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Diameter Overload Indication Conveyance

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7683.
Authors Jouni Korhonen , Steve Donovan , Ben Campbell , Lionel Morand
Last updated 2015-01-26
Replaces draft-docdt-dime-ovli
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state In WG Last Call
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Document shepherd Alan DeKok
IESG IESG state Became RFC 7683 (Proposed Standard)
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Responsible AD Kathleen Moriarty
Send notices to,,,
Diameter Maintenance and Extensions (DIME)              J. Korhonen, Ed.
Internet-Draft                                                  Broadcom
Intended status: Standards Track                         S. Donovan, Ed.
Expires: July 30, 2015                                       B. Campbell
                                                               L. Morand
                                                             Orange Labs
                                                        January 26, 2015

                Diameter Overload Indication Conveyance


   This specification defines a base solution for Diameter overload
   control, referred to as Diameter Overload Indication Conveyance

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

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

   This Internet-Draft will expire on July 30, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Abbreviations . . . . . . . . . . . . . . . .   4
   3.  Conventions Used in This Document . . . . . . . . . . . . . .   5
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Piggybacking  . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  DOIC Capability Announcement  . . . . . . . . . . . . . .   7
     4.3.  DOIC Overload Condition Reporting . . . . . . . . . . . .   9
     4.4.  DOIC Extensibility  . . . . . . . . . . . . . . . . . . .  11
     4.5.  Simplified Example Architecture . . . . . . . . . . . . .  11
   5.  Solution Procedures . . . . . . . . . . . . . . . . . . . . .  12
     5.1.  Capability Announcement . . . . . . . . . . . . . . . . .  12
       5.1.1.  Reacting Node Behavior  . . . . . . . . . . . . . . .  13
       5.1.2.  Reporting Node Behavior . . . . . . . . . . . . . . .  13
       5.1.3.  Agent Behavior  . . . . . . . . . . . . . . . . . . .  14
     5.2.  Overload Report Processing  . . . . . . . . . . . . . . .  15
       5.2.1.  Overload Control State  . . . . . . . . . . . . . . .  15
       5.2.2.  Reacting Node Behavior  . . . . . . . . . . . . . . .  19
       5.2.3.  Reporting Node Behavior . . . . . . . . . . . . . . .  20
     5.3.  Protocol Extensibility  . . . . . . . . . . . . . . . . .  22
   6.  Loss Algorithm  . . . . . . . . . . . . . . . . . . . . . . .  22
     6.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  23
     6.2.  Reporting Node Behavior . . . . . . . . . . . . . . . . .  23
     6.3.  Reacting Node Behavior  . . . . . . . . . . . . . . . . .  24
   7.  Attribute Value Pairs . . . . . . . . . . . . . . . . . . . .  24
     7.1.  OC-Supported-Features AVP . . . . . . . . . . . . . . . .  25
     7.2.  OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . .  25
     7.3.  OC-OLR AVP  . . . . . . . . . . . . . . . . . . . . . . .  25
     7.4.  OC-Sequence-Number AVP  . . . . . . . . . . . . . . . . .  26
     7.5.  OC-Validity-Duration AVP  . . . . . . . . . . . . . . . .  26
     7.6.  OC-Report-Type AVP  . . . . . . . . . . . . . . . . . . .  26
     7.7.  OC-Reduction-Percentage AVP . . . . . . . . . . . . . . .  27
     7.8.  Attribute Value Pair flag rules . . . . . . . . . . . . .  27
   8.  Error Response Codes  . . . . . . . . . . . . . . . . . . . .  28
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
     9.1.  AVP codes . . . . . . . . . . . . . . . . . . . . . . . .  28
     9.2.  New registries  . . . . . . . . . . . . . . . . . . . . .  29
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  29
     10.1.  Potential Threat Modes . . . . . . . . . . . . . . . . .  30
     10.2.  Denial of Service Attacks  . . . . . . . . . . . . . . .  31
     10.3.  Non-Compliant Nodes  . . . . . . . . . . . . . . . . . .  31
     10.4.  End-to End-Security Issues . . . . . . . . . . . . . . .  32
   11. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  33
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33

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     12.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     12.2.  Informative References . . . . . . . . . . . . . . . . .  33
   Appendix A.  Issues left for future specifications  . . . . . . .  34
     A.1.  Additional traffic abatement algorithms . . . . . . . . .  34
     A.2.  Agent Overload  . . . . . . . . . . . . . . . . . . . . .  34
     A.3.  New Error Diagnostic AVP  . . . . . . . . . . . . . . . .  34
   Appendix B.  Deployment Considerations  . . . . . . . . . . . . .  34
   Appendix C.  Requirements Conformance Analysis  . . . . . . . . .  35
     C.1.  Deferred Requirements . . . . . . . . . . . . . . . . . .  35
     C.2.  Detection of non-supporting Intermediaries  . . . . . . .  35
     C.3.  Implicit Application Indication . . . . . . . . . . . . .  36
     C.4.  Stateless Operation . . . . . . . . . . . . . . . . . . .  36
     C.5.  No New Vulnerabilities  . . . . . . . . . . . . . . . . .  36
     C.6.  Detailed Requirements . . . . . . . . . . . . . . . . . .  36
       C.6.1.  General . . . . . . . . . . . . . . . . . . . . . . .  36
       C.6.2.  Performance . . . . . . . . . . . . . . . . . . . . .  38
       C.6.3.  Heterogeneous Support for Solution  . . . . . . . . .  40
       C.6.4.  Granular Control  . . . . . . . . . . . . . . . . . .  42
       C.6.5.  Priority and Policy . . . . . . . . . . . . . . . . .  43
       C.6.6.  Security  . . . . . . . . . . . . . . . . . . . . . .  43
       C.6.7.  Flexibility and Extensibility . . . . . . . . . . . .  44
   Appendix D.  Considerations for Applications Integrating the DOIC
                Solution . . . . . . . . . . . . . . . . . . . . . .  46
     D.1.  Application Classification  . . . . . . . . . . . . . . .  46
     D.2.  Application Type Overload Implications  . . . . . . . . .  47
     D.3.  Request Transaction Classification  . . . . . . . . . . .  48
     D.4.  Request Type Overload Implications  . . . . . . . . . . .  49
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  50

1.  Introduction

   This specification defines a base solution for Diameter overload
   control, referred to as Diameter Overload Indication Conveyance
   (DOIC), based on the requirements identified in [RFC7068].

   This specification addresses Diameter overload control between
   Diameter nodes that support the DOIC 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.

   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

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   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


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


      An overload abatement treatment where the reacting node selects
      alternate destinations or paths for requests.

   Host-Routed 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)

      Internal state maintained by a reporting or reacting node
      describing occurrences of overload control.

   Overload Report (OLR)

      Overload control information for a particular overload occurrence
      sent by a reporting node.

   Reacting Node

      A Diameter node that acts upon an overload report.

   Realm-Routed Requests

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      Requests that a reacting node does not know which host will
      service the request.

   Reporting Node

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


      An abatement treatment that limits the number of requests sent by
      the DIOC reacting node.  Throttling can include a Diameter Client
      choosing to not send requests, or a Diameter Agent or Server
      rejecting requests with appropriate error responses.  In both
      cases the result of the throttling is a permanent rejection of the

3.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   RFC 2119 [RFC2119] interpretation does not apply for the above listed
   words when they are not used in all-caps format.

4.  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 Diameter Clients,
   Diameter Servers, and Diameter Agents.  DOIC nodes are further
   divided into "Reporting Nodes" and "Reacting Nodes."  A reporting
   node requests overload abatement by sending Overload Reports (OLR).

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

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   A Diameter node's role as a DOIC node is independent of its Diameter
   role.  For example, Diameter 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 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, by inserting an OC-Supported-Features AVP
   (Section 7.2) into existing requests and responses.  Reporting nodes
   send OLRs by inserting OC-OLR AVPs (Section 7.3).

   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

   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.  An overload abatement algorithm separates
   Diameter 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 6).
   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
   attempt to send requests to other 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 7.6), where the type defines such behaviors.  Report types
   are extensible.  This document defines report types for overload of a
   specific host, and for overload of an entire realm.

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   DOIC works through non supporting Diameter Agents that properly pass
   unknown AVPs unchanged.

4.1.  Piggybacking

   There is no new 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 the optional
   overload control AVPs OC-OLR and OC-Supported-Features into existing

   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 that are in response to a request that
   contained the OC-Supported-Features AVP.  Reporting nodes may include
   overload reports using the OC-OLR AVP in answer 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. sent 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

4.2.  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 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-Features AVP in the request

   The individual features supported by the DOIC nodes are indicated in
   the OC-Feature-Vector AVP.  Any semantics associated with the

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   features will be defined in extension specifications that introduce
   the features.

      Note: As discussed elsewhere in the document, agents in the path
      of the 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, Diameter Agents that support the DOIC solution
      may handle overload abatement for the non supporting Diameter
      nodes.  In this case the DOIC agent will insert the 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 always contain an indication of
   support for the loss overload abatement algorithm defined in this
   specification (see Section 6).  This ensures that a reporting node
   always supports at least one of the advertized abatement algorithms
   received in a request messages.

   The reporting node inserts the OC-Supported-Features AVP in all
   answer messages to requests that contained the OC-Supported-Features
   AVP.  The contents of the reporting node's OC-Supported-Features AVP
   indicate the set of Diameter overload features supported by the
   reporting node.  This specification defines one exception - the
   reporting node only includes an indication of support for one
   overload abatement 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.
   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

      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.

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   The DCA mechanism must also 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 can update the OC-
   Supported-Features AVP to reflect the mixture of the two sets of
   supported features.

      Note: The logic to determine if the content of the OC-Supported-
      Features AVP should be changed is out-of-scope for this document,
      as is the logic to determine the content of a modified OC-
      Supported-Features AVP.  These are left to implementation
      decisions.  Care must be taken not to introduce interoperability
      issues for downstream or upstream DOIC nodes.

4.3.  DOIC Overload Condition Reporting

   As with DOIC capability announcement, overload condition reporting
   uses new AVPs (Section 7.3) 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_REPORT" is sent to indicate the overload of a
   specific 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_REPORT", a reacting
   node applies overload abatement treatment to the host-routed requests
   identified by the overload abatement algorithm (see definition in
   Section 2) sent for this application to the overloaded host.

   A report of type "REALM_REPORT" is sent to indicate the overload of a
   realm for the 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_REPORT", a reacting node applies overload abatement treatment
   to realm-routed requests identified by the overload abatement
   algorithm (see definition in Section 2) sent for this application to
   the overloaded realm.

   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.

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      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

   Reporting nodes are responsible for determining the need for a
   reduction of traffic.  The method for making this determination is
   implementation specific and depends on the type of overload report
   being generated.  A host-report might be generated by tracking use of
   resources required by the host to handle transactions for the
   Diameter application.  A realm-report generally impacts the traffic
   sent to multiple hosts and, as such, requires tracking the capacity
   of all servers able to handle realm-routed requests for the
   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, apply the
   overload abatement algorithm to traffic impacted by the overload
   report.  The method used 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 6).  Other abatement algorithms can be defined in extensions
   to the DOIC solution.

   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 abatement 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.

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4.4.  DOIC Extensibility

   The DOIC solution is designed to be extensible.  This extensibility
   is based on existing Diameter based extensibility 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 the definition of new scopes of
   messages impacted by an overload report.

   A DOIC node communicates supported features by including them in the
   OC-Feature-Vector AVP, as a sub-AVP of OC-Supported-Features.  Any
   non-backwards compatible DOIC extensions define new values for the
   OC-Feature-Vector AVP.  DOIC extensions also have the ability to add
   new AVPs to the OC-Supported-Features AVP, if additional information
   about the new feature is required.

   Overload reports can also be extended by adding new sub-AVPs to the
   OC-OLR AVP, allowing reporting nodes to communicate additional
   information about handling an overload condition.

   If necessary, new extensions can also define new 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.

4.5.  Simplified Example Architecture

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

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    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)  <----------------------> <---------------------->
                 Diameter Application Y   Diameter Application Y

     Figure 1: Simplified architecture choices for overload indication

   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.

5.  Solution Procedures

   This section outlines the normative behavior for the DOIC solution.

5.1.  Capability Announcement

   This section defines DOIC Capability Announcement (DCA) behavior.

      Note: This specification assumes that changes in DOIC node
      capabilities are relatively rare events that occur as a result of
      administrative action.  Reacting nodes ought to minimize changes
      that force the reporting node to change the features being used,
      especially during active overload conditions.  But even if
      reacting nodes avoid such changes, reporting nodes still have to
      be prepared for them to occur.  For example, differing
      capabilities between multiple reacting nodes may still force a

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      reporting node to select different features on a per-transaction

5.1.1.  Reacting Node Behavior

   A reacting node MUST include the OC-Supported-Features AVP in all
   requests.  It MAY include the OC-Feature-Vector AVP, as a sub-avp of
   OC-Supported-Features.  If it does so, it MUST indicate support for
   the "loss" algorithm.  If the reacting node is configured to support
   features (including other algorithms) in addition to the loss
   algorithm, it MUST indicate such support 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, for example creating state for some stateful abatement
   algorithm, based on the features indicated in the OC-Feature-Vector

      Note: The loss abatement algorithm does not require stateful
      behavior when there is no active overload report.

   Reacting nodes need to be prepared for the reporting node to change
   selected algorithms.  This can happen at any time, including when the
   reporting node has sent an active overload report.  The reacting node
   can minimize the potential for changes by modifying the advertised
   abatement algorithms sent to an overloaded reporting node to the
   currently selected algorithm and loss (or just loss if it is the
   currently selected algorithm).  This has the effect of limiting the
   potential change in abatement algorithm from the currently selected
   algorithm to loss, avoiding changes to more complex abatement
   algorithms that require state to operate properly.

5.1.2.  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 in the request message.

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

      Note: Capability announcement is done on a per transaction basis.
      The reporting node cannot assume that the capabilities announced
      by a reacting node will be the same between transactions.

   A reporting node MUST NOT include the OC-Supported-Features AVP, OC-
   OLR AVP or any other overload control AVPs defined in extension

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   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.

   A reporting node knows what overload control functionality is
   supported by the reacting node based on the content or absence of the
   OC-Feature-Vector AVP within the OC-Supported-Features 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
   selected MUST indicate the abatement algorithm the reporting node
   wants the reacting node to use when the reporting node enters an
   overload condition.

   The abatement algorithm selected MUST be from the set of abatement
   algorithms contained in the request message's OC-Feature-Vector AVP.

   A reporting 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.

   The reporting node SHOULD indicate support for other DOIC features
   defined in extension drafts that it supports and that apply to the
   transaction.  It does so using the OC-Feature-Vector AVP.

      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

5.1.3.  Agent Behavior

   Diameter Agents that support DOIC can ensure that all messages
   relayed by the agent contain the OC-Supported-Features AVP.

   A Diameter Agent MAY take on reacting node behavior for Diameter
   endpoints that do not support the DOIC solution.  A Diameter Agent
   detects that a Diameter endpoint does not support DOIC reacting node
   behavior when there is no OC-Supported-Features AVP in a request

   For a Diameter Agent to be a reacting node for a non supporting
   Diameter endpoint, the Diameter Agent MUST include the OC-Supported-

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   Features AVP in request messages it relays that do not contain the
   OC-Supported-Features AVP.

   A Diameter Agent MAY take on reporting node behavior for Diameter
   endpoints that do not support the DOIC solution.  The Diameter Agent
   MUST have visibility to all traffic destined for the non supporting
   host in order to become the reporting node for the Diameter endpoint.
   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.

   If a request already has the OC-Supported-Features AVP, a Diameter
   agent MAY modify it to reflect the features appropriate for the
   transaction.  Otherwise, the agent relays the OC-Supported-Features
   AVP without change.

      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 Diameter Agent changes the OC-Supported-Features AVP in a
   request message then it is likely it will also need to modify the OC-
   Supported-Features AVP in the answer message for the transaction.  A
   Diameter Agent MAY modify the OC-Supported-Features AVP carried in
   answer messages.

   When making changes to the OC-Supported-Features or OC-OLR AVPs, the
   Diameter Agent needs to ensure consistency in its behavior with both
   upstream and downstream DOIC nodes.

5.2.  Overload Report Processing

5.2.1.  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.

   The contents of the OCS in the reporting node and in the reacting
   node represent logical constructs.  The actual internal physical
   structure of the state included in the OCS is an implementation

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   A reacting node maintains the following OCS per supported Diameter

   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 and
   the node's DiameterIdentity.

   A realm-type OCS entry is identified by the pair of application-id
   and realm.

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

   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 the OC-Supported-
      Features AVP)

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

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

   An OCS entry is identified by the tuple of Application-Id, Report-
   Type and Abatement Algorithm and includes the following information
   (the actual information stored is an implementation decision):

   o  Sequence number

   o  Validity Duration

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   o  Expiration Time

   o  Algorithm specific input data (for example, the Reduction
      Percentage for the Loss Abatement Algorithm)  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 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 of different
   supported report types, a reacting node MUST process each received

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

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

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

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

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

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

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

      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").  Reporting Node Maintenance of Overload Control State

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

      Note: If a reporting node knows through absence of the 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 SHOULD be set to
   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.

      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 sequences beginning
      with 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 a reporting node wishes to instruct reacting
      nodes to continue overload abatement for a longer period of time

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

      For instance, if 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.

   A reporting node MUST increment 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 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 a reporting node knows that the OCS entries in the
      reacting nodes are near expiration then the reporting node might
      decide not to 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.

5.2.2.  Reacting Node Behavior

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

   If the request matches an active OCS then the reacting node MUST use
   the overload abatement algorithm indicated in the OCS to determine if
   the request is to receive overload abatement treatment.

   For the Loss abatement algorithm defined in this specification, see
   Section 6 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.

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   If diversion abatement treatment is possible (i.e. a different path
   for the request can be selected where the overloaded node is not part
   of the different path), then the reacting node SHOULD apply diversion
   abatement treatment to the request.  The reacting node MUST apply
   throttling abatement treatment to requests identified for abatement
   treatment when diversion treatment is not possible or was not

      Note: This only addresses the case where there are two defined
      abatement treatments, diversion and throttling.  Any extension
      that defines a new abatement treatment must also defined the
      interaction of the new abatement treatment with existing

   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 8.

   Diameter endpoints that throttle requests need to do so according to
   the rules of the client application.  Those rules will vary by
   application, and are beyond the scope of this document.

   In the case that the OCS entry indicated no traffic was to be sent to
   the overloaded entity and the validity duration expires then overload
   abatement associated with the overload report MUST be ended in a
   controlled fashion.

5.2.3.  Reporting Node Behavior

   If there is an active OCS entry then a reporting node SHOULD include
   the OC-OLR AVP in all answers 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 depend on the 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: 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) a reporting node may not

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      be able to guarantee that the reacting node has received the

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

      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 will be explicitly
      indicated by new feature bits in the OC-Feature-Vector AVP.

   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.

   A reporting node MAY rely on the OC-Validity-Duration AVP values for
   the implicit overload control state cleanup on the reacting node.

      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

   When a reporting node sends an OLR, it effectively delegates any
   necessary throttling to downstream nodes.  If the reporting node also
   locally throttles the same set of messages, the overall number of
   throttled 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, even if the set of messages match existing OCS entries, the
   reporting node can still apply other abatement methods such as
   diversion.  The reporting node might also need to throttle requests
   for reasons other 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.  The reporting
   node also has the option to send new OLRs requesting greater
   reductions in traffic, reducing the need for local throttling.

   A reporting node SHOULD decrease requested overload abatement
   treatment in a controlled fashion to avoid oscillations in traffic.

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      For example, it might wait some period of time after overload ends
      before terminating the OLR, or it might send a series of OLRs
      indicating progressively less overload severity.

5.3.  Protocol Extensibility

   The DOIC solution can be 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 for the OC-Feature-
   Vector.  This feature bit is used to communicate support for the new

   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 or
   OC-OLR AVPs defined in this document.

   [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.

   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 OC-Supported-Feature and OC-OLR AVPs 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.  Any new sub-AVPs MUST NOT require that the
   M-bit be set.

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

   As with any Diameter specification, RFC6733 requires all new AVPs to
   be registered with IANA.  See Section 9 for the required procedures.
   New features (feature bits in the OC-Feature-Vector AVP) and report
   types (in the OC-Report-Type AVP) MUST be registered with IANA.

6.  Loss Algorithm

   This section documents the Diameter overload loss abatement

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6.1.  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 5.1.

   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 request the stateless reduction of the number of
   requests by an indicated percentage.  This percentage reduction is in
   comparison to the number of messages the node otherwise would send,
   regardless of how many requests the node might have sent in the past.

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

   1.  An overload report is received and the associated 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

   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 or equal to the indicated
       reduction percentage then the request is given abatement
       treatment, otherwise the request is given normal routing

6.2.  Reporting Node Behavior

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

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   When a reporting node that has selected the loss abatement algorithm
   determines the need to request a reduction in traffic, it includes an
   OC-OLR AVP in answer messages as described in Section 5.2.3.

   When sending the OC-OLR AVP, the reporting node MUST indicate a
   percentage reduction in the 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 5.2.3.

6.3.  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 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

   If reacting node comes out of the 100 percent traffic reduction as a
   result of the overload report timing out, 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

      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.

7.  Attribute Value Pairs

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

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7.1.  OC-Supported-Features AVP

   The OC-Supported-Features AVP (AVP code TBD1) is 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 ]

7.2.  OC-Feature-Vector AVP

   The OC-Feature-Vector AVP (AVP code TBD2) is 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.
   The absence of the OC-Feature-Vector AVP in request messages
   indicates that only the default traffic abatement algorithm described
   in this specification is supported.  The absence of the OC- Feature-
   Vector AVP in answer messages indicates that the default traffic
   abatement algorithm described in this specification is selected
   (while other traffic abatement algorithms may be supported), and no
   features other than abatement algorithms are 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.

7.3.  OC-OLR AVP

   The OC-OLR AVP (AVP code TBD3) is of type Grouped and contains the
   information necessary to convey an overload report on an overload
   condition at the reporting node.  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

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   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 ]

7.4.  OC-Sequence-Number AVP

   The OC-Sequence-Number AVP (AVP code TBD4) is of type Unsigned64.
   Its usage in the context of overload control is described in
   Section 5.2.

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

7.5.  OC-Validity-Duration AVP

   The OC-Validity-Duration AVP (AVP code TBD5) is of type Unsigned32
   and indicates in seconds the validity time of the overload report.
   The number of seconds 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 30 seconds.  When the OC-
   Validity-Duration AVP is not present in the OC-OLR AVP, the default
   value applies.  The maximum value for the OC-Validity-Duration AVP is
   86,400 seconds (24 hours).

7.6.  OC-Report-Type AVP

   The OC-Report-Type AVP (AVP code TBD6) is of type Enumerated.  The
   value of the AVP describes what the overload report concerns.  The
   following values are initially defined:

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

   REALM_REPORT 1  The overload report is for a realm.  Overload
      abatement treatment applies to realm-routed requests.

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7.7.  OC-Reduction-Percentage AVP

   The OC-Reduction-Percentage AVP (AVP code TBD7) is of type Unsigned32
   and describes the percentage of the traffic that the sender is
   requested to reduce, compared to what it otherwise would send.  The
   OC-Reduction-Percentage AVP applies to the default (loss) algorithm
   specified in this specification.  However, the AVP can be reused for
   future abatement algorithms, if its semantics fit into the new

   The value of the Reduction-Percentage AVP is between zero (0) and one
   hundred (100).  Values greater than 100 are ignored.  The value of
   100 means that all traffic is to be throttled, i.e. the reporting
   node is under a severe load and ceases to process any new messages.
   The value of 0 means that the reporting node is in a stable state and
   has no need for the reacting node to apply any traffic abatement.

7.8.  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-Feature-Vector      TBD2  6.2      Unsigned64  |    | V  |
      |OC-OLR                 TBD3  6.3      Grouped     |    | V  |
      |OC-Sequence-Number     TBD4  6.4      Unsigned64  |    | V  |
      |OC-Validity-Duration   TBD5  6.5      Unsigned32  |    | V  |
      |OC-Report-Type         TBD6  6.6      Enumerated  |    | V  |
      |OC-Reduction                                      |    |    |
      |  -Percentage          TBD7  6.7      Unsigned32  |    | V  |

   As described in the Diameter base protocol [RFC6733], the M-bit usage
   for a given AVP in a given command may be defined by the application.

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8.  Error Response Codes

   When a DOIC node rejects a Diameter request due to overload, the DOIC
   node MUST select an appropriate error response code.  This
   determination is made based on the probability of the request
   succeeding if retried on a different path.

      Note: This only applies for DOIC nodes that are not the originator
      of the request.

   A reporting node rejecting a Diameter request due to an overload
   condition SHOULD send a DIAMETER_TOO_BUSY error response, if it can
   assume that the same request may succeed on a different path.

   If a reporting node knows 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 of overload.

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

      If the request arrived at the reporting node with 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 to the same reporting node.
      DIAMETER_UNABLE_TO_COMPLY would be sent in this case.

      A second example is when an agent that supports the DOIC solution
      is performing the role of a reacting node for a non supporting
      client.  Requests that are rejected as a result of DOIC throttling
      by the agent in this scenario would generally be rejected with a
      DIAMETER_UNABLE_TO_COMPLY response code.

9.  IANA Considerations

9.1.  AVP codes

   New AVPs defined by this specification are listed in Section 7.  All
   AVP codes are allocated from the 'Authentication, Authorization, and
   Accounting (AAA) Parameters' AVP Codes registry.

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9.2.  New registries

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

   A new "Overload Control Feature Vector" registry is required.  The
   registry must contain the following:

      Feature Vector Value

      Specification - the specification that defines the new value.

   See Section 7.2 for the initial Feature Vector Value in the registry.
   This specification is the specification defining the value.  New
   values can be added into the registry using the Specification
   Required policy.  [RFC5226].

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

      Report Type Value

      Specification - the specification that defines the new value.

   See Section 7.6 for the initial assignment in the registry.  New
   types can be added using the Specification Required policy [RFC5226].

10.  Security Considerations

   DOIC gives Diameter nodes the ability to request that downstream
   nodes send fewer Diameter requests.  Nodes do this by exchanging
   overload reports that directly effect this reduction.  This exchange
   is potentially subject to multiple methods of attack, and has the
   potential to be used as a Denial-of-Service (DoS) attack vector.

   Overload reports may contain information about the topology and
   current status of a Diameter network.  This information is
   potentially sensitive.  Network operators may wish to control
   disclosure of overload 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.

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10.1.  Potential Threat Modes

   The Diameter protocol involves transactions in the form 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, or the 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 traffic between peers.
   Nodes can make authorization decisions based on the peer identities
   authenticated at the transport layer.

   When agents are involved, this presents an effectively transitive
   trust model.  That is, a Diameter client or server can authorize an
   agent for certain actions, but it must trust that agent to make
   appropriate authorization decisions about its peers, and so on.
   Since confidentiality and integrity protection occurs at the
   transport layer, agents can read, and perhaps modify, any part of a
   Diameter message, including an overload report.

   There are several ways an attacker might attempt to exploit 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 that agent fails to apply proper authorization
   policies, downstream nodes may mistakenly trust the report.  This
   attack is at least partially mitigated by the assumption that nodes
   include overload reports in Diameter answers but not in requests.
   This requires an attacker to have knowledge of the original request
   in order to construct an answer.  Such an answer would also need to
   arrive at a Diameter node via a protected transport connection.
   Therefore, implementations MUST validate that an answer containing an
   overload report is a properly constructed response to a pending
   request prior to acting on the overload report, and that the 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 realm "" might send an overload report indicating
   that a competitor's realm "" is overloaded.  If other
   nodes act on the report, they may falsely believe that ""
   is overloaded, effectively reducing that realm's capacity.
   Therefore, it's critical that nodes validate that an overload report
   received from a peer actually falls within that peer's responsibility
   before acting on the report or forwarding the report to other peers.
   For example, an overload report from a peer that applies to a realm
   not handled by that peer is suspect.

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      This attack is partially mitigated by the fact that the
      application, as well as host and realm, for a given OLR is
      determined implicitly by respective AVPs in the enclosing answer.
      If a reporting node modifies any of those AVPs, the enclosing
      transaction will also be affected.

10.2.  Denial of Service Attacks

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

   An attacker might use the information in an OLR to assist in DoS
   attacks.  For example, an attacker could use information about
   current overload conditions to time an attack for maximum effect, or
   use subsequent overload reports as a feedback mechanism to learn the
   results of a previous or ongoing attack.  Operators need the ability
   to ensure that OLRs are not leaked to untrusted parties.

10.3.  Non-Compliant Nodes

   In the absence of an overload control mechanism, Diameter nodes need
   to implement strategies to protect themselves from floods of
   requests, and to make sure that a disproportionate load from one
   source does not prevent other sources from receiving service.  For
   example, a Diameter server might throttle a certain percentage of
   requests from sources 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 the first place.
   However, the presence of an overload control mechanism does not
   remove the need for these other protection strategies.

   When a Diameter node sends an overload report, it cannot assume that
   all nodes will comply, even if they indicate support for DOIC.  A
   non-compliant node might continue to 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 solution
   cannot assume that all Diameter nodes in a network are trusted, and
   that malicious nodes not be allowed to take advantage of the overload
   control mechanism to get more than their fair share of service.

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10.4.  End-to End-Security Issues

   The lack of end-to-end integrity features makes it difficult to
   establish trust in overload reports received 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 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.  DOIC
   nodes MUST strip DOIC AVPs from messages received from peers that are
   not trusted for DOIC purposes.

   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.

      A DOIC node cannot always automatically detect that a peer also
      supports DOIC.  For example, a node might have a peer that is a
      non-supporting agent.  If nodes on the other side of that agent
      send OC-Supported-Features AVPs, the agent is likely to forward
      them as unknown AVPs.  Messages received across the non-supporting
      agent may be indistinguishable from messages received across a
      DOIC supporting agent, giving the false impression that the non-
      supporting agent actually supports DOIC.  This complicates the
      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 time of this writing, the DIME working group is studying
   requirements for adding end-to-end security features
   [I-D.ietf-dime-e2e-sec-req] 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 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

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   Diameter end-to-end security mechanism with overload control will
   require careful consideration, and are beyond the scope of this

11.  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

12.  References

12.1.  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.

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

12.2.  Informative References

   [Cx]       3GPP, , "ETSI TS 129 229 V11.4.0", August 2013.

              Tschofenig, H., Korhonen, J., Zorn, G., and K. Pillay,
              "Diameter AVP Level Security: Scenarios and Requirements",
              draft-ietf-dime-e2e-sec-req-01 (work in progress), October

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   [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.

   [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

A.1.  Additional traffic abatement algorithms

   This specification describes only means for a 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 7.1 and 9 for the required IANA

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.

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   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

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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

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.

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   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

   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

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           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

   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.

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   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

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

           *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

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           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

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           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

   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

   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

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           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

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

   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

   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

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

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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

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

   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

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.]

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   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

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

           *Partially Compliant*. (See response to previous

   REQ 30: The 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 employed with DOIC.

C.6.7.  Flexibility and Extensibility

   REQ 31: There are multiple situations where a Diameter node may be
           overloaded for some purposes but not others.  For example,
           this can happen to an agent or server that supports multiple
           applications, or when a server depends on multiple external

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           resources, some of which may become overloaded while others
           are fully available.  The solution MUST allow Diameter nodes
           to indicate overload with sufficient granularity to allow
           clients to take action based on the 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 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
           local overload for an agent.  At the time of this writing,
           the DIME working group has plans to work on an agent-overload

           DOIC allows new "scopes" through the use of extended report

   REQ 32: The solution MUST provide a method for extending the
           information communicated and the algorithms used for overload

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

   REQ 33: The solution MUST provide a default algorithm that is
           mandatory to implement.

           *Compliant*. The "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 support the solution.

           *Partially Compliant*. DOIC information can traverse non-
           supporting agents, as long as those agents do not modify
           certain AVPs. (e.g., Origin-Host).  DOIC does not provide a
           way for supporting nodes to detect such modification.

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Appendix D.  Considerations for Applications Integrating the DOIC

   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:

      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:

      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.

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   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:

      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:

      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

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   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 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 request is a request that uses the same Session-
      Id than the one used in a previous request.  An intra-session
      request generally needs to be delivered to the server that handled
      the session creating request for the session.  The STR message
      defined in [RFC6733] is an example of an intra-session request.

   Pseudo-Session Requests:

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      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:

      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 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:

      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:

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

   Intra-Session Requests:

      There are two types of intra-sessions requests, requests that
      terminate a session and the remainder of intra-session requests.
      Implementers and operators may choose to throttle session-
      terminating requests less aggressively in order to gracefully
      terminate sessions, allow 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)
   Porkkalankatu 24
   Helsinki  FIN-00180


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


   Ben Campbell
   7460 Warren Parkway
   Frisco, Texas  75034
   United States


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   Lionel Morand
   Orange Labs
   38/40 rue du General Leclerc
   Issy-Les-Moulineaux Cedex 9  92794

   Phone: +33145296257

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