Diameter Maintenance and Extensions (DIME)              J. Korhonen, Ed.
Internet-Draft                                                  Broadcom
Intended status: Standards Track                         S. Donovan, Ed.
Expires: April 30, June 6, 2015                                        B. Campbell
                                                                  Oracle
                                                               L. Morand
                                                             Orange Labs
                                                        October 27,
                                                        December 3, 2014

                Diameter Overload Indication Conveyance
                      draft-ietf-dime-ovli-04.txt
                      draft-ietf-dime-ovli-05.txt

Abstract

   This specification documents defines a Diameter Overload Control (DOC) base solution and the dissemination of the for Diameter overload report information.
   control, referred to as Diameter Overload Indication Conveyance
   (DOIC).

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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   This Internet-Draft will expire on April 30, June 6, 2015.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Abbreviations . . . . . . . . . . . . . . . .   3   4
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Piggybacking Principle  . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  DOIC Capability Announcement  . . . . . . . . . . . . . .   8
     3.3.  DOIC Overload Condition Reporting . . . . . . . . . . . .   9
     3.4.  DOIC Extensibility  . . . . . . . . . . . . . . . . . . .  10  11
     3.5.  Simplified Example Architecture . . . . . . . . . . . . .  11  12
   4.  Solution Procedures . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  Capability Announcement . . . . . . . . . . . . . . . . .  12
       4.1.1.  Reacting Node Behavior  . . . . . . . . . . . . . . .  12  13
       4.1.2.  Reporting Node Behavior . . . . . . . . . . . . . . .  12  13
       4.1.3.  Agent Behavior  . . . . . . . . . . . . . . . . . . .  13  14
     4.2.  Overload Report Processing  . . . . . . . . . . . . . . .  14  15
       4.2.1.  Overload Control State  . . . . . . . . . . . . . . .  14  15
       4.2.2.  Reacting Node Behavior  . . . . . . . . . . . . . . .  18  19
       4.2.3.  Reporting Node Behavior . . . . . . . . . . . . . . .  18  20
     4.3.  Protocol Extensibility  . . . . . . . . . . . . . . . . .  20  21
   5.  Loss Algorithm  . . . . . . . . . . . . . . . . . . . . . . .  21  22
     5.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  21  22
     5.2.  Reporting Node Behavior . . . . . . . . . . . . . . . . .  22  23
     5.3.  Reacting Node Behavior  . . . . . . . . . . . . . . . . .  22  24
   6.  Attribute Value Pairs . . . . . . . . . . . . . . . . . . . .  23  25
     6.1.  OC-Supported-Features AVP . . . . . . . . . . . . . . . .  23  25
     6.2.  OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . .  24  25
     6.3.  OC-OLR AVP  . . . . . . . . . . . . . . . . . . . . . . .  24  26
     6.4.  OC-Sequence-Number AVP  . . . . . . . . . . . . . . . . .  25  26
     6.5.  OC-Validity-Duration AVP  . . . . . . . . . . . . . . . .  25  27
     6.6.  OC-Report-Type AVP  . . . . . . . . . . . . . . . . . . .  25  27
     6.7.  OC-Reduction-Percentage AVP . . . . . . . . . . . . . . .  26  27
     6.8.  Attribute Value Pair flag rules . . . . . . . . . . . . .  27
   7.  Error Response Codes  . . . . . . . . . . . . . . . . . . . .  27  28
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28  29
     8.1.  AVP codes . . . . . . . . . . . . . . . . . . . . . . . .  28  29
     8.2.  New registries  . . . . . . . . . . . . . . . . . . . . .  28  29
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  29  30
     9.1.  Potential Threat Modes  . . . . . . . . . . . . . . . . .  29  30
     9.2.  Denial of Service Attacks . . . . . . . . . . . . . . . .  30  31
     9.3.  Non-Compliant Nodes . . . . . . . . . . . . . . . . . . .  30  32
     9.4.  End-to End-Security Issues  . . . . . . . . . . . . . . .  31  32
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  32  33
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  32  34
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  32  34
     11.2.  Informative References . . . . . . . . . . . . . . . . .  32  34
   Appendix A.  Issues left for future specifications  . . . . . . .  33  34
     A.1.  Additional traffic abatement algorithms . . . . . . . . .  33  35
     A.2.  Agent Overload  . . . . . . . . . . . . . . . . . . . . .  33  35
     A.3.  New Error Diagnostic AVP  . . . . . . . . . . . . . . . .  33  35
   Appendix B.  Deployment Considerations  . . . . . . . . . . . . .  34  35
   Appendix C.  Requirements Conformance Analysis  . . . . . . . . .  34
   Appendix D.  Considerations for Applications Integrating the DOIC
                Solution  35
     C.1.  Deferred Requirements . . . . . . . . . . . . . . . . . .  36
     C.2.  Detection of non-supporting Intermediaries  . . . . . . .  34
     D.1.  36
     C.3.  Implicit Application Classification Indication . . . . . . . . . . . . .  36
     C.4.  Stateless Operation . .  34
     D.2.  Application Type Overload Implications . . . . . . . . .  35
     D.3.  Request Transaction Classification . . . . . . . .  37
     C.5.  No New Vulnerabilities  . . . . . .  36
     D.4.  Request Type Overload Implications . . . . . . . . . . .  37
   Authors' Addresses
     C.6.  Detailed Requirements . . . . . . . . . . . . . . . . . .  37
       C.6.1.  General . . . . .  38

1.  Introduction

   This specification defines a base solution . . . . . . . . . . . . . . . . . .  37
       C.6.2.  Performance . . . . . . . . . . . . . . . . . . . . .  39
       C.6.3.  Heterogeneous Support for Diameter Overload Solution  . . . . . . . . .  41
       C.6.4.  Granular Control (DOC), referred to as Diameter Overload Indication Conveyance
   (DOIC).  The requirements for the solution are described  . . . . . . . . . . . . . . . . . .  43
       C.6.5.  Priority and
   discussed in the corresponding design requirements document
   [RFC7068].  Note that the overload control solution defined in this
   specification does not address all the requirements listed in
   [RFC7068].  A number of overload control related features are left
   for the future specifications.  See Policy . . . . . . . . . . . . . . . . .  43
       C.6.6.  Security  . . . . . . . . . . . . . . . . . . . . . .  44
       C.6.7.  Flexibility and Extensibility . . . . . . . . . . . .  45
   Appendix A D.  Considerations for Applications Integrating the DOIC
                Solution . . . . . . . . . . . . . . . . . . . . . .  46
     D.1.  Application Classification  . . . . . . . . . . . . . . .  47
     D.2.  Application Type Overload Implications  . . . . . . . . .  48
     D.3.  Request Transaction Classification  . . . . . . . . . . .  49
     D.4.  Request Type Overload Implications  . . . . . . . . . . .  50
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  51

1.  Introduction

   This specification defines a list of
   extensions that are currently being considered.  See Appendix C base solution for
   an analysis of the conformance Diameter overload
   control, referred to as Diameter Overload Indication Conveyance
   (DOIC), based on the requirements specified identified in [RFC7068].

   The solution defined in this

   This specification addresses Diameter overload control between
   Diameter nodes that support the DOIC solution.  Furthermore, the solution  The solution, which
   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

   Note that the overload control solution defined in this specification
   does not address all the requirements listed in [RFC7068].  A number
   of overload control related features are left for future
   specifications.  See Appendix A for a list of extensions that are
   currently being considered.  See Appendix C for an analysis of
   conformance to the requirements specified in [RFC7068].

2.  Terminology and Abbreviations

   Abatement

      Reaction to receipt of an overload report resulting in a reduction
      in traffic sent to the reporting node.  Abatement actions include
      diversion and throttling.

   Abatement Algorithm

      An

      A mechanism requested by reporting nodes and used by reacting
      nodes to reduce the amount of traffic sent during an occurrence of
      overload control.

   Diversion

      Abatement of traffic sent to a reporting node by a reacting node
      in response to receipt of an

      A mechanism used for overload report.  The abatement is
      achieved by diverting traffic from the reporting node to another
      Diameter node that is able to process the request. selecting a different
      path for requests.

   Host-Routed Request

      The set of requests Requests

      Requests that a reacting node knows will be served by a particular
      host, either due to the presence of a Destination-Host AVP, or by
      some other local knowledge on the part of the reacting node.

   Overload Control State (OCS)

      Reporting and reacting node internally maintained state describing
      occurrences of overload control.

   Overload Report (OLR)

      Information

      Overload control information for a particular overload occurrence
      sent by a reporting node indicating the start,
      continuation or end of an occurrence of overload control. node.

   Reacting Node

      A Diameter node that acts upon an overload report.

   Realm-Routed Request

      The set of requests Requests
      Requests that a reacting node does not know the host that will
      service the request.

   Reporting Node

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

   Throttling

      Throttling is the reduction of

      A mechanism for overload abatement that limits the number of
      requests sent to an
      entity. by the DIOC reacting node.  Throttling can include a
      Diameter Client or Diameter
      Server dropping not sending requests, or a Diameter Agent or
      Server rejecting requests with appropriate error responses.  In extreme
      both cases reporting
      nodes can also throttle requests when the requested reductions in
      traffic does not sufficiently address result of the overload scenario. throttling is a permanent rejection
      of the transaction.

3.  Solution Overview

   The Diameter Overload Information Conveyance (DOIC) solution allows
   Diameter nodes to request other Diameter nodes to perform overload
   abatement actions, that is, actions to reduce the load offered to the
   overloaded node or realm.

   A Diameter node that supports DOIC is known as a "DOIC node".  Any
   Diameter node can act as a DOIC node, including clients, servers, Diameter Clients,
   Diameter Servers, and
   agents. Diameter Agents.  DOIC nodes are further
   divided into "Reporting Nodes" and "Reacting Nodes."  A reporting
   node requests overload abatement by sending an Overload Report (OLR) to one or more reacting nodes. Reports (OLR).

   A reacting node acts upon OLRs, and performs whatever actions are
   needed to fulfil fulfill the abatement requests included in the OLRs.  A
   Reporting node may report overload on its own behalf, or on behalf of
   other (typically upstream) nodes.  Likewise, a reacting node may perform overload
   abatement on its own behalf, or on behalf of other
   (typically downstream) nodes.

   A Diameter node's role as a DOIC node is independent of its Diameter
   role.  For example, Diameter Relay and Proxy Agents may act as DOIC nodes, even
   though they are not endpoints in the Diameter sense.  Since Diameter
   enables bi-directional applications, where Diameter Servers can send
   requests towards Diameter Clients, a given Diameter node can
   simultaneously act as both a reporting node and a reacting node.

   Likewise, a relay or proxy agent Diameter Agent may act as a reacting node from the
   perspective of upstream nodes, and a reporting node from the
   perspective of downstream nodes.

   DOIC nodes do not generate new messages to carry DOIC related
   information.  Rather, they "piggyback" DOIC information over existing
   Diameter messages by inserting new AVPs into existing Diameter
   requests and responses.  Nodes indicate support for DOIC, and any
   needed DOIC parameters parameters, by inserting an OC_Supported_Features OC-Supported-Features AVP
   (Section 6.2) into existing requests and responses.  Reporting nodes
   send OLRs by inserting OC-OLR AVPs (Section 6.3).

   A given OLR applies to the Diameter realm and application of the
   Diameter message that carries it.  If a reporting node supports more
   than one realm and/or application, it reports independently for each
   combination of realm and application.  Similarly, the OC-Supported-
   Features AVP applies to the realm and application of the enclosing
   message.  This implies that a node may support DOIC for one
   application and/or realm, but not another, and may indicate different
   DOIC parameters for each application and realm for which it supports
   DOIC.

   Reacting nodes perform overload abatement according to an agreed-upon
   abatement algorithm.  An abatement algorithm defines the meaning of
   some of the parameters of an OLR and the procedures required for
   overload abatement.  This document specifies a single must-support algorithm,
   namely the "loss"  An overload abatement algorithm (Section 5).  Future specifications may
   introduce new algorithms.

   Overload conditions may vary in scope.  For example, a single separates
   Diameter node requests into two sets.  The first set contains the requests
   that are to undergo overload abatement treatment of either throttling
   or diversion.  The second set contains the requests that are to be
   given normal routing treatment.  This document specifies a single
   must-support algorithm, namely the "loss" algorithm (Section 5).
   Future specifications may introduce new algorithms.

   Overload conditions may vary in scope.  For example, a single
   Diameter node may be overloaded, in which case reacting nodes may
   reasonably
   attempt to send requests to other destinations or via
   other agents. destinations.  On the other hand,
   an entire Diameter realm may be overloaded, in which case such
   attempts would do harm.  DOIC OLRs have a concept of "report type"
   (Section 6.6), where the type defines such behaviors.  Report types
   are extensible.  This document defines report types for overload of a
   specific server, host, and for overload of an entire realm.

   A report of type host "HOST_REPORT" is sent to indicate the overload of a
   specific
   server host, identified by the Origin-Host AVP of the message
   containing the OLR, for the application-id indicated in the
   transaction.  When receiving an OLR of type host, "HOST_REPORT", a reacting
   node applies overload abatement treatment to what is referred to in this document as host-routed
   requests.  This is the set of host-routed requests that the reacting node knows
   will be served by a particular host, either due to the presence of a
   Destination-Host AVP, or
   identified by some other local knowledge on the part of the reacting node.  The reacting node applies overload abatement on
   those host-routed requests which the reacting node knows will be
   served by the server that matches the Origin-Host AVP of the received
   message that contained algorithm (see definition in
   Section 2) sent for this application to the received OLR of type overloaded host.

   A report type of realm type "REALM_REPORT" is sent to indicate the overload of all
   servers in a
   realm for the application-id. application-id indicated in the transaction.  The
   overloaded realm is identified by the Destination-Realm AVP of the
   message containing the OLR.  When receiving an OLR of type realm,
   "REALM_REPORT", a reacting node applies overload abatement treatment
   to what is
   referred to in this document as realm-routed requests.  This is the
   set of requests that are not host-routed as defined identified by the overload abatement
   algorithm (see definition in Section 2) sent for this application to
   the previous
   paragraph. overloaded realm.

   While a reporting node sends OLRs to "adjacent" reacting nodes, nodes
   that are "adjacent" for DOIC purposes may not be adjacent from a
   Diameter, or transport, perspective.  For example, one or more
   Diameter agents that do not support DOIC may exist between a given
   pair of reporting and reacting nodes, as long as those agents pass
   unknown AVPs through unchanged.  The report types described in this
   document can safely pass through non-supporting agents.  This may not
   be true for report types defined in future specifications.  Documents
   that introduce

3.1.  Piggybacking

   There is no new report types MUST describe any limitations on
   their use across non-supporting agents.

3.1.  Piggybacking Principle Diameter application defined to carry overload
   related AVPs.  The overload control AVPs defined in this
   specification have been designed to be piggybacked on top of existing
   application messages.  This is made possible by adding overload
   control top-level AVPs, the OC-OLR AVP and the OC-Supported-Features AVP, as
   optional AVPs into existing commands when the corresponding Command
   Code Format (CCF) specification allows adding new optional AVPs (see
   Section 1.3.4 of [RFC6733]).

   Reacting nodes indicate support for DOIC by including the OC-
   Supported-Features AVP in all request messages originated or relayed
   by the reacting node.

   Reporting nodes indicate support for DOIC by including the OC-
   Supported-Features AVP in all answer messages originated or relayed
   by the reporting node. node that are in response to a request that
   contained the OC-Supported-Features AVP.  Reporting nodes also
   include overload reports using the OC-OLR AVP in answer messages.

      Note: There is no new Diameter application defined to carry
      overload related AVPs.  The DOIC AVPs are carried in existing
      Diameter application messages.

   Note that the overload control solution does not have fixed server
   and client roles.  The DOIC node role is determined based on the
   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 Diameter
   Client MAY report its overload condition to the Diameter Server for
   any Diameter Server initiated message exchange.  An example of such
   is the Diameter Server requesting a re-authentication from a Diameter
   Client.

3.2.  DOIC Capability Announcement

   The DOIC solution supports the ability for Diameter nodes to
   determine if other nodes in the path of a request support the
   solution.  This capability is referred to as DOIC Capability
   Announcement (DCA) and is separate from Diameter Capability Exchange.

   The DCA solution mechanism uses the OC-Supported-Features AVPs to indicate the
   Diameter overload features supported.

   The first node in the path of a Diameter request that supports the
   DOIC solution inserts the OC-Supported-Feature OC-Supported-Features AVP in the request
   message.  This includes an indication that it supports the loss
   overload abatement algorithm defined

      Note: As discussed elsewhere in this specification (see
   Section 5).  This ensures that there is at least one commonly
   supported overload abatement algorithm between the reporting node and the reacting nodes document, agents in the path
      of the request. request can modify the OC-Supported-Features AVP.

      Note: The DOIC solution must support deployments where Diameter
      Clients and/or Diameter Servers do not support the DOIC solution.
      In this scenario, it is assumed that Diameter Agents that support the DOIC solution will
      may handle overload abatement for the non supporting Diameter
      nodes.  In this case the DOIC agent will insert the OC-
      Supporting-Features OC-Supported-
      Features AVP in requests that do not already contain one, telling
      the reporting node that there is a DOIC node that will handle
      overload abatement.  For transactions where there was an OC-
      Supporting-Features AVP in the request, the agent will insert the
      OC-Supported-Features AVP in answers, telling the reacting node
      that there is a reporting node.

   The OC-Feature-Vector AVP will contain an indication of support for
   the loss overload abatement algorithm defined in this specification
   (see Section 5).  This ensures that there is at least one commonly
   supported overload abatement algorithm between the reporting node and
   the reacting node(s) in the path of the request.

   The reporting node inserts the OC-Supported-Feature OC-Supported-Features AVP in all
   answer messages to requests that contained the OC-Supported-Feature OC-Supported-Features
   AVP.  The contents of the reporting node's OC-Supported-Feature OC-Supported-Features AVP
   indicate the set of Diameter overload features supported by the
   reporting node with node.  This specification defines one exception.

   The exception - the
   reporting node only includes an indication of support for one
   overload abatement algorithm.  This algorithm, independent of the number of overload
   abatement algorithms actually supported by the reacting node.  The
   overload abatement algorithm indicated is the algorithm that the
   reporting node intends to use should it enter an overload condition
   or requests to use while it actually is in an overload condition.
   Reacting nodes can use the indicated overload abatement algorithm to
   prepare for possible overload reports and must use the indicated
   overload abatement algorithm if traffic reduction is actually
   requested.

      Note that the loss algorithm defined in this document is a
      stateless abatement algorithm.  As a result it does not require
      any actions by reacting nodes prior to the receipt of an overload
      report.  Stateful abatement algorithms that base the abatement
      logic on a history of request messages sent might require reacting
      nodes to maintain state in advance of receiving an overload report
      to ensure that the overload reports can be properly handled.

   Reporting nodes are allowed to change the overload abatement
   algorithm indicated in the OC-Feature-Vector AVP if the reporting
   node is not currently in an overload condition and sending overload
   reports.  The reporting node is not allowed to change the overload
   abatement algorithm while the reporting node is in an overload
   condition.

   The individual features supported by the DOIC nodes are indicated in
   the OC-Feature-Vector AVP.  Any semantics associated with the
   features will be defined in extension specifications that introduce
   the features.

   The DCA mechanism must also support allow the scenario where the set of
   features supported by the sender of a request and by agents in the
   path of a request differ.  In this case, the agent updates the OC-
   Supported-Feature
   Supported-Features AVP to reflect the mixture of the two sets of
   supported features.

      Note: The logic to determine the content of the modified OC-Supported-
      Feature OC-
      Supported-Features AVP is out-of-scope for this specification and
      is left to implementation decisions.  Care must be taken not to
      introduce interoperability issues for downstream or upstream DOIC
      nodes.

3.3.  DOIC Overload Condition Reporting

   As with DOIC Capability Announcement, Overload Condition Reporting capability announcement, overload condition reporting
   uses new AVPs (Section 6.3) to indicate an overload condition.

   The OC-OLR AVP is referred to as an overload report.  The OC-OLR AVP
   includes the type of report, a sequence number, the length of time
   that the report is valid and abatement algorithm specific AVPs.

   Two types of overload reports are defined in this document, host
   reports and realm reports.

   A report of type host "HOST_REPORT" is sent to indicate the overload of a
   specific Diameter node for the application-id indicated in the
   transaction.  When receiving an OLR of type host, a reacting node
   applies overload abatement to what is referred to in this document as
   host-routed requests.  This is the set of requests that the reacting node knows
   will be served by a particular host, either due to the presence of a
   Destination-Host AVP, or by some other local knowledge on the part of
   the reacting node.  The reacting node applies overload abatement
   on those host-routed requests which the reacting node knows will be
   served by the server that matches the Origin-Host AVP of the received
   message that contained the received OLR of type host.

   Realm reports apply

   A report of type "REALM_REPORT" applies to realm-routed requests for
   a specific realm as indicated in the Destination-Realm AVP.

   This document assumes that there is a single source for realm-reports
   for a given realm, or that if multiple nodes can send realm reports,
   that each such node has full knowledge of the overload state of the
   entire realm.  A reacting node cannot distinguish between receiving
   realm-reports from a single node, or from multiple nodes.

      Note: Known issues exist if multiple sources for overload reports
      which apply to the same Diameter entity exist.  Reacting nodes
      have no way of determining the source and, as such, will treat
      them as coming from a single source.  Variance in sequence numbers
      between the two sources can then cause incorrect overload
      abatement treatment to be applied for indeterminate periods of
      time.

   Reporting nodes are responsible for determining the need for a
   reduction of traffic.  The method for making this determination is
   implementation specific and depend on the type of overload report
   being generated.  A host report, host-report, for instance, will generally be
   generated by tracking utilization of resources required by the host
   to handle transactions for the Diameter application.  A realm report
   will realm-report
   generally impact impacts the traffic sent to multiple hosts and, as such, will typically require
   requires tracking the capacity of the all servers
   able to handle for realm-routed requests
   for the application. application and realm.

   Once a reporting node determines the need for a reduction in traffic,
   it uses the DOIC defined AVPs to report on the condition.  These AVPs
   are included in answer messages sent or relayed by the reporting
   node.  The reporting node indicates the overload abatement algorithm
   that is to be used to handle the traffic reduction in the OC-
   Supported-Features AVP.  The OC-OLR AVP is used to communicate
   information about the requested reduction.

   Reacting nodes, upon receipt of an overload report, are responsible
   for applying the overload abatement algorithm to traffic impacted by
   the overload report.  The method used for that abatement is dependent on to determine the requests that
   are to receive overload abatement treatment is dependent on the
   abatement algorithm.  The loss abatement algorithm is defined in this
   document (Section 5).  Other abatement algorithms can be defined in
   extensions to the DOIC solutions.

   Two types of overload abatement treatment are defined, diversion and
   throttling.  Reacting nodes are responsible for determining which
   treatment is appropriate for individual requests.

   As the conditions that lead to the generation of the overload report
   change the reporting node can send new overload reports requesting
   greater reduction if the condition gets worse or less reduction if
   the condition improves.  The reporting node sends an overload report
   with a duration of zero to indicate that the overload condition has
   ended and need for use of the abatement algorithm to reduce traffic
   sent is no longer needed.

   The reacting node also determines when the overload report expires
   based on the OC-Validity-Duration AVP in the overload report and
   stops applying the abatement algorithm when the report expires.

3.4.  DOIC Extensibility

   The DOIC solution is designed to be extensible.  This extensibility
   is based on existing Diameter based extensibility mechanisms. mechanisms, along
   with the DOIC capability announcement mechanism.

   There are multiple categories of extensions that are expected.  This
   includes the definition of new overload abatement algorithms, the
   definition of new report types and new definitions of the scope definition of new scopes of
   messages impacted by an overload report.

   The DOIC solution uses the OC-Supported-Features AVP for DOIC nodes
   to communicate supported features.  The specific features supported
   by the DOIC node are indicated in the OC-Feature-Vector AVP.  DOIC
   extensions must that require new normative behavior define new values for
   the OC-Feature-Vector AVP.  DOIC extensions also have the ability to
   add new AVPs to the OC-
   Supported-Features OC-Supported-Features AVP, if additional
   information about the new feature is required.

   Reporting nodes use the OC-OLR AVP to communicate overload
   occurrences.  This AVP can also be extended to add new AVPs allowing
   a
   reporting nodes to communicate additional information about handling
   an overload condition.

   If necessary, new extensions can also define new top-level AVPs that are not
   part of the OC-Supported-Features and OC-OLR group AVPs.  It is,
   however, recommended that DOIC extensions use the OC-Supported-
   Features AVP and OC-OLR AVP to carry all DOIC related AVPs.

3.5.  Simplified Example Architecture

   Figure 1 illustrates the simplified architecture for Diameter
   overload information conveyance.

    Realm X                                  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'
             2)  <----------------------> <---------------------->
                 standard base protocol   standard base protocol
                 Diameter Application Y   Diameter Application Y

     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.

4.  Solution Procedures

   This section outlines the normative behavior associated with for the DOIC solution.

4.1.  Capability Announcement

   This section defines DOIC Capability Announcement (DCA) behavior.

4.1.1.  Reacting Node Behavior

   A reacting node MUST include the OC-Supported-Features AVP in all
   request messages.

   A reacting node
   requests.  It MAY include the OC-Feature-Vector AVP with an
   indication of AVP.  If it does so,
   it MUST indicate support for the loss "loss" algorithm.  A  If the reacting
   node MUST include the
   OC-Feature-Vector AVP is configured to indicate support for abatement algorithms features (including other algorithms)
   in addition to the loss algorithm.

   A reacting node SHOULD algorithm, it MUST indicate such support for all other DOIC features
   it supports.

      Not all DOIC features will necessarily apply to all transactions.
      For instance, there may be a future extension that only applies to
      session based applications.  A reacting node that supports this
      extension can choose to not include it for non session based
      applications. in
   an OC-Feature-Vector AVP.

   An OC-Supported-Features AVP in answer messages indicates there is a
   reporting node for the transaction.  The reacting node MAY take
   action
   action, for example creating state for some stateful abatement
   algorithm, based on the features indicated in the OC-Feature-Vector
   AVP.

      Note that the

      Note: The loss abatement algorithm is the only feature
      described in this document and it does not require action to be
      taken stateful
      behavior when there is an no active overload report.  This behavior
      is described in Section 4.2 and Section 5.

4.1.2.  Reporting Node Behavior

   Upon receipt of a request message, a reporting node determines if
   there is a reacting node for the transaction based on the presence of
   the OC-Supported-Features AVP. AVP in the request message.

   If the request message contains an OC-Supported-Features AVP then the a
   reporting node MUST include the OC-Supported-Features AVP in the
   answer message for that transaction.

   The

   A reporting node MUST NOT include the OC-Supported-Features AVP,
   OC-OLR OC-
   OLR AVP or any other overload control AVPs defined in extension
   drafts in response messages for transactions where the request
   message does not include the OC-Supported-Features AVP.  Lack of the
   OC-Supported-Features AVP in the request message indicates that there
   is no reacting node for the transaction.

   Based on the content of the OC-Supported-Features AVP in the request
   message, the

   A reporting node knows what overload control functionality is
   supported by the reacting node.  The reporting node then acts
   accordingly for the subsequent answer messages it initiates.

   The based on the content of the OC-
   Feature-Vector AVP in the request message.

   A reporting node MUST indicate support for one and only one abatement
   algorithm in the OC-Feature-Vector AVP.  The abatement algorithm included MUST be from the set of abatement algorithms
   contained in the request message's OC-Supported-Features AVP.  The
   abatement algorithm included
   selected MUST indicate the abatement algorithm the reporting node
   wants the reacting node to use when the reporting node enters an
   overload condition.

   For an ongoing overload state, a reacting node MUST keep the

   The abatement algorithm that was selected by MUST be from the reporting node set of abatement
   algorithms contained in further requests
   towards the request message's OC-Feature-Vector AVP.

   A reporting node.  The node that selects the loss algorithm may do so by
   including the OC-Feature-Vector AVP with an explicit indication of
   the loss algorithm, or it MAY omit OC-Feature-Vector.  If it selects
   a different algorithm, it MUST include the OC-Feature-Vector AVP with
   an explicit indication of the selected algorithm.

   For an ongoing overload condition, a reporting node SHOULD MUST NOT change
   the selected algorithm during a the period of time that it is in an
   overload condition and, as a result, is sending OC-OLR AVPs in answer
   messages.

   The reporting node MAY change the overload abatement algorithm
   indicated in the OC-Supported-Features AVP at any time as long as no
   previously sent OLRs may be active.

   The reporting node SHOULD indicate support for other DOIC features
   defined in extension drafts that it supports and that apply to the
   transaction.

      Note that not

      Note: Not all DOIC features will apply to all Diameter
      applications or deployment scenarios.  The features included in
      the OC-Feature-Vector AVP are based on local reporting node
      policy.

4.1.3.  Agent Behavior

   Diameter agents Agents that support DOIC MUST SHOULD ensure that all messages have
   the OC-Supporting-Features AVP.  If a message handled
   relayed by the DOIC agent does not include contain the OC-Supported-Features AVP then the DOIC
   agent inserts the AVP.  If the message already has the AVP then the
   agent either leaves it unchanged in

   A Diameter Agent SHOULD take on reacting node behavior for Diameter
   endpoints that do not support the relayed message or modifies
   it to reflect DOIC solution.  A Diameter Agent
   detects that a mixed set of Diameter endpoint does not support DOIC features.

   An agent MAY modify the reacting node
   behavior when there is no OC-Supported-Features AVP carried in answer
   messages. a request
   message.

   For instance, if the agent supports a superset Diameter Agent to be a reacting node for a non supporting
   Diameter endpoint, the Diameter Agent MUST include the OC-Supported-
   Features AVP in request messages it receives that do not contain the
   OC-Supported-Features AVP.

   A Diameter Agent SHOULD take on reporting node behavior for Diameter
   endpoints that do not support the DOIC solution.  A Diameter Agent
   detects that a Diameter endpoint does not support DOIC reporting node
   behavior when there is no OC-Supported-Features AVP in an answer
   message for a transaction that contained the OC-Supported-Features
   AVP in the request message.

   For a Diameter Agent to take on reporting node behavior for a non
   supporting Diameter endpoint the Diameter Agent MUST include the OC-
   Supported-Features AVP in answer messages it receives that do not
   contain the OC-Supported-Features AVP.

   As with a Diameter endpoint taking on reporting node behavior, a
   Diameter Agent MUST only include the OC-Supported-Features AVP in
   answer messages for transactions where the request message received
   by the Diameter Agent had an OC-Supported-Features AVP.

   If a request message already has the OC-Supported-Features AVP then a
   Diameter Agent MAY leave it unchanged in the relayed message or MAY
   modify it to reflect the features appropriate for the transaction.

      For instance, if the agent supports a superset of the features
      reported by the reacting node then the agent might choose, based
      on local policy, to advertise that superset of features to the
      reporting node.

   If the agent modifies Diameter Agent changes the OC-Supported-Features AVP sent to the
      reporting node in a
   request message then it might is likely it will also need to modify the OC-Supported-
      Features OC-
   Supported-Features AVP sent to a reacting node in the subsequent answer
      message, as it cannot send an indication of support message for features
      that are not supported by the reacting node.

      Editor's note: There is an open issue on the wording around agent
      behavior in this case that needs transaction.  As
   such, a Diameter Agent MAY modify the OC-Supported-Features AVP
   carried in answer messages.

   When making changes to be resolved prior the OC-Supported-Features AVP the Diameter
   Agent needs to finishing
      this document. ensure that there is no ambiguity in DOIC behavior for
   both upstream and downstream DOIC nodes.

4.2.  Overload Report Processing

4.2.1.  Overload Control State

   Both reacting and reporting nodes maintain Overload Control State
   (OCS) for active overload conditions.  The following sections define
   behavior associated with that OCS.

4.2.1.1.  Overload Control State for Reacting Nodes

   A reacting node SHOULD maintain the following OCS per supported
   Diameter application:

   o  A host-type OCS entry for each Destination-Host to which it sends
      host-type requests and

   o  A realm-type OCS entry for each Destination-Realm to which it
      sends realm-type requests.

   A host-type OCS entry is identified by the pair of Application-Id application-id and
   Host-Id.
   the node's DiameterIdentity.

   A realm-type OCS entry is identified by the pair of Application-Id application-d and Realm-Id.
   realm.

   The host-type and realm-type OCS entries MAY include the following
   information (the actual information stored is an implementation
   decision):

   o  Sequence number (as received in OC-OLR)

   o  Time of expiry (derived from OC-Validity-Duration AVP received in
      the OC-OLR AVP and time of reception of the message carrying OC-
      OLR AVP)

   o  Selected Abatement Algorithm (as received in OC-Supported-Features the OC-Supported-
      Features AVP)

   o  Abatement Algorithm specific input data (as received within in the OC-OLR
      AVP, for example, OC-Reduction-Percentage for the Loss abatement
      algorithm)

4.2.1.2.  Overload Control State for Reporting Nodes

   A reporting node SHOULD maintain OCS entries per supported Diameter
   application, per supported (and eventually selected) Abatement
   Algorithm and per report-type.

   An OCS entry is identified by the pair of Application-Id and
   Abatement Algorithm.

   The OCS entry for a given pair tuple of Application Application-Id, Report-
   Type and Abatement Algorithm and MAY include the following
   information (the actual information stored is an implementation
   decision):

   o  Report type

   o  Sequence number

   o  Validity Duration

   o  Expiration Time

   o  Algorithm specific input data (for example, the Reduction
      Percentage for the Loss Abatement Algorithm)

4.2.1.3.  Reacting Node Maintenance of Overload Control State

   When a reacting node receives an OC-OLR AVP, it MUST determine if it
   is for an existing or new overload condition.

      Note: For the remainder of this section the term OLR referres refers to the
      combination of the contents of the received OC-OLR AVP and the
      abatement algorithm indicated in the received OC-Supported-
      Features AVP.

   When receiving an answer message with multiple OLRs or different
   types, a reporting node MUST process each received OLR.

   When receiving an OC-OLR AVPs with unknown values, a reacting node
   SHOULD be silently discarded by reacting nodes and the event SHOULD
   be logged.

   The OLR is for an existing overload condition if the a reacting node has
   an OCS that matches the received OLR.

   For a host report-type host-report this means it matches the app-id application-id and host-id the
   host's DiameterIdentity in an existing host OCS entry.

   For a realm report-type realm-report this means it matches the app-id application-id and realm-id the
   realm in an existing realm OCS entry.

   If the OLR is for an existing overload condition then it a reacting node
   MUST determine if the OLR is a retransmission or an update to the
   existing OLR.

   If the sequence number for the received OLR is greater than the
   sequence number stored in the matching OCS entry then the a reacting node
   MUST update the matching OCS entry.

   If the sequence number for the received OLR is less than or equal to
   the sequence number in the matching OCS entry then the a reacting node
   MUST silently ignore the received OLR.  The matching OCS MUST NOT be
   updated in this case.

   If the received OLR is for a new overload condition then the a reacting
   node MUST generate a new OCS entry for the overload condition.

   For a host report-type host-report this means it a reacting node creates on OCS entry
   with the
   app-id of the application-id in the received message and host-id DiameterIdentity
   of the Origin-Host in the received message.

      Note: This solution assumes that the Origin-Host AVP in the answer
      message included by the reporting node is not changed along the
      path to the reacting node.

   For a realm report-type realm-report this means it a reacting node creates on OCS entry
   with the
   app-id of the application-id in the received message and realm-id realm of the
   Origin-Realm in the received message.

   If the received OLR contains a validity duration of zero ("0") then
   the a
   reacting node MUST update the OCS entry as being expired.

      Note that it

      Note: It is not necessarily appropriate to delete the OCS entry,
      as there is recommended behavior that the reacting node slowly
      returns to full traffic when ending an overload abatement period.

   The reacting node does not delete an OCS when receiving an answer
   message that does not contain an OC-OLR AVP (i.e. absence of OLR
   means "no change").

4.2.1.4.  Reporting Node Maintenance of Overload Control State

   A reporting node SHOULD create a new OCS entry when entering an
   overload condition.

      Note: If the a reporting node knows through absence of the OC-Supported-
      Features OC-
      Supported-Features AVP in received messages that there are no
      reacting nodes supporting DOIC then the reporting node can choose
      to not create OCS entries.

   When generating a new OCS entry the sequence number MAY SHOULD be set to any
   value if there is no unexpired overload report for previous overload
   conditions sent to any reacting node for the same application and
   report-type.
   zero ("0").

   When generating sequence numbers for new overload conditions, the new
   sequence number MUST be greater than any sequence number in an active
   (unexpired) overload report for the same application and report-type
   previously sent by the reporting node.  This property MUST hold over
   a reboot of the reporting node.

   The

      Note: One way of addressing this over a reboot of a reporting node
      is to use a time stamp for the first overload condition that
      occurs after the report and to start using sequence numbers of
      zero for subsequent overload conditions.

   A reporting node MUST update an OCS entry when it needs to adjust the
   validity duration of the overload condition at reacting nodes.

      For instance, if the a reporting node wishes to instruct reacting
      nodes to continue overload abatement for a longer period of time
      that
      than originally communicated.  This also applies if the reporting
      node wishes to shorten the period of time that overload abatement
      is to continue.

   A reporting node MUST NOT update the abatement algorithm in an active
   OCS entry.

   A reporting node MUST update an OCS entry when it wishes to adjust
   any abatement algorithm specific parameters, including the reduction
   percentage used for the Loss abatement algorithm.

      For instance, if the a reporting node wishes to change the reduction
      percentage either higher, if the overload condition has worsened,
      or lower, if the overload condition has improved, then the
      reporting node would update the appropriate OCS entry.

   The

   A reporting node MUST update the sequence number associated with the
   OCS entry anytime the contents of the OCS entry are changed.  This
   will result in a new sequence number being sent to reacting nodes,
   instructing the reacting nodes to process the OC-OLR AVP.

   A reporting node SHOULD update an OCS entry with a validity duration
   of zero ("0") when the overload condition ends.

      Note: If the a reporting node knows that the OCS entries in the
      reacting nodes are near expiration then the reporting node can might
      decide not to
      delete the OCS entry.

   The send an OLR with a validity duration of zero.

   A reporting node MUST keep an OCS entry with a validity duration of
   zero ("0") for a period of time long enough to ensure that any non-
   expired reacting node's OCS entry created as a result of the overload
   condition in the reporting node is deleted.

4.2.2.  Reacting Node Behavior

   When a reacting node sends a request it MUST determine if that
   request matches an active OCS.

   If the request matches and an active OCS then the reacting node MUST
   apply abatement treatment on the request.  The abatement treatment
   applied depends on use
   the overload abatement algorithm stored indicated in the OCS. OCS to determine if
   the request is to receive overload abatement treatment.

   For the Loss abatement algorithm defined in this specification, see
   Section 5 for the overload abatement algorithm logic applied.

   If the overload abatement algorithm selects the request for overload
   abatement treatment then the reacting node MUST apply overload
   abatement treatment on the request.  The abatement treatment applied
   depends on the context of the request.

   If the request is a host-routed request then the reacting node SHOULD
   apply throttling abatement treatment to the request.

   If the request is a realm-routed request then the reacting node
   SHOULD apply diversion abatement treatment to the request.

   If the overload abatement treatment results in throttling of the
   request and if the reacting node is an agent then the agent MUST send
   an appropriate error as defined in section Section 7.

   The behavior of reacting nodes that are Diameter endpoints when
   throttling requests depends on the application and is outside the
   scope of this specification.

   In the case that the OCS entry indicated no traffic was to be sent to
   the overloaded entity and the validity duration expires or has a
   validity duration of zero ("0"), meaning that it the reporting node has
   explicitly signaled the end of the overload condition then overload
   abatement associated with the overload abatement MUST be ended in a
   controlled fashion.

4.2.3.  Reporting Node Behavior

   The operation on the reporting node is straight forward.

   If there is an active OCS entry then the a reporting node SHOULD include
   the OC-OLR AVP in all answer messages to requests that contain the
   OC-Supported-Features AVP and that match the active OCS entry.

      Note: A request matches if the application-id in the request
      matches the application-id in any active OCS entry and if the
      report-type in the OCS entry matches a report-type supported by
      the reporting node as indicated in the OC-Supported-Features AVP.

   The contents of the OC-OLR AVP MUST contain all information necessary
   for the abatement algorithm indicated in the OC-Supported-Features
   AVP that is also included in depend on the answer message. selected algorithm.

   A reporting node MAY choose to not resend an overload report to a
   reacting node if it can guarantee that this overload report is
   already active in the reacting node.

      Note -

      Note: In some cases (e.g. when there are one or more agents in the
      path between reporting and reacting nodes, or when overload
      reports are discarded by reacting nodes) the a reporting node may not
      be able to guarantee that the reacting node has received the
      report.

   A reporting node MUST NOT send overload reports of a type that has
   not been advertised as supported by the reacting node.

      Note that a

      Note: A reacting node implicitly advertises support for the host
      and realm report types by including the OC-Supported-Features AVP
      in the request.  Support for other report types must will be explicitly
      indicated by new feature bits in the OC-Feature-Vector AVP.

   A reporting node MAY rely on the OC-Validity-Duration AVP values for
   the implicit overload control state cleanup on the reacting node.
   However, it is RECOMMENDED that the reporting node always explicitly
   indicates the end of a overload condition.

   The

   A reporting node SHOULD explicitly indicate the end of an overload
   occurrence by sending a new OLR with OC-Validity-Duration set to a
   value of zero ("0").  The reporting node SHOULD ensure that all
   reacting nodes receive the updated overload report.

      Note: All OLRs sent have an expiration time calculated by adding
      the validity-duration contained in the OLR to the time the message
      was sent.  Transit time for the OLR can be safely ignored.  The
      reporting node can ensure that all reacting nodes have received
      the OLR by continuing to send it in answer messages until the
      expiration time for all OLRs sent for that overload condition have
      expired.

   When a reporting node sends an OLR, it effectively delegates any
   necessary throttling to downstream nodes.  Therefore,  If the reporting node SHOULD NOT apply throttling to also
   locally throttles the same set of messages to which the
   OLR applies.  That is, messages, the same candidate set overall number of messages SHOULD NOT
   be
   throttled multiple times. requests may be higher than intended.  Therefore, before
   applying local message throttling, a reporting node needs to check if
   these messages match existing OCS entries, indicating that these
   messages have survived throttling applied by downstream nodes that
   have received the related OLR.

   However, when even if the set of messages match existing OCS entries, the
   reporting node sends and OLR downstream, it MAY can still be responsible to apply other abatement methods such as
   diversion.  The reporting node might also need to throttle requests
   for reasons other then than overload.  For example, an agent or server
   might have a configured rate limit for each client, and throttle
   requests that exceed that limit, even if such requests had already
   been candidates for throttling by downstream nodes.

   This document assumes that there is a single source for realm-reports
   for a given realm, or that if multiple nodes can send realm reports,
   that each such  The reporting
   node also has full knowledge of the overload state of option to send new OLRs requesting greater
   reductions in traffic, reducing the
   entire realm. need for local throttling.

   A reacting reporting node cannot distinguish between receiving
   realm-reports from SHOULD decrease requested overload abatement
   treatment in a single node, or from multiple nodes.

      Editor's Note: There is not yet consensus on the above two
      paragraphs.  Two alternatives are under consideration --
      synchronization of sequence numbers and attribution of reports.
      If no consensus is reached then it will be left controlled fashion to be addressed as
      an extension. avoid oscillations in traffic.

4.3.  Protocol Extensibility

   The overload control DOIC solution can be extended, e.g. with extended.  Types of potential extensions
   include new traffic abatement algorithms, new report types or other
   new functionality.

   When defining a new extension that requires new normative behavior,
   the specification MUST define a new feature bit MUST be defined for the OC-Feature-Vector. OC-Feature-
   Vector.  This feature bit is used to communicate support for the new
   feature.

   The extension MAY define new AVPs for use in DOIC Capability
   Announcement and for use in DOIC Overload reporting.  These new AVPs
   SHOULD be defined to be extensions to the OC-Supported-Features and
   OC-OLR AVPs defined in this document.

   It should be noted that

   [RFC6733] defined Grouped AVP extension mechanisms apply.  This
   allows, for example, defining a new feature that is mandatory to be
   understood even when piggybacked on an existing application.

   The handling of feature bits in the OC-Feature-Vector AVP that are
   not associated with overload abatement algorithms MUST be specified
   by the extensions that define the features.

   When defining new report type values, the corresponding specification
   MUST define the semantics of the new report types and how they affect
   the OC-OLR AVP handling.  The specification MUST also reserve a
   corresponding new feature bit in the OC-Feature-Vector AVP.

   The OC-OLR AVP can be expanded with optional sub-AVPs only if a
   legacy DOIC implementation can safely ignore them without breaking
   backward compatibility for the given OC-Report-Type AVP value.  If
   the new sub-AVPs imply new semantics for handling the indicated
   report type, then a new OC-Report-Type AVP value MUST be defined.

   Documents that introduce new report types MUST describe any
   limitations on their use across non-supporting agents.

   New features (feature bits in the OC-Feature-Vector AVP) and report
   types (in the OC-Report-Type AVP) MUST be registered with IANA.  As
   with any Diameter specification, RFC6733 requires all new AVPs MUST also to be
   registered with IANA.  See Section 8 for the required procedures.

5.  Loss Algorithm

   This section documents the Diameter overload loss abatement
   algorithm.

5.1.  Overview

   The DOIC specification supports the ability for multiple overload
   abatement algorithms to be specified.  The abatement algorithm used
   for any instance of overload is determined by the Diameter Overload
   Capability Announcement process documented in Section 4.1.

   The loss algorithm described in this section is the default algorithm
   that must be supported by all Diameter nodes that support DOIC.

   The loss algorithm is designed to be a straightforward and stateless
   overload abatement algorithm.  It is used by reporting nodes to
   request a percentage reduction in the amount of traffic sent.  The
   traffic impacted by the requested reduction depends on the type of
   overload report.

   Reporting nodes use a strategy of applying abatement logic to the
   requested percentage of request messages sent (or handled in the case
   of agents) by the reacting node that are impacted by the overload
   report.

   From a conceptual level, the logic at the reacting node could be
   outlined as follows.

   1.  An overload report is received and the associated overload state OCS is either
       saved or updated (if required) by the reacting node.

   2.  A new Diameter request is generated by the application running on
       the reacting node.

   3.  The reacting node determines that an active overload report
       applies to the request, as indicated by the corresponding OCS
       entry.

   4.  The reacting node determines if overload abatement treatment
       should be applied to the request.  One approach that could be
       taken for each request is to select a random number between 1 and
       100.  If the random number is less than the indicated reduction
       percentage then the request is given abatement treatment,
       otherwise the request is given normal routing treatment.

5.2.  Reporting Node Behavior

   The method a reporting nodes node uses to determine the amount of traffic
   reduction required to address an overload condition is an
   implementation decision.

   When a reporting node that has selected the loss abatement algorithm
   determines the need to request a traffic reduction in traffic, it includes an OC-
   OLR
   OC-OLR AVP in response messages as described in Section 4.2.3.

   The

   When sending the OC-OLR AVP, the reporting node MUST indicate a
   percentage reduction in the OC-
   Reduction-Percentage OC-Reduction-Percentage AVP.

   The reporting node MAY change the reduction percentage in subsequent
   overload reports.  When doing so the reporting node must conform to
   overload report handing specified in Section 4.2.3.

   When the reporting node determines it no longer needs a reduction in
   traffic the reporting node SHOULD send an overload report indicating
   the overload report is no longer valid, as specified in
   Section 4.2.3.

5.3.  Reacting Node Behavior

   The method

5.3.  Reacting Node Behavior

   The method a reacting node uses to determine which request messages
   are given abatement treatment is an implementation decision.

   When receiving an OC-OLR in an answer message where the algorithm
   indicated in the OC-Supported-Features AVP is the loss algorithm, the
   reacting node MUST apply abatement treatment to the requested
   percentage of request messages sent.

      Note: the The loss algorithm is a stateless algorithm.  As a result,
      the reacting node does not guarantee that there will be an
      absolute reduction in traffic sent.  Rather, it guarantees that
      the requested percentage of new requests will be given abatement
      treatment.

   When applying overload abatement treatment for the load abatement
   algorithm, the reacting node MUST abate, either by throttling or
   diversion, abate the requested percentage of
   requests that would have otherwise been sent to the reporting host or
   realm.

   If reacting node 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 reacting node sending the traffic
   should be conservative and, for example, first send "probe" messages
   to learn the overload condition of the overloaded node before
   converging to any traffic amount/rate decided by the sender.  Similar
   concerns apply in all cases when the overload report times out unless
   the previous overload report stated 0 percent reduction.

   If the reacting node does not receive an OLR in messages sent to the
   formerly overloaded node then the reacting node SHOULD slowly
   increase the rate of traffic sent to the overloaded node.

   It

   When an active overload report expires, it is suggested that the
   reacting node progressively decrease the amount of traffic given
   abatement treatment by 20% each second treatment, until the reduction is completely removed and no
   traffic is given abatement treatment.

      The goal of this behavior is to reduce the probability of overload
      condition thrashing where an immediate transition from 100%
      reduction to 0% reduction results in the reporting node moving
      quickly back into an overload condition.

6.  Attribute Value Pairs

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

   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.  It is the responsibility of the Diameter application
   designers to define how overload control mechanisms works on that
   application.

6.1.  OC-Supported-Features AVP

   The OC-Supported-Features AVP (AVP code TBD1) is type of type Grouped and
   serves two purposes.  First, it announces a node's support for the
   DOIC solution in general.  Second, it contains the description of the
   supported DOIC features of the sending node.  The OC-Supported-
   Features AVP MUST be included in every Diameter request message a
   DOIC supporting node sends.

      OC-Supported-Features ::= < AVP Header: TBD1 >
                                [ OC-Feature-Vector ]
                              * [ AVP ]

   The OC-Feature-Vector sub-AVP is used to announce the DOIC features
   supported by the DOIC node, in the form of a flag bits flag-bits field in which
   each bit announces one feature or capability supported by the node
   (see Section 6.2).  The absence of the OC-Feature-Vector AVP
   indicates that only the default traffic abatement algorithm described
   in this specification is supported.

6.2.  OC-Feature-Vector AVP

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

   The OC-Feature-Vector sub-AVP is used to announce the DOIC features
   supported by the DOIC node, in the form of a flag-bits field in which
   each bit announces one feature or capability supported by the node
   (see Section 6.2).  The absence of the OC-Feature-Vector AVP
   indicates that only the default traffic abatement algorithm described
   in this specification is supported.

   The following capabilities are defined in this document:

   OLR_DEFAULT_ALGO (0x0000000000000001)

      When this flag is set by the a DOIC reacting node it means that
      the default traffic abatement (loss) algorithm is supported.  When
      this flag is set by a DOIC reporting node it means that the loss
      algorithm will be used for requested overload abatement.

6.3.  OC-OLR AVP

   The OC-OLR AVP (AVP code TBD2) is type of type Grouped and contains the
   information necessary to convey an overload report on an overload
   condition at the reporting node.  The OC-OLR AVP does not explicitly
   contain all information needed by the reacting node to decide whether
   a subsequent request must undergo a throttling process with abatement using the received
   reduction percentage.  The value of the OC-Report-Type AVP within the
   OC-OLR AVP indicates which implicit information is relevant for this
   decision (see Section 6.6).  The application the OC-OLR AVP applies
   to is the same as the Application-Id found in the Diameter message
   header.  The host or realm the OC-OLR AVP concerns is determined from
   the Origin-Host AVP and/or Origin-Realm AVP found in the
   encapsulating Diameter command.  The OC-OLR AVP is intended to be
   sent only by a reporting node.

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

   Note that if a Diameter command were to 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 by reacting nodes
   and the event SHOULD be logged.

6.4.  OC-Sequence-Number AVP

   The OC-Sequence-Number AVP (AVP code TBD3) is type of type Unsigned64.
   Its usage in the context of overload control is described in
   Section 4.2.

   From the functionality point of view, the OC-Sequence-Number AVP MUST
   be is
   used as a non-volatile increasing counter for a sequence of overload
   reports between two DOIC nodes for the same overload occurrence.  The
   sequence number is only required to be unique between two DOIC nodes.
   Sequence numbers are treated in a uni-
   directional uni-directional manner, i.e. two
   sequence numbers on each direction between two DOIC nodes are not
   related or correlated.

6.5.  OC-Validity-Duration AVP

   The OC-Validity-Duration AVP (AVP code TBD4) is type of type Unsigned32
   and indicates in milliseconds the validity time of the overload
   report.  The number of milliseconds is measured after reception of
   the first OC-OLR AVP with a given value of OC-Sequence-Number AVP.
   The default value for the OC-Validity-Duration AVP is 5000 (i.e., 5 30000 (i.e.; 30
   seconds).  When the OC-Validity-Duration AVP is not present in the
   OC-OLR AVP, the default value applies.  Validity duration with values
   above 86400 (i.e.; 24 hours) MUST NOT be used.  Invalid duration
   values are treated as if the OC-Validity-Duration

6.6.  OC-Report-Type AVP were not
   present and result in the default value being used.

   Editor's note: There

   The OC-Report-Type AVP (AVP code TBD5) is an open discussion on whether to have an
   upper limit on the OC-Validity-Duration value, beyond that which can
   be indicated by an Unsigned32.

   A timeout of the overload report has specific concerns that need to
   be taken into account by the DOIC node acting on the earlier received
   overload report(s).  Section 6.7 discusses the impacts of timeout in
   the scope of the traffic abatement algorithms.

6.6.  OC-Report-Type AVP

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

   HOST_REPORT 0  A host report.  The overload report is for a host.  Overload abatement
      treatment should apply applies to requests host-routed requests.

   REALM_REPORT 1  The overload report is for which all of the following conditions are true:

      Either the Destination-Host a realm.  Overload
      abatement treatment applies to realm-routed requests.

6.7.  OC-Reduction-Percentage AVP

   The OC-Reduction-Percentage AVP (AVP code TBD8) is present in the request and its
      value matches the value of type Unsigned32
   and describes the Origin-Host AVP percentage of the received
      message traffic that contained the OC-OLR AVP; or the Destination-Host sender is
      not present in the request but the value of the peer identity
      associated with the connection used
   requested to reduce, compared to what it otherwise would send.  The
   OC-Reduction-Percentage AVP applies to send the request matches the value of default (loss) algorithm
   specified in this specification.  However, the Origin-Host AVP of the received message that
      contained can be reused for
   future abatement algorithms, if its semantics fit into the OC-OLR AVP. new
   algorithm.

   The value of the Destination-Realm Reduction-Percentage AVP in the request matches the is between zero (0) and one
   hundred (100).  Values greater than 100 are ignored.  The value of the Origin-Realm AVP of the received message
   100 means that
      contained all traffic is to be throttled, i.e. the OC-OLR AVP. reporting
   node is under a severe load and ceases to process any new messages.
   The value of 0 means that the Application-ID reporting node is in a stable state and
   has no need for the Diameter Header of the
      request matches the reacting node to apply any traffic abatement.
   The default value of the Application-ID of the Diameter
      Header of the received message that contained the OC-OLR AVP.

   1  A realm report.  The overload treatment should apply to requests
      for which all of OC-Reduction-Percentage AVP is 0.  When the following conditions are true:

      The Destination-Host
   OC-Reduction-Percentage AVP is absent not present in the requestand the value of
      the peer identity associated with the connection used to send the
      request does not match a server that could serve overload report,
   the request.

      The default value of the Destination-Realm applies.

6.8.  Attribute Value Pair flag rules
                                                         +---------+
                                                         |AVP flag |
                                                         |rules    |
                                                         +----+----+
                              AVP   Section              |    |MUST|
       Attribute Name         Code  Defined  Value Type  |MUST| NOT|
      +--------------------------------------------------+----+----+
      |OC-Supported-Features  TBD1  6.1      Grouped     |    | V  |
      +--------------------------------------------------+----+----+
      |OC-OLR                 TBD2  6.3      Grouped     |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Sequence-Number     TBD3  6.4      Unsigned64  |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Validity-Duration   TBD4  6.5      Unsigned32  |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Report-Type         TBD5  6.6      Enumerated  |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Reduction                                      |    |    |
      |  -Percentage          TBD8  6.7      Unsigned32  |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Feature-Vector      TBD6  6.2      Unsigned64  |    | V  |
      +--------------------------------------------------+----+----+

   As described in the request matches the
      value of Diameter base protocol [RFC6733], the Origin-Realm M-bit usage
   for a given AVP of the received message that
      contained the OC-OLR AVP.

      The value of the Application-ID in a given command may be defined by the
   application..

7.  Error Response Codes

   When a DOIC node rejects a Diameter Header of the request matches due to overload, the value of DOIC
   node MUST select an appropriate error response code.  This
   determination is made based on the Application-ID probability of the Diameter
      Header of the received message that contained the OC-OLR AVP.

   The OC-Report-Type AVP is envisioned to be useful for situations
   where request
   succeeding if retried on a reacting different path.

   A reporting node needs rejecting a Diameter request due to apply different an overload treatments
   for
   condition SHOULD send a DIAMETER-TOO-BUSY error response, if it can
   assume that the same request may succeed on a different overload contexts.  For example, path.

   If a reporting node knows or assumes that the reacting node(s)
   might need to throttle differently requests sent to same request will not
   succeed on a specific server
   (identified by different path, DIAMETER_UNABLE_TO_COMPLY error response
   SHOULD be used.  Retrying would consume valuable resources during an
   occurrence of overload.

      For instance, if the request arrived at the reporting node without
      a Destination-Host AVP in then the reporting node might determine
      that there is an alternative Diameter node that could successfully
      process the request) request and requests that can retrying the transaction would not
      negatively impact the reporting node.  DIAMETER_TOO_BUSY would be handled by any server
      sent in this case.

      If the request arrived at the reporting node with a realm.

6.7.  OC-Reduction-Percentage Destination-
      Host AVP

   The OC-Reduction-Percentage AVP (AVP code TBD8) is type of Unsigned32
   and describes the percentage of populated with its own Diameter identity then the traffic
      reporting node can assume that retrying the sender is
   requested to reduce, compared to what it otherwise request would send.  The
   OC-Reduction-Percentage AVP applies result
      in it coming to the default (loss) algorithm
   specified same reporting node.
      DIAMETER_UNABLE_TO_COMPLY would be sent in this specification.  However, case.

      A second example is when an agent that supports the AVP can be reused for
   future abatement algorithms, if its semantics fit into DOIC solution
      is performing the new
   algorithm.

   The value role of the Reduction-Percentage AVP is between zero (0) and one
   hundred (100).  Values greater than 100 a reacting node for a non supporting
      client.  Requests that are ignored.  The value rejected as a result of
   100 means that all traffic is to DOIC throttling
      by the agent in this scenario would generally be throttled, i.e. rejected with a
      DIAMETER_UNABLE_TO_COMPLY response code.

8.  IANA Considerations

8.1.  AVP codes

   New AVPs defined by this specification are listed in Section 6.  All
   AVP codes are allocated from the reporting
   node is 'Authentication, Authorization, and
   Accounting (AAA) Parameters' AVP Codes registry.

8.2.  New registries

   Two new registries are needed under a severe load the 'Authentication,
   Authorization, and ceases to process any Accounting (AAA) Parameters' registry.

   A new messages. "Overload Control Feature Vector" registry is required.  The value of 0 means
   registry must contain the following:

      Feature Vector Value

      Specification - the specification that defines the reporting node is in a stable state and
   has no need new value.

   See Section 6.2 for the reacting node to apply any traffic abatement.
   The default value of initial Feature Vector Value in the OC-Reduction-Percentage AVP registry.
   This specification is 0.  When the
   OC-Reduction-Percentage AVP is not present in specification defining the overload report, value.  New
   values can be added into the default value applies.

6.8.  Attribute registry using the Specification
   Required policy.  [RFC5226].

   A new "Overload Report Type" registry is required.  The registry must
   contain the following:

      Report Type Value Pair flag rules

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

      Specification - the specification that defines the new value.

   See Section              |    |MUST|
       Attribute Name         Code  Defined  Value Type  |MUST| NOT|
      +--------------------------------------------------+----+----+
      |OC-Supported-Features  TBD1  x.x      Grouped     |    | V  |
      +--------------------------------------------------+----+----+
      |OC-OLR                 TBD2  x.x      Grouped     |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Sequence-Number     TBD3  x.x      Unsigned64  |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Validity-Duration   TBD4  x.x      Unsigned32  |    | V  |
      +--------------------------------------------------+----+----+
      |OC-Report-Type         TBD5  x.x      Enumerated  |    | V  |
      +--------------------------------------------------+----+----+
      |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 6.2 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 initial assignment in newly
   defined Diameter applications, the DOC related AVPs SHOULD have registry.  New
   types can be added using the
   M-bit set.

7.  Error Response Codes

   When a Specification Required policy [RFC5226].

9.  Security Considerations

   DOIC node rejects a gives Diameter request due to overload, nodes the DOIC
   node MUST select an appropriate error response code. ability to request that downstream
   nodes send fewer Diameter requests.  Nodes do this by exchanging
   overload reports that directly effect this reduction.  This
   determination exchange
   is made based on the probability potentially subject to multiple methods of attack, and has the request
   succeeding if retried on
   potential to be used as a different path.

   A reporting node rejecting Denial-of-Service (DoS) attack vector.

   Overload reports may contain information about the topology and
   current status of a Diameter request due network.  This information is
   potentially sensitive.  Network operators may wish to an control
   disclosure of overload
   condition SHOULD send a DIAMETER-TOO-BUSY error response, if it can
   assume that reports to unauthorized parties to avoid its
   use for competitive intelligence or to target attacks.

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

9.1.  Potential Threat Modes

   The Diameter protocol involves transactions in the same request form of requests
   and answers exchanged between clients and servers.  These clients and
   servers may succeed on a different path.

   If be peers, that is, they may share a reporting node knows direct transport
   (e.g.  TCP or SCTP) connection, or assumes that the same request will not
   succeed on a different path, DIAMETER_UNABLE_TO_COMPLY error response
   SHOULD be used.  Retrying would consume valuable resources during an
   occurrence messages may traverse one or
   more intermediaries, known as Diameter Agents.  Diameter nodes use
   TLS, DTLS, or IPsec to authenticate peers, and to provide
   confidentiality and integrity protection of overload.

      For instance, if traffic between peers.
   Nodes can make authorization decisions based on the request arrived peer identities
   authenticated at the reporting node without
      a Destination-Host AVP then the reporting node might determine
      that there is transport layer.

   When agents are involved, this presents an alternative effectively transitive
   trust model.  That is, a Diameter node client or server can authorize an
   agent for certain actions, but it must trust that could successfully
      process the request agent to make
   appropriate authorization decisions about its peers, and that retrying the transaction would not
      negatively impact the reporting node.  DIAMETER_TOO_BUSY would be
      sent in this case.

      For instance, if the request arrived so on.
   Since confidentiality and integrity protection occurs at the reporting node with
   transport layer, agents can read, and perhaps modify, any part of a
      Destination-Host AVP populated with its own
   Diameter identity then
      the reporting node can assume that retrying the request would
      result in it coming message, including an overload report.

   There are several ways an attacker might attempt to exploit the same reporting node.
      DIAMETER_UNABLE_TO_COMPLY would be sent in
   overload control mechanism.  An unauthorized third party might inject
   an overload report into the network.  If this case.

      A second example third party is when upstream
   of an agent agent, and that supports agent fails to apply proper authorization
   policies, downstream nodes may mistakenly trust the DOIC solution report.  This
   attack is performing at least partially mitigated by the role of a reacting node for a non supporting
      client.  Requests assumption that are rejected as a result nodes
   include overload reports in Diameter answers but not in requests.
   This requires an attacker to have knowledge of DOIC throttling
      by the agent original request
   in this scenario order to construct an answer.  Such an answer would generally be rejected with also need to
   arrive at a
      DIAMETER_UNABLE_TO_COMPLY Diameter node via a protected transport connection.
   Therefore, implementations MUST validate that an answer containing an
   overload report is a properly constructed response code.

8.  IANA Considerations

8.1.  AVP codes

   New AVPs defined by this specification are listed in Section 6.  All
   AVP codes allocated from to a pending
   request prior to acting on the 'Authentication, Authorization, overload report, and
   Accounting (AAA) Parameters' AVP Codes registry.

8.2.  New registries

   Two new registries are needed under that the 'Authentication,
   Authorization, and Accounting (AAA) Parameters' registry.

   Section 6.2 defines a new "Overload Control Feature Vector" registry
   including the initial assignments.  New values can be added into the
   registry using the Specification Required policy [RFC5226].  See
   Section 6.2 answer
   was received via an appropriate transport connection.

   A similar attack involves a compromised but otherwise authorized node
   that sends an inappropriate overload report.  For example, a server
   for the initial assignment in the registry.

   Section 6.6 defines realm "example.com" might send an overload report indicating
   that a new "Overload Report Type" registry with its
   initial assignments.  New types can be added using competitor's realm "example.net" is overloaded.  If other
   nodes act on the Specification
   Required policy [RFC5226].

9.  Security Considerations

   This mechanism gives Diameter 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 ability report or forwarding the report to request other peers.
   For example, an overload report from a peer that
   downstream nodes send fewer Diameter requests.  Nodes do this applies to a realm
   not handled by
   exchanging overload reports that directly affect this reduction. peer is suspect.

      This exchange attack is potentially subject to multiple methods of attack,
   and has partially mitigated by the potential to be used fact that the
      application, as well as host and realm, for a Denial-of-Service (DoS) attack
   vector.

   Overload reports may contain information about given OLR is
      determined implicitly by respective AVPs in the topology and
   current status enclosing answer.
      If a reporting node modifies any of those AVPs, the enclosing
      transaction will also be affected.

9.2.  Denial of Service Attacks

   Diameter overload reports, especially realm-reports, can cause a node
   to cease sending some or all Diameter network. requests for an extended
   period.  This information makes them a tempting vector for DoS attacks.
   Furthermore, since Diameter is
   potentially sensitive.  Network operators may wish to control
   disclosure almost always used in support of overload reports other
   protocols, a DoS attack on Diameter is likely to unauthorized parties impact those
   protocols as well.  Therefore, Diameter nodes MUST NOT honor or
   forward OLRs received from peers that are not trusted to avoid its send them.

   An attacker might use for competitive intelligence or the information in an OLR to target assist in DoS
   attacks.

   Diameter does not include features  For example, an attacker could use information about
   current overload conditions to provide end-to-end
   authentication, integrity protection, time an attack for maximum effect, or confidentiality.  This may
   cause complications when sending
   use subsequent overload reports between non-
   adjacent nodes.

9.1.  Potential Threat Modes

   The Diameter protocol involves transactions in as a feedback mechanism to learn the form
   results of requests
   and answers exchanged between clients and servers.  These clients and
   servers may be peers, that is,they may share a direct transport (e.g.
   TCP or SCTP) connection, previous or ongoing attack.  Operators need the messages may traverse one or more
   intermediaries, known as Diameter Agents. ability
   to ensure that OLRs are not leaked to untrusted parties.

9.3.  Non-Compliant Nodes

   In the absence of an overload control mechanism, Diameter nodes use TLS,
   DTLS, or IPSec need
   to authenticate peers, and implement strategies to provide confidentiality
   and integrity protection protect themselves from floods of traffic between peers.  Nodes can
   requests, and to make
   authorization decisions based on the peer identities authenticated at
   the transport layer.

   When agents are involved, this presents an effectively hop-by-hop
   trust model.  That is, sure that a disproportionate load from one
   source does not prevent other sources from receiving service.  For
   example, a Diameter client or server might throttle a certain percentage of
   requests from sources that exceed certain limits.  Overload control
   can authorize be thought of as an
   agent optimization 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 such strategies, where
   downstream nodes never send the
   transport layer.  Agents can read, and perhaps modify, any part excess requests in the first place.
   However, the presence of an overload control mechanism does not
   remove the need for these other protection strategies.

   When a Diameter message, including node sends an overload report.

   There are several ways an attacker report, it cannot assume that
   all nodes will comply, even if they indicate support for DOIC.  A
   non-compliant node might attempt continue to exploit send requests with no reduction
   in load.  Such non-compliance could be done accidentally, or
   maliciously to gain an unfair advantage over compliant nodes.
   Requirement 28 [RFC7068] indicates that the overload control mechanism.  An unauthorized third party might inject
   an overload report into the network.  If this third party is upstream
   of an agent, and solution
   cannot assume that agent fails to apply proper authorization
   policies, downstream all Diameter nodes may mistakenly trust the report.  This
   attack is at least partially mitigated by the assumption in a network are trusted, and
   that malicious nodes
   include overload reports in Diameter answers but not in requests.
   This requires an attacker be allowed to have knowledge take advantage of the original request
   in order to construct a response.  Therefore, implementations SHOULD
   validate that an answer containing an overload report is a properly
   constructed response
   control mechanism to a pending request prior get more than their fair share of service.

9.4.  End-to End-Security Issues

   The lack of end-to-end integrity features makes it difficult to acting on
   establish trust in overload reports received from non-adjacent nodes.
   Any agents in the message path may insert or modify overload report.

   A similar attack involves an otherwise authorized Diameter node reports.
   Nodes must trust that
   sends an inappropriate their adjacent peers perform proper checks on
   overload report.  For example, reports from their peers, and so on, creating a server transitive-
   trust requirement extending for
   the realm "example.com" might send an overload report indicating that
   a competitor's realm "example.net" potentially long chains of nodes.
   Network operators must determine if this transitive trust requirement
   is overloaded.  If other nodes act
   on acceptable for their deployments.  Nodes supporting Diameter
   overload control MUST give operators the report, ability to select which
   peers are trusted to deliver overload reports, and whether they may falsely believe that "example.net" is
   overloaded, effectively reducing that realm's capacity.  Therefore,
   it's critical that nodes validate that an are
   trusted to forward overload report reports from non-adjacent nodes.  DOIC
   nodes MUST strip DOIC AVPs from messages received from a peer actually falls within peers that peer's responsibility before
   acting on the report or forwarding are
   not trusted for DOIC purposes.

   The lack of end-to-end confidentiality protection means that any
   Diameter agent in the report to other peers.  For
   example, path of an overload report from a peer can view the
   contents of that applies report.  In addition to a realm not
   handled by that peer is suspect.

   An attacker might use the information in an overload report requirement to assist
   in certain attacks.  For example, an attacker could use information
   about current overload conditions select
   which peers are trusted to time a DoS attack for maximum
   effect, or use subsequent send overload reports as a feedback mechanism reports, operators MUST be
   able to
   learn the results of a previous or ongoing attack.

9.2.  Denial of Service Attacks

   Diameter overload reports can cause a node select which peers are authorized to cease sending some or
   all Diameter requests for receive reports.  A node
   MUST not send an extended period.  This makes them overload report to a
   tempting vector for DoS tacks. peer not authorized to receive
   it.  Furthermore, since Diameter is almost
   always used in support of an agent MUST remove any overload reports that
   might have been inserted by other protocols, nodes before forwarding a DoS attack on Diameter
   message to a peer that is likely not authorized to impact those protocols as well.  Therefore, Diameter
   nodes MUST NOT honor or forward receive overload reports from unauthorized or
   otherwise untrusted sources.

9.3.  Non-Compliant Nodes

   When a Diameter reports.

      A DOIC node sends an overload report, it cannot assume always automatically detect that
   all nodes will comply.  A non-compliant a peer also
      supports DOIC.  For example, a node might continue to send
   requests with no reduction in load.  Requirement 28 [RFC7068]
   indicates that the overload control solution cannot assume that all
   Diameter nodes in have a network are necessarily trusted, and peer that
   malicious is a
      non-supporting agent.  If nodes not be allowed to take advantage of on the overload
   control mechanism to get more than their fair share other side of service.

   In that agent
      send OC-Supported-Features AVPs, the absence of an overload control mechanism, Diameter nodes need
   to implement strategies to protect themselves from floods of
   requests, and agent is likely to make sure that a disproportionate load from one
   source does not prevent other sources forward
      them as unknown AVPs.  Messages received across the non-supporting
      agent may be indistinguishable from receiving service.  For
   example, a Diameter server might reject messages received across a certain percentage of
   requests from sources
      DOIC supporting agent, giving the false impression that exceed certain limits.  Overload control
   can be thought of as an optimization for such strategies, where
   downstream nodes never send the excess requests in non-
      supporting agent actually supports DOIC.  This complicates the first place.
   However,
      transitive-trust nature of DOIC.  Operators need to be careful to
      avoid situations where a non-supporting agent is mistakenly
      trusted to enforce DOIC related authorization policies.

   At the presence time of an overload control mechanism does not
   remove this writing, the need DIME working group is studying
   requirements for these other protection strategies.

9.4.  End-to End-Security Issues

   The lack of adding end-to-end security features makes
   [I-D.ietf-dime-e2e-sec-req] to Diameter.  These features, when they
   become available, might make it far more difficult easier 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 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 is acceptable nodes 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 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 view the
   contents of that report.  In addition to 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 node
   MUST not send an overload report to a peer not authorized to receive
   it.  Furthermore, an agent MUST remove any overload reports that
   might have been inserted by other nodes before forwarding a Diameter
   message to a peer that is not authorized to receive overload reports.

   At the time of this writing, the DIME working group is studying
   requirements for 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 non-adjacent nodes for overload control purposes.  Readers should
   be reminded, however, that purposes.  Readers should be
   reminded, however, that the overload control mechanism encourages
   Diameter agents to modify AVPs in, or insert additional AVPs into,
   existing messages that are originated by other nodes.  If end-to-end
   security is enabled, there is a risk that such modification could
   violate integrity protection.  The details of using any future
   Diameter end-to-end security mechanism with overload control will
   require careful consideration, and are beyond the scope of this
   document.

10.  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  Maria Cruz Bartolome

   o  Martin Dolly

   o  Nirav Salot

   o  Susan Shishufeng

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
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and 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.

11.2.  Informative References

   [Cx]       3GPP, , "ETSI TS 129 229 V11.4.0", August 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.

   [PCC]      3GPP, , "ETSI TS 123 203 V11.12.0", December 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 the Routing of Diameter Requests Based
              on the Username and the Realm", RFC 5729, December 2009.

   [RFC7068]  McMurry, E. and B. Campbell, "Diameter Overload Control
              Requirements", RFC 7068, November 2013.

   [S13]      3GPP, , "ETSI TS 129 272 V11.9.0", December 2012.

Appendix A.  Issues left for future specifications

   The base solution for the overload control does not cover all
   possible use cases.  A number of solution aspects were intentionally
   left for future specification and protocol work.  The following sub-
   sections define some of the potential extensions to the DOIC
   solution.

A.1.  Additional traffic abatement algorithms

   This specification describes only means for a simple loss simple loss based
   algorithm.  Future algorithms can be added using the designed
   solution extension mechanism.  The new algorithms need to be
   registered with IANA.  See Sections 6.1 and 8 for the required IANA
   steps.

A.2.  Agent Overload

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

A.3.  New Error Diagnostic AVP

   This specification indicates the use of existing error messages when
   nodes reject requests due to overload.  The DIME working group is
   considering defining additional error codes or AVPs to indicate that
   overload was the reason for the rejection of the message.

Appendix B.  Deployment Considerations

   Non Supporting Agents

      Due to the way that realm-routed requests are handled in Diameter
      networks with the server selection for the request done by an
      agent, network operators should enable DOIC at agents that perform
      server selection first.

   Topology Hiding Interactions

      There exist proxies that implement what is referred to as Topology
      Hiding.  This can include cases where the agent modifies the
      Origin-Host in answer messages.  The behavior of the DOIC solution
      is not well understood when this happens.  As such, the DOIC
      solution does not address this scenario.

Appendix C.  Requirements Conformance Analysis

   This section contains the result of an analysis of the DOIC solutions
   conformance to the requirements defined in [RFC7068].

C.1.  Deferred Requirements

   The 3GPP has adopted an early version of this document as normative
   references in various Diameter related specifications to support the
   overload control mechanism in their release 12 framework.  The DIME
   working group has therefore decided to defer certain requirements in
   order to complete the design of an extensible, generic solution
   before the deadline scheduled by the 3GPP for the completion of the
   release 12 protocol work by the end of 2014.  The deferred work
   includes the following:

   o  Agent Overload - The ability for an agent to report an overload
      condition of the agent itself.

   o  Load Information - The ability for a node to report its load level
      when not overloaded.

   At the time of this writing, DIME has begun separate work efforts for
   these requirements.

C.2.  Detection of non-supporting Intermediaries

   The DOIC mechanism as currently defined does not allow supporting
   nodes to automatically determine whether OC-Supported-Features or OC-
   OLR AVPs are originated by a peer node, or by a non-peer node and
   sent across a non-supporting peer.  This makes it impossible to
   detect the presence of non-supporting nodes between supporting nodes,
   except by configuration.  The working group determined that such a
   configuration requirement is acceptable.

   This limits full compliance with certain requirements related to the
   limitation of new configuration, deployment in environments with
   mixed support, operating across non-supporting agents, and
   authorization.

C.3.  Implicit Application Indication

   The working group elected to determine the application for an
   overload report from that of the enclosing message.  This prevents
   sending an OLR for an application when there are no transactions for
   that application.

   As a consequence, DOIC does not comply with the requirement to be
   able to report overload information across quiescent connections.
   DOIC does not fully comply with requirements to operate on up-to-date
   information, since if an OLR causes all transactions to stop for an
   application, the only way traffic will resume is for the OLR to
   expire.

C.4.  Stateless Operation

   RFC7068 explicitly discourages the sending of OLRs in every answer
   message, as part of the requirement to avoid additional work for
   overloaded nodes.  DOIC recommends exactly that behavior during
   active overload conditions.  The working group determined that doing
   otherwise would reduce reliability and increase statefulness.  (Note
   that DOIC does allow nodes to avoid sending OLRs in every answer if
   they have some other method of ensuring that OLRs get to all relevant
   reacting nodes.)

C.5.  No New Vulnerabilities

   The working group believes that DOIC is compliant with the
   requirement to avoid introducing new vulnerabilities.  However, this
   requirement may warrant an early security expert review.

C.6.  Detailed Requirements

   [RFC Editor: Please remove this section and subsections prior to
   publication as an RFC.]

C.6.1.  General

   REQ 1:  The solution MUST provide a communication method for Diameter
           nodes to exchange load and overload information.

           *Partially Compliant*. The mechanism uses new AVPs
           piggybacked on existing Diameter messages to exchange
           overload information.  It does not currently support "load"
           information or the ability to report overload of an agent.
           These have been left for future extensions.

   REQ 2:  The solution MUST allow Diameter nodes to support overload
           control regardless of which Diameter applications they
           support.  Diameter clients and agents must be able to use the
           received load and overload information to support graceful
           behavior during an overload condition.  Graceful behavior
           under overload conditions is best described by REQ 3.

           *Partially Compliant*. The DOIC AVPs can be used in any
           application that allows the extension of AVPs.  However,
           "load" information is not currently supported.

   REQ 3:  The solution MUST limit the impact of overload on the overall
           useful throughput of a Diameter server, even when the
           incoming load on the network is far in excess of its
           capacity.  The overall useful throughput under load is the
           ultimate measure of the value of a solution.

           *Compliant*. DOIC provides information that nodes can use to
           reduce the impact of overload.

   REQ 4:  Diameter allows requests to be sent from either side of a
           connection, and either side of a connection may have need to
           provide its overload status.  The solution MUST allow each
           side of a connection to independently inform the other of its
           overload status.

           *Compliant*. DOIC AVPs can be included regardless of
           transaction "direction"

   REQ 5:  Diameter allows nodes to determine their peers via dynamic
           discovery or manual configuration.  The solution MUST work
           consistently without regard to how peers are determined.

           *Compliant*. DOIC contains no assumptions about how peers are
           discovered.

   REQ 6:  The solution designers SHOULD seek to minimize the amount of
           new configuration required in order to work.  For example, it
           is better to allow peers to advertise or negotiate support
           for the solution, rather than to require that this knowledge
           to be configured at each node.

           *Partially Compliant*. Most DOIC parameters are advertised
           using the DOIC capability announcement mechanism.  However,
           there are some situations where configuration is required.
           For example, a DOIC node detect the fact that a peer may not
           support DOIC when nodes on the other side of the non-
           supporting node do support DOIC without configuration.

C.6.2.  Performance

   REQ 7:  The solution and any associated default algorithm(s) MUST
           ensure that the system remains stable.  At some point after
           an overload condition has ended, the solution MUST enable
           capacity to stabilize and become equal to what it would be in
           the absence of an overload condition.  Note that this also
           requires that the solution MUST allow nodes to shed load
           without introducing non-converging oscillations during or
           after an overload condition.

           *Compliant*. The specification offers guidance that
           implementations should apply hysteresis when recovering from
           overload, and avoid sudden ramp ups in offered load when
           recovering.

   REQ 8:  Supporting nodes MUST be able to distinguish current overload
           information from stale information.

           *Partially Compliant*. DOIC overload reports are "soft
           state", that is they expire after an indicated period.  DOIC
           nodes may also send reports that end existing overload
           conditions.  DOIC requires reporting nodes to ensure that all
           relevant reacting nodes receive overload reports.

           However, since DOIC does not allow reporting nodes to send
           OLRs in watchdog messages, if an overload condition results
           in zero offered load, the reporting node cannot update the
           condition until the expiration of the original OLR.

   REQ 9:  The solution MUST function across fully loaded as well as
           quiescent transport connections.  This is partially derived
           from the requirement for stability in REQ 7.

           *Not Compliant*. DOIC does not allow OLRs to be sent over
           quiescent transport connections.  This is due to the fact
           that OLRs cannot be sent outside of the application to which
           they apply.

   REQ 10: Consumers of overload information MUST be able to determine
           when the overload condition improves or ends.

           *Partially Compliant*. (See response to previous two
           requirements.)

   REQ 11: The solution MUST be able to operate in networks of different
           sizes.

           *Compliant*. DOIC makes no assumptions about the size of the
           network.  DOIC can operate purely between clients and
           servers, or across agents.

   REQ 12: When a single network node fails, goes into overload, or
           suffers from reduced processing capacity, the solution MUST
           make it possible to limit the impact of the affected node on
           other nodes in the network.  This helps to prevent a small-
           scale failure from becoming a widespread outage.

           *Partially Compliant*. DOIC allows overload reports for an
           entire realm, where abated traffic will not be redirected
           towards another server.  But in situations where nodes choose
           to divert traffic to other nodes, DOIC offers no way of
           knowing whether the new recipients can handle the traffic if
           they have not already indicated overload.  This may be
           mitigated with the use of a future "load" extension, or with
           the use of proprietary dynamic load-balancing mechanisms.

   REQ 13: The solution MUST NOT introduce substantial additional work
           for a node in an overloaded state.  For example, a
           requirement for an overloaded node to send overload
           information every time it received a new request would
           introduce substantial work.

           *Not Compliant*. DOIC does in fact encourage an overloaded
           node to send an OLR in every response.  The working group
           that other mechanisms to ensure that every relevant node
           receives an OLR would create even more work.  [Note: This
           needs discussion.]

   REQ 14: Some scenarios that result in overload involve a rapid
           increase of traffic with little time between normal levels
           and levels that induce overload.  The solution SHOULD provide
           for rapid feedback when traffic levels increase.

           *Compliant*. The piggyback mechanism allows OLRs to be sent
           at the same rate as application traffic.

   REQ 15: The solution MUST NOT interfere with the congestion control
           mechanisms of underlying transport protocols.  For example, a
           solution that opened additional TCP connections when the
           network is congested would reduce the effectiveness of the
           underlying congestion control mechanisms.

           *Compliant*. DOIC does not require or recommend changes in
           the handling of transport protocols or connections.

C.6.3.  Heterogeneous Support for Solution

   REQ 16: The solution is likely to be deployed incrementally.  The
           solution MUST support a mixed environment where some, but not
           all, nodes implement it.

           *Partially Compliant*. DOIC works with most mixed-deployment
           scenarios.  However, it cannot work across a non-supporting
           proxy that modifies Origin-Host AVPs in answer messages.
           DOIC will have limited impact in networks where the nodes
           that perform server selections do not support the mechanism.

   REQ 17: In a mixed environment with nodes that support the solution
           and nodes that do not, the solution MUST NOT result in
           materially less useful throughput during overload as would
           have resulted if the solution were not present.  It SHOULD
           result in less severe overload in this environment.

           *Compliant*. In most mixed-support deployment, DOIC will
           offer at least some value, and will not make things worse.

   REQ 18: In a mixed environment of nodes that support the solution and
           nodes that do not, the solution MUST NOT preclude elements
           that support overload control from treating elements that do
           not support overload control in an equitable fashion relative
           to those that do.  Users and operators of nodes that do not
           support the solution MUST NOT unfairly benefit from the
           solution.  The solution specification SHOULD provide guidance
           to implementers for dealing with elements not supporting
           overload control.

           *Compliant*. DOIC provides mechanisms to abate load from non-
           supporting sources.  Furthermore, it recommends that
           reporting nodes will still need to be able to apply whatever
           protections they would ordinarily apply if DOIC were not in
           use.

   REQ 19: It MUST be possible to use the solution between nodes in
           different realms and in different administrative domains.

           *Partially Compliant*. DOIC allows sending OLRs across
           administrative domains, and potentially to nodes in other
           realms.  However, an OLR cannot indicate overload for realms
           other than the one in the Origin-Realm AVP of the containing
           answer.

   REQ 20: Any explicit overload indication MUST be clearly
           distinguishable from other errors reported via Diameter.

           *Compliant*. DOIC sends explicit overload indication in
           overload reports.  It does not depend on error result codes.

   REQ 21: In cases where a network node fails, is so overloaded that it
           cannot process messages, or cannot communicate due to a
           network failure, it may not be able to provide explicit
           indications of the nature of the failure or its levels of
           overload.  The solution MUST result in at least as much
           useful throughput as would have resulted if the solution were
           not in place.

           *Compliant*. DOIC overload reports have the primary effect of
           suppressing message retries in overload conditions.  DOIC
           recommends that messages never be silently dropped if at all
           possible.

C.6.4.  Granular Control

   REQ 22: The solution MUST provide a way for a node to throttle the
           amount of traffic it receives from a peer node.  This
           throttling SHOULD be graded so that it can be applied
           gradually as offered load increases.  Overload is not a
           binary state; there may be degrees of overload.

           *Compliant*. The "loss" algorithm expresses a percentage
           reduction.

   REQ 23: The solution MUST provide sufficient information to enable a
           load-balancing node to divert messages that are rejected or
           otherwise throttled by an overloaded upstream node to other
           upstream nodes that are the most likely to have sufficient
           capacity to process them.

           *Not Compliant*. DOIC provides no built in mechanism to
           determine the best place to divert messages that would
           otherwise be throttled.  This can be accomplished with a
           future "load" extension, or with proprietary load balancing
           mechanisms.

   REQ 24: The solution MUST provide a mechanism for indicating load
           levels, even when not in an overload condition, to assist
           nodes in making decisions to prevent overload conditions from
           occurring.

           *Not Compliant*. "Load" information has been left for a
           future extension.

C.6.5.  Priority and Policy

   REQ 25: The base specification for the solution SHOULD offer general
           guidance on which message types might be desirable to send or
           process over others during times of overload, based on
           application-specific considerations.  For example, it may be
           more beneficial to process messages for existing sessions
           ahead of new sessions.  Some networks may have a requirement
           to give priority to requests associated with emergency
           sessions.  Any normative or otherwise detailed definition of
           the relative priorities of message types during an overload
           condition will be the responsibility of the application
           specification.

           *Compliant*. The specification offers guidance on how
           requests might be prioritized for different types of
           applications.

   REQ 26: The solution MUST NOT prevent a node from prioritizing
           requests based on any local policy, so that certain requests
           are given preferential treatment, given additional
           retransmission, not throttled, or processed ahead of others.

           *Compliant*. Nothing in the specification prevents
           application-specific, implementation-specific, or local
           policies.

C.6.6.  Security

   REQ 27: The solution MUST NOT provide new vulnerabilities to
           malicious attack or increase the severity of any existing
           vulnerabilities.  This includes vulnerabilities to DoS and
           DDoS attacks as well as replay and man-in-the-middle attacks.
           Note that the Diameter base specification [RFC6733] lacks
           end-to-end security and this must be considered (see the
           Security Considerations in [RFC7068]).  Note that this
           requirement was expressed at a high level so as to not
           preclude any particular solution.  It is expected that the
           solution will address this in more detail.

           *Compliant*. The working group is not aware of any such
           vulnerabilities.  [This may need further analysis.]

   REQ 28: The solution MUST NOT depend on being deployed in
           environments where all Diameter nodes are completely trusted.
           It SHOULD operate as effectively as possible in environments
           where other nodes are malicious; this includes preventing
           malicious nodes from obtaining more than a fair share of
           service.  Note that this does not imply any responsibility on
           the solution to detect, or take countermeasures against,
           malicious nodes.

           *Partially Compliant*. Since all Diameter security is
           currently at the transport layer, nodes must trust immediate
           peers to enforce trust policies.  However, there are
           situations where a DOIC node cannot determine if an immediate
           peer supports DOIC.  The authors recommend an expert security
           review.

   REQ 29: It MUST be possible for a supporting node to make
           authorization decisions about what information will be sent
           to peer nodes based
   algorithm.  Future algorithms can on the identity of those nodes.  This
           allows a domain administrator who considers the load of their
           nodes to be added using sensitive information to restrict access to that
           information.  Of course, in such cases, there is no
           expectation that the designed solution extension mechanism. itself will help prevent
           overload from that peer node.

           *Partially Compliant*. (See response to previous
           requirement.)

   REQ 30: The new algorithms need solution MUST NOT interfere with any Diameter-compliant
           method that a node may use to protect itself from overload
           from non-supporting nodes or from denial-of-service attacks.

           *Compliant*. The specification recommends that any such
           protection mechanism needed without DOIC should continue to
           be
   registered employed with IANA.  See Sections 6.1 DOIC.

C.6.7.  Flexibility and 8 for the required IANA
   steps.

A.2.  Agent Overload

   This specification focuses on Extensibility

   REQ 31: There are multiple situations where a Diameter endpoint (server or client)
   overload.  A separate extension will node may be required
           overloaded for some purposes but not others.  For example,
           this can happen to outline the
   handling of the case of an agent overload.

A.3.  New Error Diagnostic AVP or server that supports multiple
           applications, or when a server depends on multiple external
           resources, some of which may become overloaded while others
           are fully available.  The proposal was made solution MUST allow Diameter nodes
           to add a new Error Diagnostic AVP indicate overload with sufficient granularity to allow
           clients to supplement take action based on the error responces overloaded resources
           without unreasonably forcing available capacity to go unused.
           The solution MUST support specification of overload
           information with granularities of at least "Diameter node",
           "realm", and "Diameter application" and MUST allow
           extensibility for others to be able added in the future.

           *Partially Compliant*. All DOIC overload reports are scoped
           to the specific application and realm.  Inside that scope,
           overload can be reported at the specific server or whole
           realm scope.  As currently specified, DOIC cannot indicate that
           local overload was the
   reason for an agent.  At the rejection time of this writing,
           the message.

Appendix B.  Deployment Considerations

   Non supporting agents

      Due DIME working group has plans to work on an agent-overload
           extension.

           DOIC allows new "scopes" through the way that realm-routed requests are handled in Diameter
      networks, with the server selection use of extended report
           types.

   REQ 32: The solution MUST provide a method for extending the request done by an
      agent, it is recommended that deployments enable all agents that
      do server selection to support
           information communicated and the algorithms used for overload
           control.

           *Compliant*. DOIC solution prior allows new report types and abatement
           algorithms to enabling be created.  These may be indicated using the DOIC
           OC-Supported-Features AVP.

   REQ 33: The solution in the Diameter network.

   Topology hiding interactions

      There exist proxies MUST provide a default algorithm that implement what is referred
           mandatory to as Topology
      Hiding.  This can include cases where the agent modifies the
      Origin-Host in answer messages. implement.

           *Compliant*. The behavior of the DOIC solution "loss" algorithm is mandatory to implement.

   REQ 34: The solution SHOULD provide a method for exchanging overload
           and load information between elements that are connected by
           intermediaries that do not well understood when this happens.  As such, support the solution.

           *Partially Compliant*. DOIC
      solution does information can traverse non-
           supporting agents, as long as those agents do not address this scenario.

Appendix C.  Requirements Conformance Analysis

   This section contains the result of an analysis of the modify
           certain AVPs. (e.g., Origin-Host).  DOIC solutions
   conformance does not provide a
           way for supporting nodes to the requirements defined in [RFC7068].

   To be completed. detect such modification.

Appendix D.  Considerations for Applications Integrating the DOIC
             Solution

   This section outlines considerations to be taken into account when
   integrating the DOIC solution into Diameter applications.

D.1.  Application Classification

   The following is a classification of Diameter applications and
   request types.  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 applications.
   The primary difference between these types of applications is the
   lifetime of Session-Ids.

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

   The Credit-Control application defined in [RFC4006] is an example of
   a Diameter session-based application.

   In session-less applications, the lifetime of the Session-Id is a
   single Diameter 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: Applications:

      Requests within a stateless application have no relationship to
      each other.  The 3GPP defined S13 application is an example of a
      stateless application [S13], where only a Diameter command is
      defined between a client and a server and no state is maintained
      between two consecutive transactions.

   Pseudo-session applications:

   Pseudo-Session Applications:

      Applications that do not rely on the Session-Id AVP for
      correlation of application messages related to the same session
      but use other session-related information in the Diameter requests
      for this purpose.  The 3GPP defined Cx application [Cx] is an
      example of a pseudo-session application.

   The handling of overload reports must take the type of application
   into consideration, as discussed in Appendix D.2.

D.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.  Appendix D.3 discusses considerations for handling
   various request types when the target server is known to be in an
   overloaded state.

   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: 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-session applications:

   Pseudo-Session Applications:

      For pseudo-session applications, there is an implied ordering of
      requests.  As a result, decisions about which requests towards an
      overloaded entity to reject could take the 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.

   Session-based applications:

   Session-Based Applications:

      Overload handling for session-based applications must take into
      consideration the work load associated with setting up and
      maintaining a session.  As such, the entity sending requests
      towards an overloaded Diameter entity for a session-based
      application might tend to reject new session requests prior to
      rejecting intra-session requests.  In addition, session ending
      requests might be given a lower probability of being rejected as
      rejecting session ending requests could result in session status
      being out of sync between the Diameter clients and servers.
      Application designers that would decide to reject mid-session
      requests will need to consider whether the rejection invalidates
      the session and any resulting session clean-up cleanup procedures.

D.3.  Request Transaction Classification

   Independent Request:

      An independent request is not 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 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 [PCC], where multiple
      apparently independent Diameter application sessions are actually
      correlated and must be handled by the same Diameter server.

   Intra-Session Request:

      An intra session intra-session request is a request that uses the same Session-
      Id than the one used in a previous request.  An intra session 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. request.

   Pseudo-Session Requests:

      Pseudo-session requests are independent requests and do not use
      the same Session-Id but are correlated by other session-related
      information contained in the request.  There 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
      [Cx] application are examples of pseudo-session requests.

D.4.  Request Type Overload Implications

   The request classes identified in Appendix D.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.  The
   exact behavior regarding throttling is a matter of local policy,
   unless specifically defined for the application.

   Independent requests: Requests:

      Independent requests can generally be given equal treatment when
      making throttling decisions, unless otherwise indicated by
      application requirements or local policy.

   Session-initiating requests:

   Session-Initiating Requests:

      Session-initiating requests often represent more work than
      independent or intra-session requests.  Moreover, session-
      initiating requests are typically followed by other session-
      related requests.  Since 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-initiating requests.  In the
      absence of local policies or application specific requirements to
      the contrary, Individual session-initiating requests can be given
      equal treatment when making throttling decisions.

   Correlated session-initiating requests: Session-Initiating Requests:

      A Request that results in a new binding, where the binding is used
      for routing of subsequent 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:

   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:

   Intra-Session Requests:

      There are two types of intra-sessions requests, requests that
      terminate a session and the remainder of intra-session requests.
      Implementors
      Implementers and operators may choose to throttle session-
      terminating requests less aggressively in order to gracefully
      terminate sessions, allow clean-up cleanup of the related resources (e.g.
      session state) and avoid the need for additional intra-session
      requests.  Favoring session-termination requests may reduce 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.

Authors' Addresses

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

   Email: jouni.nospam@gmail.com

   Steve Donovan (editor)
   Oracle
   7460 Warren Parkway
   Frisco, Texas  75034
   United States

   Email: srdonovan@usdonovans.com

   Ben Campbell
   Oracle
   7460 Warren Parkway
   Frisco, Texas  75034
   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