Diameter Maintenance and Extensions                     J. Korhonen, Ed.
(DIME)                                                          Broadcom
Internet-Draft                                                S. Donovan
Intended status: Standards Track                             B. Campbell
Expires: May 26, June 20, 2014                                            Oracle
                                                       November 22,
                                                               L. Morand
                                                             Orange Labs
                                                       December 17, 2013

                Diameter Overload Indication Conveyance
                      draft-ietf-dime-ovli-00.txt
                      draft-ietf-dime-ovli-01.txt

Abstract

   This specification documents a Diameter Overload Control (DOC) base
   solution and the dissemination of the overload report information.

Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 26, June 20, 2014.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology and Abbreviations  . . . . . . . . . . . . . . . .  4
   3.  Solution Overview  . . . . . . . . . . . . . . . . . . . . . .  6  5
     3.1.  Architectural Assumptions  . . . . . . . . . . . . . . . .  6  5
       3.1.1.  Application Classification . . . . . . . . . . . . . .  7  5
       3.1.2.  Application Type Overload Implications . . . . . . . .  8  6
       3.1.3.  Request Transaction Classification . . . . . . . . . .  9  8
       3.1.4.  Request Type Overload Implications . . . . . . . . . . 10  9
       3.1.5.  Diameter Deployment Scenarios  . . . . . . . . . . . . 11
       3.1.6.  Diameter Agent Behaviour . . . . . . . . . . . . . . . 12
       3.1.7. 10
       3.1.6.  Simplified Example Architecture  . . . . . . . . . . . 13 11
     3.2.  Conveyance of the Overload Indication  . . . . . . . . . . 14 11
       3.2.1.  Negotiation and Versioning . . . . . .  DOIC Capability Discovery  . . . . . . . . 14
       3.2.2.  Transmission of the Attribute Value Pairs . . . . . . 14 12
     3.3.  Overload Condition Indication  . . . . . . . . . . . . . . 15 12
   4.  Attribute Value Pairs  . . . . . . . . . . . . . . . . . . . . 15 12
     4.1.  OC-Feature-Vector  OC-Supported-Features AVP  . . . . . . . . . . . . . . . . . . 15 13
     4.2.  OC-OLR  OC-Feature-Vector AVP  . . . . . . . . . . . . . . . . . . 14
     4.3.  OC-OLR AVP . . . . . . 16
     4.3.  TimeStamp AVP . . . . . . . . . . . . . . . . . . 14
     4.4.  OC-Sequence-Number AVP . . . . 17
     4.4.  ValidityDuration AVP . . . . . . . . . . . . . . 15
     4.5.  OC-Validity-Duration AVP . . . . . 17
     4.5.  ReportType AVP . . . . . . . . . . . . 15
     4.6.  OC-Report-Type AVP . . . . . . . . . . 17
     4.6.  Reduction-Percentage AVP . . . . . . . . . . 16
     4.7.  OC-Reduction-Percentage AVP  . . . . . . . 18
     4.7. . . . . . . . . 16
     4.8.  Attribute Value Pair flag rules  . . . . . . . . . . . . . 19 17
   5.  Overload Control Operation . . . . . . . . . . . . . . . . . . 19 18
     5.1.  Overload Control Endpoints . . . . . . . . . . . . . . . . 19 18
     5.2.  Piggybacking Principle . . . . . . . . . . . . . . . . . . 23 21
     5.3.  Capability Announcement  . . . . . . . . . . . . . . . . . 23 22
       5.3.1.  Request Message Initiator  Reacting Node Endpoint Considerations  . . 24 . . . . . . 22
       5.3.2.  Answer Message Initiating  Reporting Node Endpoint Considerations . . 24 . . . . . . 23
     5.4.  Protocol Extensibility . . . . . . . . . . . . . . . . . . 25 23
     5.5.  Overload Report Processing . . . . . . . . . . . . . . . . 25 24
       5.5.1.  Sender Endpoint Considerations  Overload Control State . . . . . . . . . . . . . . . 25 . 24
       5.5.2.  Receiver Endpoint  Reacting Node Considerations . . . . . . . . . . . . . 24
       5.5.3.  Reporting Node Considerations  . . . . . . . . . . . 25 . 27
   6.  Transport Considerations . . . . . . . . . . . . . . . . . . . 25 27
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26 28
     7.1.  AVP codes  . . . . . . . . . . . . . . . . . . . . . . . . 26 28
     7.2.  New registries . . . . . . . . . . . . . . . . . . . . . . 26 28

   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 26 28
     8.1.  Potential Threat Modes . . . . . . . . . . . . . . . . . . 27 28
     8.2.  Denial of Service Attacks  . . . . . . . . . . . . . . . . 28 30
     8.3.  Non-Compliant Nodes  . . . . . . . . . . . . . . . . . . . 28 30
     8.4.  End-to End-Security Issues . . . . . . . . . . . . . . . . 28 30
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 30 31
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     11.1. 32
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 30
     11.2. 32
     10.2. Informative References . . . . . . . . . . . . . . . . . . 31 32
   Appendix A.  Issues left for future specifications . . . . . . . . 31 33
     A.1.  Additional traffic abatement algorithms  . . . . . . . . . 31 33
     A.2.  Agent Overload . . . . . . . . . . . . . . . . . . . . . . 31 33
     A.3.  DIAMETER_TOO_BUSY clarifications . . . . . . . . . . . . . 31 33
   Appendix B.  Conformance to Requirements  Examples  . . . . . . . . . . . . . 32
   Appendix C.  Examples . . . . . . . . . 33
     B.1.  Mix of Destination-Realm routed requests and
           Destination-Host routed requests . . . . . . . . . . . . . 41
     C.1.  3GPP S6a interface overload indication 33
   Authors' Addresses . . . . . . . . . . 41
     C.2.  3GPP PCC interfaces overload indication  . . . . . . . . . 41
     C.3.  Mix of Destination-Realm routed requests and
           Destination-Host reouted requests  . . . . . . . . . . . . 41
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 37

1.  Introduction

   This specification defines a base solution for the Diameter Overload
   Control (DOC).  The requirements for the solution are described and
   discussed in the corresponding design requirements document
   [I-D.ietf-dime-overload-reqs].
   [RFC7068].  Note that the overload control solution defined in this
   specification does not address all the requirements listed in [I-D.ietf-dime-overload-reqs].
   [RFC7068].  A number of overload control related features are left
   for the future specifications.  See Appendix A for more detailed discussion on
   those.

   The solution defined in this specification addresses the Diameter
   overload control between two endpoints (see Section 5.1).
   Furthermore, the solution is designed to apply to existing and future
   Diameter applications, requires no changes to the Diameter base
   protocol [RFC6733] and is deployable in environments where some
   Diameter nodes do not implement the Diameter overload control
   solution defined in this specification.

2.  Terminology and Abbreviations

   Server Farm

      A set of Diameter servers that can handle any request for a given
      set of Diameter applications.  While these servers support the
      same set of applications, they do not necessarily all have the
      same capacity.  An individual server farm might also support a
      subset of the users for a Diameter Realm.

      [OpenIssue: Is a  A server farm assumed to support a single realm?
      That is, does it support a set of applications in may host
      a single realm?]

   Server Front End

      A Server Front End (SFE) is a role that can be performed by a
      Diameter agent -- either a relay or a proxy -- that sits between multiple realms.

   Diameter clients and a Server Farm.  An SFE can perform various
      functions for the server farm it sits in front of.  This includes
      some or all of the following functions:

      * Routing:

      Diameter Routing

      *  Diameter layer load balancing

      *  Load Management
      *  Overload Management

      *  Topology Hiding

      *  Server Farm Identity Management

      [OpenIssue: We used between non-adjacent nodes relies on the concept of a server farm and SFE for
      internal discussions.  Do we still need those concepts
      Destination-Realm AVP to explain determine the mechanism?  It doesn't seem like we use them much.]

   Diameter Routing: Diameter Routing determines realm in which the destination of Diameter messages
      addressed
      request needs to either a Diameter Realm and Application be processed.  A Destination-Host AVP may also be
      present in general,
      or the request to address a specific server using Destination-Host. inside the
      Diameter realm.  This function is defined in [RFC6733].  Application  However,
      it is possible to enhance the routing decisions with application
      level knowledge as it done in 3GPP PCC [3GPP.23.203] and NAI-based
      source routing specifications
      that expand on [RFC6733] also exist.

   Diameter-layer [RFC5729].

   Diameter layer Load Balancing:

      Diameter layer load balancing allows Diameter requests to be
      distributed across the set of servers.  Definition of this
      function is outside the scope of this document.

   Load Management:

      This functionality ensures that the consolidated load state for
      the server farm is collected, and processed.  The exact algorithm
      for computing the load at the SFE is implementation specific but
      enough semantic of the conveyed load information needs to be
      specified so that deterministic behavior can be ensured.

   Overload Management:

      The SFE is the entity that understands the consolidated overload
      state for the server farm.  Just as it is outside the scope of
      this document to specify how a Diameter server calculates its
      overload state, it is also outside the scope of this document to
      specify how an SFE calculates the overload state for the set of
      servers.  This document describes how the SFE communicates
      Overload information to Diameter Clients.

   Topology Hiding:

      Topology Hiding

   Topology Hiding:

      Topology Hiding is loosely defined as ensuring that no Diameter
      topology information about the server farm a Diameter network can be discovered
      from Diameter messages sent outside a predefined boundary
      (typically an administrative domain).  This includes obfuscating
      identifiers and address information of Diameter entities in the server farm.
      Diameter network.  It can also include hiding the number of
      various Diameter entities in the server farm. Diameter network.  Identifying
      information can occur in many Diameter Attribute-Value Pairs
      (AVPs), including Origin-Host, Destination-Host, Route-Record,
      Proxy-Info, Session-ID and other AVPs.

   Server Farm Identity Management:

      Server Farm Identity Management (SFIM) is a mechanism that can be
      used by the SFE to present a single Diameter identity that can be
      used by clients to send Diameter requests to the server farm.
      This requires that the SFE modifies Origin-Host information in
      answers coming from servers in the server farm.  An agent that
      performs SFIM appears as a server from the client's perspective.

   Throttling:

      Throttling is the reduction of the number of requests sent to an
      entity.  Throttling can include a client dropping requests, or an
      agent rejecting requests with appropriate error responses.
      Clients and agents can also choose to redirect throttled requests
      to some other entity or entities capable of handling them.

   Reporting Node

      A Diameter node that generates an overload report.  (This may or
      may not be the actually overloaded node.)

   Reacting Node

      A Diameter node that consumes and acts upon a report.  Note that
      "act upon" does not necessarily mean the reacting node applies an
      abatement algorithm; it might decide to delegate that downstream,
      in which case it also becomes a "reporting node".

   OLR  Oveload  Overload Report.

3.  Solution Overview

3.1.  Architectural Assumptions

   This section describes the high-level architectural and semantic
   assumptions that underly underlie the Diameter Overload Control Mechanism.

3.1.1.  Application Classification

   The following is a classification of Diameter applications and
   requests.  This discussion is meant to document factors that play
   into decisions made by the Diameter identity responsible for handling
   overload reports.

   Section 8.1 of [RFC6733] defines two state machines that imply two
   types of applications, session-less and session-based. session-based applications.
   The primary
   differentiator difference between these types of applications is the
   lifetime of
   Session-IDs. Session-Ids.

   For session-based applications, the session-id Session-Id is used to tie
   multiple requests into a single session.

   In session-less applications, the lifetime of the session-id Session-Id is a
   single Diameter transaction. transaction, i.e. the session is implicitly
   terminated after a single Diameter transaction and a new Session-Id
   is generated for each Diameter request.

   For the purposes of this discussion, session-less applications are
   further divided into two types of applications:

   Stateless applications:

      Requests within a stateless application have no relationship to
      each other.  The 3GPP-defined S6a 3GPP defined S13 application is an example of a session-less
   application.  The following, copied from section 7.1.4 of 29.272,
   explicitly states that sessions are implicitly terminated and that
   the server does not maintain session state:

      "Between the MME and the HSS and
      stateless application [3GPP.29.272], where only a Diameter command
      is defined between the SGSN a client and the HSS a server and no state is
      maintained between two consecutive transactions.

   Pseudo-session applications:

      Applications that do not rely on the MME and the EIR, Diameter sessions shall be implicitly
      terminated.  An implicitly terminated session is one for which the
      server does not maintain state information.  The client shall not
      send any re-authorization or session termination requests to the
      server.

      The Diameter base protocol includes the Auth-Session-State Session-Id AVP as
      the mechanism for the implementation
      correlation of implicitly terminated
      sessions.

      The client (server) shall include in its requests (responses) the
      Auth-Session-State AVP set application messages related to the value NO_STATE_MAINTAINED (1),
      as described in [RFC6733].  As a consequence, the server shall not
      maintain any state information about this session and the client
      shall not send any same session termination request.  Neither the
      Authorization-Lifetime AVP nor the Session-Timeout AVP shall be
      present in requests or responses."

   For the purposes of this discussion, session-less applications are
   further divided into two types of applications:

   Stateless applications:  Requests within a stateless application have
      no relationship to each other.  The 3GPP defined S13 application
      is an example of a stateless application.

   Pseudo-session applications:  While this class of application does
      not
      but use other session-related information in the Diameter Session-ID AVP to correlate requests, there
      is an implied ordering of transactions defined by the application. requests
      for this purpose.  The 3GPP defined Cx application [reference] [3GPP.29.229]
      is an example of a pseudo-session application.

   [OpenIssue: Do we assume that all requests in a pseudo-session
   typically need to go to the same server?]

   The accounting application defined in [RFC6733] and the Credit-
   Control Credit-Control application defined in [RFC4006] are examples is an example of
   a Diameter session-based applications. application.

   The handling of overload reports must take the type of application
   into consideration, as discussed in Section 3.1.2.

3.1.2.  Application Type Overload Implications

   This section discusses considerations for mitigating overload
   reported by a Diameter entity.  This discussion focuses on the type
   of application.  Section 3.1.3 discusses considerations for handling
   various request types when the target server is known to be in an
   overloaded state.  Section 3.1.5 discusses considerations for
   handling overload conditions based on the network deployment
   scenario.

   These discussions assume that the strategy for mitigating the
   reported overload is to reduce the overall workload sent to the
   overloaded entity.  The concept of applying overload treatment to
   requests targeted for an overloaded Diameter entity is inherent to
   this discussion.  The method used to reduce offered load is not
   specified here but could include routing requests to another Diameter
   entity known to be able to handle them, or it could mean rejecting
   certain requests.  For a Diameter agent, rejecting requests will
   usually mean generating appropriate Diameter error responses.  For a
   Diameter client, rejecting requests will depend upon the application.
   For example, it could mean giving an indication to the entity
   requesting the Diameter service that the network is busy and to try
   again later.

   Stateless applications:

      By definition there is no relationship between individual requests
      in a stateless application.  As a result, when a request is sent
      or relayed to an overloaded Diameter entity - either a Diameter
      Server or a Diameter Agent - the sending or relaying entity can
      choose to apply the overload treatment to any request targeted for
      the overloaded entity.

   Pseudo-stateful

   Pseudo-session applications:  Pseudo stateful applications are also
      stateless applications in that

      For pseudo-session applications, there is no session Diameter state
      maintained between transactions.  There is, however, an implied ordering of
      requests.  As a result, decisions about which
      transactions to reject as a result of requests towards an
      overloaded entity to reject could take the command-code command code of the
      request into consideration.  This generally means that
      transactions later in the sequence of transactions should be given
      more favorable treatment than messages earlier in the sequence.
      This is because more work has already been done by the Diameter
      network for those transactions that occur later in the sequence.
      Rejecting them could result in increasing the load on the network
      as the transactions earlier in the sequence might also need to be
      repeated.

   Stateful

   Session-based applications:

      Overload handling for stateful session-based applications must take into
      consideration the work load associated with setting up
      an and
      maintaining a session.  As such, the entity handling overload
      of a sending requests
      towards an overloaded Diameter entity for a stateful session-based
      application might tend to reject new session requests before rejecting prior to
      rejecting intra-session requests.  In addition, session ending
      requests might be given a lower priority probability of being rejected as
      rejecting session ending requests could result in session status
      being out of sync between the Diameter clients and servers.  Nodes

      Application designers that would decide to reject mid-session
      requests will need to consider whether the rejection invalidates
      the session, session and any resulting session clean-up that may be required. procedures.

3.1.3.  Request Transaction Classification

   Independent Request:

      An independent request is not a part of a
      Diameter session correlated to any other requests
      and, as such, the lifetime of the session-id is constrained to an
      individual transaction.

   Session-Initiating Request:

      A session-initiating request is the initial message that
      establishes a Diameter session.  The ACR message defined in
      [RFC6733] is an example of a session-initiating request.

   Correlated Session-Initiating Request:

      There are cases, most cases when multiple session-initiated requests must be
      correlated and managed by the same Diameter server.  It is notably
      the case in the 3GPP PCC architecture, architecture [3GPP.23.203], where
      multiple apparently independent Diameter application sessions are
      actually correlated and must be handled by the same Diameter
      server.  This
      is a special case of a Session-Initiating Request.  Gx CCR-I
      requests and Rx AAR messages are examples of correlated session-
      initiating requests.

      [OpenIssue: The previous paragraph needs references.]

   Intra-Session Request:

      An intra session request is a request that uses the same
      Session-Id than the one used in a session-id for an already established previous request.  An intra
      session request generally needs to be delivered to the server that
      handled the session creating request for the session.  The STR
      message defined in [RFC6733] is an example of an intra-session
      requests.  CCR-U and CCR-T requests defined in [RFC4006] are
      further examples of intra-session requests.

   Pseudo-Session Requests:  Pseudo session

      Pseudo-session requests are independent requests and, as such, and do not use
      the request transactions same Session-Id but are not tied
      together using correlated by other session-related
      information contained in the Diameter session-id. request.  There exist exists Diameter
      applications that define an expected ordering of transactions.
      This sequencing of independent transactions results in a pseudo
      session.  The AIR, MAR and SAR requests in the 3GPP defined Cx
      application are examples of pseudo-session requests.

3.1.4.  Request Type Overload Implications

   The request classes identified in Section 3.1.3 have implications on
   decisions about which requests should be throttled first.  The
   following list of request treatment regarding throttling is provided
   as guidelines for application designers when implementing the
   Diameter overload control mechanism described in this document.
   Exact behavior regarding throttling must be defined per application.

   Independent requests:

      Independent requests can be given equal treatment when making
      throttling decisions.

   Session-creating

   Session-initiating requests:  Session-creating

      Session-initiating requests represent more work than independent
      or intra-session requests.  Moreover, session-initiating requests
      are typically followed by other related session-related requests.
      As such, as the main objective of the overload control is to
      reduce the total number of requests sent to the overloaded entity,
      throttling decisions might favor allowing intra-session requests
      over
      session-creating session-initiating requests.  Individual session-creating session-initiating
      requests can be given equal treatment when making throttling
      decisions.

   Correlated session-creating session-initiating requests:

      A Request that results in a new binding, where the binding is used
      for routing of subsequent
      session-creating requests, session-initiating requests to the same
      server, represents more work load than other requests.  As such,
      these requests might be throttled more frequently than other
      request types.

   Pseudo-session requests:

      Throttling decisions for pseudo-session requests can take into
      consideration where individual requests fit into the overall
      sequence of requests within the pseudo session.  Requests that are
      earlier in the sequence might be throttled more aggressively than
      requests that occur later in the sequence.

   Intra-session requests

      There are two classes of intra-sessions requests.  The first is a request class
      consists of requests that ends terminate a session.  The second
      is a request one
      contains the set of requests that is are used to convey session related state between by the Diameter client
      and server. server to maintain the ongoing session state.  Session ending request
      terminating requests should be throttled less aggressively in
      order to keep session state
      consistent between gracefully terminate sessions, allow clean-up of the client and server,
      related resources (e.g. session state) and possibly reduce get rid of the
      sessions need for
      other intra-session requests, reducing the session management
      impact on the overloaded entity.  The default handling of other
      intra-session requests might be to treat them equally when making
      throttling decisions.  There might also be application level
      considerations whether some request types are favored over others.

3.1.5.  Diameter Deployment Scenarios

   This section discusses various Diameter network deployment scenarios
   and Agent Behaviour

   In the implications of those deployment models on handling of
   overload reports.

   The scenarios vary based on the following:

   o  The presence or absence of Diameter agents

   o  Which Diameter entities support the DOC extension

   o  The amount of the network topology understood by Diameter clients

   o  The complexity of the Diameter server deployment for a Diameter
      application

   o  Number of Diameter applications supported by Diameter clients and
      Diameter servers

   Without consideration for which elements support the DOC extension,
   the following is a representative list of deployment scenarios:

   o  Client --- Server

   o  Client --- Multiple equivalent servers

   o  Client --- Agent --- Multiple equivalent servers

   o  Client --- Agent [ --- Agent ] --- Partitioned server

   o  Client --- Edge Agent [ --- Edge Agent] --- { Multiple Equivalent
      Servers | Partitioned Servers }

   o  Client --- Session Correlating Agent --- Multiple Equivalent
      Servers

   [OpenIssue: Do the "multiple equivalent servers" cases change for
   session-stateful applications?  Do we need to distinguish equivalence
   for session-initiation requests vs intra-session requests?]

   The following is a list of representative DOC deployment scenarios:

   o  Direct connection between a DOC client and a DOC server

   o  DOC client --- non-DOC agent --- DOC server

   o  DOC client --- DOC agent --- DOC server

   o  Non-DOC client --- DOC agent --- DOC server

   o  Non-DOC client --- DOC agent --- Mix of DOC and non-DOC servers

   o  DOC client --- agent --- Partitioned/Segmented DOC server

   o  DOC client --- agent --- agent --- Partitioned/Segmented DOC
      server

   o  DOC client --- edge agent --- edge agent --- DOC server

   [OpenIssue: In the last 3 list entries, are the agents DOC or non-
   DOC?]

3.1.6.  Diameter Agent Behaviour

   In the context context of the Diameter Overload Indication Conveyance (DOIC)
   and reacting to the overload information, the functional behaviour of
   Diameter agents in front of servers, especially Diameter proxies,
   needs to be common.  This is important because agents may actively
   participate in the handling of an overload conditions.  For example,
   they may make intelligent next hop selection decisions based on
   overload conditions, or aggregate overload information to be
   disseminated downstream.  Diameter agents may have other deployment
   related tasks that are not defined in the Diameter base protocol
   [RFC6733].  These include, among other tasks, topology hiding, and or
   agent acting as a server front end Server Front End (SFE) for a server farm of real Diameter
   servers.

   Since the solution defined in this specification must not break the
   Diameter base protocol [RFC6733] at any time, great care has to be
   taken not to assume functionality from the Diameter agents that would
   break base protocol behavior, or to assume agent functionality beyond
   the Diameter base protocol.  Effectively this means the following
   from a Diameter agent:

   o  If a Diameter agent presents itself as the "end node", perhaps as an agent
      acting as an topology hiding SFE, the DOC mechanism MUST NOT leak
      information of the Diameter nodes behind it.  From the Diameter
      client point of view agent is the final
      destination to its of requests and initiated by Diameter clients, the
      original source for the corresponding answers and server-initiated
      requests.  As a consequence, the DOIC mechanism MUST be NOT leak
      information of the Diameter agent. nodes behind it.  This requirement
      means that such a Diameter agent acts as a back-to-
      back-agent back-to-back-agent for DOC
      DOIC purposes.  How the Diameter agent in this case appears to the
      Diameter nodes it servers in the farm, is representing (i.e. specific to the real Diameter
      servers), is an implementation
      and a deployment specific within the realm the Diameter agent is deployed.

   o  This requirement also implies that if  If the Diameter agent does not impersonate the servers behind it,
      the Diameter dialogue is established between clients and servers
      and any overload information received by a client would be from a given
      the server identified by the Origin-Host identity.

   [OpenIssue: We've discussed multiple situations where an agent might
   insert an OLR.  I don't think we mean to force them to always perform
   topology hiding or SFIM identity contained in order to do so.  We cannot assume that an
   OLR is always "from" or "about" the Origin-Host.  Also, the section
   seems to assume that topology hiding agents act as b2b overload
   agents, but non-topology hiding agents never do.  It don't think
   that's the right abstraction.  It's possible that topology-hiding
   agents must do this, but I don't think we can preclude non-topology
   hiding agents from also doing it, at least some of the time.]

3.1.7.
      Diameter message.

3.1.6.  Simplified Example Architecture

   Figure 1 illustrates the simplified architecture for Diameter
   overload control. information conveyance.  See Section 5.1 for more discussion
   and details how different Diameter nodes fit into the architecture
   from the DOIC point of view.

    Realm X                                  Other                                  Same or other Realms
   <--------------------------------------> <---------------------->

   +--^-----+                 : (optional) :
   |Diameter|                 :            :
   |Server A|--+     .--.     : +---^----+ :     .--.
   +--------+  |   _(    `.   : |Diameter| :   _(    `.   +---^----+
               +--(        )--:-|  Agent |-:--(        )--|Diameter|
   +--------+  | ( `  .  )  ) : +-----^--+ : ( `  .  )  ) | Client |
   |Diameter|--+  `--(___.-'  :            :  `--(___.-'  +-----^--+
   |Server B|                 :            :
   +---^----+                 :            :

                       End-to-end Overload Indication
          1)  <----------------------------------------------->
                          Diameter Application Y

               Overload Indication A    Overload Indication A'
          1)
          2)  <----------------------> <---------------------->
              standard base protocol   standard base protocol

               End-to-end Overload Indication
          2)  <----------------------------------------------->
                          standard base protocol

     Figure 1: Simplified architecture choices for overload indication
                                 delivery

   In Figure 1, the Diameter overload indication can be conveyed (1)
   end-to-end between servers and clients or (2) between servers and
   Diameter agent inside the realm and then between the Diameter agent
   and the clients when the Diameter agent acting as back-to-back-agent
   for DOIC purposes.

3.2.  Conveyance of the Overload Indication

   The following features sections describe new Diameter AVPs used for sending
   overload reports, and for declaring support for certain DOC DOIC
   features.

3.2.1.  Negotiation and Versioning

   Since  DOIC Capability Discovery

   Support of DOIC may be specified as part of the functionality
   supported by a new Diameter overload control application.  In this way, support of the
   considered Diameter application (discovered during capabilities
   exchange phase as defined in Diameter base protocol [RFC6733])
   indicates implicit support of the DOIC mechanism.

   When the DOIC mechanism is also designed to
   work over introduced in existing application (i.e., the piggybacking principle), Diameter
   applications, a
   proper negotiation specific capability discovery mechanism is hard to accomplish. required.
   The "capability
   negotiation" "DOIC capability discovery mechanism" is based on the existense presence of
   specific non-mandatory APV, optional AVPs in the Diameter messages, such as the OC-Feature-Vector OC-
   Supported-Features AVP (see Section 4.1. 4.1).  Although the OC-
   Feature-Vector OC-Supported-
   Features AVP can be used to advertise a certain set of new or
   existing Diameter overload control capabilities, it is not a
   versioning solution per se, however, it can be used to achieve the
   same result.

3.2.2.  Transmission of

   From the Attribute Value Pairs

   The Diameter overload control APVs SHOULD always be sent as an
   optional AVPs.  This requirement stems from the fact that
   piggybacking overload control information on top of existing
   application cannot really use AVPs with the M-bit set.  However,
   there are certain exceptions as explained in Section 5.4.

   From the Diameter overload control functionality point of view, functionality point of view, the
   "Reacting node" is always the requester of the overload report information
   and the "Reporting node" is the provider of the overload report.  The overload report or the capability information
   OC-Supported-Features AVP in the request message is always
   interpreted as an announcement of a
   "capability". "DOIC supported capabilities".  The overload report and the capability information
   OC-Supported-Features AVP in the answer is always also interpreted as a
   report of "DOIC supported commond
   functionality capabilities" and as a status report at least one of an overload condition (of a
   node). supported
   capabilities MUST be common with the "Reacting node" (see
   Section 4.1).

3.3.  Overload Condition Indication

   Diameter nodes can request a reduction in offered load by indicating
   an overload condition in the form of an overload report.  The
   overload report contains information about how much load should be
   reduced, and may contain other information about the overload
   condition.  This information is encoded conveyed in Diameter Attribute Value
   Pairs (AVPs).

   Certain new AVPs may also be used to declare certain DOIC
   capabilities and extensions.

4.  Attribute Value Pairs

   This section describes the encoding and semantics of the Diameter
   Overload Indication Attribute Value Pairs (AVPs). (AVPs) defined in this
   document.

4.1.  OC-Feature-Vector  OC-Supported-Features AVP

   The OC-Feature-Vector OC-Supported-Features AVP (AVP code TBD1) is type of Unsigned64 Grouped and
   contains a 64 bit flags field of announced capabilities of an
   overload control endpoint.  Sending or receiving the OC-Feature-
   Vector AVP with the value 0 indicates that the endpoint only
   serves for two purposes.  First, it announces node's support for the capabilities defined
   DOIC in this specification.

   An overload control endpoint (a reacting node) includes this AVP to
   indicate its capabilities to the other overload control endpoint (the
   reporting node).  For example, the endpoint (reacting node) may
   indicate which (future defined) traffic abatement algorithms general.  Second, it
   supports in addition to the default.

   During the message exchange contains the overload control endpoints express
   their common set description of the
   supported capabilities.  The endpoint DOIC features of the sending node.  The OC-Supported-
   Features AVP SHOULD be included into every Diameter message a
   request (the reacting node) includes the DOIC
   supporting node sends (and intends to use for DOIC purposes).

   OC-Supported-Features ::= < AVP Header: TBD1 >
                             < OC-Sequence-Number >
                             [ OC-Feature-Vector ]
                           * [ AVP with
   those flags set that correspond what it supports. ]

   The endpoint that
   sends the answer (the reporting node) also includes the OC-Feature-
   Vector OC-Sequence-Number AVP with flags set is used to describe indicate whether the capabilities it both
   supports and agrees with contents
   of the request sender (e.g., based on OC-Supported-Features AVP has changed since last time the local
   policy and/or configuration).  The answer node
   included the OC-Supported-Features AVP (see Section 4.4).  Although
   sending endpoint (the
   reporting node) does not need the OC-Sequence-Number AVP is mandatory in the OC-Supported-
   Features AVP, the receiving node MAY always choose to advertise those capabilities ignore the
   sequence number if it can determine the feature support changes
   otherwise.

   The OC-Feature-Vector sub-AVP is
   not going used to use with announced the request sending endpoint (the reacting
   node).

   This specification does not define any additional DOIC features
   supported by the endpoint, in the form of a flag bits field in which
   each bit announces one feature or capability flag. supported by the node
   (see Section 4.2).  The implicity capability (all flags set to zero) absence of the OC-Feature-Vector AVP
   indicates that only the
   support for default traffic abatement algorithm described
   in this specification only.

4.2.  OC-OLR AVP

   The OC-OLR AVP (AVP code TBD2) is type of Grouped and contains the
   necessary information supported.

   A reacting node includes this AVP to convey an overload report.  OC-OLR may also
   be used indicate its capabilities to convey additional information about an extension that is
   declared in a
   reporting node.  For example, the OC-Feature-Vector AVP.

   The OC-OLR AVP does not contain explicit information to endpoint (reacting node) may
   indicate which
   application (future defined) traffic abatement algorithms it applies
   supports in addition to and who inserted the AVP or whom default.

   During the
   specific OC-OLR AVP concerns to.  Both these information is
   implicitly learned from message exchange the encapsulating Diameter message/command. overload control endpoints express
   their common set of supported capabilities.  The application reacting node
   includes the OC-OLR OC-Supported-Features AVP applies to is the same as the
   Application-Id found in the Diameter that announces what it
   supports.  The reporting node that sends the answer also includes the
   OC-Supported-Features AVP that describes the capabilities it
   supports.  The set of capabilities advertised by the reporting node
   depends on local policies.  At least one of the announced
   capabilities MUST match mutually.  If there is no single matching
   capability the reacting node MUST act as if it does not implement
   DOIC and cease inserting any DOIC related AVPs into any Diameter
   messages with this specific reacting node.

4.2.  OC-Feature-Vector AVP

   The OC-Feature-Vector AVP (AVP code TBD6) is type of Unsigned64 and
   contains a 64 bit flags field of announced capabilities of an
   overload control endpoint.  The value of zero (0) is reserved.

   The following capabilities are defined in this document:

   OLR_DEFAULT_ALGO (0x0000000000000001)

      When this flag is set by the overload control endpoint it means
      that the default traffic abatement (loss) algorithm is supported.

4.3.  OC-OLR AVP

   The OC-OLR AVP (AVP code TBD2) is type of Grouped and contains the
   necessary information to convey an overload report.  The OC-OLR AVP
   does not contain explicit information to which application it applies
   to and who inserted the AVP or whom the specific OC-OLR AVP concerns
   to.  Both these information is implicitly learned from the
   encapsulating Diameter message/command.  The application the OC-OLR
   AVP applies to is the same as the Application-Id found in the
   Diameter message header.  The identity the OC-OLR AVP concerns is
   determined from the Origin-Host AVP (and Origin-Realm AVP as well)
   found from the encapsulating Diameter command.  The OC-OLR AVP is
   intended to be sent only by a reporting node.

   OC-OLR ::= < AVP Header: TBD2 >
              < TimeStamp OC-Sequence-Number >
              [ Reduction-Percentage OC-Report-Type ]
              [ ValidityDuration OC-Reduction-Percentage ]
              [ ReportType OC-Validity-Duration ]
            * [ AVP ]

   The TimeStamp Sequence-Number AVP indicates when the original OC-OLR AVP with "freshness" of the
   current content was created. OC-OLR AVP.
   It is possible to replay the same OC-
   OLR OC-OLR AVP multiple times between
   the overload control endpoints, however, when the OC-OLR AVP content
   changes or the other information sending endpoint otherwise wants the receiving endpoint to
   update its overload control information, then the TimeStamp OC-Sequence-Number
   AVP MUST contain a new value.

   [OpenIssue: Is this necessarily a timestamp, or is it just greater value than the previously received.
   The receiver SHOULD discard an OC-OLR AVP with a sequence number that can be implemented as
   is less than previously received one.

   Note that if a timestamp?  Is this timestamp
   used Diameter command were to calculate expiration time? (propose no.).  We should also
   consider whether either contain multiple OC-OLR AVPs
   they all MUST have different OC-Report-Type AVP value.  OC-OLR AVPs
   with unknown values SHOULD be silently discarded and the event SHOULD
   be logged.

   The OC-OLR AVP can be expanded with optional sub-AVPs only if a timestamp or sequence number is needed
   legacy implementation can safely ignore them without breaking
   backward compatibility for
   protection against replay attacks.]

4.3.  TimeStamp the given OC-Report-Type AVP value implied
   report handling semantics.  If the new sub-AVPs imply new semantics
   for the report handling, then a new OC-Report-Type AVP value MUST be
   defined.

4.4.  OC-Sequence-Number AVP

   The TimeStamp OC-Sequence-Number AVP (AVP code TBD3) is type of Time.  Its
   usage in the context of the overload control is described in Section 4.2. Sections
   4.1 and 4.3.

   From the functionality point of view, the TimeStamp OC-Sequence-Number AVP is merely MUST
   be used as a non-volatile increasing counter between two overload
   control endpoints (neglecting the fact that the contents of the AVP
   is a 64-bit NTP timestamp [RFC5905]).  The sequence number is only
   required to be unique between two overload control endpoints.

4.4.  ValidityDuration
   Sequence numbers are treated in uni-directional manner, i.e. two
   sequence numbers on each direction between two endpoints are not
   related or correlated.

   When generating sequence numbers, the new sequence number MUST be
   greater than any sequence number previously seen between two
   endpoints within a time window that tolerates the wraparound of the
   NTP timestamp (i.e. approximately 68 years).

4.5.  OC-Validity-Duration AVP

   The ValidityDuration OC-Validity-Duration AVP (AVP code TBD4) is type of Unsigned32
   and describes the number of seconds the "new and fresh" OC-OLR AVP
   and its content is valid since the creation reception of the new OC-OLR AVP.
   The default value for the OC-Validity-Duration AVP (as indicated by value is 5 (i.e.,
   5 seconds).  When the
   TimeStamp AVP). OC-Validity-Duration AVP is not present in the
   OC-OLR AVP, the default value applies.  Validity duration values 0
   (i.e., 0 seconds) and above 86400 (i.e., 24 hours) MUST NOT be used.
   Invalid validity duration values are treated as if the OC-Validity-
   Duration AVP were not present.

   A timeout of the overload report has specific concerns that need to
   be taken into account by the endpoint acting on the earlier received
   overload report(s).  Section 4.6 4.7 discusses the impacts of timeout in
   the scope of the traffic abatement algorithms.

   As a general guidance for implementations it is RECOMMENDED never to
   let any overload report to timeout.  Rather,  Following to this rule, an
   overload endpoint should explicitly signal, e.g. signal the end of overload condition.
   condition and not rely on the expiration of the validity time of the
   overload report in the reacting node.  This leaves no need for the other overload endpoint
   reacting node to reason or guess the overload condition of the other endpoint is at.

4.5.  ReportType
   reporting node.

4.6.  OC-Report-Type AVP

   The ReportType OC-Report-Type AVP (AVP code TBD5) is type of Enumerated.  The
   value of the AVP describes what the overload report concerns.  The
   following values are initially defined:

   0  Reserved.

   1  Destination-Host  A host report.  The overload treatment should apply to requests that
      the sender reacting node knows that will reach the overloaded server. node.  For
      example, requests with a Destination-Host AVP indicating the
      server.

   2  Realm (aggregated)
      endpoint.  The reacting node learns the "host" implicitly from the
      Origin-Host AVP of the received message that contained the OC-OLR
      AVP.

   1  A realm report.  The overload treatment should apply to all
      requests bound for the overloaded realm.  The ReportType reacting node learns
      the "realm" implicitly from the Origin-Realm AVP of the received
      message that contained the OC-OLR AVP.

   The default value of the OC-Report-Type AVP is 0 (i.e. the host
   report).

   The OC-Report-Type AVP is envisioned to be useful for situations
   where a reacting node needs to apply different overload treatments
   for different "types" of overload.  For example, the reacting node(s)
   might need to throttle differently requests that are targeted sent to a specific server
   (identified by the presence of a Destination-Host AVP than for in the request) and requests
   that can be handled by any server in a realm.  The example in
   Appendix C.3 B.1 illustrates this usage.

   [OpenIssue: There is an ongoing discussion about whether

   When defining new report type values, the
   ReportType corresponding specification
   MUST define the semantics of the new report types and how they affect
   the OC-OLR AVP is handling.  The specification MUST also reserve a
   corresponding new feature, see the right way to solve that issue, OC-Supported-Features and whether it's
   needed at all.]

4.6.  Reduction-Percentage OC-
   Feature-Vector AVPs.

4.7.  OC-Reduction-Percentage AVP

   The Reduction-Percentage OC-Reduction-Percentage AVP (AVP code TBD8) is type of Unsigned32
   and describes the percentage of the traffic that the sender is
   requested to reduce, compared to what it otherwise would have sent.
   The OC-Reduction-Percentage AVP applies to the default (loss like)
   algorithm specified in this specification.  However, the AVP can be
   reused for future abatement algorithms, if its semantics fit into the
   new algorithm.

   The value of the Reduction-Percentage AVP is between zero (0) and one
   hundred (100).  Values greater than 100 are interpreted as 100.  The
   value of 100 means that no traffic is expected, i.e. the sender of
   the information reporting
   node is under a severe load and ceases to process any new messages.
   The value of 0 means that the sender of the information reporting node is in a stable state and
   has no requests to the other endpoint to apply any traffic abatement.

   [Open Issue: We should consider an algorithm independent way to end
   an overload condition.  Perhaps setting the validitytime to zero?
   Counter comment; since
   The default value of the abatement OC-Reduction-Percentage AVP is based on a specific
   algorithm, it 0.  When the
   OC-Reduction-Percentage AVP is natural to indicate that from not present in the abatement
   algorithm point of view status quo has been reached.] overload report,
   the default value applies.

   If an overload control endpoint comes out of the 100 percent traffic
   reduction as a result of the overload report timing out, the
   following concerns are RECOMMENDED to be applied.  The endpoint reacting node
   sending the traffic should be conservative and, for example, first
   send few "probe" messages to learn the overload condition of the
   other endpoint
   overloaded node before converging to any traffic amount/rate decided
   by the sender.  Similar concerns actually apply in all cases when the overload
   report times out unless the previous overload report stated 0 percent
   reduction.

   [Open Issue: It is still open whether we need an AVP to indicate the
   exact used traffic abatement algorithm.  Currently it assumed that
   the reacting node is able to figure out what to do based on the
   Reducttion-Percentage AVP and possible other embedded information
   inside the OC-OLR AVP.]

4.7.  Attribute Value Pair flag rules

                                                      +---------+
                                                      |AVP flag |
                                                      |rules    |
                                                      +----+----+

4.8.  Attribute Value Pair flag rules

                                                      +---------+
                                                      |AVP flag |
                                                      |rules    |
                                                      +----+----+
                           AVP   Section              |    |MUST|
    Attribute Name         Code  Defined  Value Type  |MUST| NOT|
   +--------------------------------------------------+----+----+
   |OC-Feature-Vector
   |OC-Supported-Features  TBD1  x.x      Unsigned64      Grouped     |    | V  |
   +--------------------------------------------------+----+----+
   |OC-OLR                 TBD2  x.x      Grouped     |    | V  |
   +--------------------------------------------------+----+----+
   |TimeStamp
   |OC-Sequence-Number     TBD3  x.x      Time        |    | V  |
   +--------------------------------------------------+----+----+
   |ValidityPeriod
   |OC-Validity-Duration   TBD4  x.x      Unsigned32  |    | V  |
   +--------------------------------------------------+----+----+
   |ReportType
   |OC-Report-Type         TBD5  x.x      Enumerated  |    | V  |
   +--------------------------------------------------+----+----+
   |Reduction
   |OC-Reduction                                      |    |    |
   |  -Percentage          TBD8  x.x      Unsigned32  |    | V  |
   +--------------------------------------------------+----+----+
   |OC-Feature-Vector      TBD6  x.x      Unsigned64  |    | V  |
   +--------------------------------------------------+----+----+

   As described in the Diameter base protocol [RFC6733], the M-bit
   setting for a given AVP is relevant to an application and each
   command within that application that includes the AVP.

   The Diameter overload control AVPs SHOULD always be sent with the
   M-bit cleared when used within existing Diameter applications to
   avoid backward compatibility issues.  Otherwise, when reused in newly
   defined Diameter applications, the DOC related AVPs SHOULD have the
   M-bit set.

5.  Overload Control Operation

5.1.  Overload Control Endpoints

   The overload control solution can be considered as an overlay on top
   of an arbitrary Diameter network.  The overload control information
   is exchanged over on a "DOIC association" established between two communicatin
   communication endpoints.  The endpoints, namely the "reacting node"
   and the "reporting node" do not need to be adjacent Diameter peer
   nodes, nor they need to be the end-to-end Diameter nodes in a typical "client-
   server"
   "client-server" deployment with multiple intermediate Diameter agent
   nodes in between.  The overload control endpoint endpoints are the two
   Diameter nodes that decide to exchange overload control information
   between each other.  How the endpoints are determined is specific to
   a deployment, a Diameter node role in that deployment and local
   configuration.

   The following diagrams illustrate the concept of Diameter Overload
   End-Points and how they differ from the standard [RFC6733] defined
   client, server and agent Diameter nodes.  The following is the key to
   the elements in the diagrams:

   C  Diameter client as defined in [RFC6733].

   S  Diameter server as defined in [RFC6733].

   A  Diameter agent, in either a relay or proxy mode, as defined in
      [RFC6733].

   DEP  Diameter Overload End-Point as defined in this document.  In the
      following figures a DEP may terminate two different DOIC
      associations being a reporter and reactor at the same time.

   Diameter Session  A Diameter session as defined in [RFC6733].

   DOIC Association  A DOIC association exists between two Diameter
      Overload End-Points.  One of the end-points is the overload
      reporter and the other is the overload reactor.

   Figure 2 illustrates the most basic configuration where a client is
   connected directly to a server.  In this case, the Diameter session
   and the DOIC association are both between the client and server.

   +-----+            +-----+
   |  C  |            |  S  |
   +-----+            +-----+
   | DEP |            | DEP |
   +--+--+            +--+--+
      |                  |
      |                  |
      |{Diameter Session}|
      |                  |
      |{DOIC Association}|
      |                  |

                      Figure 2: Basic DOIC deployment

   In Figure 3 there is an agent that is not participating directly in
   the exchange of overload reports.  As a result, the Diameter session
   and the DOIC association
   is are still established between the client and
   the server.

   +-----+            +-----+            +-----+
   |  C  |            |  A  |            |  S  |
   +-----+            +--+--+            +-----+
   | DEP |               |               | DEP |
   +--+--+               |               +--+--+
      |                  |                  |
      |                  |                  |
      |----------{Diameter Session}---------|
      |                  |                  |
      |----------{DOIC Association}---------|
      |                  |                  |

          Figure 3: DOIC deployment with non participating agent

   Figure 4 illustrates the case where the client does not support
   Diameter overload.  In this case, the DOIC association is between the
   agent and the server.  The agent handles the role of the reactor for
   overload reports generated by the server.

   +-----+            +-----+            +-----+
   |  C  |            |  A  |            |  S  |
   +--+--+            +-----+            +-----+
      |               | DEP |            | DEP |
      |               +--+--+            +--+--+
      |                  |                  |
      |                  |                  |
      |----------{Diameter Session}---------|
      |                  |                  |
      |                  |{DOIC Association}|
      |                  |                  |

   Figure 4: DOIC deployment with non-DOIC client and DOIC enabled agent

   In Figure 5 there is a DOIC association between the client and the
   agent and a second DOIC association between the agent and the server.
   One use case requiring this configuration is when the agent is
   serving as a SFE/SFIM SFE for a set of servers.

   +-----+            +-----+            +-----+
   |  C  |            |  A  |            |  S  |
   +-----+            +-----+            +-----+
   | DEP |            | DEP |            | DEP |
   +--+--+            +--+--+            +--+--+
      |                  |                  |
      |                  |                  |
      |----------{Diameter Session}---------|
      |                  |                  |
      |{DOIC Association}|{DOIC Association}|
      |                  |                and/or
      |----------{DOIC Association}---------|
      |                  |                  |

            Figure 5: A deployment where all nodes support DOIC

   Figure 6 illustrates a deployment where some clients support Diameter
   overload control and some do not.  In this case the agent must
   support Diameter overload control for the non supporting client.  It
   might also need to have a DOIC association with the server, as shown
   here, to handle overload for a server farm and/or for managing Realm
   overload.

   +-----+            +-----+            +-----+            +-----+
   | C1  |            | C2  |            |  A  |            |  S  |
   +-----+            +--+--+            +-----+            +-----+
   | DEP |               |               | DEP |            | DEP |
   +--+--+               |               +--+--+            +--+--+
      |                  |                  |                  |
      |                  |                  |                  |
      |-------------------{Diameter Session}-------------------|
      |                  |                  |                  |
      |                  |--------{Diameter Session}-----------|
      |                  |                  |                  |
      |---------{DOIC Association}----------|{DOIC Association}|
      |                  |                  |                and/or
      |-------------------{DOIC Association}-------------------|
      |                  |                  |                  |

     Figure 6: A deployment with DOIC and non-DOIC supporting clients

   Figure 7 illustrates a deployment where some agents support Diameter
   overload control and others do not.

   +-----+            +-----+            +-----+            +-----+
   |  C  |            |  A  |            |  A  |            |  S  |
   +-----+            +--+--+            +-----+            +-----+
   | DEP |               |               | DEP |            | DEP |
   +--+--+               |               +--+--+            +--+--+
      |                  |                  |                  |
      |                  |                  |                  |
      |-------------------{Diameter Session}-------------------|
      |                  |                  |                  |
      |                  |                  |                  |
      |---------{DOIC Association}----------|{DOIC Association}|
      |                  |                  |                and/or
      |-------------------{DOIC Association}-------------------|
      |                  |                  |                  |

      Figure 7: A deployment with DOIC and non-DOIC supporting agents

5.2.  Piggybacking Principle

   The overload control solution defined AVPs are essentially defined in this specification have been
   designed to be piggybacked on top of existing application message
   exchanges.  This is made possible by adding overload control top
   level AVPs, the OC-
   OLR OC-OLR AVP and the OC-Feature-Vector OC-Supported-Features AVP as
   optional AVPs into existing commands (this
   has an assumption that when the application CCF corresponding Command
   Code Format (CCF) specification allows adding new optional AVPs
   into (see
   Section 1.3.4 of [RFC6733]).

   When added to existing commands, both OC-Feature-Vector and OC-OLR
   AVPs SHOULD have the Diameter messages. M-bit flag cleared to avoid backward
   compatibility issues.

   A new application specification can incorporate the overload control
   mechanism specified in this document by making it mandatory to
   implement for the application and referencing this specification
   normatively.  In such a case of case, the OC-Feature-Vector and OC-OLR AVPs
   reused in newly defined Diameter applications, applications SHOULD have the M-bit
   flag set.  However, it is RECOMMENDED the responsibility of the Diameter
   application designers to add and defined define how overload control mechanisms works
   on that application. using OC-Feature-Vector and OC-OLR AVPs in a non-
   mandatory manner is intended only existing applications.

   Note that the overload control solution does not have fixed server
   and client roles.  The endpoint role is determined based on the sent
   message type: whether the message is a request (i.e. sent by a
   "reacting node") or an answer (i.e. send by a "reporting node").
   Therefore, in a typical "client-server" deployment, the "client" MAY
   report its overload condition to the "server" for any server
   initiated message exchange.  An example of such is the server
   requesting a re-authentication from a client.

5.3.  Capability Announcement

   Since the overload control solution relies on the piggybacking
   principle for the overload reporting and the overload control
   endpoint are likely not adjacent peers, finding out whether the other
   endpoint supports the overload control or what is the common traffic
   abatement algorithm to apply for the traffic.  The approach defined
   in this specification for the end-to-end capability capability announcement
   relies on the exchange of the OC-Feature-Vector OC-Supported-Features between the
   endpoints.  The feature announcement solution also works when carried
   out on existing applications.  For the newly defined application the
   negotiation can be more exact based on the application specification.
   The announced set of capabilities MUST NOT change during the life
   time of the Diameter session (or transaction in a case of non-session
   maintaining applications).

5.3.1.  Request Message Initiator  Reacting Node Endpoint Considerations

   The basic principle is that the request message initiating endpoint
   (i.e. the "reacting node") announces its support for the overload
   control mechanism by including in the request message the OC-Feature-
   Vector OC-
   Supported-Features AVP with those capability flag bits set that capabilities it supports and is
   willing to use for this Diameter session (or transaction in a case of
   a non-session state maintaining applications).  In a case of
   session maintaining applications the request message initiating
   endpoint does not need to do the capability announcement more than
   once applications, see Section 3.1.2 for the lifetime of the
   more details on Diameter session.  In a case of non-
   session maintaining applications, it sessions).  It is RECOMMENDED that the
   request message initiating endpoint includes the capability
   announcement into every request regardless it has had prior message
   exchanges with the give remote endpoint.

   [OpenIssue: We need to think about the lifetime  In a case of a capabilities
   declaration.  It's probably Diameter
   session maintaining application, sending the OC-Supported-Features
   AVP in every message is not really necessary after the same as for initial
   capability announcement or until there is a session.  We have
   had proposals that the feature vector needs to go into every request
   sent by an OC node.  For peer to peer cases, this can be associated
   with connection lifetime, but it's more complex for non-adjacent OC
   support.] change in supported
   features.

   Once the endpoint that initiated the request message receives an
   answer message from the remote endpoint, it can detect from the
   received answer message whether the remote endpoint supports the
   overload control solution and in a case it does, what features are
   supported.  The support for the overload control solution is based on
   the presence of the OC-Feature-Vector OC-Supported-Features AVP in the Diameter answer
   for existing application.  For the newly defined applications the support
   for the overload control MAY already be part of the application
   specification.  Based on capability knowledge the request message
   initiating endpoint can select the preferred common traffic abatement
   algorithm and act accordingly for the subsequent message exchanges.

5.3.2.  Answer Message Initiating  Reporting Node Endpoint Considerations

   When a remote endpoint (i.e. a "reporting node") receives a request
   message in
   message, it can detect whether the request message initiating
   endpoint
   has support for supports the overload control solution based on the presence
   of the OC-Feature-Vector OC-Supported-Features AVP.  For the newly defined applications
   the overload control solution support can be part of the application
   specification.  Based on the content of the OC-Feature-Vector OC-Supported-Features AVP
   the request message receiving endpoint knows what overload control
   functionality the other endpoint supports and then act accordingly
   for the subsequent answer messages it initiates.  It is RECOMMENDED
   that the  The answer message
   initiating endpoint selects one common
   traffic abatement algorithm even if MAY announce as many supported capabilities as it would support multiple.
   has (the announced set is a subject to local policy and
   configuration).  However, at least one of the announced capabilities
   MUST be the same as received in the request message.

   The answer message initiating endpoint MUST NOT include any overload
   control solution defined AVPs into its answer messages if the request
   message initiating endpoint has not indicated support at the
   beginning of the the created session (or transaction in a case of
   non-session non-
   session state maintaining applications).

5.4.  Protocol Extensibility  The overload control solution can be extended, same also applies if
   none of the announced capabilities match between the two endpoints.

5.4.  Protocol Extensibility

   The overload control solution can be extended, e.g. with new traffic
   abatement algorithms or new functionality.  The new features and
   algorithms MUST be registered with the IANA and for the ppossible possible use
   with the OC-Feature-Vector OC-Supported-Features for announcing the support for the new
   features (see Section 7 for the required procedures).

   It should be noted that [RFC6733] defined Grouped AVP extension
   mechanisms also apply.  This allows, for example, defining a new
   feature that is mandatory to understand even when piggybacked on an
   existing applications.  More specifically, the sub-AVPs inside the
   OC-OLR AVP MAY have the M-bit set.  However, when overload control
   AVPs are piggybacked on top of an existing applications, setting
   M-bit in sub-AVPs is NOT RECOMMENDED.

5.5.  Overload Report Processing

5.5.1.  Sender Endpoint Considerations

5.5.2.  Receiver Endpoint Considerations

   [OpenIssue: did we now agree that e.g.  Overload Control State

   Both reacting and reporting nodes maintain an overload condition
   state for each endpoint (a host or a server can refrain sending
   OLR in answers based on some magical algorithm?  (Note: We seem to realm) they communicate with and
   both endpoints have consensus that a server MAY repeat OLRs in subsequent messages,
   but announced support for DOIC.  See Sections 4.1 and
   5.3 for discussion about how the support for DOIC is not required to do so, based on local policy.)]

6.  Transport Considerations

   In order to reduce determined.  The
   overload control introduced additional AVP and
   message processing it might condition state SHOULD be desirable/beneficial able to signal whether
   the Diameter command carries make a difference between
   a realm and a specific host in that realm.

   The overload control condition state could include the following information that should
   be of interest
   (per host or realm):

   o  The endpoint information (Diameter identity of an the realm and/or
      host, application identifier, etc)

   o  Reduction percentage

   o  Validity period timer

   o  Sequence number

   o  Supported/selected traffic abatement algorithm

   The overload aware Diameter node.

   Should such indication control state information SHOULD be include maintained as long
   as the other endpoint is not part known to support DOIC (based on the presence
   of this specification.
   It has not either been concluded at what layer such possible
   indication should be.  Obvious candidates include transport layer
   protocols (e.g., SCTP PPID or TCP flags) the DOIC AVPs or Diameter command header
   flags.

7.  IANA by a future application specification).

5.5.2.  Reacting Node Considerations

7.1.

   Once a reacting node receives an OC-OLR AVP codes

   New AVPs defined by this specification are listed in Section 4.  All
   AVP codes allocated from a reporting node, it
   applies the 'Authentication, Authorization, and
   Accounting (AAA) Parameters' AVP Codes registry.

7.2.  New registries

   Three new registries are needed under traffic abatement based on the 'Authentication,
   Authorization, commonly supported
   algorithm with the reporting node and Accounting (AAA) Parameters' registry.

   Section 4.1 defines a new "Overload Control Feature Vector" registry
   including the initial assignments.  New values can be added into current overload condition.
   The reacting node learns the
   registry using reporting node supported abatement
   algorithms directly from the Specification Required policy [RFC5226].

   Section 4.5 defines a new "Overload Report Type" registry received answer message containing the
   OC-Supported-Features AVP or indirectly remembering the previously
   used traffic abatement algorithm with its
   initial assignments.  New types can be added using the Specification
   Required policy [RFC5226].

8.  Security Considerations

   This mechanism gives Diameter nodes given reporting node.

   The received OC-Supported-Features AVP does not change the ability to request that
   downstream nodes send fewer Diameter requests.  Nodes do this by
   exchanging existing
   overload reports condition and/or traffic abatement algorithm settings if the
   OC-Sequence-Number AVP contains a value that directly affect this reduction.
   This exchange is potentially subject equal to multiple methods of attack,
   and has the potential to be used as a Denial-of-Service (DoS) attack
   vector.

   Overload reports may contain information about
   previously received/recorded one.  If the topology OC-Supported-Features AVP
   is received for the first time for the reporting node or the OC-
   Sequence-Number AVP value is less than the previously received/
   recorded one (and is outside the valid overflow window), then either
   the sequence number is stale (e.g. an intentional or unintentional
   replay) and
   current status of a Diameter network.  This SHOULD be silently discarded.

   The OC-OLR AVP contains the necessary information is
   potentially sensitive.  Network operators may wish to control
   disclosure of the overload reports
   condition on the reporting node.  Similarly to unauthorized parties the OC-Supported-
   Features's sequence numbering, the OC-OLR AVP also has the OC-
   Sequence-Number AVP and its handling is similar to avoid the one in the OC-
   Supported-Features AVP.  The reacting node MUST update its
   use overload
   condition state whenever receiving the OC-OLR AVP for competitive intelligence or to target attacks.

   Diameter does not include features to provide end-to-end
   authentication, integrity protection, the first time
   or confidentiality.  This may
   cause complications when sending overload reports between non-
   adjacent nodes.

8.1.  Potential Threat Modes

   The Diameter protocol involves transactions the OC-Sequence-Number sub-AVP indicates a change in the form OC-OLR
   AVP.

   As described in Section 4.3, the OC-OLR AVP contains the necessary
   information of requests
   and answers exchanged between clients and servers.  These clients and
   servers may be peers, that is,they may share the overload condition on the reporting node.

   From the OC-Report-Type AVP contained in the OC-OLR AVP, the reacting
   node learns whether the overload condition report concerns a direct transport (e.g.
   TCP or SCTP) connection, or specific
   host (as identified by the messages may traverse one Origin-Host AVP of the answer message
   containing the OC-OLR AVP) or more
   intermediaries, known as Diameter Agents. the entire realm (as identified by the
   Origin-Realm AVP of the answer message containing the OC-OLR AVP).
   The reacting node learns the Diameter nodes use TLS,
   DTLS, or IPSec to authenticate peers, and application to provide confidentiality
   and integrity protection which the
   overload report applies from the Application-ID of traffic between peers.  Nodes can make
   authorization decisions based on the peer identities authenticated at answer message
   containing the transport layer.

   When agents are involved, OC-OLR AVP.  The reacting node MUST use this presents
   information as an effectively hop-by-hop
   trust model.  That is, a Diameter client or server can authorize an
   agent input for certain actions, but it must trust that agent to make
   appropriate authorization decisions about its peers, and so on.

   Since confidentiality and integrity protection occurs at traffic abatement algorithm.  The
   idea is that the
   transport layer.  Agents can read, and perhaps modify, any part reacting node applies different handling of a
   Diameter message, including an overload report.

   There the
   traffic abatement, whether sent request messages are several ways an attacker might attempt targeted to exploit a
   specific host (identified by the
   overload control mechanism.  An unauthorized third party might inject
   an overload report into Diameter-Host AVP in the network.  If this third party is upstream
   of an agent, and that agent fails request) or
   to apply proper authorization
   policies, downstream nodes may mistakenly trust any host in a realm (when only the report.  This
   attack Destination-Realm AVP is at least partially mitigated by
   present in the assumption request).  Note that nodes
   include overload reports in Diameter answers but not in requests.
   This requires an attacker to have knowledge future specifications MAY define
   new OC-Report-Type AVP values that imply different handling of the original request
   OC-OLR AVP.  For example, in order to construct a response.  Therefore, implementations SHOULD
   validate form of new additional AVPs inside the
   Grouped OC-OLR AVP that an answer containing an overload would define report is target in a properly
   constructed response to finer
   granularity than just a pending request prior to acting on host.

   In the context of this specification and the default traffic
   abatement algorithm, the OC-Reduction-Percentage AVP value MUST be
   interpreted in the following way:

   value == 0

      Indicates explicitly the end of overload report.

   A similar attack involves an otherwise authorized Diameter condition and the
      reacting node that
   sends an inappropriate overload report.  For example, a server SHOULD NOT apply the traffic abatement algorithm
      procedures anymore for the realm "example.com" might send an overload report indicating given reporting node (or realm).

   value == 100

      Indicates that
   a competitor's realm "example.net" is overloaded.  If other nodes act
   on the report, they may falsely believe that "example.net" is
   overloaded, effectively reducing that realm's capacity.  Therefore,
   it's critical that nodes validate that an overload report received reporting node (or realm) does not want to
      receive any traffic from a peer actually falls within that peer's responsibility before
   acting on the report or forwarding reacting node for the application the
      report concerns.  The reacting node MUST do all measure not to other peers.  For
   example, an overload report from an peer that applies
      send traffic to a realm not
   handled by that peer is suspect.

   An attacker might use the information in an overload report to assist
   in certain attacks.  For example, an attacker could use information
   about current reporting node (or realm) as long as the
      overload conditions to time a DoS attack for maximum
   effect, condition changes or use subsequent overload reports as expires.

   0 < value < 100

      Indicates that the reporting node urges the reacting node to
      reduce its traffic by a feedback mechanism given percentage.  For example if the
      reacting node has been sending 100 packets per second to
   learn the results of
      reporting node, then a previous or ongoing attack.

8.2.  Denial reception of Service Attacks

   Diameter overload reports can cause a OC-Reduction-Percentage value
      of 10 would mean that from now on the reacting node MUST only send
      90 packets per second.  How the reacting node achieves the "true
      reduction" transactions leading to cease sending some or
   all Diameter requests for an extended period.  This makes them a
   tempting vector for DoS tacks.  Furthermore, since Diameter is almost
   always used in support of other protocols, a DoS attack on Diameter the sent request messages is likely up
      to impact those protocols as well.  Therefore, Diameter
   nodes MUST NOT honor or forward overload reports the implementation.  The reacting node MAY simply drop every
      10th packet from unauthorized or
   otherwise untrusted sources.

8.3.  Non-Compliant Nodes

   When a Diameter its output queue and let the generic application
      logic try to recover from it.

   If the OC-OLR AVP is received for the first time, the reacting node sends
   MUST create an overload report, it cannot assume that
   all nodes will comply.  A non-compliant node might continue to send
   requests condition state associated with no reduction the related
   realm or a specific host in load.  Requirement 28
   [I-D.ietf-dime-overload-reqs] indicates that the overload control
   solution cannot assume that all Diameter nodes realm identified in a network are
   necessarily trusted, and that malicious nodes not be allowed to take
   advantage the message
   carrying the OC-OLR AVP, as described in Section 5.5.1.

   If the value of the overload control mechanism OC-Sequence-Number AVP contained in the received
   OC-OLR AVP is equal to get more or less than their
   fair share of service.

   In the absence of value stored in an existing
   overload control mechanism, Diameter nodes need
   to implement strategies to protect themselves from floods of
   requests, and to make sure that a disproportionate load from one
   source does not prevent other sources from receiving service.  For
   example, a Diameter server might reject a certain percentage of
   requests from sources that exceed certain limits.  Overload control
   can condition state, the received OC-OLR AVP SHOULD be thought silently
   discarded.  If the value of as an optimization for such strategies, where
   downstream nodes never send the excess requests OC-Sequence-Number AVP contained in
   the first place.
   However, received OC-OLR AVP is greater than the presence of value stored in an
   existing overload control mechanism does not
   remove condition state or there is no previously recorded
   sequence number, the reacting node MUST update the need for these other protection strategies.

8.4.  End-to End-Security Issues

   The lack of end-to-end security features makes it far more difficult
   to establish trust in overload reports that originate from non-
   adjacent nodes.  Any agents in condition
   state associated with the message path may insert realm or modify
   overload reports.  Nodes must trust that their adjacent peers perform
   proper checks on overload reports from their peers, and so on,
   creating a transitive-trust requirement extending for potentially
   long chains of nodes.  Network operators must determine if this
   transitive trust requirement the specific node is acceptable for their deployments.
   Nodes supporting Diameter overload control MUST give operators the
   ability to select which peers are trusted to deliver overload
   reports, and whether they are trusted to forward realm.

   When an overload reports
   from non-adjacent nodes.

   [OpenIssue: This requires that a responding condition state is created or updated, the reacting
   node be able to tell a
   peer-generated OLR from one generated by a non-adjacent node.  One
   way of doing this would be to include MUST apply the identity of traffic abatement requested in the node that
   generated OC-OLR AVP
   using the report as part of algorithm announced in the OLR]

   [OpenIssue: Do we need further language about what rules an agent
   should apply before forwarding an OLR?] OC-Supported-Features AVP
   contained in the received answer message along with the OC-OLR AVP.

   The lack validity duration of end-to-end protection creates a tension between two
      requirements from the overload control requirements document.
      [I-D.ietf-dime-overload-reqs] Requirement 34 requires the ability
      to send overload reports across intermediaries (i.e. agents) that
      do not support overload control mechanism.  Requirement 27 forbids information contained in the mechanism from adding new vulnerabilities or increasing
   OC-OLR AVP is either explicitly indicated in the
      severity of existing ones.  A non-supporting agent will most
      likely forward overload reports without inspecting them or
      applying any sort of validation OC-Validity-Duration
   AVP or authorization.  This makes the
      transitive trust issue considerably more of a problem.  Without
      the ability is implicitly equals to authenticate and integrity protect overload reports
      across a non-supporting agent, the mechanism cannot comply with
      both requirements.

      [OpenIssue: What do we want to do about this?  Req27 is a
      normative MUST, while Req34 default value (5 seconds) if the
   OC-Validity-Duration AVP is "merely" a SHOULD.  This would seem
      to imply that 27 has to take precedent.  Can we say that overload
      reports MUST NOT be sent to and/or accepted from non-supporting
      agents until such time we can use end-to-end security?]

   The lack absent of end-to-end confidentiality protection means that any
   Diameter agent the OC-OLR AVP.  The reacting
   node MUST maintain the validity duration in the path of an overload report can view condition
   state.  Once the
   contents of that report.  In addition to validity duration times out, the requirement to select
   which peers are trusted to send overload reports, operators MUST be
   able to select which peers are authorized to receive reports.  A reacting node MUST not send an
   assume the overload report to condition reported in a peer not authorized to receive
   it.  Furthermore, previous OC-OLR AVP has
   ended.

5.5.3.  Reporting Node Considerations

   A reporting node is a Diameter node inserting an agent MUST remove any overload reports that
   might have been inserted by other nodes before forwarding OC-OLR AVP in a
   Diameter message in order to inform a peer that is not authorized to receive reacting node about an overload reports.

      At
   condition and request Diameter traffic abatement.

   The operation on the time of this writing, the DIME working group reporting node is studying
      requirements for adding end-to-end security
      [I-D.ietf-dime-e2e-sec-req] features to Diameter.  These features, rather straight forward.  The
   reporting node learns the capabilities of the reacting node when they become available, might make it easier to establish
      trust in non-adjacent nodes
   receives the OC-Supported-Features AVP as part of any Diameter
   request message.  If the reporting node shares at least one common
   feature with the reacting node, then the DOIC can be enabled between
   these two endpoints.  See Section 5.3 for further discussion on the
   capability and feature announcement between two endpoints.

   When a traffic reduction is required due to an overload control purposes.
      Readers should be reminded, however, that condition and
   the overload control
      mechanism encourages solution is supported by the sender of the
   Diameter agents request, the reporting node MUST include an OC-Supported-
   Features AVP and an OC-OLR AVP in the corresponding Diameter answer.
   The OC-OLR AVP contains the required traffic reduction and the OC-
   Supported-Features AVP indicates the traffic abatement algorithm to modify AVPs in, or insert
      additional AVPs into, existing messages that are originated
   apply.  This algorithm MUST be one of the algorithms advertised by
      other nodes.  If end-to-end security is enabled, there
   the request sender.

   A reporting node MAY rely on the OC-Validity-Duration AVP values for
   the implicit overload condition state cleanup on the reacting node.
   However, it is a risk RECOMMENDED that such modification could violate integrity protection.  The
      details the reporting node always explicitly
   indicates the end of using any future Diameter end-to-end security mechanism
      with a overload condition.

6.  Transport Considerations

   In order to reduce overload control will require careful consideration, introduced additional AVP and are
      beyond
   message processing it might be desirable/beneficial to signal whether
   the scope Diameter command carries overload control information that should
   be of interest of this document.

9.  Contributors

   The following people contributed substantial ideas, feedback, and
   discussion to this document:

   o  Eric McMurry

   o  Hannes Tschofenig

   o  Ulrich Wiehe

   o  Jean-Jacques Trottin

   o  Lionel Morand

   o  Maria Cruz Bartolome

   o  Martin Dolly

   o  Nirav Salot

   o  Susan Shishufeng

10.  Acknowledgements

   ...

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an overload aware Diameter node.

   Should such indication be include is not part of this specification.
   It has not either been concluded at what layer such possible
   indication should be.  Obvious candidates include transport layer
   protocols (e.g., SCTP PPID or TCP flags) or Diameter command header
   flags.

7.  IANA Considerations Section

7.1.  AVP codes

   New AVPs defined by this specification are listed in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

11.2.  Informative References

   [I-D.ietf-dime-e2e-sec-req]
              Tschofenig, H., Korhonen, J., Zorn, G., and K. Pillay,
              "Diameter Section 4.  All
   AVP Level Security: Scenarios codes allocated from the 'Authentication, Authorization, and Requirements",
              draft-ietf-dime-e2e-sec-req-00 (work in progress),
              September 2013.

   [I-D.ietf-dime-overload-reqs]
              McMurry, E.
   Accounting (AAA) Parameters' AVP Codes registry.

7.2.  New registries

   Three new registries are needed under the 'Authentication,
   Authorization, and B. Campbell, "Diameter Overload Accounting (AAA) Parameters' registry.

   Section 4.2 defines a new "Overload Control
              Requirements", draft-ietf-dime-overload-reqs-13 (work in
              progress), September 2013.

   [RFC4006]  Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
              Loughney, "Diameter Credit-Control Application", RFC 4006,
              August 2005.

Appendix A.  Issues left for future specifications

   The base solution for Feature Vector" registry
   including the overload control does not cover all
   possible use cases.  A number of solution aspects were intentionally
   left for future specification and protocol work.

A.1.  Additional traffic abatement algorithms

   This specification describes only means for a simple loss based
   algorithm.  Future algorithms initial assignments.  New values can be added into the
   registry using the designed
   solution extension mechanism.  The new algorithms need to be
   registered with IANA. Specification Required policy [RFC5226].  See Sections 4.1 and 7
   Section 4.2 for the required IANA
   steps.

A.2.  Agent Overload

   This specification focuses on Diameter end-point (server or client)
   overload.  A separate extension will be required to outline the
   handling the case of agent overload.

A.3.  DIAMETER_TOO_BUSY clarifications

   The current [RFC6733] behaviour initial assignment in a case of DIAMETER_TOO_BUSY is
   somewhat underspecified.  For example, there is no information how
   long the specific Diameter node is willing to registry.

   Section 4.6 defines a new "Overload Report Type" registry with its
   initial assignments.  New types can be unavailable.  A
   specification updating [RFC6733] should clarify the handling of
   DIAMETER_TOO_BUSY from added using the error answer initiating Specification
   Required policy [RFC5226].

8.  Security Considerations

   This mechanism gives Diameter node
   point of view and from nodes the original ability to request initiating that
   downstream nodes send fewer Diameter node
   point of view.  Further, the inclusion requests.  Nodes do this by
   exchanging overload reports that directly affect this reduction.
   This exchange is potentially subject to multiple methods of possible additional
   information providing APVs should be discussed attack,
   and possible be
   recommended has the potential to be used.

Appendix B.  Conformance to Requirements

   The following section analyses, which Diameter Overload Control
   requirements [I-D.ietf-dime-overload-reqs] are met by this
   specification.

   Key:

      S - Supported

      P - Partial

      N - Not supported

   +------+----+-------------------------------------------------------+
   | Rqmt | S/ | Notes                                                 |
   | #    | P/ |                                                       |
   |      | N  |                                                       |
   +------+----+-------------------------------------------------------+
   | REQ  | P  | The DOIC solution only addresses overload             |
   | 1    |    | information.  Load information is left used as future      |
   |      |    | work.  In addition, the DOIC solution does not        |
   |      |    | address agent overload scenarios.                     |
   |      |    | -                                                     |
   | REQ  | P  | The DOIC solution supports overload a Denial-of-Service (DoS) attack
   vector.

   Overload reports that      |
   | 2    |    | implicitly indicate the application impacted by may contain information about the   |
   |      |    | report.  The DOIC solution does not support reporting |
   |      |    | load information.  The DOIC solution topology and
   current status of a Diameter network.  This information is thought
   potentially sensitive.  Network operators may wish to    |
   |      |    | support graceful behavior.  Allowing an application   |
   |      |    | specific capabilities negotiation mechanism violates  |
   |      |    | application-independence.  Suggested different        |
   |      |    | wording: The DOIC solution supports control
   disclosure of overload reports  |
   |      |    | that are applicable to any unauthorized parties to avoid its
   use for competitive intelligence or to target attacks.

   Diameter application.  The |
   |      |    | DOIC solution does not support reporting load         |
   |      |    | information.  The DOIC solution allows include features to support     |
   |      |    | graceful behavior; this will be enhanced provide end-to-end
   authentication, integrity protection, or confidentiality.  This may
   cause complications when sending overload reports between non-
   adjacent nodes.

8.1.  Potential Threat Modes

   The Diameter protocol involves transactions in the     |
   |      |    | Load information will form of requests
   and answers exchanged between clients and servers.  These clients and
   servers may be defined.  Comment: Can we    |
   |      |    | removed peers, that is,they may share a direct transport (e.g.

   TCP or SCTP) connection, or the words "is thought"?                       |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution is thought messages may traverse one or more
   intermediaries, known as Diameter Agents.  Diameter nodes use TLS,
   DTLS, or IPSec to address this          |
   | 3    |    | requirement.  Comment: Can we removed authenticate peers, and to provide confidentiality
   and integrity protection of traffic between peers.  Nodes can make
   authorization decisions based on the words "is   |
   |      |    | thought"?                                             |
   |      |    | -                                                     |
   | REQ  | P  | The DOIC solution does allow for both both peer identities authenticated at
   the transport layer.

   When agents are involved, this presents an effectively hop-by-hop
   trust model.  That is, a Diameter |
   | 4    |    | client or server can authorize an
   agent for certain actions, but it must trust that agent to make
   appropriate authorization decisions about its peers, and so on.

   Since confidentiality and integrity protection occurs at the
   transport layer.  Agents can read, and perhaps modify, any part of a
   Diameter client message, including an overload report.

   There are several ways an attacker might attempt to send exploit the
   overload         |
   |      |    | reports.  The DOIC solution only addresses Diameter   |
   |      |    | end-point (server and client) overload.  Agent        |
   |      |    | control mechanism.  An unauthorized third party might inject
   an overload report into the network.  If this third party is being addressed in a separate draft.      |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution does not depend on how upstream
   of an agent, and that agent fails to apply proper authorization
   policies, downstream nodes may mistakenly trust the          |
   | 5    |    | end-points are discovered.  Comment: it might be      |
   |      |    | worth working through report.  This
   attack is at least one use case showing   |
   |      |    | DNS based dynamic peer discovery to make sure we      |
   |      |    | haven't missed anything.                              |
   |      |    | -                                                     |
   | REQ  | ?  | Need to update text as some configuation is required. |
   | 6    |    | Need to determin if partially mitigated by the current discussion on         |
   |      |    | assumption that nodes
   include overload application id increases the amount of       |
   |      |    | configuration which would change this to a N.         |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution supports the loss algorithm, which  |
   | 7    |    | is expected reports in Diameter answers but not in requests.
   This requires an attacker to address this requirement.  There is    |
   |      |    | concern about have knowledge of the ability original request
   in order to address oscillations.    |
   |      |    | Wording is included for how construct a reacting node starts to |
   |      |    | increase traffic after response.  Therefore, implementations SHOULD
   validate that an answer containing an overload report expires is a properly
   constructed response to  |
   |      |    | address this concern.  Suggested different wording:   |
   |      |    | The DOIC solution supports a baseline mechanism       |
   |      |    | relying pending request prior to acting on traffic reduction percentage the
   overload report.

   A similar attack involves an otherwise authorized Diameter node that is
   sends an inappropriate overload report.  For example, a     |
   |      |    | loss algorithm, which allows to address this          |
   |      |    | requirement.  Oscillations are avoided or quite       |
   |      |    | minimized by sending successive OLR reports with server for
   the  |
   |      |    | values to converge to realm "example.com" might send an overload report indicating that
   a competitor's realm "example.net" is overloaded.  If other nodes act
   on the optimal traffic report, they may falsely believe that "example.net" is
   overloaded, effectively reducing that realm's capacity.  Therefore,
   it's critical that nodes validate that an overload report received
   from a peer actually falls within that peer's responsibility before
   acting on the report or forwarding the report to       |
   |      |    | smoothly come back to normal traffic conditions when  |
   |      |    | other peers.  For
   example, an overload decreases and ends.                          |
   |      |    | -                                                     |
   | REQ  | ?  | The DOIC solution supports a timestamp which is meant |
   | 8    |    | report from an peer that applies to serve as a realm not
   handled by that peer is suspect.

   An attacker might use the information in an overload report version indication to address    |
   |      |    | this requirement.  Comment: The assist
   in certain attacks.  For example, an attacker could use of the timestamp  |
   |      |    | is under discussion.                                  |
   |      |    | -                                                     |
   | REQ  | ?  | The DOIC solution uses information
   about current overload conditions to time a piggybacking strategy DoS attack for    |
   | 9    |    | carrying maximum
   effect, or use subsequent overload reports, which scales lineraly with |
   |      |    | reports as a feedback mechanism to
   learn the amount results of traffic.  As such, the first part a previous or ongoing attack.

8.2.  Denial of    |
   |      |    | the requirement is addressed.  The DOIC solution does |
   |      |    | not support a mechanism for sending Service Attacks

   Diameter overload reports  |
   |      |    | over can cause a quiescent transport connections or, more       |
   |      |    | generally, node to cease sending some or
   all Diameter nodes that are not producing   |
   |      |    | traffic.  Suggested different wording: The DOIC       |
   |      |    | solution uses requests for an extended period.  This makes them a piggybacking strategy
   tempting vector for carrying    |
   |      |    | overload reports.  As such, the first part DoS tacks.  Furthermore, since Diameter is almost
   always used in support of the     |
   |      |    | requirement other protocols, a DoS attack on Diameter
   is addressed.  For likely to impact those protocols as well.  Therefore, Diameter
   nodes MUST NOT honor or forward overload reports from unauthorized or
   otherwise untrusted sources.

8.3.  Non-Compliant Nodes

   When a connection Diameter node sends an overload report, it cannot assume that has  |
   |      |    | become quiescent due
   all nodes will comply.  A non-compliant node might continue to OLRs send
   requests with a 100% traffic      |
   |      |    | reduction, no reduction in load.  Requirement 28 [RFC7068]
   indicates that the validity timer allows overload control solution cannot assume that all
   Diameter nodes in a network are necessarily trusted, and that
   malicious nodes not be allowed to handle this   |
   |      |    | case.  Other cases take advantage of quiescent connections are       |
   |      |    | outside the scope of Diameter overload (e.g.
   control mechanism to get more than their    |
   |      |    | handling may be done through the watch dog fair share of service.

   In the     |
   |      |    | absence of an overload control mechanism, Diameter base protocol).                              |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution supports two methods nodes need
   to implement strategies to protect themselves from floods of
   requests, and to make sure that a disproportionate load from one
   source does not prevent other sources from receiving service.  For
   example, a Diameter server might reject a certain percentage of
   requests from sources that exceed certain limits.  Overload control
   can be thought of as an optimization for managing   |
   | 10   |    | such strategies, where
   downstream nodes never send the excess requests in the first place.
   However, the length presence of an overload condition.  First, all      |
   |      |    | control mechanism does not
   remove the need for these other protection strategies.

8.4.  End-to End-Security Issues

   The lack of end-to-end security features makes it far more difficult
   to establish trust in overload reports that originate from non-
   adjacent nodes.  Any agents in the message path may insert or modify
   overload reports.  Nodes must contain trust that their adjacent peers perform
   proper checks on overload reports from their peers, and so on,
   creating a duration indication,  |
   |      |    | after which transitive-trust requirement extending for potentially
   long chains of nodes.  Network operators must determine if this
   transitive trust requirement is acceptable for their deployments.
   Nodes supporting Diameter overload control MUST give operators the node reacting
   ability to select which peers are trusted to deliver overload
   reports, and whether they are trusted to forward overload reports
   from non-adjacent nodes.

   The lack of end-to-end confidentiality protection means that any
   Diameter agent in the path of an overload report can       |
   |      |    | consider the overload condition as ended.  Secondly,  |
   |      |    | view the solution supports the method for the node         |
   |      |    | originating the overload report to explicitly         |
   |      |    | communicate
   contents of that report.  In addition to the condition has ended.  This       |
   |      |    | latter mechanism depends on traffic requirement to select
   which peers are trusted to send overload reports, operators MUST be sent from   |
   |      |    | the reacting
   able to select which peers are authorized to receive reports.  A node and, as such, can
   MUST not be depended   |
   |      |    | upon in all circumstances.                            |
   |      |    | -                                                     |
   | REQ  | ?  | The DOIC solution works well for small network        |
   | 11   |    | configurations and for network configurations with send an overload report to a  |
   |      |    | single Diameter agent hop.  More analysis is required |
   |      |    | peer not authorized to determine how well the DOIC solution handles very  |
   |      |    | large Diameter network with partitioned or segmented  |
   |      |    | server farms requiring multiple hops through Diameter |
   |      |    | agents.                                               |
   |      |    | -                                                     |
   | REQ  | P  | The DOIC solution focuses on Diameter end-point       |
   | 12   |    | receive
   it.  Furthermore, an agent MUST remove any overload and meets this requirement for those         |
   |      |    | reports that
   might have been inserted by other nodes before forwarding a Diameter nodes.  The DOIC solution does
   message to a peer that is not address   |
   |      |    | Diameter Agent authorized to receive overload and does not meet reports.

   At the time of this        |
   |      |    | requirement writing, the DIME working group is studying
   requirements for those Diameter nodes.                 |
   |      |    | -                                                     |
   | REQ  | ?  | The DOIC solution requires including of the overload  |
   | 13   |    | report in all answer messages adding end-to-end security
   [I-D.ietf-dime-e2e-sec-req] features to Diameter.  These features,
   when they become available, might make it easier to establish trust
   in some situations.  It |
   |      |    | is not agreed, non-adjacent nodes for overload control purposes.  Readers should
   be reminded, however, that this constitutes         |
   |      |    | substantial work.  This can also be mitigated by the  |
   |      |    | sender of the overload report keeping state control mechanism encourages
   Diameter agents to record |
   |      |    | who has received overload reports.  It modify AVPs in, or insert additional AVPs into,
   existing messages that are originated by other nodes.  If end-to-end
   security is left to     |
   |      |    | implementation decisions as to which approach enabled, there is      |
   |      |    | taken -- send in all messages or send once with a     |
   |      |    | record risk that such modification could
   violate integrity protection.  The details of who has received using any future
   Diameter end-to-end security mechanism with overload control will
   require careful consideration, and are beyond the report.  Another way   |
   |      |    | is scope of this
   document.

9.  Contributors

   The following people contributed substantial ideas, feedback, and
   discussion to let the request sender (reacting node) insert   |
   |      |    | information this document:

   o  Eric McMurry

   o  Hannes Tschofenig

   o  Ulrich Wiehe

   o  Jean-Jacques Trottin

   o  Maria Cruz Bartolome

   o  Martin Dolly

   o  Nirav Salot

   o  Susan Shishufeng

10.  References
10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in the request RFCs to say whether a           |
   |      |    | throttling is actually performed.  The reporting node |
   |      |    | then can base its decision on information received in |
   |      |    | the request; no need Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for keeping state to record who  |
   |      |    | has received overload reports.  The DOIC solution     |
   |      |    | also requires capabilities negotiation Writing an
              IANA Considerations Section in every       |
   |      |    | request RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and response message, which increases the     |
   |      |    | baseline work required for any node supporting the    |
   |      |    | DOIC solution.  Suggested additional text: It does    |
   |      |    | not, however, require that the information be         |
   |      |    | recalculated or updated with each message.  The       |
   |      |    | update frequency is up to W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

10.2.  Informative References

   [3GPP.23.203]
              3GPP, "Policy and charging control architecture", 3GPP
              TS 23.203 10.9.0, September 2013.

   [3GPP.29.229]
              3GPP, "Cx and Dx interfaces based on the implementation, Diameter
              protocol; Protocol details", 3GPP TS 29.229 10.5.0,
              March 2013.

   [3GPP.29.272]
              3GPP, "Evolved Packet System (EPS); Mobility Management
              Entity (MME) and     |
   |      |    | each implementation can make decisions Serving GPRS Support Node (SGSN) related
              interfaces based on Diameter protocol", 3GPP TS 29.272
              10.8.0, June 2013.

   [I-D.ietf-dime-e2e-sec-req]
              Tschofenig, H., Korhonen, J., Zorn, G., and K. Pillay,
              "Diameter AVP Level Security: Scenarios and Requirements",
              draft-ietf-dime-e2e-sec-req-00 (work in progress),
              September 2013.

   [RFC4006]  Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
              Loughney, "Diameter Credit-Control Application", RFC 4006,
              August 2005.

   [RFC5729]  Korhonen, J., Jones, M., Morand, L., and T. Tsou,
              "Clarifications on balancing   |
   |      |    | the update Routing of overload information along with its     |
   |      |    | other priorities.  It is expected that using a        |
   |      |    | periodically updated OLR report added to all messages |
   |      |    | sent to overload control endpoints will not add       |
   |      |    | substantial additional work.  Piggyback base          |
   |      |    | transport also does not require composition, sending, |
   |      |    | or parsing of new Diameter messages for the purpose   |
   |      |    | of conveying overload control information.  There is  |
   |      |    | still discussion Requests Based
              on the substantial additional work   |
   |      |    | due to have OLR in each answer message.               |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution uses the piggybacking method to     |
   | 14   |    | deliver overload report, which scales lineraly with   |
   |      |    | the amount of traffic.  This allows for immediate     |
   |      |    | feedback to any node generating traffic toward        |
   |      |    | another overloaded node.                              |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution does not interfere with transport   |
   | 15   |    | protocols.                                            |
   |      |    | -                                                     |
   | REQ  | ?  | The DOIC solution allows for a mixed network of       |
   | 16   |    | supporting Username and non supporting Diameter end-points.    |
   |      |    | It isn't clear how realm overload is handled in a     |
   |      |    | network with agents that do not support the DOIC      |
   |      |    | solution.  Suggested additional wording: Evaluation   |
   |      |    | of Realm overload may require a DA supporting DOIC,   |
   |      |    | if the realm overload is not evaluated by the client. |
   |      |    | Realm overload handling is still under discussion.    |
   |      |    | -                                                     |
   | REQ  | ?  | Suggested wording: The DOIC solution addresses this   |
   | 17   |    | requirement through the loss algorithm (DOIC baseline |
   |      |    | mechanism) with the following possibilities.  A DA    |
   |      |    | supporting DOIC can act on behalf of clients not      |
   |      |    | supporting DOIC.  A reporting node is also aware of   |
   |      |    | the nodes not supporting the DOIC as there is no      |
   |      |    | advertisement of the DOIC support.  It may then apply |
   |      |    | a particular throttling of the requests coming from   |
   |      |    | these non supporting DOIC clients.                    |
   |      |    | -                                                     |
   | REQ  | ?  | It isn't clear yet that if this requirement is        |
   | 18   |    | addressed.  There has been a proposal to mark         |
   |      |    | messages that survived overload throttling as one     |
   |      |    | method for an overloaded node to address fairness but |
   |      |    | this proposal is not yet part of the solution.  It is |
   |      |    | also possible that the overloaded node could use      |
   |      |    | state gathered as part of the capability              |
   |      |    | advertisement mechanism to know if the sending node   |
   |      |    | supports the DOIC solution and if not, to apply a     |
   |      |    | particular throttling of the requests coming from     |
   |      |    | these non supporting DOIC clients.                    |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution supports the ability for the        |
   | 19   |    | overloaded node Realm", RFC 5729, December 2009.

   [RFC7068]  McMurry, E. and the reacting node to be in        |
   |      |    | different administrative domains.                     |
   |      |    | -                                                     |
   | REQ  | ?  | This mechanism is still under discussion.  Comment 1: |
   | 20   |    | I think this is a "S".  OLRs are clearly              |
   |      |    | distinguishable from any error code.  The fact that   |
   |      |    | an agent would need to send errors if it throttles is |
   |      |    | not an overload indication per se.  It needs to do    |
   |      |    | that even without DoC.  OTOH, if we apply some DOC    |
   |      |    | related fix to TOO_BUSY, we probably need a new code. |
   |      |    | Comment 2: New AVPs conveys overload control          |
   |      |    | information, and this is transported on existing      |
   |      |    | answer messages, so distinguishable from Diameter     |
   |      |    | errors.                                               |
   |      |    | -                                                     |
   | REQ  | S  | The inability for a node to send overload reports     |
   | 21   |    | will result in equivalent through put to a network    |
   |      |    | that does not support the DOIC solution.              |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution gives this node generating the      |
   | 22   |    | overload report the ability to control the amount of  |
   |      |    | throttling done by the reacting node using the        |
   |      |    | reduction percentage parameter in the overload        |
   |      |    | report.                                               |
   |      |    | -                                                     |
   | REQ  | ?  | Initial text: The DOIC mechanism supports two         |
   | 23   |    | abatement strategies by reacting nodes, routing to an |
   |      |    | alternative node or dropping traffic.  The routing to |
   |      |    | an alternative node will be enhanced when the Load    |
   |      |    | extension is defined.  Comment: This is a N. There's  |
   |      |    | no good way to determine which nodes are likely to    |
   |      |    | have sufficient capacity without some sort of load    |
   |      |    | metric for non-overloaded nodes.                      |
   |      |    | -                                                     |
   | REQ  | N  | The DOIC solution does not address delivering load    |
   | 24   |    | information.                                          |
   |      |    | -                                                     |
   | REQ  | S  | The DOIC solution contains some guideance.            |
   | 25   |    |                                                       |
   |      |    | -                                                     |
   | REQ  | S  | B. Campbell, "Diameter Overload Control
              Requirements", RFC 7068, November 2013.

Appendix A.  Issues left for future specifications

   The DOIC base solution for the overload control does not constrain a nodes ability  |
   | 26   |    | to determine which requests are trottled.             |
   |      |    | -                                                     |
   | REQ  | ?  | Initial text: The DOIC solution does add a new line   |
   | 27   |    | cover all
   possible use cases.  A number of attack in the ability solution aspects were intentionally
   left for future specification and protocol work.

A.1.  Additional traffic abatement algorithms

   This specification describes only means for a malicious entity to    |
   |      |    | insert overload reports that would reduce or          |
   |      |    | eliminate traffic.  This, however, is no worse than   |
   |      |    | an attacker that would assert erroneous error         |
   |      |    | responses such as a TOO BUSY response.  It is         |
   |      |    | recognized that simple loss based
   algorithm.  Future algorithms can be added using the end-to-end security designed
   solution      |
   |      |    | currently being worked on by the DIME working group   |
   |      |    | is needed extension mechanism.  The new algorithms need to close these types of vulurabilities.     |
   |      |    | Comment: Sending a malicious OLR be
   registered with a type of       |
   |      |    | "realm" will have considerably more impact than a     |
   |      |    | TOO_BUSY.  Personally, I don't think we can achieve   |
   |      |    | this requirement without either being hop-by-hop IANA.  See Sections 4.1 and 7 for the required IANA
   steps.

A.2.  Agent Overload

   This specification focuses on Diameter end-point (server or   |
   |      |    | requiring e2e security.  We probably need further     |
   |      |    | analysis client)
   overload.  A separate extension will be required to outline the
   handling the case of agent overload.

A.3.  DIAMETER_TOO_BUSY clarifications

   The current [RFC6733] behaviour in a case of DIAMETER_TOO_BUSY is
   somewhat under specified.  For example, there is no information how
   long the security implications specific Diameter node is willing to be unavailable.  A
   specification updating [RFC6733] should clarify the handling of
   DIAMETER_TOO_BUSY from the          |
   |      |    | capabilities negotiation as well.  Suggested          |
   |      |    | error answer initiating Diameter node
   point of view and from the original request initiating Diameter node
   point of view.  Further, the inclusion of possible additional verbage: An OLR only relates
   information providing AVPs should be discussed and possible be
   recommended to be used.

Appendix B.  Examples

B.1.  Mix of Destination-Realm routed requests and Destination-Host
      routed requests

   Diameter allows a client to optionally select the        |
   |      |    | traffic between destination server
   of a reporting node request, even if there are agents between the client and the
   server.  The client does this using the Destination-Host AVP.  In
   cases where the client does not care if a reacting node  |
   |      |    | and specific server receives
   the request, it can omit Destination-Host and route the request using
   the Destination-Realm and Application Id, effectively block letting an
   agent select the traffic from server.

   Clients commonly send mixtures of Destination-Host and Destination-
   Realm routed requests.  For example, in an application that uses user
   sessions, a client   |
   |      |    | typically won't care which would be an important impact.  Nevertheless     |
   |      |    | OLRs are regularly sent in all answers, so a          |
   |      |    | malicious OLR will have a short transient effect, as  |
   |      |    | quickly overridden by a new OLR.  To have a           |
   |      |    | significant impact would require server handles a continuous flow of |
   |      |    | answers with malicious OLRs.  There
   session-initiating requests.  But once the session is initiated, the
   client will send all subsequent requests in that session to the exception  |
   |      |    | of same
   server.  Therefore it would send the OLR initial request with no
   Destination-Host AVP.  If it receives a successful answer, the client
   would copy the Origin-Host value of 100% reduction traffic     |
   |      |    | which has from the answer message into a higher vulnerability and
   Destination-Host AVP in each subsequent request in the use of which |
   |      |    | should be avoided when possible.  In addition such    |
   |      |    | malicious OLRs must be session.

   An agent has very limited options in answers, which means applying overload abatement to
   requests that contain Destination-Host AVPs.  It typically cannot
   route the    |
   |      |    | capability request to insert a different server than the malicious OLR one identified in an existing |
   |      |    | answer rather than
   Destination-Host.  It's only remaining options are to create throttle such
   requests locally, or to send an answer which overload report back towards the
   client so the client can throttle the requests.  The second choice is much  |
   |      |    | less easy than
   usually more efficient, since it prevents any throttled requests from
   being sent in the first place, and removes the agent's need to create a send
   errors back to the client for each dropped request.  To have a        |
   |      |    | network wide applicability would request

   On the other hand, an agent has much more leeway to generate  |
   |      |    | malicious OLRs messages towards apply overload
   abatement for requests that do not contain Destination-Host AVPs.  If
   the agent has multiple servers in its peer table for the given realm
   and application, it can route such requests to other, less overloaded
   servers.

   If the overload severity increases, the agent may reach a point where
   there is not sufficient capacity across all reacting nodes.   |
   |      |    | It servers to handle even
   realm-routed requests.  In this case, the realm itself can be
   considered that overloaded.  The agent may need the baseline mechanism      |
   |      |    | offer a relevant level of security.  Further analysis |
   |      |    | with a security expertise would client to throttle
   realm-routed requests in addition to Destination-Host routed
   requests.  The overload severity may be beneficial.        |
   |      |    | -                                                     |
   | REQ  | ?  | See REQ 18 different for each server,
   and REQ 27.  Suggested additional verbage: |
   | 28   |    | Guidance may the severity for the realm at is likely to be provided different than for detection of non         |
   |      |    | compliant/abnormal use
   any specific server.  Therefore, an agent may need to forward, or
   originate, multiple overload reports with differing ReportType and
   Reduction-Percentage values.

   Figure 8 illustrates such a mixed-routing scenario.  In this example,
   the servers S1, S2, and S3 handle requests for the realm "realm".
   Any of OLRs, not only by endpoints |
   |      |    | but also by intermediate DA that the three can be aware handle requests that are not part of      |
   |      |    | OLRs, an example being edge DAs with external         |
   |      |    | networks.  Further analysis with a security expertise |
   |      |    | would be beneficial.                                  |
   |      |    | -                                                     | user
   session (i.e. routed by Destination-Realm).  But once a session is
   established, all requests in that session must go to the same server.

     Client     Agent      S1        S2        S3
        | REQ         | ?         | This requirement is not explicitly addressed by the         |         | 29
        |(1) Request (DR:realm)       |         | DOIC solution.  There is nothing in the DOIC solution
        |-------->|         |         |         |
        | that would prevent the goals of this requirement from         |         |         |         | being achieved.  Non-adjacent DOIC without e2e
        |         |         |         | security could be an issue here.         |
        |         |Agent selects S1   |         | -
        |         | REQ         | ?         | It isn't clear how a solution would interfere.         |
        | 30         |         | Suggested wording: A node can have methods on how to         |         |
        |         | protect from overload from nodes non supporting DOIC.         |         |         |
        | The DOIC mechanism used with DOIC supporting nodes         |(2) Request (DR:realm)       |
        |         |-------->|         |         | will not interfere with the appliance of these
        |         |         |         | methods.  There is the remark that the use of these         |
        |         |         | methods may impact the global overload of the node         |         |
        |         | and the evaluation of the traffic reduction that the         |S1 overloaded, returns OLR
        |         |         |         | reporting node will send in OLRs.  If a node has         |
        |         |         | methods to protect against denial of service attacks,         |         |
        |         | the use of DOIC will not interfere with them.  A         |         |         |
        | denial of service attack concerning the DOIC itself         |(3) Answer (OR:realm,OH:S1,OLR:RT=DH)
        |         |<--------|         |         |
        | is addressed in REQ 27.         |         |         |         | -
        |         | REQ         | ?         | Initial text with an S: The DOIC solution addresses         |
        | 31         |sees OLR,routes DR traffic to S2&S3
        |         | node and realm directly.  The application to which a         |         |         |
        | report applies is implicitly determined based on the         |         |         |         | application level message carrying the report.  Note
        |         |         |         | that there is no way with DOIC for an overloaded node         |
        |(4) Answer (OR:realm,OH:S1, OLR:RT=DH) |
        |<--------|         |         | to communicate multiple nodes, realms or applications         |
        |         |         | in a single overload report.  So the inverse of this         |         |
        |         | requirement is not supported.  Comment: The inverse         |         |         |
        |Client throttles requests with DH:S1   | is also not _required_ :-) But I think we are "P"
        |         |         |         | here, in that we don't support "node" per se. we do         |
        |         |         | support "server."  "Node" includes agents.  (I also         |         |
        |         | interpreted this to mean that each granularity needed         |         |         |
        |(5) Request (DR:realm)       | to be supported independently--that is, a potential         |
        |-------->|         |         |         | to say "all traffic to a realm" or "all traffic to a
        |         |         |         | host" independently of application.)         |
        |         |         | -         |         | REQ
        | ?         |Agent selects S2   | Initial text with an S: The DOIC solution supports         |
        | 32         |         | extensibility of both the information communicated         |         |
        |         | and in the definition of new overload abatement         |         |         |
        | algorithms.  Comment 1: Recent discussions have made         |         |         |         | this a ?.  It can be changed to S/N/P once these
        |         |(6) Request (DR:realm)       |
        |         |------------------>|         | discussions come to a conclusion and new text is
        |         |         |         | added to the draft.  Comment 2: Suggested wording -         |
        |         |         | The DOIC solution supports extensibility of both the         |         |
        |         | information communicated and in the definition of new         |         |S2 is overloaded...
        |         |         | overload abatement algorithms or strategies.  It         |         |
        |         | should be noted that, according to the applications         |         |         |
        | or to reacting node implementations, many algorithms         |         |         |         | may be applied on top of the DOIC baseline solution
        |         |(7) Answer (OH:S2, OLR:RT=DH)|
        |         |<------------------|         |
        |         |         |         |         |
        | (without contradicting it), e.g. regarding which type         |         |         |         | of request to throttle, prioritized messages
        |         |Agent sees OLR, realm now overloaded
        |         |         | handling, mapping of the reduction % to an internal         |         |
        |         | algorithm (eg 1 message out of ten etc..) but such         |         |         |
        | algorithms are out of scope of DOIC.         |         |         |         | -
        |(8) Answer (OR:realm,OH:S2, OLR:RT=DH, OLR: RT=R)
        |<--------|         |         | REQ         | ?
        | Initial text with P: The DOIC solution currently         |         | 33         |         | defines the loss algorithm as the default algorithm.
        |         |         |         | It does not specify it as mandatory to implement.         |
        |Client throttles DH:S1, DH:S2, and DR:realm
        |         |         |         | Comment 1: Then I think that's a "n".  The MTI part         |
        |         |         | is the crux of the requirement.  Comment 2: Suggested         |         |
        |         | wording: In the DOIC baseline solution, the reacting         |         |         |
        | node has to apply the received Reduction-Percentage,         |         |         |         | and for achieving this, the reacting node can do
        |         |         |         | requests rerouting (when         |

      Figure 8: Mix of Destination-Host and Destination-Realm Routed
                                 Requests

   1.  The client sends a request with no Destination-Host AVP (that is,
       a Destination-Realm routed request.)

   2.  The agent follows local policy to select a server from its peer
       table.  In this case, the agent selects S2 and forwards the
       request.

   3.  S1 is overloaded.  It sends a answer indicating success, but also
       includes an overload report.  Since the overload report only
       applies to S1, the ReportType is "Destination-Host".

   4.  The agent sees the overload report, and records that S1 is
       overloaded by the value in the Reduction-Percentage AVP.  It
       begins diverting the indicated percentage of realm-routed traffic
       from S1 to S2 and S3.  Since it can't divert Destination-Host
       routed traffic, it forwards the overload report to the client.
       This effectively delegates the throttling of traffic with
       Destination-Host:S1 to the client.

   5.  The client sends another Destination-Realm routed request.

   6.  The agent selects S2, and forwards the request.

   7.  It turns out that S2 is also overloaded, perhaps due to all that
       traffic it took over for S1.  S2 returns an successful answer
       containing an overload report.  Since this report only applies to
       S2, the ReportType is "Destination-Host".

   8.  The agent sees that S2 is possible) or           |
   |      |    | drop/reject requests. also overloaded by the value in
       Reduction-Percentage.  This DOIC baseline solution value is |
   |      |    | a loss algorithm and DOIC should not require further  |
   |      |    | specification. probably different than the
       value from S1's report.  The answer agent diverts the remaining traffic
       to REQ32 indicates S3 as best as it can, but it calculates that the     |
   |      |    | possibility remaining
       capacity across all three servers is no longer sufficient to add other algorithms on top
       handle all of the     |
   |      |    | DOIC baseline solution.  The DOIC solution currently  |
   |      |    | defines this loss algorithm as realm-routed traffic.  This means the default algorithm. |
   |      |    | It realm
       itself is still under discussion to make it as mandatory  |
   |      |    | to implement.                                         |
   |      |    | -                                                     |
   | REQ  | P  | overloaded.  The ability to communicate realm's overload reports between   |
   | 34   |    | supporting Diameter nodes does not require agents to  |
   |      |    | support the DOIC solution.  Load information exchange |
   |      |    | percentage is not currently defined.                             |
   +------+----+-------------------------------------------------------+

                                  Table 1

Appendix C.  Examples

C.1.  3GPP S6a interface overload indication

   [TBD: Would cover S6a MME-HSS communication with several topology
   choices (such as with most
       likely different than that for either S1 or without DRA, S2.  The agent
       forward's S2's report back to the client in the Diameter answer.
       Additionally, the agent generates a new report for the realm of
       "realm", and inserts that report into the answer.  The client
       throttles requests with "generic" agents).]

C.2.  3GPP PCC interfaces overload indication

   [TBD: Would cover Gx/Rx and maybe S9..]

C.3.  Mix of Destination-Realm routed Destination-Host:S1 at one rate, requests
       with Destination-Host:S2 at another rate, and Destination-Host
      reouted requests

   [TBD: Add example showing the use of with no
       Destination-Host type OLRs and
   Realm type OLRs.] AVP at yet a third rate.  (Since S3 has not
       indicated overload, the client does not throttle requests with
       Destination-Host:S3.)

Authors' Addresses

   Jouni Korhonen (editor)
   Broadcom
   Porkkalankatu 24
   Helsinki  FIN-00180
   Finland

   Email: jouni.nospam@gmail.com

   Steve Donovan
   Oracle
   17210 Campbell Road
   Dallas, Texas  75254
   United States

   Email: srdonovan@usdonovans.com

   Ben Campbell
   Oracle
   17210 Campbell Road
   Dallas, Texas  75254
   United States

   Email: ben@nostrum.com
   Lionel Morand
   Orange Labs
   38/40 rue du General Leclerc
   Issy-Les-Moulineaux Cedex 9  92794
   France

   Phone: +33145296257
   Email: lionel.morand@orange.com