8.4   Session Termination
                  8.4.1 Session-Termination-Request
                  8.4.2 Session-Termination-Answer
            8.5   Aborting a Session
                  8.5.1 Abort-Session-Request
                  8.5.2 Abort-Session-Answer
            8.6   Inferring Session Termination from Origin-State-Id
            8.7   Auth-Request-Type AVP
            8.8   Session-Id AVP
            8.9   Authorization-Lifetime AVP
            8.10  Auth-Grace-Period AVP
            8.11  Auth-Session-State AVP
            8.12  Re-Auth-Request-Type AVP



Calhoun et al.             expires April 2003                   [Page 4]


Internet-Draft                                              October 2002


            8.13  Session-Timeout AVP
            8.14  User-Name AVP
            8.15  Termination-Cause AVP
            8.16  Origin-State-Id AVP
            8.17  Session-Binding AVP
            8.18  Session-Server-Failover AVP
            8.19  Multi-Round-Time-Out AVP
            8.20  Class AVP
            8.21  Event-Timestamp AVP

      9     Accounting
            9.1   Server Directed Model
            9.2   Protocol Messages
            9.3   Application Document Requirements
            9.4   Fault Resilience
            9.5   Accounting Records
            9.6   Correlation of Accounting Records
            9.7   Accounting Command-Codes
                  9.7.1 Accounting-Request
                  9.7.2 Accounting-Answer
            9.8 Accounting AVPs
                  9.8.1 Accounting-Record-Type AVP
                  9.8.2 Acct-Interim-Interval AVP
                  9.8.3 Accounting-Record-Number AVP
                  9.8.4 Accounting-RADIUS-Session-Id AVP
                  9.8.5 Acct-Multi-Session-Id AVP
                  9.8.6 Accounting-Sub-Session-Id AVP
                  9.8.7 Accounting-Realtime-Required AVP

      10      AVP Occurrence Table
            10.1    Base Protocol Command AVP Table
            10.2    Accounting AVP Table

      11      IANA Considerations
            11.1    AVP Header
                  11.1.1  AVP Code
                  11.1.2  AVP Flags
            11.2    Diameter Header
                  11.2.1  Command Codes
                  11.2.2  Command Flags
            11.3    Application Identifiers
            11.4   AVP Values
                  11.4.1  Result-Code AVP Values
                  11.4.2  Accounting-Record-Type AVP Values
                  11.4.3  Termination-Cause AVP Values
                  11.4.4  Redirect-Host-Usage AVP Values
                  11.4.5  Session-Server-Failover AVP Values
                  11.4.6  Session-Binding AVP Values



Calhoun et al.             expires April 2003                   [Page 5]


Internet-Draft                                              October 2002


                  11.4.7  Disconnect-Cause AVP Values
                  11.4.8  Auth-Request-Type AVP Values
                  11.4.9  Auth-Session-State AVP Values
                  11.4.10 Re-Auth-Request-Type AVP Values
            11.5    Diameter TCP/SCTP Port Numbers
            11.6    NAPTR Service Fields
            11.7    Accounting-Realtime-Required AVP Values

      12      Diameter Protocol Related Configurable Parameters

      13      Security Considerations
            13.1    IPsec Usage
            13.2    TLS Usage
            13.3    Peer-to-Peer Considerations

      14      References
            14.1    Normative
            14.2    Non-Normative

      15      Acknowledgements

      16      Authors' Addresses

      17      Full Copyright Statement

      18      Expiration Date

      Appendix A.  Diameter Service Template

      Appendix B.  NAPTR Example

      Appendix C.  Duplicate Detection



















Calhoun et al.             expires April 2003                   [Page 6]


Internet-Draft                                              October 2002


1  Introduction

   Authentication, Authorization and Accounting (AAA) protocols such as
   TACACS [TACACS] and RADIUS [RADIUS] were initially deployed to
   provide dial-up PPP [PPP] and terminal server access. Over time, with
   the growth of the Internet and the introduction of new access
   technologies, including wireless, DSL, Mobile IP and Ethernet,
   routers and network access servers (NAS) have increased in complexity
   and density, putting new demands on AAA protocols.

   Network access requirements for AAA protocols are summarized in
   [AAAREQ]. These include:

      Failover. [RADIUS] does not define failover mechanisms, and as a
      result, failover behavior differs between implementations. In
      order to provide well defined failover behavior, Diameter supports
      application-layer acknowledgements, and defines failover
      algorithms and the associated state machine. This is described in
      Section 5.5 and [AAATRANS].

      Transmission-level security. [RADIUS] defines an application-layer
      authentication and integrity scheme that is required only for use
      with Response packets. While [RADEXT] defines an additional
      authentication and integrity mechanism, use is only required
      during Extensible Authentication Protocol (EAP) sessions. While
      attribute-hiding is supported, [RADIUS] does not provide support
      for per-packet confidentiality. In accounting, [RADACCT] assumes
      that replay protection is provided by the backend billing server,
      rather than within the protocol itself.

      While [RFC3162] defines the use of IPsec with RADIUS, support for
      IPsec is not required. Since within [IKE] authentication occurs
      only within Phase 1 prior to the establishment of IPsec SAs in
      Phase 2, it is typically not possible to define separate trust or
      authorization schemes for each application. This limits the
      usefulness of IPsec in inter-domain AAA applications (such as
      roaming) where it may be desirable to define a distinct
      certificate hierarchy for use in a AAA deployment. In order to
      provide universal support for transmission-level security, and
      enable both intra- and inter-domain AAA deployments, IPsec support
      is mandatory in Diameter, and TLS support is optional. Security is
      discussed in Section 13.

      Reliable transport. RADIUS runs over UDP, and does not define
      retransmission behavior; as a result, reliability varies between
      implementations. As described in [ACCMGMT], this is a major issue
      in accounting, where packet loss may translate directly into
      revenue loss. In order to provide well defined transport behavior,



Calhoun et al.             expires April 2003                   [Page 7]


Internet-Draft                                              October 2002


      Diameter runs over reliable transport mechanisms (TCP, SCTP) as
      defined in [AAATRANS].

      Agent support. [RADIUS] does not provide for explicit support for
      agents, including Proxies, Redirects and Relays. Since the
      expected behavior is not defined, it varies between
      implementations. Diameter defines agent behavior explicitly; this
      is described in Section 2.8.

      Server-initiated messages. While RADIUS server-initiated messages
      are defined in [DYNAUTH], support is optional. This makes it
      difficult to implement features such as unsolicited disconnect or
      reauthentication/reauthorization on demand across a heterogeneous
      deployment. Support for server-initiated messages is mandatory in
      Diameter, and is described in Section 8.

      Auditability. RADIUS does not define data-object security
      mechanisms, and as a result, untrusted proxies may modify
      attributes or even packet headers without being detected. Combined
      with lack of support for capabilities negotiation, this makes it
      very difficult to determine what occurred in the event of a
      dispute. While implementation of data object security is not
      mandatory within Diameter, these capabilities are supported, and
      are described in [AAACMS].

      Transition support. While Diameter does not share a common
      protocol data unit (PDU) with RADIUS, considerable effort has been
      expended in enabling backward compatibility with RADIUS, so that
      the two protocols may be deployed in the same network. Initially,
      it is expected that Diameter will be deployed within new network
      devices, as well as within gateways enabling communication between
      legacy RADIUS devices and s. This capability, described in
      [NASREQ], enables Diameter support to be added to legacy networks,
      by addition of a gateway or server speaking both RADIUS and
      Diameter.

   In addition to addressing the above requirements, Diameter also
   provides support for the following:

      Capability negotiation. RADIUS does not support error messages,
      capability negotiation, or a mandatory/non-mandatory flag for
      attributes. Since RADIUS clients and servers are not aware of each
      other's capabilities, they may not be able to successfully
      negotiate a mutually acceptable service, or in some cases, even be
      aware of what service has been implemented. Diameter includes
      support for error handling (section 7), capability negotiation
      (section 5.3), and mandatory/non-mandatory attribute-value pairs
      (AVPs) (Section 4.1).



Calhoun et al.             expires April 2003                   [Page 8]


Internet-Draft                                              October 2002


      Peer discovery and configuration. RADIUS implementations typically
      require that the name or address of servers or clients be manually
      configured, along with the corresponding shared secrets. This
      results in a large administrative burden, and creates the
      temptation to reuse the RADIUS shared secret, which can result in
      major security vulnerabilities if the Request Authenticator is not
      globally and temporally unique as required in [RADIUS]. Through
      DNS, Diameter enables dynamic discovery of peers. Derivation of
      dynamic session keys is enabled via transmission-level security.

      Roaming support. The ROAMOPS WG provided a survey of roaming
      implementations [ROAMREV], detailed roaming requirements
      [ROAMCRIT], defined the Network Access Identifier (NAI) [NAI], and
      documented existing implementations (and imitations) of RADIUS-
      based roaming [PROXYCHAIN]. In order to improve scalability,
      [PROXYCHAIN] introduced the concept of proxy chaining via an
      intermediate server, facilitating roaming between providers.
      However, since RADIUS does not provide explicit support for
      proxies, and lacks auditability and transmission-level security
      features, RADIUS-based roaming is vulnerable to attack from
      external parties as well as susceptible to fraud perpetrated by
      the roaming partners themselves. As a result, it is not suitable
      for wide-scale deployment on the Internet [PROXYCHAIN]. By
      providing explicit support for inter-domain roaming and message
      routing (Sections 2.7 and 6), auditability [AAACMS], and
      transmission-layer security (Section 13) features, Diameter
      addresses these limitations and provides for secure and scalable
      roaming.

   In the decade since AAA protocols were first introduced, the
   capabilities of Network Access Server (NAS) devices have increased
   substantially. As a result, while Diameter is a considerably more
   sophisticated protocol than RADIUS, it remains feasible to implement
   within embedded devices, given improvements in processor speeds and
   the widespread availability of embedded IPsec and TLS
   implementations.

1.1  Diameter Protocol

   The Diameter base protocol provides the following facilities:

      - Delivery of AVPs (attribute value pairs)
      - Capabilities negotiation
      - Error notification
      - Extensibility, through addition of new commands and AVPs
        (required in [AAAREQ]).
      - Basic services necessary for applications, such as handling of
        user sessions or accounting



Calhoun et al.             expires April 2003                   [Page 9]


Internet-Draft                                              October 2002


   All data delivered by the protocol is in the form of an AVP. Some of
   these AVP values are used by the Diameter protocol itself, while
   others deliver data associated with particular applications that
   employ Diameter. AVPs may be added arbitrarily to Diameter messages,
   so long as the required AVPs are included and AVPs that are
   explicitly excluded are not included. AVPs are used by the base
   Diameter protocol to support the following required features:

      - Transporting of user authentication information, for the
        purposes of enabling the Diameter server to authenticate the
        user.
      - Transporting of service specific authorization information,
        between client and servers, allowing the peers to decide whether
        a user's access request should be granted.
      - Exchanging resource usage information, which MAY be used for
        accounting purposes, capacity planning, etc.
      - Relaying, proxying and redirecting of Diameter messages through
        a server hierarchy.

   The Diameter base protocol provides the minimum requirements needed
   for a AAA protocol, as required by [AAAREQ]. The base protocol may be
   used by itself for accounting purposes only, or it may be used with a
   Diameter application, such as Mobile IP [DIAMMIP], or network access
   [NASREQ]. It is also possible for the base protocol to be extended
   for use in new applications, via the addition of new commands or
   AVPs. At this time the focus of Diameter is network access and
   accounting applications. A truly generic AAA protocol used by many
   applications might provide functionality not provided by Diameter.
   Therefore, it is imperative that the designers of new applications
   understand their requirements before using Diameter. See section 2.4
   for more information on Diameter applications.

   Any node can initiate a request. In that sense, Diameter is a peer-
   to-peer protocol. In this document, a Diameter Client is a device at
   the edge of the network that performs access control, such as a
   Network Access Server (NAS) or a Foreign Agent (FA). A Diameter
   client generates Diameter messages to request authentication,
   authorization, and accounting services for the user. A Diameter agent
   is a node that does not authenticate and/or authorize messages
   locally; agents include proxies, redirects and relay agents. A
   Diameter server performs authentication and/or authorization of the
   user. A Diameter node MAY act as an agent for certain requests while
   acting as a server for others.

   The Diameter protocol also supports server-initiated messages, such
   as a request to abort service to a particular user.

1.1.1  Description of the Document Set



Calhoun et al.             expires April 2003                  [Page 10]


Internet-Draft                                              October 2002


   Currently, the Diameter specification consists of a base
   specification (this document), Transport Profile [AAATRANS] and
   applications: Mobile IPv4 [DIAMMIP], and NASREQ [NASREQ].

   The Transport Profile document [AAATRANS] discusses transport layer
   issues that arise with AAA protocols and recommendations on how to
   overcome these issues. This document also defines the Diameter
   failover algorithm and state machine.

   The Mobile IPv4 [DIAMMIP] application defines a Diameter application
   that allows a Diameter server to perform AAA functions for Mobile
   IPv4 services to a mobile node.

   The NASREQ [NASREQ] application defines a Diameter Application that
   allows a Diameter server to be used in a PPP/SLIP Dial-Up and
   Terminal Server Access environment. Consideration was given for
   servers that need to perform protocol conversion between Diameter and
   RADIUS.

   In summary, this document defines the base protocol specification for
   AAA, which includes support for accounting. The MIPv4 and the NASREQ
   documents describe applications that use this base specification for
   Authentication, Authorization and Accounting.

1.2  Approach to Extensibility

   The Diameter protocol is designed to be extensible, using several
   mechanisms, including:

      - Defining new AVP values.
      - Creating new AVPs
      - Creating new authentication/authorization applications
      - Creating new accounting applications
      - Application authentication procedures

   Reuse of existing AVP values, AVPs, applications are strongly
   recommended. Reuse simplifies standardization and implementation and
   avoids potential interoperability issues. It is expected that command
   codes are reused; new command codes can only be created by IETF
   Consensus (see section 11.2.1).

1.2.1  Defining New AVP Values

   New applications should attempt to reuse AVPs defined in existing
   applications when possible, as opposed to creating new AVPs. For AVPs
   of type Enumerated, an application may require a new value to
   communicate some service-specific information.




Calhoun et al.             expires April 2003                  [Page 11]


Internet-Draft                                              October 2002


   In order to allocate a new AVP value, a request MUST be sent to IANA
   [IANA], along with an explanation of the new AVP value. IANA
   considerations for Diameter are discussed in Section 11.

1.2.2  Creating New AVPs

   When no existing AVP can be used, a new AVP should be created. The
   new AVP being defined MUST use one of the data types listed in
   section 4.3.

   In the event that a logical grouping of AVPs is necessary, and
   multiple "groups" are possible in a given command, it is recommended
   that a Grouped AVP be used (see Section 4.5).

   In order to create a new AVP, a request MUST be sent to IANA, with a
   specification for the AVP. The request MUST include the commands that
   would make use of the AVP.

1.2.3  Creating New Authentication Applications

   Every Diameter application specification MUST have an IANA assigned
   Application Identifier (see section 2.4) or a vendor specific
   Application Identifier.

   Should a new Diameter usage scenario find itself unable to fit within
   an existing application without requiring major changes to the
   specification, it may be desirable to create a new Diameter
   application. Major changes to an application include:

      - Adding new AVPs to the command, which have the "M" bit set.
      - Requiring a command that has a different number of round trips
        to satisfy a request (e.g. application foo has a command that
        requires one round trip, but new application bar has a command
        that requires two round trips to complete).
      - Adding support for an authentication method requiring definition
        of new AVPs for use with the application. Since a new EAP
        authentication method can be supported within Diameter without
        requiring new AVPs, addition of EAP methods does not require the
        creation of a new authentication application.

   Creation of a new application should be viewed as a last resort. An
   implementation MAY add arbitrary non-mandatory AVPs to any command
   defined in an application, including vendor-specific AVPs without
   needing to define a new application. Please refer to section 11.1.1
   for details.

   In order to justify allocation of a new application identifier,
   Diameter applications MUST define one Command Code, or add new



Calhoun et al.             expires April 2003                  [Page 12]


Internet-Draft                                              October 2002


   mandatory AVPs to the ABNF.

   The expected AVPs MUST be defined in an ABNF [ABNF] grammar (see
   section 3.2). If the Diameter application has accounting
   requirements, it MUST also specify the AVPs that are to be present in
   the Diameter Accounting messages (see section 9.3). However, just
   because a new authentication application id is required, does not
   imply that a new accounting application id is required.

   When possible, a new Diameter application SHOULD reuse existing
   Diameter AVPs, in order to avoid defining multiple AVPs that carry
   similar information.

1.2.4  Creating New Accounting Applications

   There are services that only require Diameter accounting. Such
   services need to define the AVPs carried in the ACR/ACA messages, but
   do not need to define new command codes. An implementation MAY add
   arbitrary non-mandatory AVPs (AVPs with the "M" bit not set) to any
   command defined in an application, including vendor-specific AVPs,
   without needing to define a new accounting application. Please refer
   to section 11.1.1 for details.

   Application Identifiers are still required for Diameter capability
   exchange. Every Diameter accounting application specification MUST
   have an IANA assigned Application Identifier (see section 2.4) or a
   vendor specific Application Identifier.

   Since every Diameter implementation MUST support accounting, there is
   no need to advertise support for the Base accounting application
   within the CER/CEA, since this is implicit. This basic accounting
   support is sufficient to handle any application that uses the ACR/ACA
   commands defined in this document, as long as no new mandatory AVPs
   are added. A mandatory AVP is defined as one which has the "M" bit
   set when sent within an accounting command, regardless of whether it
   is required or optional within the ABNF for the accounting
   application.

   The creation of a new accounting application should be viewed as a
   last resort and MUST NOT be used unless a new command or additional
   mechanisms (e.g. application defined state machine) is defined within
   the application, or new mandatory AVPs are added to the ABNF.

   Within an accounting command, setting the "M" bit implies that a
   backend server (e.g. billing server) or the accounting server itself
   MUST understand the AVP in order to compute a correct bill. If the
   AVP is not relevant to the billing process, when the AVP is included
   within an accounting command, it MUST NOT have the "M" bit set, even



Calhoun et al.             expires April 2003                  [Page 13]


Internet-Draft                                              October 2002


   if the "M" bit is set when the same AVP is used within other Diameter
   commands (i.e. authentication/authorization commands).

   A DIAMETER base accounting implementation MUST be configurable to
   advertise supported accounting applications in order to prevent the
   accounting server from accepting accounting requests for unbillable
   services. The combination of the home domain and the accounting
   application Id can be used in order to route the request to the
   appropriate accounting server.

   When possible, a new Diameter accounting application SHOULD attempt
   to reuse existing AVPs, in order to avoid defining multiple AVPs that
   carry similar information.

   If the base accounting is used without any mandatory AVPs, new
   commands or additional mechanisms (e.g. application defined state
   machine), then the base protocol defined standard accounting
   application Id (section 2.4) MUST be used in ACR/ACA commands.

1.2.5  Application Authentication Procedures

   When possible, applications SHOULD be designed such that new
   authentication methods MAY be added without requiring changes to the
   application. This MAY require that new AVP values be assigned to
   represent the new authentication transform, or any other scheme that
   produces similar results. When possible, authentication frameworks,
   such as Extensible Authentication Protocol [EAP], SHOULD be used.

1.3  Requirements Language

   In this document, the key words "MAY", "MUST", "MUST NOT",
   "OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be
   interpreted as described in [KEYWORDS].


1.4  Terminology


   AAA
      Authentication, Authorization and Accounting.

   Accounting
      The act of collecting information on resource usage for the
      purpose of capacity planning, auditing, billing or cost
      allocation.

   Accounting Record
      A session record represents a summary of the resource consumption



Calhoun et al.             expires April 2003                  [Page 14]


Internet-Draft                                              October 2002


      of a user over the entire session. Accounting servers creating the
      session record may do so by processing interim accounting events
      or accounting events from several devices serving the same user.

   Authentication
      The act of verifying the identity of an entity (subject).

   Authorization
      The act of determining whether a requesting entity (subject) will
      be allowed access to a resource (object).

   AVP
      The Diameter protocol consists of a header followed by one or more
      Attribute-Value-Pairs (AVPs). An AVP includes a header and is used
      to encapsulate protocol-specific data (e.g. routing information)
      as well as authentication, authorization or accounting
      information.

   Broker
      A broker is a business term commonly used in AAA infrastructures.
      A broker is either a relay, proxy or redirect agent, and MAY be
      operated by roaming consortiums. Depending on the business model,
      a broker may either choose to  deploy relay agents or proxy
      agents.

   Diameter Agent
      A Diameter Agent is a Diameter node that provides either relay,
      proxy, redirect or translation services.

   Diameter Client
      A Diameter Client is a device at the edge of the network that
      performs access control. An example of a Diameter client is a
      Network Access Server (NAS) or a Foreign Agent (FA).

   Diameter Node
      A Diameter node is a host process that implements the Diameter
      protocol, and acts either as a Client, Agent or Server.

   Diameter Peer
      A Diameter Peer is a Diameter Node to which a given Diameter Node
      has a direct transport connection.

   Diameter Security Exchange
      A Diameter Security Exchange is a process through which two
      Diameter nodes establish end-to-end security.

   Diameter Server
      A Diameter Server is one that handles authentication,



Calhoun et al.             expires April 2003                  [Page 15]


Internet-Draft                                              October 2002


      authorization and accounting requests for a particular realm. By
      its very nature, a Diameter Server MUST support Diameter
      applications in addition to the base protocol.

   Downstream
      Downstream is used to identify the direction of a particular
      Diameter message from the home server towards the access device.

   End-to-End Security
      TLS and IPsec provide hop-by-hop security, or security across a
      transport connection. When relays or proxy are involved, this hop-
      by-hop security does not protect the entire Diameter user session.
      End-to-end security is security across a Diameter session.

   Home Realm
      A Home Realm is the administrative domain with which the user
      maintains an account relationship.

   Home Server
      See Diameter Server.

   Interim accounting
      An interim accounting message provides a snapshot of usage during
      a user's session. It is typically implemented in order to provide
      for partial accounting of a user's session in the case of a device
      reboot or other network problem prevents the reception of a
      session summary message or session record.

   Local Realm
      A local realm is the administrative domain providing services to a
      user. An administrative domain MAY act as a local realm for
      certain users, while being a home realm for others.

   Multi-session
      A multi-session represents a logical linking of several sessions.
      Multi-sessions are tracked by using the Acct-Multi-Session-Id. An
      example of a multi-session would be a Multi-link PPP bundle. Each
      leg of the bundle would be a session while the entire bundle would
      be a multi-session.

   Network Access Identifier
      The Network Access Identifier, or NAI [NAI], is used in the
      Diameter protocol to extract a user's identity and realm. The
      identity is used to identify the user during authentication and/or
      authorization, while the realm is used for message routing
      purposes.

   Proxy Agent or Proxy



Calhoun et al.             expires April 2003                  [Page 16]


Internet-Draft                                              October 2002


      In addition to forwarding requests and responses, proxies make
      policy decisions relating to resource usage and provisioning. This
      is typically accomplished by tracking the state of NAS devices.
      While proxies typically do not respond to client Requests prior to
      receiving a Response from the server, they may originate Reject
      messages in cases where policies are violated. As a result,
      proxies need to understand the semantics of the messages passing
      through them, and may not support all Diameter applications.

   Realm
      The string in the NAI that immediately follows the '@' character.
      NAI realm names are required to be unique, and are piggybacked on
      the administration of the DNS namespace. Diameter makes use of the
      realm, also loosely referred to as domain, to determine whether
      messages can be satisfied locally, or whether they must be routed
      or redirected.  In RADIUS, realm names are not necessarily
      piggybacked on the DNS namespace but may be independent of it.

   Real-time Accounting
      Real-time accounting involves the processing of information on
      resource usage within a defined time window. Time constraints are
      typically imposed in order to limit financial risk.

   Relay Agent or Relay
      Relays forward requests and responses based on routing-related
      AVPs and realm routing table entries. Since relays do not make
      policy decisions, they do not examine or alter non-routing AVPs.
      As a result, relays never originate messages, do not need to
      understand the semantics of messages or non-routing AVPs, and are
      capable of handling any Diameter application or message type.
      Since relays make decisions based on information in routing AVPs
      and realm forwarding tables they do not keep state on NAS resource
      usage or sessions in progress.

   Redirect Agent
      Rather than forwarding requests and responses between clients and
      servers, redirect agents refer clients to servers and allow them
      to communicate directly. Since redirect agents do not sit in the
      forwarding path, they do not alter any AVPs transiting between
      client and server. Redirect agents do not originate messages and
      are capable of handling any message type, although they may be
      configured only to redirect messages of certain types, while
      acting as relay or proxy agents for other types.  As with proxy
      agents, redirect agents do not keep state with respect to sessions
      or NAS resources.

   Roaming Relationships
      Roaming relationships include relationships between companies and



Calhoun et al.             expires April 2003                  [Page 17]


Internet-Draft                                              October 2002


      ISPs, relationships among peer ISPs within a roaming consortium,
      and relationships between an ISP and a roaming consortium.

   Security Association
      A security association is an association between two endpoints in
      a Diameter session which allows the endpoints to communicate with
      integrity and confidentially, even in the presense of relays
      and/or proxies.

   Session
      A session is a related progression of events devoted to a
      particular activity. Each application SHOULD provide guidelines as
      to when a session begins and ends. All Diameter packets with the
      same Session-Identifier are considered to be part of the same
      session.

   Session state

      A stateful agent is one that maintains session state information,
      by keeping track of all authorized active sessions. Each
      authorized session is bound to a particular service, and its state
      is considered active either until it is notified otherwise, or by
      expiration.

   Sub-session
      A sub-session represents a distinct service (e.g. QoS or data
      characteristics) provided to a given session.  These services may
      happen concurrently (e.g. simultaneous voice and data transfer
      during the same session) or serially. These changes in sessions
      are tracked with the Accounting-Sub-Session-Id.

   Transaction state

      The Diameter protocol requires that agents maintain transaction
      state, which is used for failover purposes. Transaction state
      implies that upon forwarding a request, the Hop-by-Hop identifier
      is saved; the field is replaced with a locally unique identifier,
      which is restored to its original value when the corresponding
      answer is received. The request's state is released upon receipt
      of the answer. A stateless agent is one that only maintains
      transaction state.

   Translation Agent
      A translation agent is a stateful Diameter node that performs
      protocol translation between Diameter and another AAA protocol,
      such as RADIUS.

   Tranport Connection



Calhoun et al.             expires April 2003                  [Page 18]


Internet-Draft                                              October 2002


      A transport connection is a TCP or SCTP connection existing
      directy between two Diameter peers, otherwise known as a Peer-to-
      Peer Connection.

   Upstream
      Upstream is used to identify the direction of a particular
      Diameter message from the access device towards the home server.


2  Protocol Overview

   The base Diameter protocol may be used by itself for accounting
   applications, but for use in authentication and authorization it is
   always extended for a particular application.  Two Diameter
   applications are defined by companion documents:  NASREQ [NASREQ],
   Mobile IP [DIAMMIP]. These applications are introduced in this
   document but specified elsewhere.  Additional Diameter applications
   MAY be defined in the future (see Section 11.3).

   Diameter Clients MUST support the base protocol, which includes
   accounting.  In addition, they MUST fully support each Diameter
   application that is needed to implement the client's service, e.g.
   NASREQ and/or Mobile IP. A Diameter Client that does not support both
   NASREQ and Mobile IP, MUST be referred to as "Diameter X Client"
   where X is the application which it supports, and not a "Diameter
   Client."

   Diameter Servers MUST support the base protocol, which includes
   accounting. In addition, they MUST fully support each Diameter
   application that is needed to implement the intended service, e.g.
   NASREQ and/or Mobile IP. A Diameter Server that does not support both
   NASREQ and Mobile IP, MUST be referred to as "Diameter X Server"
   where X is the application which it supports, and not a "Diameter
   Server."

   Diameter Relays and Redirect agents are, by definition, protocol
   transparent, and MUST transparently support the Diameter base
   protocol, which includes accounting, and all Diameter applications.

   Diameter Proxies MUST support the base protocol, which includes
   accounting.  In addition, they MUST fully support each Diameter
   application that is needed to implement proxied services, e.g. NASREQ
   and/or Mobile IP. A Diameter Proxy which does not support also both
   NASREQ and Mobile IP, MUST be referred to as "Diameter X Proxy" where
   X is the application which it supports, and not a "Diameter Proxy."

   The base Diameter protocol concerns itself with capabilities
   negotiation, how messages are sent and how peers may eventually be



Calhoun et al.             expires April 2003                  [Page 19]


Internet-Draft                                              October 2002


   abandoned.  The base protocol also defines certain rules that apply
   to all exchanges of messages between Diameter nodes.

   Communication between Diameter peers begins with one peer sending a
   message to another Diameter peer. The set of AVPs included in the
   message is determined by a particular Diameter application. One AVP
   that is included to reference a user's session is the Session-Id.

   The initial request for authentication and/or authorization of a user
   would include the Session-Id. The Session-Id is then used in all
   subsequent messages to identify the user's session (see section 8 for
   more information). The communicating party may accept the request, or
   reject it by returning an answer message with the Result-Code AVP set
   to indicate an error occurred. The specific behavior of the Diameter
   server or client receiving a request depends on the Diameter
   application employed.

   Session state (associated with a Session-Id) MUST be freed upon
   receipt of the Session-Termination-Request, Session-Termination-
   Answer, expiration of authorized service time in the Session-Timeout
   AVP, and according to rules established in a particular Diameter
   application.


2.1  Transport

   Transport profileis defined in [AAATRANS].

   The base Diameter protocol is run on port TBD of both TCP [TCP] and
   SCTP [SCTP] transport protocols (for interoperability test purposes
   port 1812 will be used until IANA assigns a port to the protocol).

   Diameter clients MUST support either TCP or SCTP, while agents and
   servers MUST support both. Future versions of this specification MAY
   mandate that clients support SCTP.

   A Diameter node MAY initiate connections from a source port other
   than the one that it declares it accepts incoming connections on, and
   MUST be prepared to receive connections on port TBD. A given Diameter
   instance of the peer state machine MUST NOT use more than one
   transport connection to communicate with a given peer, unless
   multiple instances exist on the peer in which case a separate
   connection per process is allowed.

   When no transport connection exists with a peer, an attempt to
   connect SHOULD be periodically attempted. This behavior is handled
   via the Tc timer, whose recommended value is 30 seconds. There are
   certain exceptions to this rule, such as when a peer has terminated



Calhoun et al.             expires April 2003                  [Page 20]


Internet-Draft                                              October 2002


   the transport connection stating that it does not wish to
   communicate.

   When connecting to a peer and either zero or more transports are
   specified, SCTP SHOULD be tried first, followed by TCP. See section
   5.2 for more information on peer discovery.

   Diameter implementations SHOULD be able to interpret ICMP protocol
   port unreachable messages as explicit indications that the server is
   not reachable, subject to security policy on trusting such messages.
   Diameter implementations SHOULD also be able to interpret
   ECONNREFUSED (a reset from the transport) and timed-out connection
   attempts.

   If Diameter receives data up from TCP that cannot be parsed or
   identified as a Diameter error made by the peer, the stream is
   compromised and cannot be recovered.  The transport connection MUST
   be closed using a RESET call (graceful closure is also compromised).


2.1.1  SCTP Guidelines

   The following are guidelines for Diameter implementations that
   support SCTP:

      1. For interoperability: All Diameter nodes MUST be prepared to
         receive Diameter messages on any SCTP stream in the
         association.
      2. To prevent blocking: All Diameter nodes SHOULD utilize all SCTP
         streams available to the association to prevent head-of-the-
         line blocking.


2.2  Securing Diameter Messages

   Diameter clients, such as Network Access Servers (NASes) and Mobility
   Agents MUST support IP Security [SECARCH], and MAY support TLS [TLS].
   Diameter servers MUST support TLS and IPsec. The Diameter protocol
   MUST NOT be used without any security mechanism (TLS or IPsec).

   It is suggested that IPsec can be used primarily at the edges and in
   intra-domain traffic, such as using pre-shared keys between a NAS a
   local AAA proxy. This also eases the requirements on the NAS to
   support certificates. It is also suggested that inter-domain traffic
   would primarily use TLS. See sections 13.1 and 13.2 for more details
   on IPsec and TLS usage.





Calhoun et al.             expires April 2003                  [Page 21]


Internet-Draft                                              October 2002


2.3  Diameter Application Compliance

   Application Identifiers are advertised during the capabilities
   exchange phase (see section 5.3). For a given application,
   advertising support of an application implies that the sender
   supports all command codes, and the AVPs specified in the associated
   ABNFs, described in the specification.

   An implementation MAY add arbitrary non-mandatory AVPs to any command
   defined in an application, including vendor-specific AVPs. Please
   refer to section 11.1.1 for details.


2.4  Application Identifiers

   Each Diameter application MUST have an IANA assigned Application
   Identifier (see section 11.3). The base protocol does not require an
   Application Identifier since its support is mandatory. During the
   capabilities exchange, Diameter nodes inform their peers of locally
   supported applications. Furthermore, all Diameter messages contain an
   Application Identifier, which is used in the message forwarding
   process.

   The following Application Identifier values are defined:

      NASREQ                        1 [NASREQ]
      Mobile-IP                     4 [DIAMMIP]
      Diameter Base Accounting      5
      Relay                         0xffffffff

   Relay and redirect agents MUST advertise the Relay Application
   Identifier, while all other Diameter nodes MUST advertise locally
   supported applications. The receiver of a Capabilities Exchange
   message advertising Relay service MUST assume that the sender
   supports all current and future applications.

   Diameter relay and proxy agents are responsible for finding an
   upstream server that supports the application of a particular
   message. If none can be found, an error message is returned with the
   Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER.


2.5  Connections vs. Sessions

   This section attempts to provide the reader with an understanding of
   the difference between connection and session, which are terms used
   extensively throughout this document.




Calhoun et al.             expires April 2003                  [Page 22]


Internet-Draft                                              October 2002


   A connection is a transport level connection between two peers, used
   to send and receive Diameter messages. A session is a logical concept
   at the application layer, and is shared between an access device and
   a server, and is identified via the Session-Id AVP

     +--------+          +-------+          +--------+
     | Client |          | Relay |          | Server |
     +--------+          +-------+          +--------+
              <---------->       <---------->
           peer connection A   peer connection B

              <----------------------------->
                      User session x
                Figure 1: Diameter connections and sessions

   In the example provided in Figure 1, peer connection A is established
   between the Client and its local Relay. Peer connection B is
   established between the Relay and the Server. User session X spans
   from the Client via the Relay to the Server. Each "user" of a service
   causes an auth request to be sent, with a unique session identifier.
   Once accepted by the server, both the client and the server are aware
   of the session. It is important to note that there is no relationship
   between a connection and a session, and that Diameter messages for
   multiple sessions are all multiplexed through a single connection.


2.6  Peer Table

   The Diameter Peer Table is used in message forwarding, and referenced
   by the Realm Routing Table. A Peer Table entry contains the following
   fields:

      - Host identity. Following the conventions described for the
        DiameterIdentity derived AVP data format in section 4.4. This
        field contains the contents of the Origin-Host AVP found in the
        CER or CEA message.
      - Status. This is the state of the peer entry, and MUST match one
        of the values listed in section 5.6.
      - Static or Dynamic. Specifies whether a peer entry was statically
        configured, or dynamically discovered.
      - Expiration time. Specifies the time at which dynamically
        discovered peer table entries are to be either refreshed, or
        expired.
      - TLS Enabled. Specifies whether TLS is to be used when
        communicating with the peer.
      - Additional security information, when needed (e.g. keys,
        certificates)




Calhoun et al.             expires April 2003                  [Page 23]


Internet-Draft                                              October 2002


2.7  Realm-Based Routing Table

   All Realm-Based routing lookups are performed against what is
   commonly known as the Realm Routing Table (see section 12). A Realm
   Routing Table Entry contains the following fields:

      - Realm Name. This is the field that is typically used as a
        primary key in the routing table lookups. Note that some
        implementations perform their lookups based on longest-match-
        from-the-right on the realm rather than requiring an exact
        match.
      - Application Identifier. An application is identified by a vendor
        id and an application id. For all IETF standards track Diameter
        applications, the vendor id is zero. A route entry can have a
        different destination based on the application identification
        avp of the message.  This field MUST be used as a secondary key
        field in routing table lookups.
      - Local Action. The Local Action field is used to identify how a
        message should be treated. The following actions are supported:
           1. LOCAL - Diameter messages that resolve to a route entry
              with the Local Action set to Local can be satisfied
              locally, and do not need to be routed to another server.
           2. RELAY - All Diameter messages that fall within this
              category MUST be routed to a next hop server, without
              modifying any non-routing AVPs. See section 6.1.8 for
              relaying guidelines
           3. PROXY - All Diameter messages that fall within this
              category MUST be routed to a next hop server. The local
              server MAY apply its local policies to the message by
              including new AVPs to the message prior to routing. See
              section 6.1.8 for proxying guidelines.
           4. REDIRECT - Diameter messages that fall within this
              category MUST have the identity of the home Diameter
              server(s) appended, and returned to the sender of the
              message. See section 6.1.7 for redirect guidelines.
      - Server Identifier. One or more servers the message is to be
        routed to. These servers MUST also be present in the Peer table.
        When the Local Action is set to RELAY or PROXY, this field
        contains the identity of the server(s) the message must be
        routed to. When the Local Action field is set to REDIRECT, this
        field contains the identity of one or more servers the message
        should be redirected to.
      - Static or Dynamic. Specifies whether a route entry was
        statically configured, or dynamically discovered.
      - Expiration time. Specifies the time which a dynamically
        discovered route table entry expires.

   It is important to note that Diameter agents MUST support at least



Calhoun et al.             expires April 2003                  [Page 24]


Internet-Draft                                              October 2002


   one of the LOCAL, RELAY, PROXY or REDIRECT modes of operation. Agents
   do not need to support all modes of operation in order to conform
   with the protocol specification, but MUST follow the protocol
   compliance guidelines in section 2. Relay agents MUST NOT reorder
   AVPs, and proxies MUST NOT reorder AVPs.

   The routing table MAY include a default entry that MUST be used for
   any requests not matching any of the other entries. The routing table
   MAY consist of only such an entry.

   When a request is routed, the target server MUST have advertised the
   Application Identifier (see section 2.4) for the given message, or
   have advertised itself as a relay or proxy agent. Otherwise, an error
   is returned with the Result-Code AVP set to
   DIAMETER_UNABLE_TO_DELIVER.


2.8  Role of Diameter Agents

   In addition to client and servers, the Diameter protocol introduces
   relay, proxy, redirect, and translation agents, each of which is
   defined in Section 1.4. These Diameter agents are useful for several
   reasons:

      - They can distribute administration of systems to a configurable
        grouping, including the maintenance of security associations.
      - They can be used for concentration of requests from an number of
        co-located or distributed NAS equipment sets to a set of like
        user groups.
      - They can do value-added processing to the requests or responses.
      - They can be used for load balancing.
      - A complex network will have multiple authentication sources,
        they can sort requests and forward towards the correct target.

   The Diameter protocol requires that agents maintain transaction
   state, which is used for failover purposes. Transaction state implies
   that upon forwarding a request, its Hop-by-Hop identifier is saved;
   the field is replaced with a locally unique identifier, which is
   restored to its original value when the corresponding answer is
   received. The request's state is released upon receipt of the answer.
   A stateless agent is one that only maintains transaction state.

   The Proxy-Info AVP allows stateless agents to add local state to a
   Diameter request, with the guarantee that the same state will be
   present in the answer. However, the protocol's failover procedures
   require that agents maintain a copy of pending requests.

   A stateful agent is one that maintains session state information; by



Calhoun et al.             expires April 2003                  [Page 25]


Internet-Draft                                              October 2002


   keeping track of all authorized active sessions. Each authorized
   session is bound to a particular service, and its state is considered
   active either until it is notified otherwise, or by expiration. Each
   authorized session has an expiration, which is communicated by
   Diameter servers via the Session-Timeout AVP.

   Maintaining session state MAY be useful in certain applications, such
   as:

      - Protocol translation (e.g. RADIUS <-> Diameter)
      - Limiting resources authorized to a particular user
      - Per user or transaction auditing

   A Diameter agent MAY act in a stateful manner for some requests and
   be stateless for others. A Diameter implementation MAY act as one
   type of agent for some requests, and as another type of agent for
   others.


2.8.1  Relay Agents

   Relay Agents are Diameter agents that accept requests and route
   messages to other Diameter nodes based on information found in the
   messages (e.g. Destination-Realm). This routing decision is performed
   using a list of supported realms, and known peers. This is known as
   the Realm Routing Table, as is defined further in section 2.7.

   Relays MAY be used to aggregate requests from multiple Network Access
   Servers (NASes) within a common geographical area (POP). The use of
   Relays is advantageous since it eliminates the need for NASes to be
   configured with the necessary security information they would
   otherwise require to communicate with Diameter servers in other
   realms. Likewise, this reduces the configuration load on Diameter
   servers that would otherwise be necessary when NASes are added,
   changed or deleted.

   Relays modify Diameter messages by inserting and removing routing
   information, but do not modify any other portion of a message. Relays
   SHOULD NOT maintain session state but MUST maintain transaction
   state.











Calhoun et al.             expires April 2003                  [Page 26]


Internet-Draft                                              October 2002


      +------+    --------->     +------+     --------->    +------+
      |      |    1. Request     |      |     2. Request    |      |
      | NAS  |                   | DRL  |                   | HMS  |
      |      |    4. Answer      |      |     3. Answer     |      |
      +------+    <---------     +------+     <---------    +------+
      mno.net                     mno.net                    abc.com
                  Figure 2: Relaying of Diameter messages

   The example provided in Figure 2 depicts a request issued from NAS,
   which is an access device, for the user bob@abc.com. Prior to issuing
   the request, NAS performs a Diameter route lookup, using "abc.com" as
   the key, and determines that the message is to be relayed to DRL,
   which is a Diameter Relay. DRL performs the same route lookup as NAS,
   and relays the message to HMS, which is abc.com's Home Diameter
   Server. HMS identifies that the request can be locally supported (via
   the realm), processes the authentication and/or authorization
   request, and replies with an answer, which is routed back to NAS
   using saved transaction state.

   Since Relays do not perform any application level processing, they
   provide relaying services for all Diameter applications, and
   therefore MUST advertise the Relay Application Identifier.


2.8.2  Proxy Agents

   Similarly to Relays, Proxy agents route Diameter messages using the
   Diameter Routing Table. However, they differ since they modify
   messages to implement policy enforcement. This requires that proxies
   maintain the state of their downstream peers (e.g. access devices) to
   enforce resource usage, provide admission control, and provisioning.

   It is important to note that although proxies MAY provide a value-add
   function for NASes, they do not allow access devices to use end-to-
   end security, since modifying messages breaks authentication.

   Proxies MAY be used in call control centers or access ISPs that
   provide outsourced connections, they can monitor the number and types
   of ports in use, and make allocation and admission decisions
   according to their configuration.

   Proxies that wish to limit resources MUST maintain session state. All
   proxies MUST maintain transaction state.

   Since enforcing policies requires an understanding of the service
   being provided, Proxies MUST only advertise the Diameter applications
   they support.




Calhoun et al.             expires April 2003                  [Page 27]


Internet-Draft                                              October 2002


2.8.3  Redirect Agents

   Since Redirect agents do not perform any application level
   processing, the provide services for all Diameter applications, and
   therefore MUST advertise the Relay Application Identifier.

   Redirect agents are useful in scenarios where the Diameter routing
   configuration needs to be centralized. An example is a redirect agent
   that provides services to all members of a consortium, but does not
   wish to be burdened with relaying all messages between realms. This
   scenario is advantageous since it does not require that the
   consortium provide routing updates to its members when changes are
   made to a member's infrastructure.

   Since redirect agents do not relay messages, and only return an
   answer with the information necessary for Diameter agents to
   communicate directly, they do not modify messages. Since redirect
   agents do not receive answer messages, they cannot maintain session
   state. Further, since redirect agents never relay requests, they are
   not required to maintain transaction state.

   The example provided in Figure 3 depicts a request issued from the
   access device, NAS, for the user bob@abc.com. The message is
   forwarded by the NAS to its relay, DRL, which does not have a routing
   entry in its Diameter Routing Table for abc.com. DRL has a default
   route configured to DRD, which is a redirect agent that returns a
   redirect notification to DRL, as well as HMS' contact information.
   Upon receipt of the redirect notification, DRL establishes a
   transport connection with HMS, if one doesn't already exist, and
   forwards the request to it.

                                 +------+
                                 |      |
                                 | DRD  |
                                 |      |
                                 +------+
                                  ^    |
                      2. Request  |    | 3. Redirection
                                  |    |    Notification
                                  |    v
      +------+    --------->     +------+     --------->    +------+
      |      |    1. Request     |      |     4. Request    |      |
      | NAS  |                   | DRL  |                   | HMS  |
      |      |    6. Answer      |      |     5. Answer     |      |
      +------+    <---------     +------+     <---------    +------+
      mno.net                     mno.net                    abc.com
                 Figure 3: Redirecting a Diameter Message




Calhoun et al.             expires April 2003                  [Page 28]


Internet-Draft                                              October 2002


   Since Redirect agents do not perform any application level
   processing, they provide relaying services for all Diameter
   applications, and therefore MUST advertise the Relay Application
   Identifier.


2.8.4  Translation Agents

   A Translation Agent is a device that provides translation between two
   protocols (e.g. RADIUS<->Diameter, TACACS+<->Diameter). Translation
   agents are likely to be used as aggregation servers to communicate
   with a Diameter infrastructure, while allowing for the embedded
   systems to be migrated at a slower pace.

   Given that the Diameter protocol introduces the concept of long-lived
   authorized sessions, translation agents MUST be session stateful and
   MUST maintain transaction state.

   Translation of messages can only occur if the agent recognizes the
   application of a particular request, and therefore translation agents
   MUST only advertise their locally supported applications.

      +------+    --------->     +------+     --------->    +------+
      |      |  RADIUS Request   |      |  Diameter Request |      |
      | NAS  |                   | TLA  |                   | HMS  |
      |      |  RADIUS Answer    |      |  Diameter Answer  |      |
      +------+    <---------     +------+     <---------    +------+
      mno.net                     mno.net                    abc.com
                Figure 4: Translation of RADIUS to Diameter

2.9 End-to-End Security Framework

   End-to-end security services include confidentiality and message
   origin authentication. These services are provided by supporting AVP
   integrity and confidentiality between two peers, communicating
   through agents.

   End-to-end security is provided via the End-to-End security
   extension, described in [AAACMS]. The circumstances requiring the use
   of end-to-end security are determined by policy on each of the peers.
   Security policies, which are not the subject of standardization, may
   be applied by next hop Diameter peer or by destination realm. For
   example, where TLS or IPsec transmission-level security is
   sufficient, there may be no need for end-to-end security.

   End-to-end security policies include:

      - Never use end-to-end security.



Calhoun et al.             expires April 2003                  [Page 29]


Internet-Draft                                              October 2002


      - Use end-to-end security on messages containing sensitive AVPs.
        Which AVPs are sensitive is determined by service provider
        policy.  AVPs containing keys and passwords should be considered
        sensitive.  Accounting AVPs may be considered sensitive.  Any
        AVP for which the P bit may be set or which may be encrypted may
        be considered sensitive.

      - Always use end-to-end security.

   It is strongly recommended that all Diameter implementations support
   end-to-end security.

3  Diameter Header

   A summary of the Diameter header format is shown below. The fields
   are transmitted in network byte order.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Ver      |                 Message Length                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |R P E T r r r r|                  Command-Code                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Application-ID                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Hop-by-Hop Identifier                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      End-to-End Identifier                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  AVPs ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-

   Version
      This Version field MUST be set to 1 to indicate Diameter Version
      1.

   Message Length
      The Message Length field is three octets and indicates the length
      of the Diameter message including the header fields.

   Command Flags
      The Command Flags field is eight bits.  The following bits are
      assigned:

         R(equest)   - If set, the message is a request. If cleared, the
                       message is an answer.
         P(roxiable) - If set, the message MAY be proxied, relayed or



Calhoun et al.             expires April 2003                  [Page 30]


Internet-Draft                                              October 2002


                       redirected. If cleared, the message MUST be
                       locally processed.
         E(rror)     - If set, the message contains a protocol error,
                       and the message will not conform to the ABNF
                       described for this command. Messages with the 'E'
                       bit set are commonly referred to as an error
                       messages. This bit MUST NOT be set in request
                       messages. See section 7.2.
         T(Potentialy re-transmitted message)
                     - This flag is defined only for request messages
                       sent by Diameter clients or agents. This flag is
                       used as an indication of an application layer
                       retransmission event, e.g. due to failover to an
                       alternate server. If a Diameter client or agent
                       knows that it is sending this request or
                       accounting record contained in the request for
                       the first time, it MUST reset this flag. Diameter
                       agents only need to be concerned about the number
                       of requests they send based on a single received
                       request; retransmissions by other entities need
                       not be tracked. However, Diameter agents that
                       receive a request with the T flag set, MUST keep
                       the T flag set in the forwarded request. If
                       request is either known to be a retransmission or
                       the Diameter client or agent is unable to assure
                       that it is the first such request, it MUST set
                       this flag. For instance, after a reboot, a client
                       may not know whether it has already tried to send
                       the accounting records in its non-volatile memory
                       before the reboot occurred. Diameter servers MAY
                       use the T flag as an aid when processing requests
                       and detecting duplicate messages. However,
                       servers that do this MUST ensure that duplicates
                       are found even when the first transmitted request
                       arrives at the server after the retransmitted
                       request. This flag MUST NOT be set if an error
                       answer message (e.g. a protocol error) has been
                       received for the earlier message. It can be used
                       only in cases where no answer has been received
                       from the Server for a request and the request is
                       sent again, (e.g. due to a failover to an
                       alternate peer, due to a recovered primary peer
                       or due to a client re-sending a stored record
                       from non-volatile memory such as after reboot of
                       a client or agent).This flag MUST NOT be set in
                       answer messages.
         r(eserved)  - these flag bits are reserved for future use, and
                       MUST be set to zero, otherwise an error MUST be



Calhoun et al.             expires April 2003                  [Page 31]


Internet-Draft                                              October 2002


                       sent to the sender.


   Command-Code
      The Command-Code field is three octets, and is used in order to
      communicate the command associated with the message. The 24-bit
      address space is managed by IANA (see section 11.2.1).

      Command-Code values in the range 0xfffffe through 0xffffff are
      reserved for experimental use (see Section 11.3).  Commands in
      this range MUST also include a Vendor-Specific Application ID AVP
      (see section 6.11).


   Application-ID

      Application-ID is four octets and is used to identify to which
      application the message is applicable for.  The application can be
      an authentication application, an accounting application or a
      vendor specific application.  See section 11.3 for the possible
      values that the application-id may use.

      The application-id in the header MUST be the same as what is
      contained in any relevant AVPs contained in the message.

   Hop-by-Hop Identifier
      The Hop-by-Hop Identifier is an unsigned 32-bit integer field (in
      network byte order) and aids in matching requests and replies. The
      sender MUST ensure that the Hop-by-Hop identifier in a request is
      unique on a given connection at any given time, and MAY attempt to
      ensure that the number is unique across reboots. The sender of an
      Answer message MUST ensure that the Hop-by-Hop Identifier field
      contains the same value that was found in the corresponding
      request. The Hop-by-Hop identifier is normally a monotonically
      increasing number, whose start value was randomly generated. An
      answer message that is received with an unknown Hop-by-Hop
      Identifier MUST be discarded.

   End-to-End Identifier
      The End-to-End Identifier is an unsigned 32-bit integer field (in
      network byte order) and is used to detect duplicate messages. Upon
      reboot implementations MAY set the high order 12 bits to contain
      the low order 12 bits of current time, and the low order 20 bits
      to a random value. Senders of request messages MUST insert a
      unique identifier on each message. The identifier MUST remain
      locally unique for a period of at least 4 minutes, even across
      reboots. The originator of an Answer message MUST ensure that the
      End-to-End Identifier field contains the same value that was found



Calhoun et al.             expires April 2003                  [Page 32]


Internet-Draft                                              October 2002


      in the corresponding request. The End-to-End Identifier MUST NOT
      be modified by Diameter agents of any kind. The combination of the
      Origin-Host and this field is used to detect duplicates. Duplicate
      requests SHOULD cause the same answer to be transmitted (modulo
      the hop-by-hop Identifier field and any routing AVPs that may be
      present), and MUST NOT affect any state that was set when the
      original request was processed. Duplicate answer messages that are
      to be locally consumed (see Section 6.2) SHOULD be silently
      discarded.

   AVPs
      AVPs are a method of encapsulating information relevant to the
      Diameter message. See section 4 for more information on AVPs.


3.1  Command Codes

   Each command Request/Answer pair is assigned a command code, and the
   sub-type (i.e. - request or answer) is identified via the 'R' bit in
   the Command Flags field of the Diameter header.

   Every Diameter message MUST contain a command code in its header's
   Command-Code field, which is used to determine the action that is to
   be taken for a particular message. The following Command Codes are
   defined in the Diameter base protocol:

         Command-Name             Abbrev.    Code       Reference
         --------------------------------------------------------
         Abort-Session-Request     ASR       274           8.5.1
         Abort-Session-Answer      ASA       274           8.5.2
         Accounting-Request        ACR       271           9.7.1
         Accounting-Answer         ACA       271           9.7.2
         Capabilities-Exchange-    CER       257           5.3.1
            Request
         Capabilities-Exchange-    CEA       257           5.3.2
            Answer
         Device-Watchdog-Request   DWR       280           5.5.1
         Device-Watchdog-Answer    DWA       280           5.5.2
         Disconnect-Peer-Request   DPR       282           5.4.1
         Disconnect-Peer-Answer    DPA       282           5.4.2
         Re-Auth-Request           RAR       258           8.3.1
         Re-Auth-Answer            RAA       258           8.3.2
         Session-Termination-      STR       275           8.4.1
            Request
         Session-Termination-      STA       275           8.4.2
            Answer





Calhoun et al.             expires April 2003                  [Page 33]


Internet-Draft                                              October 2002


3.2  Command Code ABNF specification

   Every Command Code defined MUST include a corresponding ABNF
   specification, which is used to define the AVPs that MUST or MAY be
   present. The following format is used in the definition:

      command-def      = command-name "::=" diameter-message

      command-name     = diameter-name

      diameter-name    = ALPHA *(ALPHA / DIGIT / "-")

      diameter-message = header  [ *fixed] [ *required] [ *optional]
                         [ *fixed]

      header           = "<" Diameter-Header:" command-id
                         [r-bit] [p-bit] [e-bit] ">"


      command-id       = 1*DIGIT
                         ; The Command Code assigned to the command

      r-bit            = ", REQ"
                         ; If present, the 'R' bit in the Command
                         ; Flags is set, indicating that the message
                         ; is a request, as opposed to an answer.

      p-bit            = ", PXY"
                         ; If present, the 'P' bit in the Command
                         ; Flags is set, indicating that the message
                         ; is proxiable.

      e-bit            = ", ERR"
                         ; If present, the 'E' bit in the Command
                         ; Flags is set, indicating that the answer
                         ; message contains a Result-Code AVP in
                         ; the "protocol error" class.

      fixed            = [qual] "<" avp-spec ">"
                         ; Defines the fixed position of an AVP

      required         = [qual] "{" avp-spec "}"
                         ; The AVP MUST be present and can appear
                         ; anywhere in the message.

      optional         = [qual] "[" avp-name "]"
                         ; The avp-name in the 'optional' rule cannot
                         ; evaluate to any AVP Name which is included



Calhoun et al.             expires April 2003                  [Page 34]


Internet-Draft                                              October 2002


                         ; in a fixed or required rule. The AVP can
                         ; appear anywhere in the message.

      qual             = [min] "*" [max]
                         ; See ABNF conventions, RFC 2234 section 6.6.
                         ; The absence of any qualifiers depends on whether
                         ; it precedes a fixed, required, or optional
                         ; rule.  If a fixed or required rule has no
                         ; qualifier, then exactly one such AVP MUST
                         ; be present.  If an optional rule has no
                         ; qualifier, then 0 or 1 such AVP may be
                         ; present.
                         ;
                         ; NOTE:  "[" and "]" have a different meaning
                         ; than in ABNF (see the optional rule, above).
                         ; These braces cannot be used to express
                         ; optional fixed rules (such as an optional
                         ; ICV at the end.)  To do this, the convention
                         ; is '0*1fixed'.

      min              = 1*DIGIT
                         ; The minimum number of times the element may
                         ; be present. The default value is zero.

      max              = 1*DIGIT
                         ; The maximum number of times the element may
                         ; be present. The default value is infinity. A
                         ; value of zero implies the AVP MUST NOT be
                         ; present.

      avp-spec         = diameter-name
                         ; The avp-spec has to be an AVP Name, defined
                         ; in the base or extended Diameter
                         ; specifications.

      avp-name         = avp-spec / "AVP"
                         ; The string "AVP" stands for *any* arbitrary
                         ; AVP Name, which does not conflict with the
                         ; required or fixed position AVPs defined in
                         ; the command code definition.

   The following is a definition of a fictitious command code:

      Example-Request ::= < "Diameter-Header: 9999999, REQ, PXY >
                          { User-Name }
                        * { Origin-Host }
                        * [ AVP ]




Calhoun et al.             expires April 2003                  [Page 35]


Internet-Draft                                              October 2002


3.3  Diameter Command Naming Conventions

   Diameter command names typically includes one or more English words
   followed by the verb Request or Answer. Each English word is
   delimited by a hyphen. A three-letter acronym for both the request
   and answer is also normally provided.

   An example is a message set used to terminate a session. The command
   name is Session-Terminate-Request and Session-Terminate-Answer, while
   the acronyms are STR and STA, respectively.

   Both the request and the answer for a given command share the same
   command code. The request is identified by the R(equest) bit in the
   Diameter header set to one (1), to ask that a particular action be
   performed, such as authorizing a user or terminating a session.  Once
   the receiver has completed the request it issues the corresponding
   answer, which includes a result code that communicates one of the
   following:

      - The request was successful
      - The request failed
      - An additional request must be sent to provide information the
        peer requires prior to returning a successful or failed answer.
      - The receiver could not process the request, but provides
        information about a Diameter peer that is able to satisfy the
        request, known as redirect.

        Additional information, encoded within AVPs, MAY also be
        included in answer  messages.


4  Diameter AVPs

   Diameter AVPs carry specific authentication, accounting,
   authorization, routing and security information as well as
   configuration details for the request and reply.

   Some AVPs MAY be listed more than once. The effect of such an AVP is
   specific, and is specified in each case by the AVP description.

   Each AVP of type OctetString MUST be padded to align on a 32-bit
   boundary, while other AVP types align naturally. Zero bytes are added
   to the end of the AVP Data field till a word boundary is reached. The
   length of the padding is not reflected in the AVP Length field.


4.1  AVP Header




Calhoun et al.             expires April 2003                  [Page 36]


Internet-Draft                                              October 2002


   The fields in the AVP header MUST be sent in network byte order. The
   format of the header is:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           AVP Code                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |V M P r r r r r|                  AVP Length                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Vendor-ID (opt)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Data ...
      +-+-+-+-+-+-+-+-+

   AVP Code
      The AVP Code, combined with the Vendor-Id field, identifies the
      attribute uniquely. AVP numbers 0 through 255, with the Vendor-Id
      set to zero (0) are reserved for backward compatibility with
      RADIUS. AVP numbers 256 and above are used for Diameter, which are
      allocated by IANA (see section 11.1).

   AVP Flags
      The AVP Flags field informs the receiver how each attribute must
      be handled. The 'r' (reserved) bits are unused and SHOULD be set
      to 0. Note that subsequent Diameter applications MAY define
      additional bits within the AVP Header, and an unrecognized bit
      SHOULD be considered an error. The 'P' bit indicates the need for
      encryption for end-to-end security.

      The 'M' Bit, known as the Mandatory bit, indicates whether support
      of the AVP is required. If an AVP with the 'M' bit set is received
      by a Diameter client, server, proxy, or translation agent and
      either the AVP or its value is unrecognized, the message MUST be
      rejected. Diameter Relay and Redirect agents MUST NOT reject
      messages with unrecognized AVPs.

      The 'M' bit MUST be set according to the rules defined for the AVP
      containing it.  In order to preserve interoperability, a Diameter
      implementation MUST be able to exclude from a Diameter message any
      Mandatory AVP which is neither defined in the base Diameter
      standard nor in any of the Diameter Application specifications
      governing the message in which it appears.  It MAY do this in one
      of the following ways:

      1) If a message is rejected because it contains a Mandatory AVP
        which is neither defined in the base Diameter standard nor in
        any of the Diameter Application specifications governing the



Calhoun et al.             expires April 2003                  [Page 37]


Internet-Draft                                              October 2002


        message in which it appears, the implementation may resend the
        message without the AVP, possibly inserting additional standard
        AVPs instead.

      2) A configuration option may be provided on a system wide, per
        peer, or per realm basis that would allow/prevent particular
        Mandatory AVPs to be sent.  Thus an administrator could change
        the configuration to avoid interoperability problems.

      Diameter implementations are required to support all Mandatory
      AVPs which are allowed by the message's formal syntax and defined
      either in the base Diameter standard or in one of the Diameter
      Application specifications governing the message.

      AVPs with the 'M' bit cleared are informational only and a
      receiver that receives a message with such an AVP that is not
      supported, or whose value is not supported, MAY simply ignore the
      AVP.

      The 'V' bit, known as the Vendor-Specific bit, indicates whether
      the optional Vendor-ID field is present in the AVP header. When
      set the AVP Code belongs to the specific vendor code address
      space.

      Unless otherwise noted, AVPs will have the following default AVP
      Flags field settings:

         The 'M' bit MUST be set. The 'V' bit MUST NOT be set.

   AVP Length
      The AVP Length field is three octets, and indicates the number of
      octets in this AVP including the AVP Code, AVP Length, AVP Flags,
      Vendor-ID field (if present) and the AVP data. If a message is
      received with an invalid attribute length, the message SHOULD be
      rejected.


4.2  Optional Header Elements

   The AVP Header contains one optional field. This field is only
   present if the respective bit-flag is enabled.

   Vendor-ID
      The Vendor-ID field is present if the 'V' bit is set in the AVP
      Flags field. The optional four-octet Vendor-ID field contains the
      IANA assigned "SMI Network Management Private Enterprise Codes"
      [ASSIGNNO] value, encoded in network byte order. Any vendor
      wishing to implement a vendor-specific Diameter AVP MUST use their



Calhoun et al.             expires April 2003                  [Page 38]


Internet-Draft                                              October 2002


      own Vendor-ID along with their privately managed AVP address
      space, guaranteeing that they will not collide with any other
      vendor's vendor-specific AVP(s), nor with future IETF
      applications.

      A vendor ID value of zero (0) corresponds to the IETF adopted AVP
      values, as managed by the IANA. Since the absence of the vendor ID
      field implies that the AVP in question is not vendor specific,
      implementations MUST NOT use the zero (0) vendor ID.


4.3  Basic AVP Data Formats

   The Data field is zero or more octets and contains information
   specific to the Attribute. The format and length of the Data field is
   determined by the AVP Code and AVP Length fields. The format of the
   Data field MUST be one of the following base data types or a data
   type derived from the base data types.  In the event that a new Basic
   AVP Data Format is needed, a new version of this RFC must be created.

      OctetString
         The data contains arbitrary data of variable length. Unless
         otherwise noted, the AVP Length field MUST be set to at least 8
         (12 if the 'V' bit is enabled).  AVP Values of this type that
         are not a multiple of four-octets in length is followed by the
         necessary padding so that the next AVP (if any) will start on a
         32-bit boundary.

      Integer32
         32 bit signed value, in network byte order. The AVP Length
         field MUST be set to 12 (16 if the 'V' bit is enabled).

      Integer64
         64 bit signed value, in network byte order. The AVP Length
         field MUST be set to 16 (20 if the 'V' bit is enabled).

      Unsigned32
         32 bit unsigned value, in network byte order. The AVP Length
         field MUST be set to 12 (16 if the 'V' bit is enabled).

      Unsigned64
         64 bit unsigned value, in network byte order. The AVP Length
         field MUST be set to 16 (20 if the 'V' bit is enabled).

      Float32
         This represents floating point values of single precision as
         described by [FLOATPOINT].  The 32-bit value is transmitted in
         network byte order. The AVP Length field MUST be set to 12 (16



Calhoun et al.             expires April 2003                  [Page 39]


Internet-Draft                                              October 2002


         if the 'V' bit is enabled).

      Float64
         This represents floating point values of double precision as
         described by [FLOATPOINT].  The 64-bit value is transmitted in
         network byte order. The AVP Length field MUST be set to 16 (20
         if the 'V' bit is enabled).

      Grouped
         The Data field is specified as a sequence of AVPs.  Each of
         these AVPs follows - in the order in which they are specified -
         including their headers and padding.  The AVP Length field is
         set to 8 (12 if the 'V' bit is enabled) plus the total length
         of all included AVPs, including their headers and padding. Thus
         the AVP length field of an AVP of type Grouped is always a
         multiple of 4.

4.4  Derived AVP Data Formats

   In addition to using the Basic AVP Data Formats, applications may
   define data formats derived from the Basic AVP Data Formats. An
   application that defines new AVP Derived Data Formats MUST include
   them in a section entitled "AVP Derived Data Formats", using the same
   format as the definitions below. Each new definition must be either
   defined or listed with a reference to the RFC that defines the
   format.

   The below AVP Derived Data Formats are commonly used by applications.

      IPAddress
         The IPAddress format is derived from the OctetString AVP Base
         Format. It represents 32 bit (IPv4) [IPV4] or 128-bit (IPv6)
         [IPV6] address, most significant octet first. The format of the
         address (IPv4 or IPv6) is determined by the length. If the
         attribute value is an IPv4 address, the AVP Length field MUST
         be 12 (16 if 'V' bit is enabled); otherwise, the AVP Length
         field MUST be set to 24 (28 if the 'V' bit is enabled) for IPv6
         addresses.

      Time
         The Time format is derived from the OctetString AVP Base
         Format. The string MUST contain four octets, in the same format
         as the first four bytes are in the NTP timestamp format. The
         NTP Timestamp format is defined in chapter 3 of [SNTP].

         This represents the number of seconds since 0h on 1 January
         1900 with respect to the Coordinated Universal Time (UTC).




Calhoun et al.             expires April 2003                  [Page 40]


Internet-Draft                                              October 2002


         On 6h 28m 16s UTC, 7 February 2036 the time value will
         overflow. SNTP [SNTP] describes a procedure to extend the time
         to 2104. This procedure MUST be supported by all DIAMETER
         nodes.

      UTF8String
         The UTF8String format is derived from the OctetString AVP Base
         Format. This is a human readable string represented using the
         ISO/IEC IS 10646-1 character set, encoded as an OctetString
         using the UTF-8 [UFT8] transformation format described in RFC
         2279.

         Since additional code points are added by amendments to the
         10646 standard from time to time, implementations MUST be
         prepared to encounter any code point from 0x00000001 to
         0x7fffffff. Byte sequences that do not correspond to the valid
         encoding of a code point into UTF-8 charset or are outside this
         range are prohibited.

         The use of control codes SHOULD be avoided. When it is
         necessary to represent a newline, the control code sequence CR
         LF SHOULD be used.

         The use of leading or trailing white space SHOULD be avoided.

         For code points not directly supported by user interface
         hardware or software, an alternative means of entry and
         display, such as hexadecimal, MAY be provided.

         For information encoded in 7-bit US-ASCII, the UTF-8 charset is
         identical to the US-ASCII charset.

         UTF-8 may require multiple bytes to represent a single
         character / code point; thus the length of an UTF8String in
         octets may be different from the number of characters encoded.

         Note that the AVP Length field of an UTF8String is measured in
         octets, not characters.

      DiameterIdentity
         The DiameterIdentity format is derived from the OctetString AVP
         Base Format.

            DiameterIdentity  = fqdn

         DiameterIdentity value is used to uniquely identify a Diameter
         node for purposes of duplicate connection and routing loop
         detection.



Calhoun et al.             expires April 2003                  [Page 41]


Internet-Draft                                              October 2002


         The contents of the string MUST be the fqdn of the Diameter
         node. If multiple Diameter nodes run on the same host, each
         Diameter node MUST be assigned a unique DiameterIdentity. If a
         Diameter node can be identified by several FQDNs, a single FQDN
         should be picked at startup, and used as the only
         DiameterIdentity for that node, whatever the connection it is
         sent on.

      DiameterURI

         The DiameterURI MUST follow the Uniform Resource Identifiers
         (URI) syntax [URI] rules specified below:

         "aaa://" fqdn [ port ] [ transport ] [ protocol ]

                         ; No transport security

         "aaas://" fqdn [ port ] [ transport ] [ protocol ]

                         ; Transport security used

         fqdn               = Fully Qualified Host Name

         port               = ":" 1*DIGIT

                         ; One of the ports used to listen for
                         ; incoming connections.
                         ; If absent,
                         ; the default Diameter port (TBD) is
                         ; assumed.

         transport          = ";transport=" transport-protocol

                         ; One of the transports used to listen
                         ; for incoming connections. If absent,
                         ; the default SCTP [SCTP] protocol is
                         ; assumed. UDP MUST NOT be used when
                         ; the aaa-protocol field is set to
                         ; diameter.

         transport-protocol = ( "tcp" / "sctp" / "udp" )

         protocol           = ";protocol=" aaa-protocol

                         ; If absent, the default AAA protocol
                         ; is diameter.

         aaa-protocol       = ( "diameter" / "radius" / "tacacs+" )



Calhoun et al.             expires April 2003                  [Page 42]


Internet-Draft                                              October 2002


         The following are examples of valid Diameter host identities:

         aaa://host.abc.com;transport=tcp
         aaa://host.abc.com:6666;transport=tcp
         aaa://host.abc.com;protocol=diameter
         aaa://host.abc.com:6666;protocol=diameter
         aaa://host.abc.com:6666;transport=tcp;protocol=diameter
         aaa://host.abc.com:1813;transport=udp;protocol=radius


      Enumerated
         Enumerated is derived from the Integer32 AVP Base Format. The
         definition contains a list of valid values and their
         interpretation and is described in the Diameter application
         introducing the AVP.

      IPFilterRule
         The IPFilterRule format is derived from the OctetString AVP
         Base Format.  It uses the ASCII charset. Packets may be
         filtered based on the following information that is associated
         with it:

            Direction                          (in or out)
            Source and destination IP address  (possibly masked)
            Protocol
            Source and destination port        (lists or ranges)
            TCP flags
            IP fragment flag
            IP options
            ICMP types

         Rules for the appropriate direction are evaluated in order,
         with the first matched rule terminating the evaluation. Each
         packet is evaluated once. If no rule matches, the packet is
         dropped if the last rule evaluated was a permit, and passed if
         the last rule was a deny.

         IPFilterRule filters MUST follow the format:

            action dir proto from src to dst [options]

            action       permit - Allow packets that match the rule.
                         deny   - Drop packets that match the rule.

            dir          "in" is from the terminal, "out" is to the
                         terminal.

            proto        An IP protocol specified by number.  The "ip"



Calhoun et al.             expires April 2003                  [Page 43]


Internet-Draft                                              October 2002


                         keyword means any protocol will match.

            src and dst  <address/mask> [ports]

                         The <address/mask> may be specified as:
                         ipno       An IPv4 or IPv6 number in dotted-
                                    quad or canonical IPv6 form. Only
                                    this exact IP number will match the
                                    rule.
                         ipno/bits  An IP number as above with a mask
                                    width of the form 1.2.3.4/24. In
                                    this case, all IP numbers from
                                    1.2.3.0 to 1.2.3.255 will match.
                                    The bit width MUST be valid for the
                                    IP version and the IP number MUST
                                    NOT have bits set beyond the mask.
                                    For a match to occur, the same IP
                                    version must be present in the
                                    packet that was used in describing
                                    the IP address. To test for a
                                    particular IP version, the bits part
                                    can be set to zero. The keyword
                                    "any" is 0.0.0.0/0 or the IPv6
                                    equivalent.  The keyword "assigned"
                                    is the address or set of addresses
                                    assigned to the terminal.  For IPv4,
                                    a typical first rule is often "deny
                                    in ip! assigned"

                         The sense of the match can be inverted by
                         preceding an address with the not modifier (!),
                         causing all other addresses to be matched
                         instead.  This does not affect the selection of
                         port numbers.

                         With the TCP, UDP and SCTP protocols, optional
                         ports may be specified as:

                            {port/port-port}[,ports[,...]]

                         The '-' notation specifies a range of ports
                         (including boundaries).

                         Fragmented packets that have a non-zero offset
                         (i.e. not the first fragment) will never match
                         a rule that has one or more port
                         specifications.  See the frag option for
                         details on matching fragmented packets.



Calhoun et al.             expires April 2003                  [Page 44]


Internet-Draft                                              October 2002


            options:
               frag    Match if the packet is a fragment and this is not
                       the first fragment of the datagram.  frag may not
                       be used in conjunction with either tcpflags or
                       TCP/UDP port specifications.

               ipoptions spec
                       Match if the IP header contains the comma
                       separated list of options specified in spec. The
                       supported IP options are:

                       ssrr (strict source route), lsrr (loose source
                       route), rr (record packet route) and ts
                       (timestamp). The absence of a particular option
                       may be denoted with a '!'.

               tcpoptions spec
                       Match if the TCP header contains the comma
                       separated list of options specified in spec. The
                       supported TCP options are:

                       mss (maximum segment size), window (tcp window
                       advertisement), sack (selective ack), ts (rfc1323
                       timestamp) and cc (rfc1644 t/tcp connection
                       count).  The absence of a particular option may
                       be denoted with a '!'.

               established
                       TCP packets only. Match packets that have the RST
                       or ACK bits set.

               setup   TCP packets only. Match packets that have the SYN
                       bit set but no ACK bit.

               tcpflags spec
                       TCP packets only. Match if the TCP header
                       contains the comma separated list of flags
                       specified in spec. The supported TCP flags are:

                       fin, syn, rst, psh, ack and urg. The absence of a
                       particular flag may be denoted with a '!'. A rule
                       that contains a tcpflags specification can never
                       match a fragmented packet that has a non-zero
                       offset.  See the frag option for details on
                       matching fragmented packets.

               icmptypes types
                       ICMP packets only.  Match if the ICMP type is in



Calhoun et al.             expires April 2003                  [Page 45]


Internet-Draft                                              October 2002


                       the list types. The list may be specified as any
                       combination of ranges or individual types
                       separated by commas.  Both the numeric values and
                       the symbolic values listed below can be used. The
                       supported ICMP types are:

                       echo reply (0), destination unreachable (3),
                       source quench (4), redirect (5), echo request
                       (8), router advertisement (9), router
                       solicitation (10), time-to-live exceeded (11), IP
                       header bad (12), timestamp request (13),
                       timestamp reply (14), information request (15),
                       information reply (16), address mask request (17)
                       and address mask reply (18).

         There is one kind of packet that the access device MUST always
         discard, that is an IP fragment with a fragment offset of one.
         This is a valid packet, but it only has one use, to try to
         circumvent firewalls.

            An access device that is unable to interpret or apply a deny
            rule MUST terminate the session.  An access device that is
            unable to interpret or apply a permit rule MAY apply a more
            restrictive rule.  An access device MAY apply deny rules of
            its own before the supplied rules, for example to protect
            the access device owner's infrastructure.

         The rule syntax is a modified subset of ipfw(8) from FreeBSD,
         and the ipfw.c code may provide a useful base for
         implementations.

      QoSFilterRule
         The QosFilterRule format is derived from the OctetString AVP
         Base Format.  It uses the ASCII charset. Packets may be marked
         or metered based on the following information that is
         associated with it:

            Direction                          (in or out)
            Source and destination IP address  (possibly masked)
            Protocol
            Source and destination port        (lists or ranges)
            DSCP values                        (no mask or range)

         Rules for the appropriate direction are evaluated in order,
         with the first matched rule terminating the evaluation. Each
         packet is evaluated once. If no rule matches, the packet is
         treated as best effort. An access device that is unable to
         interpret or apply a QoS rule SHOULD NOT terminate the session.



Calhoun et al.             expires April 2003                  [Page 46]


Internet-Draft                                              October 2002


         QoSFilterRule filters MUST follow the format:

            action dir proto from src to dst [options]

                         tag    - Mark packet with a specific DSCP
                                  [DIFFSERV]. The DSCP option MUST be
                                  included.
                         meter  - Meter traffic. The metering options
                                  MUST be included.

            dir    The format is as described under IPFilterRule.

                         proto        The format is as described under
                         IPFilterRule.

                         src and dst  The format is as described under
                         IPFilterRule.


4.5  Grouped AVP Values

   The Diameter protocol allows AVP values of type 'Grouped.' This
   implies that the Data field is actually a sequence of AVPs. It is
   possible to include an AVP with a Grouped type within a Grouped type,
   that is, to nest them. AVPs within an AVP of type Grouped have the
   same padding requirements as non-Grouped AVPs, as defined in section
   4.

   The AVP Code numbering space of all AVPs included in a Grouped AVP is
   the same as for non-grouped AVPs. Further, if any of the AVPs
   encapsulated within a Grouped AVP has the 'M' (mandatory) bit set,
   the Grouped AVP itself MUST also include the 'M' bit set.

   Every Grouped AVP defined MUST include a corresponding grammar, using
   ABNF [ABNF] (with modifications), as defined below.

      grouped-avp-def  = name "::=" avp

      name-fmt         = ALPHA *(ALPHA / DIGIT / "-")

      name             = name-fmt
                         ; The name has to be the name of an AVP,
                         ; defined in the base or extended Diameter
                         ; specifications.

      avp              = header  [ *fixed] [ *required] [ *optional]
                         [ *fixed]




Calhoun et al.             expires April 2003                  [Page 47]


Internet-Draft                                              October 2002


      header           = "<" "AVP-Header:" avpcode [vendor] ">"

      avpcode          = 1*DIGIT
                         ; The AVP Code assigned to the Grouped AVP

      vendor           = 1*DIGIT
                         ; The Vendor-ID assigned to the Grouped AVP.
                         ; If absent, the default value of zero is
                         ; used.


4.5.1  Example AVP with a Grouped Data type

   The Example-AVP (AVP Code 999999) is of type Grouped and is used to clarify how Grouped AVP values work.  The Grouped Data field has the following ABNF grammar:

      Example-AVP  ::= < AVP Header: 999999 >
                       { Origin-Host }
                     1*{ Session-Id }
                      *[ AVP ]

   An Example-AVP with Grouped Data follows.

   The Origin-Host AVP is required.  In this case:

      Origin-Host = "abc.com".

   One or more Session-Ids must follow.  Here there are two:

      Session-Id =
        "grump.abc.com:33041;23432;893;0AF3B81"

      Session-Id =
        "grump.abc.com:33054;23561;2358;0AF3B82"

   optional AVPs included are

      Recovery-Policy = <binary>
         2163bc1d0ad82371f6bc09484133c3f09ad74a0dd5346d54195a7cf0b35
         2cabc881839a4fdcfbc1769e2677a4c1fb499284c5f70b48f58503a45c5
         c2d6943f82d5930f2b7c1da640f476f0e9c9572a50db8ea6e51e1c2c7bd
         f8bb43dc995144b8dbe297ac739493946803e1cee3e15d9b765008a1b2a
         cf4ac777c80041d72c01e691cf751dbf86e85f509f3988e5875dc905119
         26841f00f0e29a6d1ddc1a842289d440268681e052b30fb638045f7779c
         1d873c784f054f688f5001559ecff64865ef975f3e60d2fd7966b8c7f92

      Futuristic-Acct-Record = <binary>
         fe19da5802acd98b07a5b86cb4d5d03f0314ab9ef1ad0b67111ff3b90a0
         57fe29620bf3585fd2dd9fcc38ce62f6cc208c6163c008f4258d1bc88b8



Calhoun et al.             expires April 2003                  [Page 48]


Internet-Draft                                              October 2002


         17694a74ccad3ec69269461b14b2e7a4c111fb239e33714da207983f58c
         41d018d56fe938f3cbf089aac12a912a2f0d1923a9390e5f789cb2e5067
         d3427475e49968f841

   The data for the optional AVPs is represented in hex since the format
   of these AVPs is neither known at the time of definition of the
   Example-AVP group, nor (likely) at the time when the example instance
   of this AVP is interpreted - except by Diameter implementations which
   support the same set of AVPs.  The encoding example illustrates how
   padding is used and how length fields are calculated. Also note that
   AVPs may be present in the Grouped AVP value which the receiver
   cannot interpret (here, the Recover-Policy and Futuristic-Acct-Record
   AVPs).

   This AVP would be encoded as follows:




































Calhoun et al.             expires April 2003                  [Page 49]


Internet-Draft                                              October 2002


           0       1       2       3       4       5       6       7
       +-------+-------+-------+-------+-------+-------+-------+-------+
     0 |     Example AVP Header (AVP Code = 999999), Length = 468      |
       +-------+-------+-------+-------+-------+-------+-------+-------+
     8 |     Origin-Host AVP Header (AVP Code = 264), Length = 19      |
       +-------+-------+-------+-------+-------+-------+-------+-------+
    16 |  'e'  |  'x'  |  'a'  |  'm'  |  'p'  |  'l'  |  'e'  |  '.'  |
       +-------+-------+-------+-------+-------+-------+-------+-------+
    24 |  'c'  |  'o'  |  'm'  |Padding|     Session-Id AVP Header     |
       +-------+-------+-------+-------+-------+-------+-------+-------+
    32 | (AVP Code = 263), Length = 50 |  'g'  |  'r'  |  'u'  |  'm'  |
       +-------+-------+-------+-------+-------+-------+-------+-------+
                                     . . .
       +-------+-------+-------+-------+-------+-------+-------+-------+
    64 |  'A'  |  'F'  |  '3'  |  'B'  |  '8'  |  '1'  |Padding|Padding|
       +-------+-------+-------+-------+-------+-------+-------+-------+
    68 |     Session-Id AVP Header (AVP Code = 263), Length = 51       |
       +-------+-------+-------+-------+-------+-------+-------+-------+
    72 |  'g'  |  'r'  |  'u'  |  'm'  |  'p'  |  '.'  |  'e'  |  'x'  |
       +-------+-------+-------+-------+-------+-------+-------+-------+
                                     . . .
       +-------+-------+-------+-------+-------+-------+-------+-------+
   104 |  '0'  |  'A'  |  'F'  |  '3'  |  'B'  |  '8'  |  '2'  |Padding|
       +-------+-------+-------+-------+-------+-------+-------+-------+
   112 |   Recovery-Policy Header (AVP Code = 8341), Length = 223      |
       +-------+-------+-------+-------+-------+-------+-------+-------+
   120 |  0x21 | 0x63  | 0xbc  | 0x1d  | 0x0a  | 0xd8  | 0x23  | 0x71  |
       +-------+-------+-------+-------+-------+-------+-------+-------+
                                     . . .
       +-------+-------+-------+-------+-------+-------+-------+-------+
   320 |  0x2f | 0xd7  | 0x96  | 0x6b  | 0x8c  | 0x7f  | 0x92  |Padding|
       +-------+-------+-------+-------+-------+-------+-------+-------+
   328 | Futuristic-Acct-Record Header (AVP Code = 15930), Length = 137|
       +-------+-------+-------+-------+-------+-------+-------+-------+
   336 |  0xfe | 0x19  | 0xda  | 0x58  | 0x02  | 0xac  | 0xd9  | 0x8b  |
       +-------+-------+-------+-------+-------+-------+-------+-------+
                                     . . .
       +-------+-------+-------+-------+-------+-------+-------+-------+
   464 |  0x41 |Padding|Padding|Padding|
       +-------+-------+-------+-------+


4.6  Diameter Base Protocol AVPs

   The following table describes the Diameter AVPs defined in the base
   protocol, their AVP Code values, types, possible flag values and
   whether the AVP MAY be encrypted.  For the originator of a Diameter
   message, "MAY Encr" means that if a message containing that AVP is to



Calhoun et al.             expires April 2003                  [Page 50]


Internet-Draft                                              October 2002


   be sent via a  Diameter agent (proxy, redirect or relay) then the
   message MUST NOT be sent unless there is end-to-end security between
   the originator and the recipient and integrity / confidentiality
   protection is offered for this AVP OR the originator has locally
   trusted configuration that indicates that end-to-end security is not
   needed. Similarly, for the originator of a Diameter message, a "P" in
   the "MAY" column means that if a message containing that AVP is to be
   sent via a  Diameter agent (proxy, redirect or relay) then the
   message MUST NOT be sent unless there is end-to-end security between
   the originator and the recipient or the originator has locally
   trusted configuration that indicates that end-to-end security is not
   needed.

   Due to space constraints, the short form DiamIdent is used to
   represent DiameterIdentity.




































Calhoun et al.             expires April 2003                  [Page 51]


Internet-Draft                                              October 2002


                                            +---------------------+
                                            |    AVP Flag rules   |
                                            |----+-----+----+-----|----+
                   AVP  Section             |    |     |SHLD| MUST|MAY |
   Attribute Name  Code Defined  Data Type  |MUST| MAY | NOT|  NOT|Encr|
   -----------------------------------------|----+-----+----+-----|----|
   Accounting-       85  9.8.2   Unsigned32 | M  |  P  |    |  V  | Y  |
     Interim-Interval                       |    |     |    |     |    |
   Accounting-      483  9.8.7   Unsigned32 | M  |  P  |    |  V  | Y  |
     Realtime-Required                      |    |     |    |     |    |
   Acct-            50   9.8.5   UTF8String | M  |  P  |    |  V  | Y  |
     Multi-Session-Id                       |    |     |    |     |    |
   Accounting-      485  9.8.3   Unsigned32 | M  |  P  |    |  V  | Y  |
     Record-Number                          |    |     |    |     |    |
   Accounting-      480  9.8.1   Enumerated | M  |  P  |    |  V  | Y  |
     Record-Type                            |    |     |    |     |    |
   Accounting-       44  9.8.4   OctetString| M  |  P  |    |  V  | Y  |
     RADIUS-Session-Id                      |    |     |    |     |    |
   Accounting-      287  9.8.6   Unsigned64 | M  |  P  |    |  V  | Y  |
     Sub-Session-Id                         |    |     |    |     |    |
   Acct-            259  6.9     Integer32  | M  |  P  |    |  V  | N  |
     Application-Id                         |    |     |    |     |    |
   Auth-            258  6.8     Integer32  | M  |  P  |    |  V  | N  |
     Application-Id                         |    |     |    |     |    |
   Auth-Request-    274  8.7     Enumerated | M  |  P  |    |  V  | N  |
      Type                                  |    |     |    |     |    |
   Authorization-   291  8.9     Unsigned32 | M  |  P  |    |  V  | N  |
     Lifetime                               |    |     |    |     |    |
   Auth-Grace-      276  8.10    Unsigned32 | M  |  P  |    |  V  | N  |
     Period                                 |    |     |    |     |    |
   Auth-Session-    277  8.11    Enumerated | M  |  P  |    |  V  | N  |
     State                                  |    |     |    |     |    |
   Re-Auth-Request- 285  8.12    Enumerated | M  |  P  |    |  V  | N  |
     Type                                   |    |     |    |     |    |
   Class             25  8.20    OctetString| M  |  P  |    |  V  | Y  |
   Destination-Host 293  6.5     DiamIdent  | M  |  P  |    |  V  | N  |
   Destination-     283  6.6     UTF8String | M  |  P  |    |  V  | N  |
     Realm                                  |    |     |    |     |    |
   Disconnect-Cause 273  5.4.3   Enumerated | M  |  P  |    |  V  | N  |
   Error-Message    281  7.3     OctetString|    |  P  |    | V,M | N  |
   Error-Reporting- 294  7.4     UTF8String |    |  P  |    | V,M | N  |
     Host                                   |    |     |    |     |    |
   Event-Timestamp   55  8.21    Time       | M  |  P  |    |  V  | N  |
   Experimental-    297  7.6     Grouped    | M  |  P  |    |  V  | N  |
      Result                                |    |     |    |     |    |
   Experimental-    298  7.7     Unsigned32 | M  |  P  |    |  V  | N  |
      Result-Code                           |    |     |    |     |    |
   -----------------------------------------|----+-----+----+-----|----|



Calhoun et al.             expires April 2003                  [Page 52]


Internet-Draft                                              October 2002


                                            +---------------------+
                                            |    AVP Flag rules   |
                                            |----+-----+----+-----|----+
                   AVP  Section             |    |     |SHLD| MUST|MAY |
   Attribute Name  Code Defined  Data Type  |MUST| MAY | NOT|  NOT|Encr|
   -----------------------------------------|----+-----+----+-----|----|
   Failed-AVP       279  7.5     Grouped    | M  |  P  |    |  V  | N  |
   Firmware-        267  5.3.4   Unsigned32 |    |     |    |P,V,M| N  |
     Revision                               |    |     |    |     |    |
   Host-IP-Address  257  5.3.5   IPAddress  | M  |  P  |    |  V  | N  |
   Inband-Security                          |    |     |    |     |    |
      -Id           299  6.10    Unsigned32 |    |     |    |     |    |
   Multi-Round-     272  8.19    Unsigned32 | M  |  P  |    |  V  | Y  |
     Time-Out                               |    |     |    |     |    |
   Origin-Host      264  6.3     DiamIdent  | M  |  P  |    |  V  | N  |
   Origin-Realm     296  6.4     UTF8String | M  |  P  |    |  V  | N  |
   Origin-State-Id  278  8.16    Unsigned32 | M  |  P  |    |  V  | N  |
   Product-Name     269  5.3.7   UTF8String |    |     |    |P,V,M| N  |
   Proxy-Host       280  6.7.3   DiamIdent  | M  |     |    | P,V | N  |
   Proxy-Info       284  6.7.2   Grouped    | M  |     |    | P,V | N  |
   Proxy-State       33  6.7.4   OctetString| M  |     |    | P,V | N  |
   Redirect-Host    292  6.12    DiamURI    | M  |  P  |    |  V  | N  |
   Redirect-Host-   261  6.13    Enumerated | M  |  P  |    |  V  | N  |
      Usage                                 |    |     |    |     |    |
   Redirect-Max-    262  6.14    Unsigned32 | M  |  P  |    |  V  | N  |
      Cache-Time                            |    |     |    |     |    |
   Result-Code      268  7.1     Unsigned32 | M  |  P  |    |  V  | N  |
   Route-Record     282  6.7.1   DiamIdent  | M  |     |    | P,V | N  |
   Session-Id       263  8.8     UTF8String | M  |  P  |    |  V  | Y  |
   Session-Timeout   27  8.13    Unsigned32 | M  |  P  |    |  V  | N  |
   Session-Binding  270  8.17    Unsigned32 | M  |  P  |    |  V  | Y  |
   Session-Server-  271  8.18    Enumerated | M  |  P  |    |  V  | Y  |
     Failover                               |    |     |    |     |    |
   Supported-       265  5.3.6   Unsigned32 | M  |  P  |    |  V  | N  |
     Vendor-Id                              |    |     |    |     |    |
   Termination-     295  8.15    Enumerated | M  |  P  |    |  V  | N  |
      Cause                                 |    |     |    |     |    |
   User-Name          1  8.14    UTF8String | M  |  P  |    |  V  | Y  |
   Vendor-Id        266  5.3.3   Unsigned32 | M  |  P  |    |  V  | N  |
   Vendor-Specific- 260  6.11    Grouped    | M  |  P  |    |  V  | N  |
      Application-Id                        |    |     |    |     |    |
   -----------------------------------------|----+-----+----+-----|----|


5  Diameter Peers

   This section describes how Diameter nodes establish connections and
   communicate with peers.



Calhoun et al.             expires April 2003                  [Page 53]


Internet-Draft                                              October 2002


5.1  Peer Connections

   Although a Diameter node may have many possible peers that it is able
   to communicate with, it may not be economical to have an established
   connection to all of them. At a minimum, a Diameter node SHOULD have
   an established connection with two peers per realm, known as the
   primary and secondary peers. Of course, a node MAY have additional
   connections, if it is deemed necessary. Typically, all messages for a
   realm are sent to the primary peer, but in the event that failover
   procedures are invoked, any pending requests are sent to the
   secondary peer. However, implementations are free to load balance
   requests between a set of peers.

   Note that a given peer MAY act as a primary for a given realm, while
   acting as a secondary for another realm.

   When a peer is deemed suspect, which could occur for various reasons,
   including not receiving a DWA within an allotted timeframe, no new
   requests should be forwarded to the peer, but failover procedures are
   invoked. When an active peer is moved to this mode, additional
   connections SHOULD be established to ensure that the necessary number
   of active connections exists.

   There are two ways that a peer is removed from the suspect peer list:
      1. The peer is no longer reachable, causing the transport
         connection to be shutdown. The peer is moved to the closed
         state.
      2. Three watchdog messages are exchanged with accepted round trip
         times, and the connection to the peer is considered stabilized.

   In the event the peer being removed is either the primary or
   secondary, an alternate peer SHOULD replace the deleted peer, and
   assume the role of either primary or secondary.


5.2  Diameter Peer Discovery

   Allowing for dynamic Diameter agent discovery will make it possible
   for simpler and more robust deployment of Diameter services.  In
   order to promote interoperable implementations of Diameter peer
   discovery, the following mechanisms are described.  These are based
   on existing IETF standards.  The first option (manual configuration)
   MUST be supported by all DIAMETER nodes, while the latter two options
   (SRVLOC and DNS) MAY be supported.

   There are two cases where Diameter peer discovery may be performed.
   The first is when a Diameter client needs to discover a first-hop
   Diameter agent.  The second case is when a Diameter agent needs to



Calhoun et al.             expires April 2003                  [Page 54]


Internet-Draft                                              October 2002


   discover another agent - for further handling of a Diameter
   operation. In both cases, the following 'search order' is
   recommended:

      1. The Diameter implementation consults its list of static
         (manually) configured Diameter agent locations.  These will be
         used if they exist and respond.

      2. The Diameter implementation uses SLPv2 [SLP] to discover
         Diameter services.  The Diameter service template [TEMPLATE] is
         included in Appendix A. It is recommended that SLPv2 security
         be deployed (this requires distributing keys to SLPv2 agents).
         This is discussed further in Appendix A.

         SLPv2 will allow Diameter implementations to discover the
         location of Diameter agents in the local site, as well as their
         characteristics.  Diameter agents with specific capabilities
         (say support for the Mobile IP application) can be requested,
         and only those will be discovered.

      3. The Diameter implementation performs a NAPTR query for a server
         in a particular realm.  The Diameter implementation has to know
         in advance which realm to look for a Diameter agent in.  This
         could be deduced, for example, from the 'realm' in a NAI that a
         Diameter implementation needed to perform a Diameter operation
         on.

        3.1 The services relevant for the task of transport protocol
            selection are those with NAPTR service fields with values
            "AAA+D2x", where x is a letter that corresponds to a
            transport protocol supported by the domain. This
            specification defines D2T for TCP and D2S for SCTP. We also
            establish an IANA registry for NAPTR service name to
            transport protocol mappings.

            These NAPTR records provide a mapping from a domain, to the
            SRV record for contacting a server with the specific
            transport protocol in the NAPTR services field. The resource
            record will contain an empty regular expression and a
            replacement value, which is the SRV record for that
            particular transport protocol. If the server supports
            multiple transport protocols, there will be multiple NAPTR
            records, each with a different service value. As per RFC
            2915 [NAPTR], the client discards any records whose services
            fields are not applicable. For the purposes of this
            specification, several rules are defined.

        3.2 A client MUST discard any service fields that identify a



Calhoun et al.             expires April 2003                  [Page 55]


Internet-Draft                                              October 2002


            resolution service whose value is not "D2X", for values of X
            that indicate transport protocols supported by the client.
            The NAPTR processing as described in RFC 2915 will result in
            discovery of the most preferred transport protocol of the
            server that is supported by the client, as well as an SRV
            record for the server.

            The domain suffixes in the NAPTR replacement field SHOULD
            match the domain of the original query. It is not necessary
            for the domain suffixes in the NAPTR replacement field to
            match the domain of the original query.

        3.3 If no NAPTR records are found, the requester queries for
            those address records for the destination address,
            '_diameter._sctp'.realm or '_diameter._tcp'.realm. Address
            records include A RR's, AAAA RR's or other similar records,
            chosen according to the requestor's network protocol
            capabilities. If the DNS server returns no address records,
            the requestor gives up.

         If the server is using a site certificate, the domain name in
         the query and the domain name in the replacement field MUST
         both be valid based on the site certificate handed out by the
         server in the TLS exchange. Similarly, the domain name in the
         SRV query and the domain name in the target in the SRV record
         MUST both be valid based on the same site certificate.
         Otherwise, an attacker could modify the DNS records to contain
         replacement values in a different domain, and the client could
         not validate that this was the desired behavior, or the result
         of an attack.

   A dynamically discovered peer causes an entry in the Peer Table (see
   section 2.6) to be created. Note that entries created via DNS MUST
   expire (or be refreshed) within the DNS TTL. If a peer is discovered
   outside of the local realm, a routing table entry (see Section 2.7)
   for the peer's realm is created. The routing table entry's expiration
   MUST match the peer's expiration value.


5.3  Capabilities Exchange

   When two Diameter peers establish a transport connection, they MUST
   exchange the Capabilities Exchange messages, as specified in the peer
   state machine (see section 5.6). This message allows the discovery of
   a peer's identity and its capabilities (protocol version number,
   supported Diameter applications, security model, etc.)

   The receiver only issues commands to its peers that have advertised



Calhoun et al.             expires April 2003                  [Page 56]


Internet-Draft                                              October 2002


   support for the Diameter application that defines the command. A
   Diameter node MUST cache the supported applications in order to
   ensure that unrecognized commands and/or AVPs are not unnecessarily
   sent to a peer.

   A receiver of a Capabilities-Exchange-Req (CER) message that does not
   have any applications in common with the sender MUST return a
   Capabilities-Exchange-Answer (CEA) with the Result-Code AVP set to
   DIAMETER_NO_COMMON_APPLICATION, and SHOULD disconnect the transport
   layer connection. Note that receiving a CER or CEA from a peer
   advertising itself as a Relay (see section 2.4) MUST be interpreted
   as having common applications with the peer.

   Similarly, a receiver of a Capabilities-Exchange-Req (CER) message
   that does not have any security model in common with the sender MUST
   return a Capabilities-Exchange-Answer (CEA) with the Result-Code AVP
   set to DIAMETER_NO_COMMON_SECURITY, and SHOULD disconnect the
   transport layer connection.

   CERs received from unknown peers MAY be silently discarded, or a CEA
   MAY be issued with the Result-Code AVP set to DIAMETER_UNKNOWN_PEER.
   In both cases, the transport connection is closed. If the local
   policy permits receiving CERs from unknown hosts, a successful CEA
   MAY be returned.  If a CER from an unknown peer is answered with a
   successful CEA, the lifetime of the peer entry is equal to the
   lifetime of the transport connection. In case of a transport failure,
   all the pending transactions destined to the unknown peer can be
   discarded.

   The CER and CEA messages MUST NOT be proxied, or redirected.

   Since the CER/CEA messages cannot be proxied, it is still possible
   that an upstream agent receives a message for which it has no
   available peers to handle the application that corresponds to the
   Command-Code. In such instances, the 'E' bit is set in the answer
   message (see Section 7.2) with the Result-Code AVP set to
   DIAMETER_UNABLE_TO_DELIVER to inform the downstream to take action
   (e.g. re-routing request to an alternate peer).

   With the exception of the Capabilities-Exchange-Request message, a
   message of type Request that includes the Auth-Application-Id or
   Acct-Application-Id AVPs, or a message with an application-specific
   command code, MAY only be forwarded to a host that has explicitly
   advertised support for the application (or has advertised the Relay
   Application Identifier).


5.3.1  Capabilities-Exchange-Request



Calhoun et al.             expires April 2003                  [Page 57]


Internet-Draft                                              October 2002


   The Capabilities-Exchange-Request (CER), indicated by the Command-
   Code set to 257 and the Command Flags' 'R' bit set, is sent to
   exchange local capabilities. Upon detection of a transport failure,
   this message MUST NOT be sent to an alternate peer.

   When Diameter is run over SCTP [SCTP], which allows for connections
   to span multiple interfaces and multiple IP addresses, the
   Capabilities-Exchange-Request message MUST contain one Host-IP-
   Address AVP for each potential IP address that MAY be locally used
   when transmitting Diameter messages.

   Message Format

      <CER> ::= < Diameter Header: 257, REQ >
                { Origin-Host }
                { Origin-Realm }
             1* { Host-IP-Address }
                { Vendor-Id }
                { Product-Name }
                [ Origin-State-Id ]
              * [ Supported-Vendor-Id ]
              * [ Auth-Application-Id ]
              * [ Inband-Security-Id ]
              * [ Acct-Application-Id ]
              * [ Vendor-Specific-Application-Id ]
                [ Firmware-Revision ]
              * [ AVP ]


5.3.2  Capabilities-Exchange-Answer

   The Capabilities-Exchange-Answer (CEA), indicated by the Command-Code
   set to 257 and the Command Flags' 'R' bit cleared, is sent in
   response to a CER message.

   When Diameter is run over SCTP [SCTP], which allows connections to
   span multiple interfaces, hence, multiple IP addresses, the
   Capabilities-Exchange-Answer message MUST contain one Host-IP-Address
   AVP for each potential IP address that MAY be locally used when
   transmitting Diameter messages.

   Message Format









Calhoun et al.             expires April 2003                  [Page 58]


Internet-Draft                                              October 2002


      <CEA> ::= < Diameter Header: 257 >
                { Result-Code }
                { Origin-Host }
                { Origin-Realm }
             1* { Host-IP-Address }
                { Vendor-Id }
                { Product-Name }
                [ Origin-State-Id ]
                [ Error-Message ]
              * [ Failed-AVP ]
              * [ Supported-Vendor-Id ]
              * [ Auth-Application-Id ]
              * [ Inband-Security-Id ]
              * [ Acct-Application-Id ]
              * [ Vendor-Specific-Application-Id ]
                [ Firmware-Revision ]
              * [ AVP ]


5.3.3  Vendor-Id AVP

   The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains
   the IANA "SMI Network Management Private Enterprise Codes" [ASSIGNNO]
   value assigned to the vendor of the Diameter device.  In combination
   with the Supported-Vendor-Id AVP (section 5.3.6), this MAY be used in
   order to know which vendor specific attributes may be sent to the
   peer. It is also envisioned that the combination of the Vendor-Id,
   Product-Name (section 5.3.7) and the Firmware-Revision (section
   5.3.4) AVPs MAY provide very useful debugging information.

   A Vendor-Id value of zero in the CER or CEA messages is reserved and
   indicates that the Diameter peer is in the experimental or concept
   stage and that an IANA Private Enterprise Number has yet to be
   obtained by the implementer.


5.3.4  Firmware-Revision AVP

   The Firmware-Revision AVP (AVP Code 267) is of type Unsigned32 and is
   used to inform a Diameter peer of the firmware revision of the
   issuing device.

   For devices that do not have a firmware revision (general purpose
   computers running Diameter software modules, for instance), the
   revision of the Diameter software module may be reported instead.


5.3.5  Host-IP-Address AVP



Calhoun et al.             expires April 2003                  [Page 59]


Internet-Draft                                              October 2002


   The Host-IP-Address AVP (AVP Code 257) is of type IPAddress and is
   used to inform a Diameter peer of the sender's IP address. All source
   addresses that a Diameter node expects to use with SCTP [SCTP] MUST
   be advertised in the CER and CEA messages by including a Host-IP-
   Address AVP for each address. This AVP MUST ONLY be used in the CER
   and CEA messages.


5.3.6  Supported-Vendor-Id AVP

   The Supported-Vendor-Id AVP (AVP Code 265) is of type Unsigned32 and
   contains the IANA "SMI Network Management Private Enterprise Codes"
   [ASSIGNNO] value assigned to a vendor other than the device vendor.
   This is used in the CER and CEA messages in order to inform the peer
   that the sender supports a subset of the vendor-specific AVPs defined
   by the vendor identified in this AVP.


5.3.7  Product-Name AVP

   The Product-Name AVP (AVP Code 269) is of type UTF8String, and
   contains the vendor assigned name for the product. The Product-Name
   AVP SHOULD remain constant across firmware revisions for the same
   product.


5.4  Disconnecting Peer connections

   When a Diameter node disconnects one of its transport connections,
   its peer cannot know the reason for the disconnect, and will most
   likely assume that a connectivity problem occurred, or that the peer
   has rebooted. In these cases, the peer may periodically attempt to
   reconnect, as stated in section 2.1. In the event that the disconnect
   was a result of either a shortage of internal resources, or simply
   that the node in question has no intentions of forwarding any
   Diameter messages to the peer in the foreseeable future, a periodic
   connection request would not be welcomed. The Disconnection-Reason
   AVP contains the reason the Diameter node issued the Disconnect-Peer-
   Request message.

   The Disconnect-Peer-Request message is used by a Diameter node to
   inform its peer of its intent to disconnect the transport layer, and
   that the peer shouldn't reconnect unless it has a valid reason to do
   so (e.g. message to be forwarded). Upon receipt of the message, the
   Disconnect-Peer-Answer is returned, which SHOULD contain an error if
   messages have recently been forwarded, and are likely in flight,
   which would otherwise cause a race condition.




Calhoun et al.             expires April 2003                  [Page 60]


Internet-Draft                                              October 2002


   The receiver of the Disconnect-Peer-Answer initiates the transport
   disconnect.


5.4.1  Disconnect-Peer-Request

   The Disconnect-Peer-Request (DPR), indicated by the Command-Code set
   to 282 and the Command Flags' 'R' bit set, is sent to a peer to
   inform its intentions to shutdown the transport connection. Upon
   detection of a transport failure, this message MUST NOT be sent to an
   alternate peer.

   Message Format

      <DPR>  ::= < Diameter Header: 282, REQ >
                 { Origin-Host }
                 { Origin-Realm }
                 { Disconnect-Cause }


5.4.2  Disconnect-Peer-Answer

   The Disconnect-Peer-Answer (DPA), indicated by the Command-Code set
   to 282 and the Command Flags' 'R' bit cleared, is sent as a response
   to the Disconnect-Peer-Request message. Upon receipt of this message,
   the transport connection is shutdown.

   Message Format

      <DPA>  ::= < Diameter Header: 282 >
                 { Result-Code }
                 { Origin-Host }
                 { Origin-Realm }
                 [ Error-Message ]
               * [ Failed-AVP ]

5.4.3  Disconnect-Cause AVP

   The Disconnect-Cause AVP (AVP Code 273) is of type Enumerated. A
   Diameter node MUST include this AVP in the Disconnect-Peer-Request
   message to inform the peer of the reason for its intention to
   shutdown the transport connection. The following values are
   supported:

      REBOOTING                         0
         A scheduled reboot is imminent.

      BUSY                              1



Calhoun et al.             expires April 2003                  [Page 61]


Internet-Draft                                              October 2002


         The peer's internal resources are constrained, and it has
         determined that the transport connection needs to be closed.

      DO_NOT_WANT_TO_TALK_TO_YOU        2
         The peer has determined that it does not see a need for the
         transport connection to exist, since it does not expect any
         messages to be exchanged in the near future.


5.5  Transport Failure Detection

   Given the nature of the Diameter protocol, it is recommended that
   transport failures be detected as soon as possible. Detecting such
   failures will minimize the occurrence of messages sent to unavailable
   agents, resulting in unnecessary delays, and will provide better
   failover performance. The Device-Watchdog-Request and Device-
   Watchdog-Answer messages, defined in this section, are used to pro-
   actively detect transport failures.


5.5.1  Device-Watchdog-Request

   The Device-Watchdog-Request (DWR), indicated by the Command-Code set
   to 280 and the Command Flags' 'R' bit set, is sent to a peer when no
   traffic has been exchanged between two peers (see Section 5.5.3).
   Upon detection of a transport failure, this message MUST NOT be sent
   to an alternate peer.

   Message Format

      <DWR>  ::= < Diameter Header: 280, REQ >
                 { Origin-Host }
                 { Origin-Realm }
                 [ Origin-State-Id ]


5.5.2  Device-Watchdog-Answer

   The Device-Watchdog-Answer (DWA), indicated by the Command-Code set
   to 280 and the Command Flags' 'R' bit cleared, is sent as a response
   to the Device-Watchdog-Request message.

   Message Format








Calhoun et al.             expires April 2003                  [Page 62]


Internet-Draft                                              October 2002


      <DWA>  ::= < Diameter Header: 280 >
                 { Result-Code }
                 { Origin-Host }
                 { Origin-Realm }
                 [ Error-Message ]
               * [ Failed-AVP ]
                 [ Original-State-Id ]


5.5.3  Transport Failure Algorithm

   The transport failure algorithm is defined in [AAATRANS]. All
   Diameter implementations MUST support the algorithm defined in the
   specification in order to be compliant to the Diameter base protocol.


5.5.4  Failover and Failback Procedures

   In the event that a transport failure is detected with a peer, it is
   necessary for all pending request messages to be forwarded to an
   alternate agent, if possible. This is commonly referred to as
   failover.

   In order for a Diameter node to perform failover procedures, it is
   necessary for the node to maintain a pending message queue for a
   given peer. When an answer message is received, the corresponding
   request is removed from the queue. The Hop-by-Hop Identifier field is
   used to match the answer with the queued request.

   When a transport failure is detected, if possible all messages in the
   queue are sent to an alternate agent with the T flag set. On booting
   a Diameter client or agent, the T flag is also set on any records
   still remaining to be transmitted in non-volatile storage. An example
   of a case where it is not possible to forward the message to an
   alternate server is when the message has a fixed destination, and the
   unavailable peer is the message's final destination (see Destination-
   Host AVP). Such an error requires that the agent return an answer
   message with the 'E' bit set and the Result-Code AVP set to
   DIAMETER_UNABLE_TO_DELIVER.

   It is important to note that multiple identical requests or answers
   MAY be received as a result of a failover. The End-to-End Identifier
   field in the Diameter header along with the Origin-Host AVP MUST be
   used to identify duplicate messages.

   As described in section 2.1, a connection request should be
   periodically attempted with the failed peer in order to re-establish
   the transport connection. Once a connection has been successfully



Calhoun et al.             expires April 2003                  [Page 63]


Internet-Draft                                              October 2002


   established, messages can once again be forwarded to the peer. This
   is commonly referred to as failback.


5.6  Peer State Machine

   This section contains a finite state machine that MUST be observed by
   all Diameter implementations. Each Diameter node MUST follow the
   state machine described below when communicating with each peer.
   Multiple actions are separated by commas, and may continue on
   succeeding lines, as space requires. Similarly, state and next state
   may also span multiple lines, as space requires.

   This state machine is closely coupled with the state machine
   described in [AAATRANS], which is used to open, close, failover,
   probe, and reopen transport connections. Note in particular that
   [AAATRANS] requires the use of watchdog messages to probe
   connections. For Diameter, DWR and DWA messages are to be used.

   I- is used to represent the initiator (connecting) connection, while
   the R- is used to represent the responder (listening) connection. The
   lack of a prefix indicates that the event or action is the same
   regardless of the connection on which the event occurred.

   The stable states that a state machine may be in are Closed, I-Open
   and R-Open; all other states are intermediate. Note that I-Open and
   R-Open are equivalent except for whether the initiator or responder
   transport connection is used for communication.

   A CER message is always sent on the initiating connection immediately
   after the connection request is successfully completed. In the case
   of an election, one of the two connections will shut down. The
   responder connection will survive if the Origin-Host of the local
   Diameter entity is higher than that of the peer; the initiator
   connection will survive if the peer's Origin-Host is higher. All
   subsequent messages are sent on the surviving connection. Note that
   the results of an election on one peer are guaranteed to be the
   inverse of the results on the other.

   For TLS usage, a TLS handshake will begin when both ends are in the
   open state. If the TLS handshake is successful, all further messages
   will be sent via TLS. If the handshake fails, both ends move to the
   closed state.

   The state machine constrains only the behavior of a Diameter
   implementation as seen by Diameter peers through events on the wire.
   Any implementation that produces equivalent results is considered
   compliant.



Calhoun et al.             expires April 2003                  [Page 64]


Internet-Draft                                              October 2002


      state            event              action         next state
      -----------------------------------------------------------------
      Closed           Start            I-Snd-Conn-Req   Wait-Conn-Ack
                       R-Conn-CER       R-Accept,        R-Open
                                        Process-CER,
                                        R-Snd-CEA

      Wait-Conn-Ack    I-Rcv-Conn-Ack   I-Snd-CER        Wait-I-CEA
                       I-Rcv-Conn-Nack  Cleanup          Closed
                       R-Conn-CER       R-Accept,        Wait-Conn-Ack/
                                        Process-CER      Elect
                       Timeout          Error            Closed

      Wait-I-CEA       I-Rcv-CEA        Process-CEA      I-Open
                       R-Conn-CER       R-Accept,        Wait-Returns
                                        Process-CER,
                                        Elect
                       I-Peer-Disc      I-Disc           Closed
                       I-Rcv-Non-CEA    Error            Closed
                       Timeout          Error            Closed

      Wait-Conn-Ack/   I-Rcv-Conn-Ack   I-Snd-CER,Elect  Wait-Returns
      Elect            I-Rcv-Conn-Nack  R-Snd-CEA        R-Open
                       R-Peer-Disc      R-Disc           Wait-Conn-Ack
                       R-Conn-CER       R-Reject         Wait-Conn-Ack/
                                                         Elect
                       Timeout          Error            Closed

      Wait-Returns     Win-Election     I-Disc,R-Snd-CEA R-Open
                       I-Peer-Disc      I-Disc,          R-Open
                                        R-Snd-CEA
                       I-Rcv-CEA        R-Disc           I-Open
                       R-Peer-Disc      R-Disc           Wait-I-CEA
                       R-Conn-CER       R-Reject         Wait-Returns
                       Timeout          Error            Closed

      R-Open           Send-Message     R-Snd-Message    R-Open
                       R-Rcv-Message    Process          R-Open
                       R-Rcv-DWR        Process-DWR,     R-Open
                                        R-Snd-DWA
                       R-Rcv-DWA        Process-DWA      R-Open
                       R-Conn-CER       R-Reject         R-Open
                       Stop             R-Snd-DPR        Closing
                       R-Rcv-DPR        R-Snd-DPA,       Closed
                                        R-Disc
                       R-Peer-Disc      R-Disc           Closed
                       R-Rcv-CER        R-Snd-CEA        R-Open
                       R-Rcv-CEA        Process-CEA      R-Open



Calhoun et al.             expires April 2003                  [Page 65]


Internet-Draft                                              October 2002


      I-Open           Send-Message     I-Snd-Message    I-Open
                       I-Rcv-Message    Process          I-Open
                       I-Rcv-DWR        Process-DWR,     I-Open
                                        I-Snd-DWA
                       I-Rcv-DWA        Process-DWA      I-Open
                       R-Conn-CER       R-Reject         I-Open
                       Stop             I-Snd-DPR        Closing
                       I-Rcv-DPR        I-Snd-DPA,       Closed
                                        I-Disc
                       I-Peer-Disc      I-Disc           Closed
                       I-Rcv-CER        I-Snd-CEA        I-Open
                       I-Rcv-CEA        Process-CEA      I-Open

      Closing          I-Rcv-DPA        I-Disc           Closed
                       R-Rcv-DPA        R-Disc           Closed
                       Timeout          Error            Closed
                       I-Peer-Disc      I-Disc           Closed
                       R-Peer-Disc      R-Disc           Closed


5.6.1  Incoming connections

   When a connection request is received from a Diameter peer, it is
   not, in the general case, possible to know the identity of that peer
   until a CER is received from it. This is because host and port
   determine the identity of a Diameter peer; and the source port of an
   incoming connection is arbitrary. Upon receipt of CER, the identity
   of the connecting peer can be uniquely determined from Origin-Host.

   For this reason, a Diameter peer must employ logic separate from the
   state machine to receive connection requests, accept them, and await
   CER. Once CER arrives on a new connection, the Origin-Host that
   identifies the peer is used to locate the state machine associated
   with that peer, and the new connection and CER are passed to the
   state machine as an R-Conn-CER event.

   The logic that handles incoming connections SHOULD close and discard
   the connection if any message other than CER arrives, or if an
   implementation-defined timeout occurs prior to receipt of CER.

   Because handling of incoming connections up to and including receipt
   of CER requires logic, separate from that of any individual state
   machine associated with a particular peer, it is described separately
   in this section rather than in the state machine above.


5.6.2  Events




Calhoun et al.             expires April 2003                  [Page 66]


Internet-Draft                                              October 2002


   Transitions and actions in the automaton are caused by events. In
   this section, we will ignore the -I and -R prefix, since the actual
   event would be identical, but would occur on one of two possible
   connections.

      Start          The Diameter application has signaled that a
                     connection should be initiated with the peer.

      R-Conn-CER     An acknowledgement is received stating that the
                     transport connection has been established, and the
                     associated CER has arrived.

      Rcv-Conn-Ack   A positive acknowledgement is received confirming
                     that the transport connection is established.

      Rcv-Conn-Nack  A negative acknowledgement was received stating
                     that the transport connection was not established.

      Timeout        An application-defined timer has expired while
                     waiting for some event.

      Rcv-CER        A CER message from the peer was received.

      Rcv-CEA        A CEA message from the peer was received.

      Rcv-Non-CEA    A message other than CEA from the peer was
                     received.

      Peer-Disc      A disconnection indication from the peer was
                     received.

      Rcv-DPR        A DPR message from the peer was received.

      Rcv-DPA        A DPA message from the peer was received.

      Win-Election   An election was held, and the local node was the
                     winner.

      Send-Message   A message is to be sent.

      Rcv-Message    A message other than CER, CEA, DPR, DPA, DWR or DWA
                     was received.

      Stop           The Diameter application has signaled that a
                     connection should be terminated (e.g., on system
                     shutdown).





Calhoun et al.             expires April 2003                  [Page 67]


Internet-Draft                                              October 2002


5.6.3  Actions

   Actions in the automaton are caused by events and typically indicate
   the transmission of packets and/or an action to be taken on the
   connection. In this section we will ignore the I- and R- prefix,
   since the actual action would be identical, but would occur on one of
   two possible connections.

      Snd-Conn-Req   A transport connection is initiated with the peer.

      Accept         The incoming connection associated with the R-Conn-
                     CER is accepted as the responder connection.

      Reject         The incoming connection associated with the R-Conn-
                     CER is disconnected.

      Process-CER    The CER associated with the R-Conn-CER is
                     processed.

      Snd-CER        A CER message is sent to the peer.

      Snd-CEA        A CEA message is sent to the peer.

      Cleanup        If necessary, the connection is shutdown, and any
                     local resources are freed.

      Error          The transport layer connection is disconnected,
                     either politely or abortively, in response to an
                     error condition. Local resources are freed.

      Process-CEA    A received CEA is processed.

      Snd-DPR        A DPR message is sent to the peer.

      Snd-DPA        A DPA message is sent to the peer.

      Disc           The transport layer connection is disconnected, and
                     local resources are freed.

      Elect          An election occurs (see Section 5.6.4 for more
                     information).

      Snd-Message    A message is sent.

      Snd-DWR        A DWR message is sent.

      Snd-DWA        A DWA message is sent.




Calhoun et al.             expires April 2003                  [Page 68]


Internet-Draft                                              October 2002


      Process-DWR    The DWR message is serviced.

      Process-DWA    The DWA message is serviced.

      Process        A message is serviced.


5.6.4  The Election Process

   The election is performed on the responder. The responder compares
   the Origin-Host received in the CER sent by its peer with its own
   Origin-Host. If the local Diameter entity's Origin-Host is higher
   than the peer's, a Win-Election event is issued locally.

   The comparison proceeds by considering the shorter OctetString to be
   padded with zeros so that it length is the same as the length of the
   longer, then performing an octet-by-octet unsigned comparison with
   the first octet being most significant. Hanging octets are assumed to
   have value 0x80.


6  Diameter message processing

   This section describes how Diameter requests and answers are created
   and processed.


6.1  Diameter Request Routing Overview

   A request is sent towards its final destination using a combination
   of the Destination-Realm and Destination-Host AVPs, in one of these
   three combinations:
      - a request that is not able to be proxied (such as CER) MUST NOT
        contain either Destination-Realm or Destination-Host AVPs.
      - a request that needs to be sent to a home server serving a
        specific realm, but not to a specific server (such as the first
        request of a series of round-trips), MUST contain a Destination-
        Realm AVP, but MUST NOT contain a Destination-Host AVP.
      - otherwise, a request that needs to be sent to a specific home
        server among those serving a given realm, MUST contain both the
        Destination-Realm and Destination-Host AVPs.

   The Destination-Host AVP is used as described above when the
   destination of the request is fixed, which includes:
      - Authentication requests that span multiple round trips
      - A Diameter message that uses a security mechanism that makes use
        of a pre-established session key shared between the source and
        the final destination of the message.



Calhoun et al.             expires April 2003                  [Page 69]


Internet-Draft                                              October 2002


      - Server initiated messages that MUST be received by a specific
        Diameter client (e.g. access device), such as the Abort-Session-
        Request message, which is used to request that a particular
        user's session be terminated.

   Note that an agent can forward a request to a host described in the
   Destination-Host AVP only if the host in question is included in its
   peer table (see section 2.7). Otherwise, the request is routed based
   on the Destination-Realm only (see sections 6.1.6).

   The Destination-Realm AVP MUST be present if the message is
   proxiable. Request messages that may be forwarded by Diameter agents
   (proxies, redirects or relays) MUST also contain an Acct-Application-
   Id AVP, an Auth-Application-Id AVP or a Vendor-Specific-Application-
   Id AVP. A message that MUST NOT be forwarded by Diameter agents
   (proxies, redirects or relays) MUST not include the Destination-Realm
   in its ABNF. The value of the Destination-Realm AVP MAY be extracted
   from the User-Name AVP, or other application-specific methods.

   When a message is received, the message is processed in the following
   order:
      1. If the message is destined for the local host, the procedures
         listed in section 6.1.4 are followed.
      2. If the message is intended for a Diameter peer with whom the
         local host is able to directly communicate, the procedures
         listed in section 6.1.5 are followed. This is known as Request
         Forwarding.
      3. The procedures listed in section 6.1.6 are followed, which is
         known as Request Routing.
      4. If none of the above is successful, an answer is returned with
         the Result-Code set to DIAMETER_UNABLE_TO_DELIVER.

   For routing of Diameter messages to work within an administrative
   domain, all Diameter nodes within the realm MUST be peers.

   Note the processing rules contained in this section are intended to
   be used as general guidelines to Diameter developers. Certain
   implementations MAY use different methods than the ones described
   here, and still comply with the protocol specification.


6.1.1  Originating a Request

   When creating a request, in addition to any other procedures
   described in the application definition for that specific request,
   the following procedures MUST be followed:
      - the Command-Code should be set to the appropriate value
      - the 'R' bit should be set



Calhoun et al.             expires April 2003                  [Page 70]


Internet-Draft                                              October 2002


      - the End-to-End Identifier should be set to a locally unique
        value
      - the Origin-Host and Origin-Realm AVPs MUST be set to the
        appropriate values, used to identify the source of the message
      - the Destination-Host and Destination-Realm AVPs MUST be set to
        the appropriate values as described in section 6.1.
      - an Acct-Application-Id AVP, an Auth-Application-Id or a Vendor-
        Specific-Application-Id AVP must be included if the request is
        proxiable.

6.1.2  Sending a Request

   When sending a request, originated either locally, or as the result
   of a forwarding or routing operation, the following procedures MUST
   be followed:
      - the Hop-by-Hop Identifier should be set to a locally unique
        value
      - The message should be saved in the list of pending requests.

   Other actions to perform on the message based on the particular role
   the agent is playing are described in the following sections.


6.1.3  Receiving Requests

   A relay or proxy agent MUST check for forwarding loops when receiving
   requests. A loop is detected if the server finds its own identity in
   a Route-Record AVP. When such an event occurs, the agent MUST answer
   with the Result-Code AVP set to DIAMETER_LOOP_DETECTED.


6.1.4  Processing Local Requests

   A request is known to be for local consumption when one of the
   following conditions occur:
      - The Destination-Host AVP contains the local host's identity,
      - The Destination-Host AVP is not present, the Destination-Realm
        AVP contains a realm the server is configured to process
        locally, and the Diameter application is locally supported, or
      - Both the Destination-Host and the Destination-Realm are not
        present.

   When a request is locally processed, the rules in section 6.2 should
   be used to generate the corresponding answer.


6.1.5  Request Forwarding




Calhoun et al.             expires April 2003                  [Page 71]


Internet-Draft                                              October 2002


   Request forwarding is done using the Diameter Peer Table. The
   Diameter peer table contains all of the peers that the local node is
   able to directly communicate with.

   When a request is received, and the host encoded in the Destination-
   Host AVP is one that is present in the peer table, the message SHOULD
   be forwarded to the peer.


6.1.6  Request Routing

   Diameter request message routing is done via realms and applications.
   A Diameter message that may be forwarded by Diameter agents (proxies,
   redirects or relays) MUST include the target realm in the
   Destination-Realm AVP and one of the application identification AVPs
   Auth-Application-Id, Acct-Application-Id or Vendor-Specific-
   Application-Id. The realm MAY be retrieved from the User-Name AVP,
   which is in the form of a Network Access Identifier (NAI). The realm
   portion of the NAI is inserted in the Destination-Realm AVP.

   Diameter agents MAY have a list of locally supported realms and
   applications, and MAY have a list of externally supported realms and
   applications. When a request is received that includes a realm and/or
   application that is not locally supported, the message is routed to
   the peer configured in the Realm Routing Table table (see section
   2.7).


6.1.7  Redirecting requests

   When a redirect agent receives a request whose routing entry is set
   to REDIRECT, it MUST reply with an answer message with the 'E' bit
   set, while maintaining the Hop-by-Hop Identifier in the header, and
   include the Result-Code AVP to DIAMETER_REDIRECT_INDICATION. Each of
   the servers associated with the routing entry are added in separate
   Redirect-Host AVP.















Calhoun et al.             expires April 2003                  [Page 72]


Internet-Draft                                              October 2002


                     +------------------+
                     |     Diameter     |
                     |  Redirect Agent  |
                     +------------------+
                      ^    |    2. command + 'E' bit
       1. Request     |    |    Result-Code =
          joe@xyz.com |    |    DIAMETER_REDIRECT_INDICATION +
                      |    |    Redirect-Host AVP(s)
                      |    v
                    +---------+  3. Request  +----------+
                    | abc.net |------------->| xyz.net  |
                    |  Relay  |              | Diameter |
                    |  Agent  |<-------------|  Server  |
                    +---------+  4. Answer   +----------+
                     Figure 6: Diameter Redirect Agent

   The receiver of the answer message with the 'E' bit set, and the
   Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the hop-by-
   hop field in the Diameter header to identify the request in the
   pending message queue (see Section 5.3) that is to be redirected. If
   no transport connection exists with the new agent, one is created,
   and the request is sent directly to it.

   Multiple Redirect-Host AVPs are allowed. The receiver of the answer
   message with the 'E' bit set selects exactly one of these hosts as
   the destination of the redirected message.

6.1.8  Relaying and Proxying Requests

   A relay or proxy agent MUST append a Route-Record AVP to all requests
   forwarded. The AVP contains the identity of the peer the request was
   received from.

   The Hop-by-Hop identifier in the request is saved, and replaced with
   a locally unique value. The source of the request is also saved,
   which includes the IP address, port and protocol.

   A Relay or Proxy agent MAY include the Proxy-Info AVP in requests if
   it requires access to any local state information when the
   corresponding response is received. Alternatively, it MAY simply use
   local storage to store state information.

   The message is then forwarded to the next hop, as identified in the
   Realm Routing Table.

   Figure 7 provides an example of message routing using the procedures
   listed in these sections.




Calhoun et al.             expires April 2003                  [Page 73]


Internet-Draft                                              October 2002


          (Origin-Host=nas.mno.net)    (Origin-Host=nas.mno.net)
          (Origin-Realm=mno.net)       (Origin-Realm=mno.net)
          (Destination-Realm=abc.com)  (Destination-Realm=abc.com)
                                       (Route-Record=nas.mno.net)
      +------+      ------>      +------+      ------>      +------+
      |      |     (Request)     |      |      (Request)    |      |
      | NAS  +-------------------+ DRL  +-------------------+ HMS  |
      |      |                   |      |                   |      |
      +------+      <------      +------+      <------      +------+
      mno.net      (Answer)      mno.net       (Answer)     abc.com
          (Origin-Host=hms.abc.com)   (Origin-Host=hms.abc.com)
          (Origin-Realm=abc.com)      (Origin-Realm=abc.com)
                  Figure 7: Routing of Diameter messages


6.2  Diameter Answer Processing

   When a request is locally processed, the following procedures MUST be
   applied to create the associated answer, in addition to any
   additional procedures that MAY be discussed in the Diameter
   application defining the command:

      - The same Hop-by-Hop identifier in the request is used in the
        answer.
      - The local host's identity is encoded in the Origin-Host AVP.
      - The Destination-Host and Destination-Realm AVPs MUST NOT be
        present in the answer message.
      - The Result-Code AVP is added with its value indicating success
        or failure.
      - If the Session-Id is present in the request, it MUST be included
        in the answer.
      - Any Proxy-Info AVPs in the request MUST be added to the answer
        message, in the same order they were present in the request.
      - The 'P' bit is set to the same value as the one in the request.
      - The same End-to-End identifier in the request is used in the
        answer.

   Note that the error messages (see section 7.2) are also subjected to
   the above processing rules.


6.2.1  Processing received Answers

   A Diameter client or proxy MUST match the Hop-by-Hop Identifier in an
   answer received against the list of pending requests. The
   corresponding message should be removed from the list of pending
   requests. It SHOULD ignore answers received that do not match a known
   Hop-by-Hop Identifier.



Calhoun et al.             expires April 2003                  [Page 74]


Internet-Draft                                              October 2002


6.2.2  Relaying and Proxying Answers

   If the answer is for a request which was proxied or relayed, the
   agent MUST restore the original value of the Diameter header's Hop-
   by-Hop Identifier field.

   If the last Proxy-Info AVP in the message is targeted to the local
   Diameter server, the AVP MUST be removed before the answer is
   forwarded.

   If a relay or proxy agent receives an answer with a Result-Code AVP
   indicating a failure, it MUST NOT modify the contents of the AVP. Any
   additional local errors detected SHOULD be logged, but not reflected
   in the Result-Code AVP. If the agent receives an answer message with
   a Result-Code AVP indicating success, and it wishes to modify the AVP
   to indicate an error, it MUST modify the Result-Code AVP to contain
   the appropriate error in the message destined towards the access
   device as well as include the Error-Reporting-Host AVP and it MUST
   issue an STR on behalf of the access device.

   The agent MUST then send the answer to the host that it received the
   original request from.


6.3  Origin-Host AVP

   The Origin-Host AVP (AVP Code 264) is of type DiameterIdentity, and
   MUST be present in all Diameter messages. This AVP identifies the
   endpoint that originated the Diameter message. Relay agents MUST NOT
   modify this AVP.

   The value of the Origin-Host AVP is guaranteed to be unique within a
   single host.

   Note that the Origin-Host AVP may resolve to more than one address as
   the Diameter peer may support more than one address.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.


6.4  Origin-Realm AVP

   The Origin-Realm AVP (AVP Code 296) is of type DiameterIdentity. This
   AVP contains the Realm of the originator of any Diameter message and
   MUST be present in all messages.

   This AVP SHOULD be placed as close to the Diameter header as



Calhoun et al.             expires April 2003                  [Page 75]


Internet-Draft                                              October 2002


   possible.


6.5  Destination-Host AVP

   The Destination-Host AVP (AVP Code 293) is of type DiameterIdentity.
   This AVP MUST be present in all unsolicited agent initiated messages,
   MAY be present in request messages, and MUST NOT be present in Answer
   messages.

   The absence of the Destination-Host AVP will cause a message to be
   sent to any Diameter server supporting the application within the
   realm specified in Destination-Realm AVP.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.


6.6  Destination-Realm AVP

   The Destination-Realm AVP (AVP Code 283) is of type DiameterIdentity,
   and contains the realm the message is to be routed to. The
   Destination-Realm AVP MUST NOT be present in Answer messages.
   Diameter Clients insert the realm portion of the User-Name AVP.
   Diameter servers initiating a request message use the value of the
   Origin-Realm AVP from a previous message received from the intended
   target host (unless it is known a priori). When present, the
   Destination-Realm AVP is used to perform message routing decisions.

   Request messages whose ABNF does not list the Destination-Realm AVP
   as a mandatory AVP are inherently non-routable messages.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.


6.7  Routing AVPs

   The AVPs defined in this section are Diameter AVPs used for routing
   purposes. These AVPs change as Diameter messages are processed by
   agents, and therefore MUST NOT be protected by end-to-end security.


6.7.1  Route-Record AVP

   The Route-Record AVP (AVP Code 282) is of type DiameterIdentity. The
   identity added in this AVP MUST be the same as the one received in
   the Origin-Host of the Capabilities Exchange message.



Calhoun et al.             expires April 2003                  [Page 76]


Internet-Draft                                              October 2002


6.7.2  Proxy-Info AVP

   The Proxy-Info AVP (AVP Code 284) is of type Grouped.  The Grouped
   Data field has the following ABNF grammar:

      Proxy-Info ::= < AVP Header: 284 >
                     { Proxy-Host }
                     { Proxy-State }
                   * [ AVP ]


6.7.3  Proxy-Host AVP

   The Proxy-Host AVP (AVP Code 280) is of type DiameterIdentity. This
   AVP contains the identity of the host that added the Proxy-Info AVP.


6.7.4  Proxy-State AVP

   The Proxy-State AVP (AVP Code 33) is of type OctetString, and
   contains state local information, and MUST be treated as opaque data.


6.8  Auth-Application-Id AVP

   The Auth-Application-Id AVP (AVP Code 258) is of type Unsigned32 and
   is used in order to advertise support of the Authentication and
   Authorization portion of an application (see Section 2.4). The Auth-
   Application-Id MUST also be present in all Authentication and/or
   Authorization messages that are defined in a separate Diameter
   specification and have an Application ID assigned.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.


6.9  Acct-Application-Id AVP

   The Acct-application-Id AVP (AVP Code 259) is of type Unsigned32 and
   is used in order to advertise support of the Accounting portion of an
   application (see Section 2.4). The Acct-Application-Id MUST also be
   present in all Accounting messages.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.


6.10 Inband-Security-Id AVP



Calhoun et al.             expires April 2003                  [Page 77]


Internet-Draft                                              October 2002


   The Inband-Security-Id AVP (AVP Code 299) is of type Unsigned32 and
   is used in order to advertise support of the Security portion of the
   application.

   Currently, the following values are supported, but there is ample
   room to add new security Ids.

   NO_INBAND_SECURITY                   0
         This peer does not support the TLS security model.  This is the
         default value, if the AVP is omitted.

   TLS                               1
         This node supports TLS security, as defined by [TLS].


6.11  Vendor-Specific-Application-Id AVP

   The Vendor-Specific-Application-Id AVP (AVP Code 260) is of type
   Grouped and is used to advertise support of a vendor-specific
   Diameter Application. Exactly one of the Auth-Application-Id and
   Acct-Application-Id AVPs MAY be present.

   This AVP MUST also be present as the first AVP in all experimental
   commands defined in the vendor-specific application.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.

   AVP Format

      <Vendor-Specific-Application-Id> ::= < AVP Header: 260 >
                                        1* [ Vendor-Id ]
                                        0*1{ Auth-Application-Id }
                                        0*1{ Acct-Application-Id }


6.12  Redirect-Host AVP

   One or more of instances of this AVP MUST be present if the answer
   message's 'E' bit is set and the Result-Code AVP is set to
   DIAMETER_REDIRECT_INDICATION.

   Upon receiving the above, the receiving Diameter node SHOULD forward
   the request directly to one of the hosts identified in these AVPs.
   The server contained in the selected Redirect-Host AVP SHOULD be used
   for all messages pertaining to this session.

6.13  Redirect-Host-Usage AVP



Calhoun et al.             expires April 2003                  [Page 78]


Internet-Draft                                              October 2002


   The Redirect-Host-Usage AVP (AVP Code 261) is of type Enumerated.
   This AVP MAY be present in answer messages whose 'E' bit is set and
   the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION.

   When present, this AVP dictates how the routing entry resulting from
   the Redirect-Host is to be used. The following values are supported:

      DONT_CACHE                        0
         The host specified in the Redirect-Host AVP should not be
         cached. This is the default value.

      ALL_SESSION                       1
         All messages within the same session, as defined by the same
         value of the Session-ID AVP MAY be sent to the host specified
         in the Redirect-Host AVP.

      ALL_REALM                         2
         All messages destined for the realm requested MAY be sent to
         the host specified in the Redirect-Host AVP.

      REALM_AND_APPLICATION             3
         All messages for the application requested to the realm
         specified MAY be sent to the host specified in the Redirect-
         Host AVP.

      ALL_APPLICATION                   4
         All messages for the application requested MAY be sent to the
         host specified in the Redirect-Host AVP.

      ALL_HOST                          5
         All messages that would be sent to the host that generated the
         Redirect-Host MAY be sent to the host specified in the
         Redirect-Host AVP.

      ALL_USER                          6
         All messages for the user requested MAY be sent to the host
         specified in the Redirect-Host AVP.

6.14  Redirect-Max-Cache-Time AVP

   The Redirect-Max-Cache-Time AVP (AVP Code 262) is of type Unsigned32.
   This AVP MUST be present in answer messages whose 'E' bit is set, the
   Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION and the
   Redirect-Host-Usage AVP set to a non-zero value.

   This AVP contains the maximum number of seconds the peer and route
   table entries, created as a result of the Redirect-Host, will be
   cached. Note that once a host created due to a redirect indication is



Calhoun et al.             expires April 2003                  [Page 79]


Internet-Draft                                              October 2002


   no longer reachable, any associated peer and routing table entries
   MUST be deleted.

6.15  E2E-Sequence AVP

   The E2E-Sequence AVP provides anti-replay protection for end to end
   messages and is of type grouped. It contains a random value (an
   OctetString with a nonce) and counter (an Integer). For each end-to-
   end peer with which a node communicates (or remembers communicating)
   a different nonce value MUST be used and the counter is intitiated at
   zero and increases by one each time this AVP is emitted to that peer.
   This AVP MUST be included in all messages which use end-to-end
   protection (e.g. CMS signing or encryption).


7  Error Handling

   There are two different types of errors in Diameter; protocol and
   application errors. A protocol error is one that occurs at the base
   protocol level, and MAY require per hop attention (e.g. message
   routing error). Application errors, on the other hand, are generally
   occur due to a problem with a function specified in a Diameter
   application (e.g. user authentication, Missing AVP).

   Result-Code AVP values that are used to report protocol errors MUST
   only be present in answer messages whose 'E' bit is set. When a
   request message is received that causes a protocol error, an answer
   message is returned with the 'E' bit set, and the Result-Code AVP is
   set to the appropriate protocol error value. As the answer is sent
   back towards the originator of the request, each proxy or relay agent
   MAY take action on the message.

                    1. Request        +---------+ Link Broken
          +-------------------------->|Diameter |----///----+
          |     +---------------------|         |           v
   +------+--+  | 2. answer + 'E' set | Relay 2 |     +--------+
   |Diameter |<-+ (Unable to Forward) +---------+     |Diameter|
   |         |                                        |  Home  |
   | Relay 1 |--+                     +---------+     | Server |
   +---------+  |   3. Request        |Diameter |     +--------+
                +-------------------->|         |           ^
                                      | Relay 3 |-----------+
                                      +---------+
        Figure 8:  Example of Protocol Error causing answer message

   Figure 8 provides an example of a message forwarded upstream by a
   Diameter relay. When the message is received by Relay 2, and it
   detects that it cannot forward the request to the home server, an



Calhoun et al.             expires April 2003                  [Page 80]


Internet-Draft                                              October 2002


   answer message is returned with the 'E' bit set and the Result-Code
   AVP set to DIAMETER_UNABLE_TO_DELIVER. Given that this error falls
   within the protocol error category, Relay 1 would take special
   action, and given the error, attempt to route the message through its
   alternate Relay 3.

   +---------+ 1. Request  +---------+ 2. Request  +---------+
   | Access  |------------>|Diameter |------------>|Diameter |
   |         |             |         |             |  Home   |
   | Device  |<------------|  Relay  |<------------| Server  |
   +---------+  4. Answer  +---------+  3. Answer  +---------+
              (Missing AVP)           (Missing AVP)
           Figure 9: Example of Application Error Answer message

   Figure 9 provides an example of a Diameter message that caused an
   application error. When application errors occur, the Diameter entity
   reporting the error clears the 'R' bit in the Command Flags, and adds
   the Result-Code AVP with the proper value. Application errors do not
   require any proxy or relay agent involvement, and therefore the
   message would be forwarded back to the originator of the request.

   There are certain Result-Code AVP application errors that require
   additional AVPs to be present in the answer. In these cases, the
   Diameter node that sets the Result-Code AVP to indicate the error
   MUST add the AVPs. Examples are:

      - An unrecognized AVP is received with the 'M' bit (Mandatory bit)
        set, causes an answer to be sent with the Result-Code AVP set to
        DIAMETER_AVP_UNSUPPORTED, and the Failed-AVP AVP containing the
        offending AVP.
      - An AVP that is received with an unrecognized value causes an
        answer to be returned with the Result-Code AVP set to
        DIAMETER_INVALID_AVP_VALUE, with the Failed-AVP AVP containing
        the AVP causing the error.
      - A command is received with an AVP that is omitted, yet is
        mandatory according to the command's ABNF. The receiver issues
        an answer with the Result-Code set to DIAMETER_MISSING_AVP, and
        creates an AVP with the AVP Code and other fields set as
        expected in the missing AVP. The created AVP is then added to
        the Failed-AVP AVP.

   The Result-Code AVP describes the error that the Diameter node
   encountered in its processing. In case there are multiple errors, the
   Diameter node MUST report only the first error it encountered
   (detected possibly in some implementation dependent order). The
   specific errors that can be described by this AVP are described in
   the following section.




Calhoun et al.             expires April 2003                  [Page 81]


Internet-Draft                                              October 2002


7.1  Result-Code AVP

   The Result-Code AVP (AVP Code 268) is of type Unsigned32 and
   indicates whether a particular request was completed successfully or
   whether an error occurred. All Diameter answer messages defined in
   IETF applications MUST include one Result-Code AVP. A non-successful
   Result-Code AVP (one containing a non 2xxx value other than
   DIAMETER_REDIRECT_INDICATION) MUST include the Error-Reporting-Host
   AVP if the host setting the Result-Code AVP is different from the
   identity encoded in the Origin-Host AVP.

   The Result-Code data field contains an IANA-managed 32-bit address
   space representing errors (see section 11.4). Diameter provides the
   following classes of errors, all identified by the thousands digit in
   the decimal notation:
      - 1xxx (Informational)
      - 2xxx (Success)
      - 3xxx (Protocol Errors)
      - 4xxx (Transient Failures)
      - 5xxx (Permanent Failure)

   A non-recognize class (one whose first digit is not defined in this
   section) MUST be handled as a permanent failure.


7.1.1  Informational

   Errors that fall within this category are used to inform the
   requester that a request could not be satisfied, and additional
   action is required on its part before access is granted.

      DIAMETER_MULTI_ROUND_AUTH         1001
         This informational error is returned by a Diameter server to
         inform the access device that the authentication mechanism
         being used required multiple round trips, and a subsequent
         request needs to be issued in order for access to be granted.


7.1.2  Success

   Errors that fall within the Success category are used to inform a
   peer that a request has been successfully completed.

      DIAMETER_SUCCESS                   2001
         The Request was successfully completed.

      DIAMETER_LIMITED_SUCCESS           2002
         When returned, the request was successfully completed, but



Calhoun et al.             expires April 2003                  [Page 82]


Internet-Draft                                              October 2002


         additional processing is required by the application in order
         to provide service to the user.


7.1.3  Protocol Errors

   Errors that fall within the Protocol Error category SHOULD be treated
   on a per-hop basis, and Diameter proxies MAY attempt to correct the
   error, if it is possible. Note that these and only these errors MUST
   only be used in answer messages whose 'E' bit is set.

      DIAMETER_COMMAND_UNSUPPORTED       3001
         The Request contained a Command-Code that the receiver did not
         recognize or support.  This MUST be used when when a Diameter
         node receives an experimental command that it does not
         understand.

      DIAMETER_UNABLE_TO_DELIVER         3002
         This error is given when Diameter can not deliver the message
         to the destination, either because no host within the realm
         supporting the required application was available to process
         the request, or because Destination-Host AVP was given without
         the associated Destination-Realm AVP.

      DIAMETER_REALM_NOT_SERVED          3003
         The intended realm of the request is not recognized.

      DIAMETER_TOO_BUSY                  3004
         When returned, a Diameter node SHOULD attempt to send the
         message to an alternate peer. This error MUST only be used when
         a specific server is requested, and it cannot provide the
         requested service.

      DIAMETER_LOOP_DETECTED             3005
         An agent detected a loop while trying to get the message to the
         intended recipient. The message MAY be sent to an alternate
         peer, if one is available, but the peer reporting the error has
         identified a configuration problem.

      DIAMETER_REDIRECT_INDICATION       3006
         A redirect agent has determined that the request could not be
         satisfied locally and the initiator of the request should
         direct the request directly to the server, whose contact
         information has been added to the response. When set, the
         Redirect-Host AVP MUST be present.

      DIAMETER_APPLICATION_UNSUPPORTED   3007
         A request was sent for an application that is not supported.



Calhoun et al.             expires April 2003                  [Page 83]


Internet-Draft                                              October 2002


      DIAMETER_INVALID_HDR_BITS          3008
         A request was received whose bits in the Diameter header were
         either set to an invalid combination, or to a value that is
         inconsistent with the command code's definition.

      DIAMETER_INVALID_AVP_BITS          3009
         A request was received that included an AVP whose flag bits are
         set to an unrecognized value, or that is inconsistent with the
         AVP's definition.

      DIAMETER_UNKNOWN_PEER              3010
         A CER was received from an unknown peer.


7.1.4  Transient Failures

   Errors that fall within the transient failures category are used to
   inform a peer that the request could not be satisfied at the time it
   was received, but MAY be able to satisfy the request in the future.

      DIAMETER_AUTHENTICATION_REJECTED   4001
         The authentication process for the user failed, most likely due
         to an invalid password used by the user. Further attempts MUST
         only be tried after prompting the user for a new password.

      DIAMETER_OUT_OF_SPACE              4002
         A Diameter node received the accounting request but was unable
         to commit it to stable storage due to a temporary lack of
         space.

      ELECTION_LOST                      4003
         The peer has determined that it has lost the election process
         and has therefore disconnected the transport connection.


7.1.5  Permanent Failures

   Errors that fall within the permanent failures category are used to
   inform the peer that the request failed, and should not be attempted
   again.

      DIAMETER_AVP_UNSUPPORTED           5001
         The peer received a message that contained an AVP that is not
         recognized or supported and was marked with the Mandatory bit.
         A Diameter message with this error MUST contain one or more
         Failed-AVP AVP containing the AVPs that caused the failure.

      DIAMETER_UNKNOWN_SESSION_ID        5002



Calhoun et al.             expires April 2003                  [Page 84]


Internet-Draft                                              October 2002


         The request contained an unknown Session-Id.

      DIAMETER_AUTHORIZATION_REJECTED    5003
         A request was received for which the user could not be
         authorized. This error could occur if the service requested is
         not permitted to the user.

      DIAMETER_INVALID_AVP_VALUE         5004
         The request contained an AVP with an invalid value in its data
         portion. A Diameter message indicating this error MUST include
         the offending AVPs within a Failed-AVP AVP.

      DIAMETER_MISSING_AVP               5005
         The request did not contain an AVP that is required by the
         Command Code definition. If this value is sent in the Result-
         Code AVP, a Failed-AVP AVP SHOULD be included in the message.
         The Failed-AVP AVP MUST contain an example of the missing AVP
         complete with the Vendor-Id if applicable. The value field of
         the missing AVP should be of correct minimum length and contain
         zeroes.

      DIAMETER_RESOURCES_EXCEEDED        5006
         A request was received that cannot be authorized because the
         user has already expended allowed resources. An example of this
         error condition is a user that is restricted to one dial-up PPP
         port, attempts to establish a second PPP connection.

      DIAMETER_CONTRADICTING_AVPS        5007
         The Home Diameter server has detected AVPs in the request that
         contradicted each other, and is not willing to provide service
         to the user. One or more Failed-AVP AVPs MUST be present,
         containing the AVPs that contradicted each other.

      DIAMETER_AVP_NOT_ALLOWED           5008
         A message was received with an AVP that MUST NOT be present.
         The Failed-AVP AVP MUST be included and contain a copy of the
         offending AVP.

      DIAMETER_AVP_OCCURS_TOO_MANY_TIMES 5009
         A message was received that included an AVP that appeared more
         often than permitted in the message definition. The Failed-AVP
         AVP MUST be included and contain a copy of the first instance
         of the offending AVP that exceeded the maximum number of
         occurrences

      DIAMETER_NO_COMMON_APPLICATION     5010
         This error is returned when a CER message is received, and
         there are no common applications supported between the peers.



Calhoun et al.             expires April 2003                  [Page 85]


Internet-Draft                                              October 2002


      DIAMETER_UNSUPPORTED_VERSION       5011
         This error is returned when a request was received, whose
         version number is unsupported.

      DIAMETER_UNABLE_TO_COMPLY          5012
         This error is returned when a request is rejected for
         unspecified reasons.

      DIAMETER_INVALID_BIT_IN_HEADER     5013
         This error is returned when an unrecognized bit in the Diameter
         header is set to one (1).

      DIAMETER_INVALID_AVP_LENGTH        5014
         The request contained an AVP with an invalid length. A Diameter
         message indicating this error MUST include the offending AVPs
         within a Failed-AVP AVP.

      DIAMETER_INVALID_MESSAGE_LENGTH    5015
         This error is returned when a request is received with an
         invalid message length.

      DIAMETER_INVALID_AVP_BIT_COMBO     5016
         The request contained an AVP with which is not allowed to have
         the given value in the AVP Flags field. A Diameter message
         indicating this error MUST include the offending AVPs within a
         Failed-AVP AVP.


7.2  Error Bit

   The 'E' (Error Bit) in the Diameter header is set when the request
   caused a protocol-related error (see section 7.1.3). A message with
   the 'E' bit MUST NOT be sent as a response to an answer message. Note
   that a message with the 'E' bit set is still subjected to the
   processing rules defined in section 6.2. When set, the answer message
   will not conform to the ABNF specification for the command, and will
   instead conform to the following ABNF:

   Message Format












Calhoun et al.             expires April 2003                  [Page 86]


Internet-Draft                                              October 2002


      <answer-message> ::= < Diameter Header: code, ERR [PXY] >
                        0*1< Session-Id >
                           { Origin-Host }
                           { Origin-Realm }
                           { Result-Code }
                           [ Origin-State-Id ]
                           [ Error-Reporting-Host ]
                           [ Proxy-Info ]
                         * [ AVP ]

   Note that the code used in the header is the same that the one found
   in the request message, but with the 'R' bit cleared and the 'E' bit
   set. The 'P' bit in the header is set to the same value as the one
   found in the request message.


7.3  Error-Message AVP

   The Error-Message AVP (AVP Code 281) is of type UTF8String.  It MAY
   accompany a Result-Code AVP as a human readable error message. The
   Error-Message AVP is not intended to be useful in real-time, and
   SHOULD NOT be expected to be parsed by network entities.


7.4  Error-Reporting-Host AVP

   The Error-Reporting-Host AVP (AVP Code 294) is of type
   DiameterIdentity. This AVP contains the identity of the Diameter host
   that sent the Result-Code AVP to a value other than 2001 (Success),
   only if the host setting the Result-Code is different from the one
   encoded in the Origin-Host AVP. This AVP is intended to be used for
   troubleshooting purposes, and MUST be set when the Result-Code AVP
   indicates a failure.


7.5  Failed-AVP AVP

   The Failed-AVP AVP (AVP Code 279) is of type Grouped and provides
   debugging information in cases where a request is rejected or not
   fully processed due to erroneous information in a specific AVP. The
   value of the Result-Code AVP will provide information on the reason
   for the Failed-AVP AVP.

   The possible reasons for this AVP are the presence of an improperly
   constructed AVP, an unsupported or unrecognized AVP, an invalid AVP
   value, the omission of a required AVP, the presence of an explicitly
   excluded AVP (see tables in section 10), or the presence of two or
   more occurrences of an AVP which is restricted to 0, 1, or 0-1



Calhoun et al.             expires April 2003                  [Page 87]


Internet-Draft                                              October 2002


   occurrences.

   A Diameter message MAY contain one Failed-AVP AVP, containing the
   entire AVP that could not be processed successfully. If the failure
   reason is omission of a required AVP, an AVP with the missing AVP
   code, the missing vendor id, and a zero filled payload of the minimum
   required length for the omitted AVP will be added.

   AVP Format

      <Failed-AVP> ::= < AVP Header: 279 >
                    1* {AVP}


7.6 Experimental-Result AVP

   The Experimental-Result AVP (AVP Code 297) is of type Grouped, and
   indicates whether a particular vendor-specific request was completed
   successfully or whether an error occurred. Its Data field has the
   following ABNF grammar:

   AVP Format

      Experimental-Result ::= < AVP Header: 297 >
                                 { Vendor-Id }
                                 { Experimental-Result-Code }

   The Vendor-Id AVP (see Section 5.3.3) in this grouped AVP identifies
   the vendor responsible for the assignment of the result code which
   follows. All Diameter answer messages defined in vendor-specific
   applications MUST include either one Result-Code AVP or one
   Experimental-Result AVP.

7.7 Experimental-Result-Code AVP

   The Experimental-Result-Code AVP (AVP Code 298) is of type Unsigned32
   and contains a vendor-assigned value representing the result of
   processing the request.

   It is recommended that vendor-specific result codes follow the same
   conventions given for the Result-Code AVP regarding the different
   types of result codes and the handling of errors (for non 2xxx
   values).

8  Diameter User Sessions

   Diameter can provide two different types of services to applications.
   The first involves authentication and authorization, and can



Calhoun et al.             expires April 2003                  [Page 88]


Internet-Draft                                              October 2002


   optionally make use of accounting. The second only makes use of
   accounting.

   When a service makes use of the authentication and/or authorization
   portion of an application, and a user requests access to the network,
   the Diameter client issues an auth request to its local server. The
   auth request is defined in a service specific Diameter application
   (e.g. NASREQ). The request contains a Session-Id AVP, which is used
   in subsequent messages (e.g. subsequent authorization, accounting,
   etc) relating to the user's session. The Session-Id AVP is a means
   for the client and servers to correlate a Diameter message with a
   user session.

   When a Diameter server authorizes a user to use network resources for
   a finite amount of time, and it is willing to extend the
   authorization via a future request, it MUST add the Authorization-
   Lifetime AVP to the answer message. The Authorization-Lifetime AVP
   defines the maximum number of seconds a user MAY make use of the
   resources before another authorization request is expected by the
   server. The Auth-Grace-Period AVP contains the number of seconds
   following the expiration of the Authorization-Lifetime, after which
   the server will release all state information related to the user's
   session. Note that if payment for services is expected by the serving
   realm from the user's home realm, the Authorization-Lifetime AVP,
   combined with the Auth-Grace-Period AVP, implies the maximum length
   of the session the home realm is willing to be fiscally responsible
   for. Services provided past the expiration of the Authorization-
   Lifetime and Auth-Grace-Period AVPs are the responsibility of the
   access device. Of course, the actual cost of services rendered is
   clearly outside the scope of the protocol.

   An access device that does not expect to send a re-authorization or a
   session termination request to the server MAY include the Auth-
   Session-State AVP with the value set to NO_STATE_MAINTAINED as a hint
   to the server. If the server accepts the hint, it agrees that since
   no session termination message will be received once service to the
   user is terminated, it cannot maintain state for the session. If the
   answer message from the server contains a different value in the
   Auth-Session-State AVP (or the default value if the AVP is absent),
   the access device MUST follow the server's directives.  Note that the
   value NO_STATE_MAINTAINED MUST NOT be set in subsequent re-
   authorization requests and answers.

   The base protocol does not include any authorization request
   messages, since these are largely application-specific and are
   defined in a Diameter application document. However, the base
   protocol does define a set of messages that is used to terminate user
   sessions. These are used to allow servers that maintain state



Calhoun et al.             expires April 2003                  [Page 89]


Internet-Draft                                              October 2002


   information to free resources.

   When a service only makes use of the Accounting portion of the
   Diameter protocol, even in combination with an application, the
   Session-Id is still used to identify user sessions. However, the
   session termination messages are not used, since a session is
   signaled as being terminated by issuing an accounting stop message.


8.1  Authorization Session State Machine

   This section contains a set of finite state machines, representing
   the life cycle of Diameter sessions, and which MUST be observed by
   all Diameter implementations that make use of the authentication
   and/or authorization portion of a Diameter application. The term
   Service-Specific below refers to a message defined in a Diameter
   application (e.g. Mobile IP, NASREQ).

   There are four different authorization session state machines
   supported in the Diameter base protocol. The first two describe a
   session in which the server is maintaining session state, indicated
   by the value of the Auth-Session-State AVP (or its absence).  One
   describes the session from a client perspective, the other from a
   server perspective. The second two state machines are used when the
   server does not maintain session state. Here again, one describes the
   session from a client perspective, the other from a server
   perspective.

   When a session is moved to the Idle state, any resources that were
   allocated for the particular session must be released.  Any event not
   listed in the state machines MUST be considered as an error
   condition, and an answer, if applicable, MUST be returned to the
   originator of the message.

   In the state table, the event 'Failure to send X' means that the
   Diameter agent is unable to send command X to the desired
   destination. This could be due to the peer being down, or due to the
   peer sending back a transient failure or temporary protocol error
   notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the
   Result-Code AVP of the corresponding Answer command.  The event 'X
   successfully sent' is the complement of 'Failure to send X'.

   The following state machine is observed by a client when state is
   maintained on the server:







Calhoun et al.             expires April 2003                  [Page 90]


Internet-Draft                                              October 2002


                              CLIENT, STATEFUL
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      Client or Device Requests      Send       Pending
                access                         service
                                               specific
                                               auth req

      Idle      ASR Received                   Send ASA   Idle
                for unknown session            with
                                               Result-Code
                                               = UNKNOWN_
                                               SESSION_ID

      Pending   Successful Service-specific    Grant      Open
                authorization answer           Access
                received with default
                Auth-Session-State value

      Pending   Successful Service-specific    Sent STR   Discon
                authorization answer received
                but service not provided

      Pending   Error processing successful    Sent STR   Discon
                Service-specific authorization
                answer

      Pending   Failed Service-specific        Cleanup    Idle
                authorization answer received

      Open      User or client device          Send       Open
                requests access to service     service
                                               specific
                                               auth req

      Open      Successful Service-specific    Provide    Open
                authorization answer received  Service

      Open      Failed Service-specific        Discon.    Idle
                authorization answer           user/device
                received.

      Open      Session-Timeout Expires on     Send STR   Discon
                Access Device

      Open      ASR Received,                  Send ASA   Discon
                client will comply with        with
                request to end the session     Result-Code



Calhoun et al.             expires April 2003                  [Page 91]


Internet-Draft                                              October 2002


                                               = SUCCESS,
                                               Send STR.

      Open      ASR Received,                  Send ASA   Open
                client will not comply with    with
                request to end the session     Result-Code
                                               != SUCCESS

      Open      Authorization-Lifetime +       Send STR   Discon
                Auth-Grace-Period expires on
                access device

      Discon    ASR Received                   Send ASA   Discon

      Discon    STA Received                   Discon.    Idle
                                               user/device

   The following state machine is observed by a server when it is
   maintaining state for the session:
































Calhoun et al.             expires April 2003                  [Page 92]


Internet-Draft                                              October 2002


                             SERVER, STATEFUL
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      Service-specific authorization Send       Open
                request received, and          successful
                user is authorized             serv.
                                               specific answer

      Idle      Service-specific authorization Send       Idle
                request received, and          failed serv.
                user is not authorized         specific answer

      Open      Service-specific authorization Send       Open
                request received, and user     successful
                is authorized                  serv. specific
                                                     answer

      Open      Service-specific authorization Send       Idle
                request received, and user     failed serv.
                is not authorized              specific
                                               answer,
                                               Cleanup

      Open      Home server wants to           Send ASR   Discon
                terminate the service

      Open      Authorization-Lifetime (and    Cleanup    Idle
                Auth-Grace-Period) expires
                on home server.

      Open      Session-Timeout expires on     Cleanup    Idle
                home server

      Discon    Failure to send ASR            Wait,      Discon
                                               resend ASR

      Discon    ASR successfully sent and      Cleanup    Idle
                ASA Received with Result-Code

      Not       ASA Received                   None       No Change.
      Discon

      Any       STR Received                   Send STA,  Idle
                                               Cleanup.
      fi

   The following state machine is observed by a client when state is not maintained on the server:




Calhoun et al.             expires April 2003                  [Page 93]


Internet-Draft                                              October 2002


                              CLIENT, STATELESS
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      Client or Device Requests      Send       Pending
                access                         service
                                               specific
                                               auth req

      Pending   Successful Service-specific    Grant      Open
                authorization answer           Access
                received with Auth-Session-
                State set to
                NO_STATE_MAINTAINED

      Pending   Failed Service-specific        Cleanup    Idle
                authorization answer
                received

      Open      Session-Timeout Expires on     Discon.    Idle
                Access Device                  user/device

      Open      Service to user is terminated  Discon.    Idle
                                               user/device

   The following state machine is observed by a server when it is not
   maintaining state for the session:

                              SERVER, STATELESS
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      Service-specific authorization Send serv. Idle
                request received, and          specific
                successfully processed         answer



8.2  Accounting Session State Machine

   The following state machines MUST be supported for applications that
   have an accounting portion or that require only accounting services.
   The first state machine is to be observed by clients.

   See section 9.7 for Accounting Command Codes and section 9.8 for
   Accounting AVPs.

   The server side in the accounting state machine depends in some cases
   on the particular application. The Diameter base protocol defines a
   default state machine that MUST be followed by all applications that



Calhoun et al.             expires April 2003                  [Page 94]


Internet-Draft                                              October 2002


   have not specified other state machines. This is the second state
   machine in this section described below.

   The default server side state machine requires the reception of
   accounting records in any order and at any time, and does not place
   any standards requirement on the processing of these records.
   Implementations of Diameter MAY perform checking, ordering,
   correlation, fraud detection, and other tasks based on these records.
   Both base Diameter AVPs as well as application specific AVPs MAY be
   inspected as a part of these tasks. The tasks can happen either
   immediately after record reception or in a post-processing phase.
   However, as these tasks are typically application or even policy
   dependent, they are not standardized by the Diameter specifications.
   Applications MAY define requirements on when to accept accounting
   records based on the used value of Accounting-Realtime-Required AVP,
   credit limits checks, and so on.

   However, the Diameter base protocol defines one optional server side
   state machine that MAY be followed by applications that require
   keeping track of the session state at the accounting server. Note
   that such tracking is incompatible with the ability to sustain long
   duration connectivity problems. Theferore, the use of this state
   machine is recommended only in applications where the value of the
   Accounting-Realtime-Required AVP is DELIVER_AND_GRANT, and hence
   accounting connectivity problems are required to cause the serviced
   user to be disconnected. Otherwise, records produced by the client
   may be lost by the server which no longer accepts them after the
   connectivity is re-established. This state machine is the third state
   machine in this section. The state machine is supervised by a
   supervision session timer Ts, which the value should be reasonably
   higher than the Interim_Record_Interval value. Ts MAY be set to two
   times the value of the Interim_Record_Interval so as to avoid the
   accounting session in the Diameter server to change to Idle state in
   case of short transient network failure.

   Any event not listed in the state machines MUST be considered as an
   error condition, and a corresponding answer, if applicable, MUST be
   returned to the originator of the message.

   In the state table, the event 'Failure to send' means that the
   Diameter client is unable to communicate with the desired
   destination. This could be due to the peer being down, or due to the
   peer sending back a transient failure or temporary protocol error
   notification DIAMETER_OUT_OF_SPACE, DIAMETER_TOO_BUSY, or
   DIAMETER_LOOP_DETECTED in the Result-Code AVP of the Accounting
   Answer command.

   The event 'Failed answer' means that the Diameter client received a



Calhoun et al.             expires April 2003                  [Page 95]


Internet-Draft                                              October 2002


   non-transient failure notification in the Accounting Answer command.

   Note that the action 'Disconnect user/dev' MUST have an effect also
   to the authorization session state table, e.g. cause the STR message
   to be sent, if the given application has both
   authentication/authorization and accounting portions.

   The states PendingS, PendingI, PendingL, PendingE and PendingB stand
   for pending states to wait for an answer to an accounting request
   related to a Start, Interim, Stop, Event or buffered record,
   respectively.








































Calhoun et al.             expires April 2003                  [Page 96]


Internet-Draft                                              October 2002


                            CLIENT, ACCOUNTING
      State     Event                          Action     New State
      -------------------------------------------------------------
      Idle      Client or device requests      Send       PendingS
                access                         accounting
                                               start req.

      Idle      Client or device requests      Send       PendingE
                a one-time service             accounting
                                               event req

      Idle      Records in storage             Send       PendingB
                                               record

      PendingS  Successful accounting                     Open
                start answer received

      PendingS  Failure to send and buffer     Store      Open
                space available and realtime   Start
                not equal to DELIVER_AND_GRANT Record

      PendingS  Failure to send and no buffer             Open
                space available and realtime
                equal to GRANT_AND_LOSE

      PendingS  Failure to send and no buffer  Disconnect Idle
                space available and realtime   user/dev
                not equal to
                GRANT_AND_LOSE

      PendingS  Failed accounting start answer            Open
                received and realtime equal
                to GRANT_AND_LOSE

      PendingS  Failed accounting start answer Disconnect Idle
                received and realtime not      user/dev
                equal to GRANT_AND_LOSE

      PendingS  User service terminated        Store      PendingS
                                               stop
                                               record

      Open      Interim interval elapses       Send       PendingI
                                               accounting
                                               interim
                                               record

      Open      User service terminated        Send       PendingL



Calhoun et al.             expires April 2003                  [Page 97]


Internet-Draft                                              October 2002


                                               accounting
                                               stop req.

      PendingI  Successful accounting interim             Open
                answer received

      PendingI  Failure to send and (buffer    Store      Open
                space available or old record  interim
                can be overwritten) and        record
                realtime not equal to
                DELIVER_AND_GRANT

      PendingI  Failure to send and no buffer             Open
                space available and realtime
                equal to GRANT_AND_LOSE

      PendingI  Failure to send and no buffer  Disconnect Idle
                space available and realtime   user/dev
                not equal to GRANT_AND_LOSE

      PendingI  Failed accounting interim                 Open
                answer received and realtime
                equal to GRANT_AND_LOSE

      PendingI  Failed accounting interim      Disconnect Idle
                answer received and realtime   user/dev
                not equal to GRANT_AND_LOSE

      PendingI  User service terminated        Store      PendingI
                                               stop
                                               record

      PendingE  Successful accounting                     Idle
                event answer received

      PendingE  Failure to send and buffer     Store      Idle
                space available                event
                                               record

      PendingE  Failure to send and no buffer             Idle
                space available

      PendingE  Failed accounting event answer            Idle
                received

      PendingB  Successful accounting answer   Delete     Idle
                received                       record




Calhoun et al.             expires April 2003                  [Page 98]


Internet-Draft                                              October 2002


      PendingB  Failure to send                           Idle

      PendingB  Failed accounting answer       Delete     Idle
                received                       record

      PendingL  Successful accounting                     Idle
                stop answer received

      PendingL  Failure to send and buffer     Store      Idle
                space available                stop
                                               record

      PendingL  Failure to send and no buffer             Idle
                space available

      PendingL  Failed accounting stop answer             Idle
                received


































Calhoun et al.             expires April 2003                  [Page 99]


Internet-Draft                                              October 2002


                       SERVER, STATELESS ACCOUNTING
      State     Event                          Action     New State
      -------------------------------------------------------------

      Idle      Accounting start request       Send       Idle
                received, and successfully     accounting
                processed.                     start
                                               answer

      Idle      Accounting event request       Send       Idle
                received, and successfully     accounting
                processed.                     event
                                               answer

      Idle      Interim record received,       Send       Idle
                and successfully processed.    accounting
                                               interim
                                               answer

      Idle      Accounting stop request        Send       Idle
                received, and successfully     accounting
                processed                      stop answer

      Idle      Accounting request received,   Send       Idle
                no space left to store         accounting
                records                        answer,
                                               Result-Code
                                               = OUT_OF_
                                               SPACE






















Calhoun et al.             expires April 2003                 [Page 100]


Internet-Draft                                              October 2002


                            SERVER, STATEFUL ACCOUNTING
      State     Event                          Action     New State
      -------------------------------------------------------------

      Idle      Accounting start request       Send       Open
                received, and successfully     accounting
                processed.                     start
                                               answer,
                                               Start Ts

      Idle      Accounting event request       Send       Idle
                received, and successfully     accounting
                processed.                     event
                                               answer

      Idle      Accounting request received,   Send       Idle
                no space left to store         accounting
                records                        answer,
                                               Result-Code
                                               = OUT_OF_
                                               SPACE

      Open      Interim record received,       Send       Open
                and successfully processed.    accounting
                                               interim
                                               answer,
                                               Restart Ts

      Open      Accounting stop request        Send       Idle
                received, and successfully     accounting
                processed                      stop answer,
                                               Stop Ts

      Open      Accounting request received,   Send       Idle
                no space left to store         accounting
                records                        answer,
                                               Result-Code
                                               = OUT_OF_
                                               SPACE,
                                               Stop Ts

      Open      Session supervision timer Ts   Stop Ts    Idle
                expired


8.3  Server-Initiated Re-Auth

   A Diameter server may initiate a re-authentication and/or re-



Calhoun et al.             expires April 2003                 [Page 101]


Internet-Draft                                              October 2002


   authorization service for a particular session by issuing a Re-Auth-
   Request (RAR).

   For example, for pre-paid services, the Diameter server that
   originally authorized a session may need some confirmation that the
   user is still using the services.

   An access device that receives a RAR message with Session-Id equal to
   a currently active session MUST initiate a re-auth towards the user,
   if the service supports this particular feature. Each Diameter
   application MUST state whether service-initiated re-auth is
   supported, since some applications do not allow access devices to
   prompt the user for re-auth.


8.3.1  Re-Auth-Request

   The Re-Auth-Request (RAR), indicated by the Command-Code set to 258
   and the message flags' 'R' bit set, may be sent by any server to the
   access device that is providing session service, to request that the
   user be re-authenticated and/or re-authorized.

   Message Format

      <RAR>  ::= < Diameter Header: 258, REQ, PXY >
                 < Session-Id >
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { Destination-Host }
                 { Auth-Application-Id }
                 { Re-Auth-Request-Type }
                 [ User-Name ]
                 [ Origin-State-Id ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]


8.3.2  Re-Auth-Answer

   The Re-Auth-Answer (RAA), indicated by the Command-Code set to 258
   and the message flags' 'R' bit clear, is sent in response to the RAR.
   The Result-Code AVP MUST be present, and indicates the disposition of
   the request.

   A successful RAA message MUST be followed by an application-specific
   authentication and/or authorization message.



Calhoun et al.             expires April 2003                 [Page 102]


Internet-Draft                                              October 2002


   Message Format

      <RAA>  ::= < Diameter Header: 258, PXY >
                 < Session-Id >
                 { Result-Code }
                 { Origin-Host }
                 { Origin-Realm }
                 [ User-Name ]
                 [ Origin-State-Id ]
                 [ Error-Message ]
                 [ Error-Reporting-Host ]
               * [ Failed-AVP ]
               * [ Redirected-Host ]
                 [ Redirected-Host-Usage ]
                 [ Redirected-Host-Cache-Time ]
               * [ Proxy-Info ]
               * [ AVP ]


8.4  Session Termination

   It is necessary for a Diameter server that authorized a session, for
   which it is maintaining state, to be notified when that session is no
   longer active, both for tracking purposes as well as to allow
   stateful agents to release any resources that they may have provided
   for the user's session. For sessions whose state is not being
   maintained, this section is not used.

   When a user session that required Diameter authorization terminates,
   the access device that provided the service MUST issue a Session-
   Termination-Request (STR) message to the Diameter server that
   authorized the service, to notify it that the session is no longer
   active. An STR MUST be issued when a user session terminates for any
   reason, including user logoff, expiration of Session-Timeout,
   administrative action, termination upon receipt of an Abort-Session-
   Request (see below), orderly shutdown of the access device, etc.

   The access device also MUST issue an STR for a session that was
   authorized but never actually started. This could occur, for example,
   due to a sudden resource shortage in the access device, or because
   the access device is unwilling to provide the type of service
   requested in the authorization, or because the access device does not
   support a mandatory AVP returned in the authorization, etc.

   It is also possible that a session that was authorized is never
   actually started due to action of a proxy. For example, a proxy may
   modify an authorization answer, converting the result from success to
   failure, prior to forwarding the message to the access device. If the



Calhoun et al.             expires April 2003                 [Page 103]


Internet-Draft                                              October 2002


   answer did not contain an Auth-Session-State AVP with the value
   NO_STATE_MAINTAINED, a proxy that causes an authorized session not to
   be started MUST issue an STR to the Diameter server that authorized
   the session, since the access device has no way of knowing that the
   session had been authorized.

   A Diameter server that receives an STR message MUST clean up
   resources (e.g., session state) associated with the Session-Id
   specified in the STR, and return a Session-Termination-Answer.

   A Diameter server also MUST clean up resources when the Session-
   Timeout expires, or when the Authorization-Lifetime and the Auth-
   Grace-Period AVPs expires without receipt of a re-authorization
   request, regardless of whether an STR for that session is received.
   The access device is not expected to provide service beyond the
   expiration of these timers; thus, expiration of either of these
   timers implies that the access device may have unexpectedly shut
   down.


8.4.1  Session-Termination-Request

   The Session-Termination-Request (STR), indicated by the Command-Code
   set to 275 and the Command Flags' 'R' bit set, is sent by the access
   device to inform the Diameter Server that an authenticated and/or
   authorized session is being terminated.

   Message Format

      <STR> ::= < Diameter Header: 275, REQ, PXY >
                < Session-Id >
                { Origin-Host }
                { Origin-Realm }
                { Destination-Realm }
                { Auth-Application-Id }
                { Termination-Cause }
                [ User-Name ]
                [ Destination-Host ]
              * [ Class ]
                [ Origin-State-Id ]
              * [ Proxy-Info ]
              * [ Route-Record ]
              * [ AVP ]


8.4.2  Session-Termination-Answer

   The Session-Termination-Answer (STA), indicated by the Command-Code



Calhoun et al.             expires April 2003                 [Page 104]


Internet-Draft                                              October 2002


   set to 275 and the message flags' 'R' bit clear, is sent by the
   Diameter Server to acknowledge the notification that the session has
   been terminated. The Result-Code AVP MUST be present, and MAY contain
   an indication that an error occurred while servicing the STR.

   Upon sending or receipt of the STA, the Diameter Server MUST release
   all resources for the session indicated by the Session-Id AVP. Any
   intermediate server in the Proxy-Chain MAY also release any
   resources, if necessary.

   Message Format

      <STA>  ::= < Diameter Header: 275, PXY >
                 < Session-Id >
                 { Result-Code }
                 { Origin-Host }
                 { Origin-Realm }
                 [ User-Name ]
               * [ Class ]
                 [ Error-Message ]
                 [ Error-Reporting-Host ]
               * [ Failed-AVP ]
                 [ Origin-State-Id ]
               * [ Redirect-Host ]
                 [ Redirect-Host-Usase ]
                 [ Redirect-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ AVP ]


8.5  Aborting a Session

   A Diameter server may request that the access device stop providing
   service for a particular session by issuing an Abort-Session-Request
   (ASR).

   For example, the Diameter server that originally authorized the
   session may be required to cause that session to be stopped for
   credit or other reasons that were not anticipated when the session
   was first authorized. On the other hand, an operator may maintain a
   management server for the purpose of issuing ASRs to administratively
   remove users from the network.

   An access device that receives an ASR with Session-ID equal to a
   currently active session MAY stop the session. Whether the access
   device stops the session or not is implementation- and/or
   configuration-dependent. For example, an access device may honor ASRs
   from certain agents only. In any case, the access device MUST respond



Calhoun et al.             expires April 2003                 [Page 105]


Internet-Draft                                              October 2002


   with an Abort-Session-Answer, including a Result-Code AVP to indicate
   what action it took.

   Note that if the access device does stop the session upon receipt of
   an ASR, it issues an STR to the authorizing server (which may or may
   not be the agent issuing the ASR) just as it would if the session
   were terminated for any other reason.


8.5.1  Abort-Session-Request

   The Abort-Session-Request (ASR), indicated by the Command-Code set to
   274 and the message flags' 'R' bit set, may be sent by any server to
   the access device that is providing session service, to request that
   the session identified by the Session-Id be stopped.

   Message Format

      <ASR>  ::= < Diameter Header: 274, REQ, PXY >
                 < Session-Id >
                 { Origin-Host }
                 { Origin-Realm }
                 { Destination-Realm }
                 { Destination-Host }
                 { Auth-Application-Id }
                 [ User-Name ]
                 [ Origin-State-Id ]
               * [ Proxy-Info ]
               * [ Route-Record ]
               * [ AVP ]


8.5.2  Abort-Session-Answer

   The Abort-Session-Answer (ASA), indicated by the Command-Code set to
   274 and the message flags' 'R' bit clear, is sent in response to the
   ASR. The Result-Code AVP MUST be present, and indicates the
   disposition of the request.

   If the session identified by Session-Id in the ASR was successfully
   terminated, Result-Code is set to DIAMETER_SUCCESS. If the session is
   not currently active, Result-Code is set to
   DIAMETER_UNKNOWN_SESSION_ID. If the access device does not stop the
   session for any other reason, Result-Code is set to
   DIAMETER_UNABLE_TO_COMPLY.

   Message Format




Calhoun et al.             expires April 2003                 [Page 106]


Internet-Draft                                              October 2002


      <ASA>  ::= < Diameter Header: 274, PXY >
                 < Session-Id >
                 { Result-Code }
                 { Origin-Host }
                 { Origin-Realm }
                 [ User-Name ]
                 [ Origin-State-Id ]
                 [ Error-Message ]
                 [ Error-Reporting-Host ]
               * [ Failed-AVP ]
               * [ Redirected-Host ]
                 [ Redirected-Host-Usage ]
                 [ Redirected-Max-Cache-Time ]
               * [ Proxy-Info ]
               * [ AVP ]


8.6  Inferring Session Termination from Origin-State-Id

   Origin-State-Id is used to allow rapid detection of terminated
   sessions for which no STR would have been issued, due to
   unanticipated shutdown of an access device.

   By including Origin-State-Id in CER/CAA messages, an access device
   allows a next-hop server to determine immediately upon connection
   whether the device has lost its sessions since the last connection.

   By including Origin-State-Id in request messages, an access device
   also allows a server with which it communicates via proxy to make
   such a determination. However, a server that is not directly
   connected with the access device will not discover that the access
   device has been restarted unless and until it receives a new request
   from the access device. Thus, use of this mechanism across proxies is
   opportunistic rather than reliable, but useful nonetheless.

   When a Diameter server receives an Origin-State-Id that is greater
   than the Origin-State-Id previously received from the same issuer, it
   may assume that the issuer has lost state since the previous message
   and that all sessions that were active under the lower Origin-State-
   Id have been terminated. The Diameter server MAY clean up all session
   state associated with such lost sessions, and MAY also issues STRs
   for all such lost sessions that were authorized on upstream servers,
   to allow session state to be cleaned up globally.


8.7  Auth-Request-Type AVP

   The Auth-Request-Type AVP (AVP Code 274) is of type Enumerated and is



Calhoun et al.             expires April 2003                 [Page 107]


Internet-Draft                                              October 2002


   included in application-specific auth requests to inform the peers
   whether a user is to be authenticated only, authorized only or both.
   Note any value other than both MAY cause RADIUS interoperability
   issues. The following values are defined:

      AUTHENTICATE_ONLY          1
         The request being sent is for authentication only, and MUST
         contain the relevant application specific authentication AVPs
         that are needed by the Diameter server to authenticate the
         user.

      AUTHORIZE_ONLY             2
         The request being sent is for authorization only, and MUST
         contain the application specific authorization AVPs that are
         necessary to identify the service being requested/offered.

      AUTHORIZE_AUTHENTICATE     3
         The request contains a request for both authentication and
         authorization. The request MUST include both the relevant
         application specific authentication information, and
         authorization information necessary to identify the service
         being requested/offered.


8.8  Session-Id AVP

   The Session-Id AVP (AVP Code 263) is of type UTF8String and is used
   to identify a specific session (see section 8). All messages
   pertaining to a specific session MUST include only one Session-Id AVP
   and the same value MUST be used throughout the life of a session.
   When present, the Session-Id SHOULD appear immediately following the
   Diameter Header (see section 3).

   The Session-Id MUST be globally and eternally unique, as it is meant
   to uniquely identify a user session without reference to any other
   information, and may be needed to correlate historical authentication
   information with accounting information. The Session-Id includes a
   mandatory portion and an implementation-defined portion; a
   recommended format for the implementation-defined portion is outlined
   below.

   The Session-Id MUST begin with the sender's identity encoded in the
   DiameterIdentity type (see section 4.4). The remainder of the
   Session-Id MAY be any sequence that the client can guarantee to be
   eternally unique; however, the following format is recommended,
   (square brackets [] indicate an optional element):

   <DiameterIdentity>;<high 32 bits>;<low 32 bits>[;<optional value>]



Calhoun et al.             expires April 2003                 [Page 108]


Internet-Draft                                              October 2002


   <high 32 bits> and <low 32 bits> are decimal representations of the
   high and low 32 bits of a monotonically increasing 64-bit value. The
   64-bit value is rendered in two part to simplify formatting by 32-bit
   processors. At startup, the high 32 bits of the 64-bit value MAY be
   initialized to the time, and the low 32 bits MAY be initialized to
   zero. This will for practical purposes eliminate the possibility of
   overlapping Session-Ids after a reboot, assuming the reboot process
   takes longer than a second. Alternatively, an implementation MAY keep
   track of the increasing value in non-volatile memory.

   <optional value> is implementation specific but may include a modem's
   device Id, a layer 2 address, timestamp, etc.

   Example, in which there is no optional value:
      accesspoint7.acme.com;1876543210;523

   Example, in which there is an optional value:
      accesspoint7.acme.com;1876543210;523;mobile@200.1.1.88

   The Session-Id is created by the Diameter device initiating the
   session, which in most cases is done by the client. Note that a
   Session-Id MAY be used for both the authorization and accounting
   commands of a given application.


8.9  Authorization-Lifetime AVP

   The Authorization-Lifetime AVP (AVP Code 291) is of type Unsigned32
   and contains the maximum number of seconds of service to be provided
   to the user before the user is to be re-authenticated and/or re-
   authorized. Great care should be taken when the Authorization-
   Lifetime value is determined, since a low, non-zero, value could
   create significant Diameter traffic, which could congest both the
   network and the agents.

   A value of zero (0) means that immediate re-auth is necessary by the
   access device. This is typically used in cases where multiple
   authentication methods are used, and a successful auth response with
   this AVP set to zero is used to signal that the next authentication
   method is to be immediately initiated. The absence of this AVP, or a
   value of all ones (meaning all bits in the 32 bit field are set to
   one) means no re-auth is expected.

   If both this AVP and the Session-Timeout AVP are present in a
   message, the value of the latter MUST NOT be smaller than the
   Authorization-Lifetime AVP.

   An Authorization-Lifetime AVP MAY be present in re-authorization



Calhoun et al.             expires April 2003                 [Page 109]


Internet-Draft                                              October 2002


   messages, and contains the number of seconds the user is authorized
   to receive service from the time the re-auth answer message is
   received by the access device.

   This AVP MAY be provided by the client as a hint of the maximum
   lifetime that it is willing to accept. However, the server MAY return
   a value that is equal to, or smaller, than the one provided by the
   client.


8.10  Auth-Grace-Period AVP

   The Auth-Grace-Period AVP (AVP Code 276) is of type Unsigned32 and
   contains the number of seconds the Diameter server will wait
   following the expiration of the Authorization-Lifetime AVP before
   cleaning up resources for the session.


8.11  Auth-Session-State AVP

   The Auth-Session-State AVP (AVP Code 277) is of type Enumerated and
   specifies whether state is maintained for a particular session. The
   client MAY include this AVP in requests as a hint to the server, but
   the value in the server's answer message is binding. The following
   values are supported:

      STATE_MAINTAINED              0
         This value is used to specify that session state is being
         maintained, and the access device MUST issue a session
         termination message when service to the user is terminated.
         This is the default value.

      NO_STATE_MAINTAINED           1
         This value is used to specify that no session termination
         messages will be sent by the access device upon expiration of
         the Authorization-Lifetime.


8.12  Re-Auth-Request-Type AVP

   The Re-Auth-Request-Type AVP (AVP Code 285) is of type Enumerated and
   is included in application-specific auth answers to inform the client
   of the action expected upon expiration of the Authorization-Lifetime.
   If the answer message contains an Authorization-Lifetime AVP with a
   positive value, the Re-Auth-Request-Type AVP MUST be present in an
   answer message. The following values are defined:

      AUTHORIZE_ONLY             0



Calhoun et al.             expires April 2003                 [Page 110]


Internet-Draft                                              October 2002


         An authorization only re-auth is expected upon expiration of
         the Authorization-Lifetime. This is the default value if the
         AVP is not present in answer messages that include the
         Authorization-Lifetime.

      AUTHORIZE_AUTHENTICATE     1
         An authentication and authorization re-auth is expected upon
         expiration of the Authorization-Lifetime.


8.13  Session-Timeout AVP

   The Session-Timeout AVP (AVP Code 27) [RADIUS] is of type Unsigned32
   and contains the maximum number of seconds of service to be provided
   to the user before termination of the session. When both the Session-
   Timeout and the Authorization-Lifetime AVPs are present in an answer
   message, the former MUST be equal to or greater than the value of the
   latter.

   A session that terminates on an access device due to the expiration
   of the Session-Timeout MUST cause an STR to be issued, unless both
   the access device and the home server had previously agreed that no
   session termination messages would be sent (see section 8.9).

   A Session-Timeout AVP MAY be present in a re-authorization answer
   message, and contains the remaining number of seconds from the
   beginning of the re-auth.

   A value of zero, or the absence of this AVP, means that this session
   has an unlimited number of seconds before termination.

   This AVP MAY be provided by the client as a hint of the maximum
   timeout that it is willing to accept. However, the server MAY return
   a value that is equal to, or smaller, than the one provided by the
   client.


8.14  User-Name AVP

   The User-Name AVP (AVP Code 1) [RADIUS] is of type UTF8String, which
   contains the User-Name, in a format consistent with the NAI
   specification [NAI].


8.15  Termination-Cause AVP

   The Termination-Cause AVP (AVP Code 295) is of type Enumerated, and
   is used to indicate the reason why a session was terminated on the



Calhoun et al.             expires April 2003                 [Page 111]


Internet-Draft                                              October 2002


   access device. The following values are defined:

      DIAMETER_LOGOUT                   1
         The user initiated a disconnect

      DIAMETER_SERVICE_NOT_PROVIDED     2
         This value is used when the user disconnected prior to the
         receipt of the authorization answer message.

      DIAMETER_BAD_ANSWER               3
         This value indicates that the authorization answer received by
         the access device was not processed successfully.

      DIAMETER_ADMINISTRATIVE           4
         The user was not granted access, or was disconnected, due to
         administrative reasons, such as the receipt of a Abort-Session-
         Request message.

      DIAMETER_LINK_BROKEN              5
         The communication to the user was abruptly disconnected.

      DIAMETER_AUTH_EXPIRED             6
         The user's access was terminated since its authorized session
         time has expired.

      DIAMETER_USER_MOVED               7
         The user is receiving services from another access device.

      DIAMETER_SESSION_TIMEOUT          8
         The user's session has timed out, and service has been
         terminated.


8.16  Origin-State-Id AVP

   The Origin-State-Id AVP (AVP Code 278), of type Unsigned32, is a
   monotonically increasing value that is advanced whenever a Diameter
   entity restarts with loss of previous state, for example upon reboot.
   Origin-State-Id MAY be included in any Diameter message, including
   CER.

   A Diameter entity issuing this AVP MUST create a higher value for
   this AVP each time its state is reset. A Diameter entity MAY set
   Origin-State-Id to the time of startup, or it MAY use an incrementing
   counter retained in non-volatile memory across restarts.

   The Origin-State-Id, if present, MUST reflect the state of the entity
   indicated by Origin-Host. If a proxy modifies Origin-Host, it MUST



Calhoun et al.             expires April 2003                 [Page 112]


Internet-Draft                                              October 2002


   either remove Origin-State-Id or modify it appropriately as well.

   Typically, Origin-State-Id is used by an access device that always
   starts up with no active sessions; that is, any session active prior
   to restart will have been lost. By including Origin-State-Id in a
   message, it allows other Diameter entities to infer that sessions
   associated with a lower Origin-State-Id are no longer active. If an
   access device does not intend for such inferences to be made, it MUST
   either not include Origin-State-Id in any message, or set its value
   to 0.


8.17  Session-Binding AVP

   The Session-Binding AVP (AVP Code 270) is of type Unsigned32, and MAY
   be present in application-specific authorization answer messages. If
   present, this AVP MAY inform the Diameter client that all future
   application-specific re-auth messages for this session MUST be sent
   to the same authorization server. This AVP MAY also specify that a
   Session-Termination-Request message for this session MUST be sent to
   the same authorizing server.

   This field is a bit mask, and the following bits have been defined:

      RE_AUTH                    1
         When set, future re-auth messages for this session MUST NOT
         include the Destination-Host AVP. When cleared, the default
         value, the Destination-Host AVP MUST be present in all re-auth
         messages for this session.

      STR                        2
         When set, the STR message for this session MUST NOT include the
         Destination-Host AVP. When cleared, the default value, the
         Destination-Host AVP MUST be present in the STR message for
         this session.

      ACCOUNTING                 4
         When set, all accounting messages for this session MUST NOT
         include the Destination-Host AVP. When cleared, the default
         value, the Destination-Host AVP, if known, MUST be present in
         all accounting messages for this session.


8.18  Session-Server-Failover AVP

   The Session-Server-Failover AVP (AVP Code 271) is of type Enumerated,
   and MAY be present in application-specific authorization answer
   messages that either do not include the Session-Binding AVP or



Calhoun et al.             expires April 2003                 [Page 113]


Internet-Draft                                              October 2002


   include the Session-Binding AVP with any of the bits set to a zero
   value. If present, this AVP MAY inform the Diameter client that if a
   re-auth or STR message fails due to a delivery problem, the Diameter
   client SHOULD issue a subsequent message without the Destination-Host
   AVP. When absent, the default value is REFUSE_SERVICE.

   The following values are supported:

      REFUSE_SERVICE             0
         If either the re-auth or the STR message delivery fails,
         terminate service with the user, and do not attempt any
         subsequent attempts.

      TRY_AGAIN                  1
         If either the re-auth or the STR message delivery fails, resend
         the failed message without the Destination-Host AVP present.

      ALLOW_SERVICE              2
         If re-auth message delivery fails, assume that re-authorization
         succeeded.  If STR message delivery fails, terminate the
         session.

      TRY_AGAIN_ALLOW_SERVICE    3
         If either the re-auth or the STR message delivery fails, resend
         the failed message without the Destination-Host AVP present.
         If the second delivery fails for re-auth, assume re-
         authorization succeeded.  If the second delivery fails for STR,
         terminate the session.


8.19  Multi-Round-Time-Out AVP

   The Multi-Round-Time-Out AVP (AVP Code 272) is of type Unsigned32,
   and SHOULD be present in application-specific authorization answer
   messages whose Result-Code AVP is set to DIAMETER_MULTI_ROUND_AUTH.
   This AVP contains the maximum number of seconds that the access
   device MUST provide the user in responding to an authentication
   request.


8.20  Class AVP

   The Class AVP (AVP Code 25) is of type OctetString and is used to by
   Diameter servers to return state information to the access device.
   When one or more Class AVPs are present in application-specific
   authorization answer messages, they MUST be present in subsequent re-
   authorization, session termination and accounting messages. Class
   AVPs found in a re-authorization answer message override the ones



Calhoun et al.             expires April 2003                 [Page 114]


Internet-Draft                                              October 2002


   found in any previous authorization answer message. Diameter server
   implementations SHOULD NOT return Class AVPs that require more than
   4096 bytes of storage on the Diameter client. A Diameter client that
   receives Class AVPs whose size exceeds local available storage MUST
   terminate the session.

8.21  Event-Timestamp AVP

   The Event-Timestamp (AVP Code 55) is of type Time, and MAY be
   included in an Accounting-Request and Accounting-Answer messages to
   record the time that the reported event occurred, in seconds since
   January 1, 1970 00:00 UTC.

9  Accounting

   This accounting protocol is based on a server directed model with
   capabilities for real-time delivery of accounting information.
   Several fault resilience methods [ACCMGMT] have been built in to the
   protocol in order minimize loss of accounting data in various fault
   situations and under different assumptions about the capabilities of
   the used devices.


9.1  Server Directed Model

   The server directed model means that the device generating the
   accounting data gets information from either the authorization server
   (if contacted) or the accounting server regarding the way accounting
   data shall be forwarded. This information includes accounting record
   timeliness requirements.

   As discussed in [ACCMGMT], real-time transfer of accounting records
   is a requirement, such as the need to perform credit limit checks and
   fraud detection. Note that batch accounting is not a requirement, and
   is therefore not supported by Diameter. Should batched accounting be
   required in the future, a new Diameter application will need to be
   created, or it could be handled using another protocol. Note,
   however, that even if at the Diameter layer accounting requests are
   processed one by one, transport protocols used under Diameter
   typically batch several requests in the same packet under heavy
   traffic conditions. This may be sufficient for many applications.

   The authorization server (chain) directs the selection of proper
   transfer strategy, based on its knowledge of the user and
   relationships of roaming partnerships. The server (or agents) uses
   the Acct-interim-Interval and Accounting-Realtime-Required AVPs to
   control the operation of the Diameter peer operating as a client. The
   Acct-interim-Interval AVP, when present, instructs the Diameter node



Calhoun et al.             expires April 2003                 [Page 115]


Internet-Draft                                              October 2002


   acting as a client to produce accounting records continuously even
   during a session. Accounting-Realtime-Required AVP is used to control
   the behavior of the client when the transfer of accounting records
   from the Diameter client is delayed or unsuccessful.

   The Diameter accounting server MAY override the interim interval or
   the realtime requirements by including the Acct-interim-Interval or
   Accounting-Realtime-Required AVP in the Accounting-Answer message.
   When one of these AVPs is present, the latest value received SHOULD
   be used in further accounting activities for the same session.

9.2  Protocol Messages

   A Diameter node that receives a successful authentication and/or
   authorization messages from the Home AAA server MUST collect
   accounting information for the session. The Accounting-Request
   message is used to transmit the accounting information to the Home
   AAA server, which MUST reply with the Accounting-Answer message to
   confirm reception. The Accounting-Answer message includes the Result-
   Code AVP, which MAY indicate that an error was present in the
   accounting message. A rejected Accounting-Request message MAY cause
   the user's session to be terminated, depending on the value of the
   Accounting-Realtime-Required AVP received earlier for the session in
   question.

   Each Diameter Accounting protocol message MAY be compressed, in order
   to reduce network bandwidth usage. If IPsec and IKE are used to
   secure the Diameter session, then IP compression [IPComp] MAY be used
   and IKE [IKE] MAY be used to negotiate the compression parameters. If
   TLS is used to secure the Diameter session, then TLS compression
   [TLS] MAY be used.


9.3  Application document requirements

   Each Diameter application (e.g. NASREQ, MobileIP), MUST define their
   Service-Specific AVPs that MUST be present in the Accounting-Request
   message in a section entitled "Accounting AVPs". The application MUST
   assume that the AVPs described in this document will be present in
   all Accounting messages, so only their respective service-specific
   AVPs need to be defined in this section.


9.4  Fault Resilience

   Diameter Base protocol mechanisms are used to overcome small message
   loss and network faults of temporary nature.




Calhoun et al.             expires April 2003                 [Page 116]


Internet-Draft                                              October 2002


   Diameter peers acting as clients MUST implement the use of failover
   to guard against server failures and certain network failures.
   Diameter peers acting as agents or related off-line processing
   systems MUST detect duplicate accounting records caused by the
   sending of same record to several servers and duplication of messages
   in transit. This detection MUST be based on the inspection of the
   Session-Id and Accounting-Record-Number AVP pairs. Appendix C
   discusses duplicate detection needs and implementation issues.

   Diameter clients MAY have non-volatile memory for the safe storage of
   accounting records over reboots or extended network failures, network
   partitions, and server failures. If such memory is available, the
   client SHOULD store new accounting records there as soon as the
   records are created and until a positive acknowledgement of their
   reception from the Diameter Server has been received. Upon a reboot,
   the client MUST starting sending the records in the non-volatile
   memory to the accounting server with appropriate modifications in
   termination cause, session length, and other relevant information in
   the records.

   A further application of this protocol may include AVPs to control
   how many accounting records may at most be stored in the Diameter
   client without committing them to the non-volatile memory or
   transferring them to the Diameter server.

   The client SHOULD NOT remove the accounting data from any of its
   memory areas before the correct Accounting-Answer has been received.
   The client MAY remove oldest, undelivered or yet unacknowledged
   accounting data if it runs out of resources such as memory. It is an
   implementation dependent matter for the client to accept new sessions
   under this condition.


9.5  Accounting Records

   In all accounting records, the Session-Id AVP MUST be present; the
   User-Name AVP MUST be present if it is available to the Diameter
   client. If strong authentication across agents is required, end-to-
   end security may be used for authentication purposes.

   Different types of accounting records are sent depending on the
   actual type of accounted service and the authorization server's
   directions for interim accounting. If the accounted service is a one-
   time event, meaning that the start and stop of the event are
   simultaneous, then the Accounting-Record-Type AVP MUST be present and
   set to the value EVENT_RECORD.

   If the accounted service is of a measurable length, then the AVP MUST



Calhoun et al.             expires April 2003                 [Page 117]


Internet-Draft                                              October 2002


   use the values START_RECORD, STOP_RECORD, and possibly,
   INTERIM_RECORD. If the authorization server has not directed interim
   accounting to be enabled for the session, two accounting records MUST
   be generated for each service of type session. When the initial
   Accounting-Request for a given session is sent, the Accounting-
   Record-Type AVP MUST be set to the value START_RECORD. When the last
   Accounting-Request is sent, the value MUST be STOP_RECORD.

   If the authorization server has directed interim accounting to be
   enabled, the Diameter client MUST produce additional records between
   the START_RECORD and STOP_RECORD, marked INTERIM_RECORD. The
   production of these records is directed by Acct-interim-Interval as
   well as any re-authentication or re-authorization of the session.
   The Diameter client MUST overwrite any previous interim accounting
   records that are locally stored for delivery, if a new record is
   being generated for the same session. This ensures that only one
   pending interim record can exist on an access device for any given
   session.

   A particular value of Accounting-Sub-Session-Id MUST appear only in
   one sequence of accounting records from a DIAMETER client, except for
   the purposes of retransmission.  The one sequence that is sent MUST
   be either one record with Accounting-Record-Type AVP set to the value
   EVENT_RECORD, or several records starting with one having the value
   START_RECORD, followed by zero or more INTERIM_RECORD and a single
   STOP_RECORD. A particular Diameter application specification MUST
   define the type of sequences that MUST be used.


9.6  Correlation of Accounting Records

   The Diameter protocol's Session-Id AVP, which is globally unique (see
   section 8.8), is used during the authorization phase to identify a
   particular session. Services that do not require any authorization
   still use the Session-Id AVP to identify sessions.  Accounting
   messages MAY use a different Session-Id from that sent in
   authorization messages.  Specific applications MAY require different
   a Session-ID for accounting messages.

   However, there are certain applications that require multiple
   accounting sub-sessions. Such applications would send messages with a
   constant Session-Id AVP, but a different Accounting-Sub-Session-Id
   AVP. In these cases, correlation is performed using the Session-Id.
   It is important to note that receiving a STOP_RECORD with no
   Accounting-Sub-Session-Id AVP when sub-sessions were originally used
   in the START_RECORD messages implies that all sub-sessions are
   terminated.




Calhoun et al.             expires April 2003                 [Page 118]


Internet-Draft                                              October 2002


   Furthermore, there are certain applications where a user receives
   service from different access devices (e.g. Mobile IP), each with
   their own unique Session-Id. In such cases, the Acct-Multi-Session-Id
   AVP is used for correlation. During authorization, a server that
   determines that a request is for an existing session SHOULD include
   the Acct-Multi-Session-Id AVP, which the access device MUST include
   in all subsequent accounting messages.

   The Acct-Multi-Session-Id AVP MAY include the value of the original
   Session-Id. It's contents are implementation specific, but MUST be
   globally unique across other Acct-Multi-Session-Id, and MUST NOT
   change during the life of a session.

   A Diameter application document MUST define the exact concept of a
   session that is being accounted, and MAY define the concept of a
   multi-session. For instance, the NASREQ DIAMETER application treats a
   single PPP connection to a Network Access Server as one session, and
   a set of Multilink PPP sessions as one multi-session.


9.7  Accounting Command-Codes

   This section defines new Command-Code values that MUST be supported
   by all Diameter implementations that provide Accounting services.


9.7.1  Accounting-Request

   The Accounting-Request (ACR) command, indicated by the Command-Code
   field set to 271 and the Command Flags' 'R' bit set, is sent by a
   Diameter node, acting as a client, in order to exchange accounting
   information with a peer.

   One of Acct-Application-Id and Vendor-Specific-Application-Id AVPs
   MUST be present. If the Vendor-Specific-Application-Id grouped AVP is
   present, it must have an Acct-Application-Id inside.

   The AVP listed below SHOULD include service specific accounting AVPs,
   as described in section 9.3.












Calhoun et al.             expires April 2003                 [Page 119]


Internet-Draft                                              October 2002


   Message Format

      <ACR> ::= < Diameter Header: 271, REQ, PXY >
                < Session-Id >
                { Origin-Host }
                { Origin-Realm }
                { Destination-Realm }
                { Accounting-Record-Type }
                { Accounting-Record-Number }
                [ Acct-Application-Id ]
                [ Vendor-Specific-Application-Id ]
                [ User-Name ]
                [ Accounting-Sub-Session-Id ]
                [ Accounting-RADIUS-Session-Id ]
                [ Acct-Multi-Session-Id ]
                [ Acct-interim-Interval ]
                [ Accounting-Realtime-Required ]
                [ Origin-State-Id ]
                [ Event-Timestamp ]
              * [ Proxy-Info ]
              * [ Route-Record ]
              * [ AVP ]

9.7.2  Accounting-Answer

   The Accounting-Answer (ACA) command, indicated by the Command-Code
   field set to 271 and the Command Flags' 'R' bit cleared, is used to
   acknowledge an Accounting-Request command. The Accounting-Answer
   command contains the same Session-Id and includes the usage AVPs only
   if CMS is in use when sending this command. Note that the inclusion
   of the usage AVPs when CMS is not being used leads to unnecessarily
   large answer messages, and can not be used as a server's proof of the
   receipt of these AVPs in an end-to-end fashion. If the Accounting-
   Request was protected by end-to-end security, then the corresponding
   ACA message MUST be protected by end-to-end security.

   Only the target Diameter Server, known as the home Diameter Server,
   SHOULD respond with the Accounting-Answer command.

   One of Acct-Application-Id and Vendor-Specific-Application-Id AVPs
   MUST be present. If the Vendor-Specific-Application-Id grouped AVP is
   present, it must have an Acct-Application-Id inside.

   The AVP listed below SHOULD include service specific accounting AVPs,
   as described in section 9.3.






Calhoun et al.             expires April 2003                 [Page 120]


Internet-Draft                                              October 2002


   Message Format

      <ACA> ::= < Diameter Header: 271, PXY >
                < Session-Id >
                { Result-Code }
                { Origin-Host }
                { Origin-Realm }
                { Accounting-Record-Type }
                { Accounting-Record-Number }
                [ Acct-Application-Id ]
                [ Vendor-Specific-Application-Id ]
                [ User-Name ]
                [ Accounting-Sub-Session-Id ]
                [ Accounting-RADIUS-Session-Id ]
                [ Acct-Multi-Session-Id ]
                [ Error-Reporting-Host ]
                [ Acct-interim-Interval ]
                [ Accounting-Realtime-Required ]
                [ Origin-State-Id ]
                [ Event-Timestamp ]
              * [ Proxy-Info ]
              * [ AVP ]


9.8  Accounting AVPs

   This section contains AVPs that describe accounting usage information
   related to a specific session.


9.8.1  Accounting-Record-Type AVP

   The Accounting-Record-Type AVP (AVP Code 480) is of type Enumerated
   and contains the type of accounting record being sent. The following
   values are currently defined for the Accounting-Record-Type AVP:

      EVENT_RECORD                    1
         An Accounting Event Record is used to indicate that a one-time
         event has occurred (meaning that the start and end of the event
         are simultaneous).  This record contains all information
         relevant to the service, and is the only record of the service.

      START_RECORD                    2
         An Accounting Start, Interim, and Stop Records are used to
         indicate that a service of a measurable length has been given.
         An Accounting Start Record is used to initiate an accounting
         session, and contains accounting information that is relevant
         to the initiation of the session.



Calhoun et al.             expires April 2003                 [Page 121]


Internet-Draft                                              October 2002


      INTERIM_RECORD                  3
         An Interim Accounting Record contains cumulative accounting
         information for an existing accounting session. Interim
         Accounting Records SHOULD be sent every time a re-
         authentication or re-authorization occurs. Further, additional
         interim record triggers MAY be defined by application-specific
         Diameter applications. The selection of whether to use
         INTERIM_RECORD records is done by the Acct-interim-Interval
         AVP.

      STOP_RECORD                     4
         An Accounting Stop Record is sent to terminate an accounting
         session and contains cumulative accounting information relevant
         to the existing session.


9.8.2  Acct-interim-Interval AVP

   The Acct-interim-Interval AVP (AVP Code 85) is of type Unsigned32 and
   is sent from the Diameter home authorization server to the Diameter
   client. The client uses information in this AVP to decide how and
   when to produce accounting records. With different values in this
   AVP, service sessions can result in one, two, or two+N accounting
   records, based on the needs of the home-organization. The following
   accounting record production behavior is directed by the inclusion of
   this AVP:

      1. The omission of the Acct-interim-Interval AVP or its inclusion
         with Value field set to 0 means that EVENT_RECORD,
         START_RECORD, and STOP_RECORD are produced, as appropriate for
         the service.

      2. The inclusion of the AVP with Value field set to a non-zero
         value means that INTERIM_RECORD records MUST be produced
         between the START_RECORD and STOP_RECORD records. The Value
         field of this AVP is the nominal interval between these records
         in seconds. The Diameter node that originates the accounting
         information, known as the client, MUST produce the first
         INTERIM_RECORD record roughly at the time when this nominal
         interval has elapsed from the START_RECORD, the next one again
         as the interval has elapsed once more, and so on until the
         session ends and a STOP_RECORD record is produced.

         The client MUST ensure that the interim record production times
         are randomized so that large accounting message storms are not
         created either among records or around a common service start
         time.




Calhoun et al.             expires April 2003                 [Page 122]


Internet-Draft                                              October 2002


9.8.3  Accounting-Record-Number AVP

   The Accounting-Record-Number AVP (AVP Code 485) is of type Unsigned32
   and identifies this record within one session. As Session-Id AVPs are
   globally unique, the combination of Session-Id and Accounting-Record-
   Number AVPs is also globally unique, and can be used in matching
   accounting records with confirmations.  An easy way to produce unique
   numbers is to set the value to 0 for records of type EVENT_RECORD and
   START_RECORD, and set the value to 1 for the first INTERIM_RECORD, 2
   for the second, and so on until the value for STOP_RECORD is one more
   than for the last INTERIM_RECORD.


9.8.4  Accounting-RADIUS-Session-Id AVP

   The Accounting-RADIUS-Session-Id AVP (AVP Code 44) is of type
   OctetString is only used when RADIUS/Diameter translation occurs.
   This AVP contains the contents of the RADIUS Accounting-Session-Id
   attribute.


9.8.5  Acct-Multi-Session-Id AVP

   The Acct-Multi-Session-Id AVP (AVP Code 50) is of type UTF8String,
   following the format specified in section 8.8. The Acct-Multi-
   Session-Id AVP is used to link together multiple related accounting
   sessions, where each session would have a unique Session-Id, but the
   same Acct-Multi-Session-Id AVP. This AVP MAY be returned by the
   Diameter server in an authorization answer, and MUST be used in all
   accounting messages for the given session.


9.8.6  Accounting-Sub-Session-Id AVP

   The Accounting-Sub-Session-Id AVP (AVP Code 287) is of type
   Unsigned64 and contains the accounting sub-session identifier. The
   combination of the Session-Id and this AVP MUST be unique per sub-
   session, and the value of this AVP MUST be monotonically increased by
   one for all new sub-sessions. The absence of this AVP implies no sub-
   sessions are in use, with the exception of an Accounting-Request
   whose Accounting-Record-Type is set to STOP_RECORD. A STOP_RECORD
   message with no Accounting-Sub-Session-Id AVP present will signal the
   termination of all sub-sessions for a given Session-Id.

9.8.7  Accounting-Realtime-Required AVP

   The Accounting-Realtime-Required AVP (AVP Code 483) is of type
   Enumerated and is sent from the Diameter home authorization server to



Calhoun et al.             expires April 2003                 [Page 123]


Internet-Draft                                              October 2002


   the Diameter client or in the Accounting-Answer from the accounting
   server. The client uses information in this AVP to decide what to do
   if the sending of accounting records to the accounting server has
   been temporarily prevented due to, for instance, a network problem.

      DELIVER_AND_GRANT                           1

         The AVP with Value field set to DELIVER_AND_GRANT means that
         the service MUST only be granted as long as there is a
         connection to an accounting server. Note that the set of
         alternative accounting servers are treated as one server in
         this sense. Having to move the accounting record stream to a
         backup server is not a reason to discontinue the service to the
         user.

      GRANT_AND_STORE                             2

         The AVP with Value field set to GRANT_AND_STORE means that
         service SHOULD be granted if there is a connection, or as long
         as records can still be stored as described in section 9.4.

         This is the default behaviour if the AVP isn't included in the
         reply from the authorization server.

      GRANT_AND_LOSE                              3

         The AVP with Value field set to GRANT_AND_LOSE means that
         service SHOULD be granted even if the records can not be
         delivered or stored.

10  AVP Occurrence Table

   The following tables presents the AVPs defined in this document, and
   specifies in which Diameter messages they MAY, or MAY NOT be present.
   Note that AVPs that can only be present within a Grouped AVP are not
   represented in this table.

   The table uses the following symbols:
      0     The AVP MUST NOT be present in the message.
      0+    Zero or more instances of the AVP MAY be present in the
            message.
      0-1   Zero or one instance of the AVP MAY be present in the
            message. It is considered an error if there are more than
            once instance of the AVP.
      1     One instance of the AVP MUST be present in the message.
      1+    At least one instance of the AVP MUST be present in the
            message.




Calhoun et al.             expires April 2003                 [Page 124]


Internet-Draft                                              October 2002


10.1  Base Protocol Command AVP Table

   The table in this section is limited to the non-accounting Command
   Codes defined in this specification.















































Calhoun et al.             expires April 2003                 [Page 125]


Internet-Draft                                              October 2002


                       +-----------------------------------------------+
                       |                  Command-Code                 |
                       |---+---+---+---+---+---+---+---+---+---+---+---+
   Attribute Name      |CER|CEA|DPR|DPA|DWR|DWA|RAR|RAA|ASR|ASA|STR|STA|
   --------------------|---+---+---+---+---+---+---+---+---+---+---+---|
   Acct-Interim-       |0  |0  |0  |0  |0  |0  |0-1|0  |0  |0  |0  |0  |
     Interval          |   |   |   |   |   |   |   |   |   |   |   |   |
   Accounting-Realtime-|0  |0  |0  |0  |0  |0  |0-1|0  |0  |0  |0  |0  |
     Required          |   |   |   |   |   |   |   |   |   |   |   |   |
   Acct-Application-Id |0+ |0+ |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Auth-Application-Id |0+ |0+ |0  |0  |0  |0  |1  |0  |1  |0  |1  |0  |
   Auth-Grace-Period   |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Auth-Request-Type   |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Auth-Session-State  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Authorization-      |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
     Lifetime          |   |   |   |   |   |   |   |   |   |   |   |   |
   Class               |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0+ |0+ |
   Destination-Host    |0  |0  |0  |0  |0  |0  |1  |0  |1  |0  |0-1|0  |
   Destination-Realm   |0  |0  |0  |0  |0  |0  |1  |0  |1  |0  |1  |0  |
   Disconnect-Cause    |0  |0  |1  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Error-Message       |0  |0-1|0  |0-1|0  |0-1|0  |0-1|0  |0-1|0  |0-1|
   Error-Reporting-Host|0  |0  |0  |0  |0  |0  |0  |0-1|0  |0-1|0  |0-1|
   Failed-AVP          |0  |0+ |0  |0+ |0  |0+ |0  |0+ |0  |0+ |0  |0+ |
   Firmware-Revision   |0-1|0-1|0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Host-IP-Address     |1+ |1+ |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Inband-Security-Id  |0+ |0+ |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Multi-Round-Time-Out|0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Origin-Host         |1  |1  |1  |1  |1  |1  |1  |1  |1  |1  |1  |1  |
   Origin-Realm        |1  |1  |1  |1  |1  |1  |1  |1  |1  |1  |1  |1  |
   Origin-State-Id     |0-1|0-1|0  |0  |0-1|0-1|0-1|0-1|0-1|0-1|0-1|0-1|
   Product-Name        |1  |1  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Proxy-Info          |0  |0  |0  |0  |0  |0  |0+ |0+ |0+ |0+ |0+ |0+ |
   Redirect-Host       |0  |0  |0  |0  |0  |0  |0  |0+ |0  |0+ |0  |0+ |
   Redirect-Host-Usage |0  |0  |0  |0  |0  |0  |0  |0-1|0  |0-1|0  |0-1|
   Redirect-Max-Cache- |0  |0  |0  |0  |0  |0  |0  |0-1|0  |0-1|0  |0-1|
     Time              |   |   |   |   |   |   |   |   |   |   |   |   |
   Result-Code         |0  |1  |0  |1  |0  |1  |0  |1  |0  |0  |0  |1  |
   Re-Auth-Request-Type|0  |0  |0  |0  |0  |0  |1  |0  |0  |0  |0  |0  |
   Route-Record        |0  |0  |0  |0  |0  |0  |0+ |0  |0+ |0  |0+ |0  |
   Session-Binding     |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Session-Id          |0  |0  |0  |0  |0  |0  |1  |1  |1  |1  |1  |1  |
   Session-Server-     |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
     Failover          |   |   |   |   |   |   |   |   |   |   |   |   |
   Session-Timeout     |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Supported-Vendor-Id |0+ |0+ |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
   Termination-Cause   |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |1  |0  |
   User-Name           |0  |0  |0  |0  |0  |0  |0-1|0-1|0-1|0-1|0-1|0-1|
   Vendor-Id           |1  |1  |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |



Calhoun et al.             expires April 2003                 [Page 126]


Internet-Draft                                              October 2002


   Vendor-Specific-    |0+ |0+ |0  |0  |0  |0  |0  |0  |0  |0  |0  |0  |
     Application-Id    |   |   |   |   |   |   |   |   |   |   |   |   |
   --------------------|---+---+---+---+---+---+---+---+---+---+---+---|


10.2  Accounting AVP Table

   The table in this section is used to represent which AVPs defined in
   this document are to be present in the Accounting messages.  These
   AVP occurrence requirements are guidelines, which may be expanded,
   and/or overriden by application-specific requirements in the Diameter
   applications documents.

                                 +-----------+
                                 |  Command  |
                                 |    Code   |
                                 |-----+-----+
   Attribute Name                | ACR | ACA |
   ------------------------------|-----+-----+
   Acct-Interim-Interval         | 0-1 | 0-1 |
   Acct-Multi-Session-Id         | 0-1 | 0-1 |
   Accounting-Record-Number      | 1   | 1   |
   Accounting-Record-Type        | 1   | 1   |
   Accounting-RADIUS-Session-Id  | 0-1 | 0-1 |
   Accounting-Sub-Session-Id     | 0-1 | 0-1 |
   Accounting-Realtime-Required  | 0-1 | 0-1 |
   Acct-Application-Id           | 0-1 | 0-1 |
   Auth-Application-Id           | 0   | 0   |
   Class                         | 0+  | 0+  |
   Destination-Host              | 0-1 | 0   |
   Destination-Realm             | 1   | 0   |
   Error-Reporting-Host          | 0   | 0+  |
   Event-Timestamp               | 0-1 | 0-1 |
   Origin-Host                   | 1   | 1   |
   Origin-Realm                  | 1   | 1   |
   Proxy-Info                    | 0+  | 0+  |
   Route-Record                  | 0+  | 0+  |
   Result-Code                   | 0   | 1   |
   Session-Id                    | 1   | 1   |
   Termination-Cause             | 0-1 | 0-1 |
   User-Name                     | 0-1 | 0-1 |
   Vendor-Specific-Application-Id| 0-1 | 0-1 |
   ------------------------------|-----+-----+


11  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers



Calhoun et al.             expires April 2003                 [Page 127]


Internet-Draft                                              October 2002


   Authority (IANA) regarding registration of values related to the
   Diameter protocol, in accordance with BCP 26 [IANA].  The following
   policies are used here with the meanings defined in BCP 26: "Private
   Use", "First Come First Served", "Expert Review", "Specification
   Required", "IETF Consensus", "Standards Action".

   This section explains the criteria to be used by the IANA for
   assignment of numbers within namespaces defined within this document.

   Diameter is not intended as a general purpose protocol, and
   allocations SHOULD NOT be made for purposes unrelated to
   authentication, authorization or accounting.

   For registration requests where a Designated Expert should be
   consulted, the responsible IESG area director should appoint the
   Designated Expert. For Designated Expert with Specification Required,
   the request is posted to the AAA WG mailing list (or, if it has been
   disbanded, a successor designated by the Area Director) for comment
   and review, and MUST include a pointer to a public specification.
   Before a period of 30 days has passed, the Designated Expert will
   either approve or deny the registration request and publish a notice
   of the decision to the AAA WG mailing list or its sucessor. A denial
   notice must be justified by an explanation and, in the cases  where
   it is possible, concrete suggestions on how the request can be
   modified so as to become acceptable.


11.1  AVP Header

   As defined in section 4, the AVP header contains three fields that
   requires IANA namespace management; the AVP Code, Application-ID and
   Flags field.


11.1.1  AVP Code

   The AVP Code namespace is used to identify attributes. When the
   Vendor ID value is set to zero (0), IANA will maintain a registry of
   assigned AVP codes and in some cases also their values.

   AVP Codes 0-254 are managed separately as RADIUS Attribute Types
   [RADTYPE]. This document defines the AVP Codes 257-274, 276-285, 287,
   291-299, 480, 483 and 485-486. See section 4.6 for the assignment of
   the namespace in this specification.

   AVPs may be allocated following Designated Expert with Specification
   Required [IANA]. Release of blocks of AVPs (more than 3 at a time for
   a given purpose) should require IETF Consensus.



Calhoun et al.             expires April 2003                 [Page 128]


Internet-Draft                                              October 2002


   Note that Diameter defines a mechanism for Vendor-Specific AVPs,
   where the Vendor-Id field in the AVP header is set to a non-zero
   value. Vendor-Specific AVPs codes are for Private Use and should be
   encouraged instead of allocation of global attribute types, for
   functions specific only to one vendor's implementation of Diameter,
   where no interoperability is deemed useful. Where a Vendor-Specific
   AVP is implemented by more than one vendor, allocation of global AVPs
   should be encouraged instead.

11.1.2  AVP Flags

   There are 8 bits in the AVP Flags field of the AVP header, defined in
   section 4. This document assigns bit 8 ('V'endor Specific), bit 7
   ('M'andatory) and bit 6 ('P'rotected). The remaining bits should only
   be assigned via a Standards Action [IANA].


11.2  Diameter Header

   As defined in section 3, the Diameter header contains two fields that
   require IANA namespace management; Command Code and Command Flags.


11.2.1  Command Codes

   The Command Code namespace is used to identify Diameter commands. The
   values 0-255 are reserved for RADIUS backward compatibility, and are
   defined as "RADIUS Packet Type Codes" in [RADTYPE].  Values
   256-16,777,213 are for permanent, standard commands, allocated by
   IETF Consensus [IANA]. This document defines the Command Codes 257,
   258, 271, 274-275, 280 and 282. See section 3.1 for the assignment of
   the namespace in this specification.

   ---> 2 experimental command codes.

   The values 16,777,214 and 16,777,215 (hexidecimal values FFFFFE -
   FFFFFF) are reserved for experimental commands. As these codes are
   only for experimental and testing purposes, no guarantee is made for
   interoperability between Diameter peers using experimental commands,
   as outlined in [IANA-EXP].


11.2.2  Command Flags

   There are eight bits in the Command Flags field of the Diameter
   header. This document assigns bit 8 ('R'equest), bit 7 ('P'roxy) and
   bit 6 ('E'rror). Bits 1 through 5 MUST only be assigned via a
   Standards Action [IANA].



Calhoun et al.             expires April 2003                 [Page 129]


Internet-Draft                                              October 2002


11.3  Application Identifiers

   As defined in section 2.4, the Application Identifier is used to
   identify a specific Diameter Application. There are standards-track
   application ids and vendor specific application ids.

   IANA [IANA] will assign the range 0x00000001 to 0x00ffffff for
   standards-track applications; and 0xff00000000 - 0xfffffffe for
   vendor specific applications, on a first-come, first-served basis.
   Assignment of standards-track application IDs are by Designated
   Expert with Specification Required [IANA].

   Both Application-Id and Acct-Application-Id AVPs use the same
   Application Identifier space.

   Vendor-Specific Application Identifiers, are for Private Use.
   Vendor-Specific Application Identifiers are assigned on a First Come,
   First Served basis by IANA.

   Note that the Diameter protocol is not intended to be extended for
   any purpose. Any applications defined MUST ensure that they fit
   within the existing framework, and that no changes to the base
   protocol are required.


11.4    AVP Values

   Certain AVPs in Diameter define a list of values with various
   meanings. For attributes other than those specified in this section,
   adding additional values to the list can be done on a First Come,
   First Served basis by IANA.

11.4.1  Result-Code AVP Values

   As defined in Section 7.1, the Result-Code AVP (AVP Code 268) defines
   the values 1001, 2001-2002, 3001-3010, 4001-4002 and 5001-5017.

   All remaining values are available for assignment via IETF Consensus
   [IANA].


11.4.2  Accounting-Record-Type AVP Values

   As defined in Section 9.8.1, the Accounting-Record-Type AVP (AVP Code
   480) defines the values 1-4. All remaining values are available for
   assignment via IETF Consensus [IANA].





Calhoun et al.             expires April 2003                 [Page 130]


Internet-Draft                                              October 2002


11.4.3  Termination-Cause AVP Values

   As defined in Section 8.15, the Termination-Cause AVP (AVP Code 295)
   defines the values 1-8. All remaining values are available for
   assignment via IETF Consensus [IANA].


11.4.4  Redirect-Host-Usage AVP Values

   As defined in Section 6.13, the Redirect-Host-Usage AVP (AVP Code
   261) defines the values 0-5. All remaining values are available for
   assignment via IETF Consensus [IANA].


11.4.5  Session-Server-Failover AVP Values

   As defined in Section 8.18, the Session-Server-Failover AVP (AVP Code
   271) defines the values 0-3. All remaining values are available for
   assignment via IETF Consensus [IANA].


11.4.6  Session-Binding AVP Values

   As defined in Section 8.17, the Session-Binding AVP (AVP Code 270)
   defines the bits 1-4. All remaining bits are available for assignment
   via IETF Consensus [IANA].


11.4.7  Disconnect-Cause AVP Values

   As defined in Section 5.4.3, the Disconnect-Cause AVP (AVP Code 273)
   defines the values 0-2. All remaining values are available for
   assignment via IETF Consensus [IANA].


11.4.8  Auth-Request-Type AVP Values

   As defined in Section 8.7, the Auth-Request-Type AVP (AVP Code 274)
   defines the values 1-3. All remaining values are available for
   assignment via IETF Consensus [IANA].


11.4.9  Auth-Session-State AVP Values

   As defined in Section 8.11, the Auth-Session-State AVP (AVP Code 277)
   defines the values 0-1. All remaining values are available for
   assignment via IETF Consensus [IANA].




Calhoun et al.             expires April 2003                 [Page 131]


Internet-Draft                                              October 2002


11.4.10 Re-Auth-Request-Type AVP Values

   As defined in Section 8.12, the Re-Auth-Request-Type AVP (AVP Code
   285) defines the values 0-1. All remaining values are available for
   assignment via IETF Consensus [IANA].

11.5    Diameter TCP/SCTP Port Numbers

   An IANA request has been placed for TCP and SCTP port numbers. The
   IANA has informed the authors that "TBD" should be used in section
   2.1 and throughout this document, and will be updated by the RFC
   editor during the RFC publication process.

   IANA should also replace "TBD" in sections 4.4 and 5.2 with the port
   number assigned in section 2.1.


11.6   NAPTR Service Fields

   The registration in the RFC MUST include the following information:

   Service Field: The service field being registered. An example for a
   new fictitious transport protocol called NCTP might be "AAA+D2N".

   Protocol: The specific transport protocol associated with that
   service field. This MUST include the name and acronym for the
   protocol, along with reference to a document that describes the
   transport protocol. For example - "New Connectionless Transport
   Protocol (NCTP), RFC 5766".

   Name and Contact Information: The name, address, email address and
   telephone number for the person performing the registration.

   The following values are to be placed into the registry:

      Services Field               Protocol
      AAA+D2T                       TCP
      AAA+D2S                       SCTP

11.7   Accounting-Realtime-Required AVP Values

   As defined in Section 9.8.7, the Accounting-Realtime-Required AVP
   (AVP Code 483) defines the values 1-3. All remaining values are
   available for assignment via IETF Consensus [IANA].

12  Diameter protocol related configurable parameters

   This section contains the configurable parameters that are found



Calhoun et al.             expires April 2003                 [Page 132]


Internet-Draft                                              October 2002


   throughout this document:

      Diameter Peer
         A Diameter entity MAY communicate with peers that are
         statically configured. A statically configured Diameter peer
         would require that either the IP address or the fully qualified
         domain name (FQDN) be supplied, which would then be used to
         resolve through DNS.

      Realm Routing Table
         A Diameter Proxy server routes messages based on the realm
         portion of a Network Access Identifier (NAI). The server MUST
         have a table of Realms Names, and the address of the peer to
         which the message must be forwarded to. The routing table MAY
         also include a "default route", which is typically used for all
         messages that cannot be locally processed.

      Tc timer
         The Tc timer controls the frequency that transport connection
         attempts are done to a peer with whom no active transport
         connection exists. The recommended value is 30 seconds.

13  Security Considerations

   The Diameter base protocol assumes that messages are secured by using
   either IPSec or TLS. This security model is acceptable in
   environments where there is no untrusted third party agent.  In other
   situations, end-to-end security is needed.

   Diameter clients, such as Network Access Servers (NASes) and Mobility
   Agents MUST support IP Security [SECARCH] and MAY support TLS [TLS].
   Diameter servers MUST support TLS and IPsec. Diameter implementations
   MUST use transmission-level security of some kind (IPsec or TLS) on
   each connection.

   If a Diameter connection is not protected by IPsec, then the CER/CEA
   exchange MUST include an Inband-Security-ID AVP with a value of TLS.
   For TLS usage, a TLS handshake will begin when both ends are in the
   open state, after completion of the CER/CEA exchange. If the TLS
   handshake is successful, all further messages will be sent via TLS.
   If the handshake fails, both ends move to the closed state.

   It is suggested that IPsec be used primarily at the edges for intra-
   domain exchanges. For NAS devices without certificate support, pre-
   shared keys can be used between the NAS and a local AAA proxy.

   For protection of inter-domain exchanges, TLS is recommended. See
   sections 13.1 and 13.2 for more details on IPsec and TLS usage.



Calhoun et al.             expires April 2003                 [Page 133]


Internet-Draft                                              October 2002


13.1  IPsec Usage

   All Diameter implementations MUST support IPsec ESP [IPsec] in
   transport mode with with non-null encryption and authentication
   algorithms to provide per-packet authentication, integrity protection
   and confidentiality, and MUST support the replay protection
   mechanisms of IPsec.

   Diameter implementations MUST support IKE for peer authentication,
   negotiation of security associations, and key management, using the
   IPsec DOI [IPSECDOI]. Diameter implementations MUST support peer
   authentication using a pre-shared key, and MAY support certificate-
   based peer authentication using digital signatures. Peer
   authentication using the public key encryption methods outlined in
   IKE's sections 5.2 and 5.3 [IKE] SHOULD NOT be used.

   Conformant implementations MUST support both IKE Main Mode and
   Aggressive Mode. When pre-shared keys are used for authentication,
   IKE Aggressive Mode SHOULD be used, and IKE Main Mode SHOULD NOT be
   used. When digital signatures are used for authentication, either IKE
   Main Mode or IKE Aggressive Mode MAY be used.

   When digital signatures are used to achieve authentication, an IKE
   negotiator SHOULD use IKE Certificate Request Payload(s) to specify
   the certificate authority (or authorities) that are trusted in
   accordance with its local policy. IKE negotiators SHOULD use
   pertinent certificate revocation checks before accepting a PKI
   certificate for use in IKE's authentication procedures.

   The Phase 2 Quick Mode exchanges used to negotiate protection for
   Diameter connections MUST explicitly carry the Identity Payload
   fields (IDci and IDcr). The DOI provides for several types of
   identification data. However, when used in conformant
   implementations, each ID Payload MUST carry a single IP address and a
   single non-zero port number, and MUST NOT use the IP Subnet or IP
   Address Range formats. This allows the Phase 2 security association
   to correspond to specific TCP and SCTP connections.

   Since IPsec acceleration hardware may only be able to handle a
   limited number of active IKE Phase 2 SAs, Phase 2 delete messages may
   be sent for idle SAs, as a means of keeping the number of active
   Phase 2 SAs to a minimum. The receipt of an IKE Phase 2 delete
   message SHOULD NOT be interpreted as a reason for tearing down a
   Diameter connection. Rather, it is preferable to leave the connection
   up, and if additional traffic is sent on it, to bring up another IKE
   Phase 2 SA to protect it. This avoids the potential for continually
   bringing connections up and down.




Calhoun et al.             expires April 2003                 [Page 134]


Internet-Draft                                              October 2002


13.2  TLS Usage

   A Diameter node that initiates a connection to another Diameter node
   acts as a TLS client according to [TLS], and a Diameter node that
   accepts a connection acts as a TLS server.  Diameter nodes
   implementing TLS for security MUST mutually authenticate as part of
   TLS session establishment.  In order to ensure mutual authentication,
   the Diameter node acting as TLS server must request a certificate
   from the Diameter node acting as TLS client, and the Diameter node
   acting as TLS client MUST be prepared to supply a certificate on
   request.

   Diameter nodes MUST be able to negotiate the following TLS cipher
   suites:

      TLS_RSA_WITH_RC4_128_MD5
      TLS_RSA_WITH_RC4_128_SHA
      TLS_RSA_WITH_3DES_EDE_CBC_SHA

   Diameter nodes SHOULD be able to negotiate the following TLS cipher
   suite:

      TLS_RSA_WITH_AES_128_CBC_SHA

   Diameter nodes MAY negotiate other TLS cipher suites.

13.3 Peer-to-Peer Considerations

   As with any peer-to-peer protocol, proper configuration of the trust
   model within a Diameter peer is essential to security. When
   certificates are used, it is necessary to configure the root
   certificate authorities trusted by the Diameter peer. These root CAs
   are likely to be unique to Diameter usage and distinct from the root
   CAs that might be trusted for other purposes such as Web browsing. In
   general, it is expected that those root CAs will be configured so as
   to reflect the business relationships between the organization
   hosting the Diameter peer and other organizations. As a result, a
   Diameter peer will typically not be configured to allow connectivity
   with any arbitrary peer. When certificate authentication Diameter
   peers may not be known beforehand, and therefore peer discovery may
   be required.

   Note that IPsec is considerably less flexible than TLS when it comes
   to configuring root CAs. Since use of Port identifiers is prohibited
   within IKE Phase 1, within IPsec it is not possible to uniquely
   configure trusted root CAs for each application individually; the
   same policy must be used for all applications. This implies, for
   example, that a root CA trusted for use with Diameter must also be



Calhoun et al.             expires April 2003                 [Page 135]


Internet-Draft                                              October 2002


   trusted to protect SNMP. These restrictions can be awkward at best.
   Since TLS supports application-level granularity in certificate
   policy, TLS SHOULD be used to protect Diameter connections between
   administrative domains. IPsec is most appropriate for intra-domain
   usage when pre-shared keys are used as a security mechanism.

   When pre-shared key authentication is used with IPsec to protect
   Diameter, unique pre-shared keys are configured with Diameter peers,
   who are identified by their IP address (Main Mode), or possibly their
   FQDN (Aggressive Mode). As a result, it is necessary for the set of
   Diameter peers to be known beforehand. Therefore, peer discovery is
   typically not necessary.

   The following is intended to provide some guidance on the issue.

   It is recommended that a Diameter peer implement the same security
   mechanism (IPsec or TLS) across all its peer-to-peer connections.
   Inconsistent use of security mechanisms can result in redundant
   security mechanisms being used (e.g. TLS over IPsec) or worse,
   potential security vulnerabilities. When IPsec is used with Diameter,
   a typical security policy for outbound traffic is "Initiate IPsec,
   from me to any, destination port Diameter"; for inbound traffic, the
   policy would be "Require IPsec, from any to me, destination port
   Diameter".

   This policy causes IPsec to be used whenever a Diameter peer
   initiates a connection to another Diameter peer, and to be required
   whenever an inbound Diameter connection occurs. This policy is
   attractive, since it does not require policy to be set for each peer
   or dynamically modified each time a new Diameter connection is
   created; an IPsec SA is automatically created based on a simple
   static policy. Since IPsec extensions are typically not available to
   the sockets API on most platforms, and IPsec policy functionality is
   implementation dependent, use of a simple static policy is the often
   the simplest route to IPsec-enabling a Diameter implementation.

   One implication of the recommended policy is that if a node is using
   both TLS and IPsec, there is not a convenient way in which to use
   either TLS or IPsec, but not both, without reserving an additional
   port for TLS usage. Since Diameter uses the same port for TLS and
   non-TLS usage, where the recommended IPsec policy is put in place, a
   TLS-protected connection will match the IPsec policy, and both IPsec
   and TLS will be used to protect the Diameter connection. To avoid
   this, it would be necessary to plumb peer-specific policies either
   statically or dynamically.

   If IPsec is used to secure Diameter peer-to-peer connections, IPsec
   policy SHOULD be set so as to require IPsec protection for inbound



Calhoun et al.             expires April 2003                 [Page 136]


Internet-Draft                                              October 2002


   connections, and to initiate IPsec protection for outbound
   connections. This can be accomplished via use of inbound and outbound
   filter policy.


14  References

14.1  Normative


[AAATRANS]     B. Aboba, J. Wood, "Authentication, Authorization and
               Accounting (AAA) Transport Profile", IETF Work in
               Progress.

[ABNF]         D. Crocker, P. Overell, "Augmented BNF for Syntax Speci­
               fications: ABNF", RFC 2234, November 1997.

[ASSIGNNO]     Reynolds, Postel, "Assigned Numbers", RFC 1700, October
               1994.

[DIFFSERV]     K. Nichols, S. Blake, F. Baker, D. Black, "Definition of
               the Differentiated Services Field (DS Field) in the IPv4
               and IPv6 Headers," RFC 2474, December 1998.

[DIFFSERVAF]   J. Heinanen, F. Baker, W. Weiss, J. Wroclawski, "Assured
               Forwarding PHB Group," RFC 2597, June 1999.

[DIFFSERVEF]   V. Jacobson, K. Nichols, K. Poduri, "An Expedited For­
               warding PHB", RFC 2598, June 1999.

[DNSSRV]       A. Gulbrandsen, P. Vixie, L. Esibov, "A DNS RR for speci­
               fying the location of services (DNS SRV)", RFC 2782,
               February 2000.

[EAP]          L. J. Blunk, J. R. Vollbrecht, "PPP Extensible Authenti­
               cation Protocol (EAP)." RFC 2284, March 1998.

[FLOATPOINT]   Institute of Electrical and Electronics Engineers, "IEEE
               Standard for Binary Floating-Point Arithmetic", ANSI/IEEE
               Standard 754-1985, August 1985.

[IANA]         Narten, Alvestrand, "Guidelines for Writing an IANA Con­
               siderations Section in RFCs", BCP 26, RFC 2434, October
               1998

[IANAWEB]      IANA, "Number assignment", http://www.iana.org





Calhoun et al.             expires April 2003                 [Page 137]


Internet-Draft                                              October 2002


[IKE]          D. Harkins, D. Carrel, "The Internet Key Exchange (IKE)",
               RFC 2409, November 1998.

[IPComp]       A. Shacham, R. Monsour, R. Pereira, M. Thomas, "IP Pay­
               load Compression Protocol (IPComp)", RFC 2393, December
               1998.

[IPSECDOI]     D. Piper, "The Internet IP Security Domain of Interpreta­
               tion for ISAKMP", RFC 2407, November 1998.

[IPV4]         ISI, "Internet Protocol", RFC 791, September 1981.

[IPV6]         Hinden, Deering, "IP Version 6 Addressing Architecture",
               RFC 2373, July 1998.

[KEYWORDS]     S. Bradner, "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

[NAI]          Aboba, Beadles "The Network Access Identifier." RFC 2486.
               January 1999.

[NAPTR]        M. Mealling and R. Daniel, "The naming authority pointer
               (NAPTR) DNS resource record," Request for Comments 2915,
               Internet Engineering Task Force, Sept. 2000.

[RADTYPE]      IANA, "RADIUS Types", http://www.iana.org/assign­
               ments/radius-types

[SCTP]         R. Stewart et al., "Stream Control Transmission Proto­
               col". RFC 2960. October 2000.

[SLP]          E. Guttman, C. Perkins, J. Veizades, M. Day. "Service
               Location Protocol, Version 2", RFC 2165, June 1999.

[SNTP]         Mills, "Simple Network Time Protocol (SNTP) Version 4 for
               IPv4, IPv6 and OSI, RFC 2030, October 1996.

[TCP]          Postel, J. "Transmission Control Protocol", RFC 793, Jan­
               uary 1981.

[TEMPLATE]     E. Guttman, C. Perkins, J. Kempf, "Service Templates and
               Service: Schemes", RFC 2609, June 1999.

[TLS]          T. Dierks, C. Allen, "The TLS Protocol Version 1.0", RFC
               2246, January 1999.

[TLSSCTP]      M. Tuexen, et al. "TLS over SCTP" IETF Work in Progress.




Calhoun et al.             expires April 2003                 [Page 138]


Internet-Draft                                              October 2002


[URI]          T. Berners-Lee, R. Fielding, U.C. Irvine, L. Masinter,
               "Uniform Resource Identifiers (URI): Generic Syntax". RFC
               2396, August 1998.

[UTF8]         F. Yergeau, "UTF-8, a transformation format of ISO
               10646", RFC 2279, January 1998.

14.2  Non-Normative


[AAACMS]       P. Calhoun, W. Bulley, S. Farrell, "Diameter CMS Security
               application," IETF Work in Progress.

[AAAREQ]       Aboba, B. et al., "Criteria for Evaluating AAA Protocols
               for Network Access", RFC 2989, November 2000.

[ACCMGMT]      B. Aboba, J. Arkko, D. Harrington. "Introduction to
               Accounting Management", RFC 2975, October 2000.

[CDMA2000]     T. Hiller and al, "CDMA2000 Wireless Data Requirements
               for AAA", RFC 3141, June 2001.

[DIAMMIP]      P. Calhoun, C. Perkins, "Diameter Mobile IP Application",
               IETF work in progress.

[DYNAUTH]      Chiba, M., et al., "Dynamic Authorization Extensions to
               RADIUS", IETF work in progress.

[IANA-EXP]     T. Narten, "Assigning Experimental and Testing Numbers
               Considered Useful", IETF Work in Progress.

[MIPV4]        C. Perkins, Editor.  IP Mobility Support.  RFC 3220, Jan­
               uary 2002.

[MIPREQ]       S. Glass, S. Jacobs, C. Perkins, "Mobile IP Authentica­
               tion, Authorization, and Accounting Requirements". RFC
               2977. October 2000.

[NASNG]        D. Mitton, M. Beadles, "Network Access Server Require­
               ments Next Generation (NASREQNG) NAS Model", RFC 2881.
               July 2000.

[NASREQ]       P. Calhoun, W. Bulley, A. Rubens, J. Haag, "Diameter NAS­
               REQ Application", IETF work in progress.

[NASCRIT]      M. Beadles, D. Mitton, "Criteria for Evaluating Network
               Access Server Protocols", RFC 3169, September 2001.




Calhoun et al.             expires April 2003                 [Page 139]


Internet-Draft                                              October 2002


[PPP]          W. Simpson, "The Point-to-Point Protocol (PPP)", RFC
               1661, STD 51, July 1994.

[PROXYCHAIN]   B. Aboba, J. Vollbrecht, "Proxy Chaining and Policy
               Implementation in Roaming", RFC 2607, June 1999.

[RADACCT]      Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.

[RADEXT]       Rigney, C., Willats W., Calhoun P., "RADIUS Extensions",
               RFC 2869, June 2000.

[RADIUS]       C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote
               Authentication Dial In User Service (RADIUS)", RFC 2865,
               June 2000.

[ROAMCRIT]     B. Aboba, G. Zorn, "Criteria for Evaluating Roaming Pro­
               tocols", RFC 2477, January 1999.

[SECARCH]      S. Kent, R. Atkinson, "Security Architecture for the
               Internet Protocol", RFC 2401, November 1998.

[TACACS]       Finseth, C., "An Access Control Protocol, Sometimes
               Called TACACS", RFC 1492, July 1993.


15  Acknowledgements

   The authors would like to thank Nenad Trifunovic, Tony Johansson and
   Pankaj Patel for their participation in the pre-IETF Document Reading
   Party.  Allison Mankin, Jonathan Wood and Bernard Aboba provided
   invaluable assistance in working out transport issues, and similarly
   with Steven Bellovin in the security area.

   Paul Funk and David Mitton were instrumental in getting the Peer
   State Machine correct, and our deep thanks go to them for their time.
   Text in this document was also provided by Paul Funk, Mark Eklund,
   Mark Jones and Dave Spence. Jacques Caron provided many great com­
   ments as a result of a thorough review of the spec.

   The authors would also like to acknowledge the following people for
   their contribution in the development of the Diameter protocol:

   Allan C. Rubens, Haseeb Akhtar, William Bulley, Stephen Farrell,
   David Frascone, Daniel C. Fox, Lol Grant, Ignacio Goyret, Nancy
   Greene, Peter Heitman, Fredrik Johansson, Mark Jones, Martin Julien,
   Bob Kopacz, Paul Krumviede, Fergal Ladley, Ryan Moats, Victor Muslin,
   Kenneth Peirce, John Schnizlein, Sumit Vakil, John R. Vollbrecht and
   Jeff Weisberg.



Calhoun et al.             expires April 2003                 [Page 140]


Internet-Draft                                              October 2002


   Finally, Pat Calhoun would like to thank Sun Microsystems since most
   of the effort put into this document was done while he was in their
   employ.


16  Authors' Addresses

   Questions about this memo can be directed to:

      Pat R. Calhoun
      Black Storm Networks
      250 Cambridge Avenue, Suite 200
      Palo Alto, California, 94306
      USA

       Phone:  +1 650-617-2932
         Fax:  +1 650-786-6445
      E-mail:  pcalhoun@bstormnetworks.com


      John Loughney
      Nokia Research Center
      Itämerenkatu 11-13
      00180 Helsinki
      Finland

       Phone:  +358 50 483 6242
      E-mail:  john.Loughney@nokia.com


      Jari Arkko
      Ericsson
      02420 Jorvas
      Finland

       Phone: +358 40 5079256
      E-Mail: Jari.Arkko@ericsson.com














Calhoun et al.             expires April 2003                 [Page 141]


Internet-Draft                                              October 2002


      Erik Guttman
      Solaris Advanced Development
      Sun Microsystems, Inc.
      Eichhoelzelstr. 7
      74915 Waibstadt
      Germany

       Phone:  +49-7263-911-701
      E-mail:  erik.guttman@germany.sun.com


      Glen Zorn
      Cisco Systems, Inc.
      500 108th Avenue N.E., Suite 500
      Bellevue, WA 98004
      USA

       Phone:  +1 425 438 8218


17  Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this docu­
   ment itself may not be modified in any way, such as by removing the
   copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of develop­
   ing Internet standards in which case the procedures for copyrights
   defined in the Internet Standards process must be followed, or as
   required to translate it into languages other than English. The lim­
   ited permissions granted above are perpetual and will not be revoked
   by the Internet Society or its successors or assigns. This document
   and the information contained herein is provided on an "AS IS" basis
   and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DIS­
   CLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
   TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
   INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
   FITNESS FOR A PARTICULAR PURPOSE.


18  Expiration Date




Calhoun et al.             expires April 2003                 [Page 142]


Internet-Draft                                              October 2002


   This memo is filed as <draft-ietf-aaa-diameter-15.txt> and expires in
   April 2003.

















































Calhoun et al.             expires April 2003                 [Page 143]


Internet-Draft                                              October 2002


Appendix A. Diameter Service Template

   The following service template describes the attributes used by Diam­
   eter servers to advertise themselves.  This simplifies the process of
   selecting an appropriate server to communicate with.  A Diameter
   client can request specific Diameter servers based on characteristics
   of the Diameter service desired (for example, an AAA server to use
   for accounting.)

   Name of submitter:  "Erik Guttman" <Erik.Guttman@sun.com>
   Language of service template:  en


   Security Considerations:
      Diameter clients and servers use various cryptographic mechanisms
      to protect communication integrity, confidentiality as well as
      perform end-point authentication.  It would thus be difficult if
      not impossible for an attacker to advertise itself using SLPv2 and
      pose as a legitimate Diameter peer without proper preconfigured
      secrets or cryptographic keys.  Still, as Diameter services are
      vital for network operation it is important to use SLPv2 authenti­
      cation to prevent an attacker from modifying or eliminating ser­
      vice advertisements for legitimate Diameter servers.

   Template text:
   -------------------------template begins here-----------------------
   template-type=service:diameter

   template-version=0.0

   template-description=
     The Diameter protocol is defined by draft-ietf-aaa-diameter-09.txt

   template-url-syntax=
     url-path= ; The Diameter URL format is described in section 2.9.
               ; Example: 'aaa://aaa.abc.com:1812;transport=tcp















Calhoun et al.             expires April 2003                 [Page 144]


Internet-Draft                                              October 2002


      supported-auth-applications= string L M
      # This attribute lists the Diameter applications supported by the
      # AAA implementation.  The applications currently defined are:
      #  Application Name     Defined by
      #  ----------------     -----------------------------------
      #  NASREQ               draft-ietf-aaa-diameter-nasreq-09.txt
      #  MobileIP             draft-ietf-aaa-diameter-mobileip-09.txt
      #
      # Notes:
      #   . Diameter implementations support one or more applications.
      #   . Additional applications may be defined in the future.
      #     An updated service template will be created at that time.
      #
      NASREQ,MobileIP

      supported-acct-applications= string L M
      # This attribute lists the Diameter applications supported by the
      # AAA implementation.  The applications currently defined are:
      #  Application Name     Defined by
      #  ----------------     -----------------------------------
      #  NASREQ               draft-ietf-aaa-diameter-nasreq-09.txt
      #  MobileIP             draft-ietf-aaa-diameter-mobileip-09.txt
      #
      # Notes:
      #   . Diameter implementations support one or more applications.
      #   . Additional applications may be defined in the future.
      #     An updated service template will be created at that time.
      #
      NASREQ,MobileIP

      supported-transports= string L M
      SCTP
      # This attribute lists the supported transports that the Diameter
      # implementation accepts.  Note that a compliant Diameter
      # implementation MUST support SCTP, though it MAY support other
      # transports, too.
      SCTP,TCP

   -------------------------template ends here-----------------------

Appendix B.  NAPTR Example

   As an example, consider a client that wishes to resolve aaa:ex.com.
   The client performs a NAPTR query for that domain, and the following
   NAPTR records are returned:

   ;;          order pref flags service           regexp  replacement
      IN NAPTR 50   50  "s"  "AAA+D2S"           ""



Calhoun et al.             expires April 2003                 [Page 145]


Internet-Draft                                              October 2002


      _diameter._sctp.ex.com.  IN NAPTR 100  50  "s"  "AAA+D2T"
      ""  _aaa._tcp.ex.com


   This indicates that the server supports SCTP, and TCP, in that order.
   If the client supports over SCTP, SCTP will be used, targeted to a
   host determined by an SRV lookup of _diameter._sctp.ex.com. That
   lookup would return:


   ;;          Priority Weight Port   Target
      IN SRV  0        1      5060   server1.ex.com IN SRV  0        2
      5060   server2.ex.com

Appendix C.  Duplicate Detection

   As described in section 9.4, accounting record duplicate detection is
   based on session identifiers. Duplicates can appear for various rea­
   sons:

      - Failover to an alternate server. Where close to real-time per­
        formance is required, failover thresholds need to be kept low
        and this may lead to an increased likelihood of duplicates.
        Failover can occur at the client or within Diameter agents.
      - Failure of a client or agent after sending of a record from non-
        volatile memory, but prior to receipt of an application layer
        ACK and deletion of the record. record to be sent. This will
        result in retransmission of the record soon after the client or
        agent has rebooted.
      - Duplicates received from RADIUS gateways. Since the retransmis­
        sion behavior of RADIUS is not defined within [RFC2865], the
        likelihood of duplication will vary according to the implementa­
        tion.
      - Implementation problems and misconfiguration.

   In some cases the Diameter accounting server can delay the duplicate
   detection and accounting record processing until a post-processing
   phase takes place. At that time records are likely to be sorted
   according to the included User-Name and duplicate elimination is easy
   in this case.  In other situations it may be necessary to perform
   real-time duplicate detection, such as when credit limits are imposed
   or real-time fraud detection is desired.

   In general, only generation of duplicates due to failover or re-send­
   ing of records in non-volatile storage can be reliably detected by
   Diameter clients or agents. In such cases the Diameter client or
   agents can mark the message as possible duplicate by setting the T
   flag. Since the Diameter server is responsible for duplicate



Calhoun et al.             expires April 2003                 [Page 146]


Internet-Draft                                              October 2002


   detection, it can choose to make use of the T flag or not, in order
   to optimize duplicate detection. Since the T flag does not affect
   interoperability, and may not be needed by some servers, generation
   of the T flag is REQUIRED for Diameter clients and agents, but MAY be
   implemented by Diameter servers.

   As an example, it can be usually be assumed that duplicates appear
   within a time window of longest recorded network partition or device
   fault, perhaps a day. So only records within this time window need to
   be looked at in the backward direction. Secondly, hashing techniques
   or other schemes, such as the use of the T flag in the received mes­
   sages, may be used to eliminate the need to do a full search even in
   this set except for rare cases.

   The following is an example of how the T flag may be used by the
   server to detect duplicate requests.

      A Diameter server MAY check the T flag of the received message to
      determine if the record is a possible duplicate. If the T flag is
      set in the request message, the server searches for a duplicate
      within a configurable duplication time window backward and for­
      ward. This limits database searching to those records where the T
      flag is set.  In a well run network, network partitions and device
      faults will presumably be rare events, so this approach represents
      a substantial optimization of the duplicate detection process.
      During failover, it is possible for the original record to be
      received after the T flag marked record, due to differences in
      network delays experienced along the path by the original and
      duplicate transmissions. The likelihood of this occurring
      increases as the failover interval is decreased. In order to be
      able to detect out of order duplicates, the Diameter server should
      use backward and forward time windows when performing duplicate
      checking for the T flag marked request. For example, in order to
      allow time for the original record to exit the network and be
      recorded by the accounting server, the Diameter server can delay
      processing records with the T flag set until a time period
      TIME_WAIT + RECORD_PROCESSING_TIME has elapsed after the closing
      of the original transport connection.  After this time period has
      expired, then it may check the T flag marked records against the
      database with relative assurance that the original records, if
      sent, have been received and recorded.










Calhoun et al.             expires April 2003                 [Page 147]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/