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rfc:rfc7683

Internet Engineering Task Force (IETF) J. Korhonen, Ed. Request for Comments: 7683 Broadcom Corporation Category: Standards Track S. Donovan, Ed. ISSN: 2070-1721 B. Campbell

                                                                Oracle
                                                             L. Morand
                                                           Orange Labs
                                                          October 2015
              Diameter Overload Indication Conveyance

Abstract

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

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7683.

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
 (http://trustee.ietf.org/license-info) 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
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Korhonen, et al. Standards Track [Page 1] RFC 7683 DOIC October 2015

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Terminology and Abbreviations . . . . . . . . . . . . . . . .   3
 3.  Conventions Used in This Document . . . . . . . . . . . . . .   5
 4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   5
   4.1.  Piggybacking  . . . . . . . . . . . . . . . . . . . . . .   6
   4.2.  DOIC Capability Announcement  . . . . . . . . . . . . . .   7
   4.3.  DOIC Overload Condition Reporting . . . . . . . . . . . .   9
   4.4.  DOIC Extensibility  . . . . . . . . . . . . . . . . . . .  11
   4.5.  Simplified Example Architecture . . . . . . . . . . . . .  12
 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  . . . . . . . . . . . . . . . . . . . . . . .  23
   6.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  23
   6.2.  Reporting Node Behavior . . . . . . . . . . . . . . . . .  24
   6.3.  Reacting Node Behavior  . . . . . . . . . . . . . . . . .  24
 7.  Attribute Value Pairs . . . . . . . . . . . . . . . . . . . .  25
   7.1.  OC-Supported-Features AVP . . . . . . . . . . . . . . . .  25
   7.2.  OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . .  25
   7.3.  OC-OLR AVP  . . . . . . . . . . . . . . . . . . . . . . .  26
   7.4.  OC-Sequence-Number AVP  . . . . . . . . . . . . . . . . .  26
   7.5.  OC-Validity-Duration AVP  . . . . . . . . . . . . . . . .  26
   7.6.  OC-Report-Type AVP  . . . . . . . . . . . . . . . . . . .  27
   7.7.  OC-Reduction-Percentage AVP . . . . . . . . . . . . . . .  27
   7.8.  AVP Flag Rules  . . . . . . . . . . . . . . . . . . . . .  28
 8.  Error Response Codes  . . . . . . . . . . . . . . . . . . . .  28
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
   9.1.  AVP Codes . . . . . . . . . . . . . . . . . . . . . . . .  29
   9.2.  New Registries  . . . . . . . . . . . . . . . . . . . . .  29
 10. Security Considerations . . . . . . . . . . . . . . . . . . .  30
   10.1.  Potential Threat Modes . . . . . . . . . . . . . . . . .  30
   10.2.  Denial-of-Service Attacks  . . . . . . . . . . . . . . .  31
   10.3.  Noncompliant Nodes . . . . . . . . . . . . . . . . . . .  32
   10.4.  End-to-End Security Issues . . . . . . . . . . . . . . .  32
 11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
   11.1.  Normative References . . . . . . . . . . . . . . . . . .  34
   11.2.  Informative References . . . . . . . . . . . . . . . . .  34

Korhonen, et al. Standards Track [Page 2] RFC 7683 DOIC October 2015

 Appendix A.  Issues Left for Future Specifications  . . . . . . .  35
   A.1.  Additional Traffic Abatement Algorithms . . . . . . . . .  35
   A.2.  Agent Overload  . . . . . . . . . . . . . . . . . . . . .  35
   A.3.  New Error Diagnostic AVP  . . . . . . . . . . . . . . . .  35
 Appendix B.  Deployment Considerations  . . . . . . . . . . . . .  35
 Appendix C.  Considerations for Applications Integrating the DOIC
              Solution . . . . . . . . . . . . . . . . . . . . . .  36
   C.1.  Application Classification  . . . . . . . . . . . . . . .  36
   C.2.  Implications of Application Type Overload . . . . . . . .  37
   C.3.  Request Transaction Classification  . . . . . . . . . . .  38
   C.4.  Request Type Overload Implications  . . . . . . . . . . .  39
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  41
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

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

2. Terminology and Abbreviations

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

Korhonen, et al. Standards Track [Page 3] RFC 7683 DOIC October 2015

 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.
 Diversion
    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 Attribute
    Value Pair (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
    Requests sent by a reacting node where the reacting node does not
    know to which host the request will be routed.
 Reporting Node
    A Diameter node that generates an overload report.  (This may or
    may not be the overloaded node.)

Korhonen, et al. Standards Track [Page 4] RFC 7683 DOIC October 2015

 Throttling
    An abatement treatment that limits the number of requests sent by
    the 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 transaction.

3. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].
 The interpretation from RFC 2119 [RFC2119] does not apply for the
 above listed words when they are not used in all caps.

4. Solution Overview

 The Diameter Overload Information Conveyance (DOIC) solution allows
 Diameter nodes to request that other Diameter nodes 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 (OLRs).
 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.
 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 bidirectional 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.

Korhonen, et al. Standards Track [Page 5] RFC 7683 DOIC October 2015

 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 7.1) 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
 DOIC.
 Reacting nodes perform overload abatement according to an agreed-upon
 abatement algorithm.  An abatement algorithm defines the meaning of
 some of the parameters of an OLR and the procedures required for
 overload abatement.  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.
 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

Korhonen, et al. Standards Track [Page 6] RFC 7683 DOIC October 2015

 application messages.  This is made possible by adding the optional
 overload control AVPs OC-OLR and OC-Supported-Features into existing
 commands.
 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 that are originated
 or relayed by the reporting node and 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
 Client.

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 the 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
 message.
 The individual features supported by the DOIC nodes are indicated in
 the OC-Feature-Vector AVP.  Any semantics associated with the
 features will be defined in extension specifications that introduce
 the features.
    Note: As discussed elsewhere in the document, agents in the path
    of the request can modify the OC-Supported-Features AVP.

Korhonen, et al. Standards Track [Page 7] RFC 7683 DOIC October 2015

    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 advertised 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
 requested.
    Note that the loss algorithm defined in this document is a
    stateless abatement algorithm.  As a result, it does not require
    any actions by reacting nodes prior to the receipt of an overload
    report.  Stateful abatement algorithms that base the abatement
    logic on a history of request messages sent might require reacting
    nodes to maintain state in advance of receiving an overload report
    to ensure that the overload reports can be properly handled.
 While it should only be done in exceptional circumstances and not
 during an active occurrence of overload, a reacting node that wishes
 to transition to a different abatement algorithm can stop advertising
 support for the algorithm indicated by the reporting node, as long as
 support for the loss algorithm is always advertised.

Korhonen, et al. Standards Track [Page 8] RFC 7683 DOIC October 2015

 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.  As such, the agent
    must act as a fully compliant reporting node to the downstream
    reacting node and as a fully compliant reacting node to the
    upstream reporting node.

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 AVPs specific to the abatement
 algorithm.
 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 (as defined 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 (as defined in Section 2) sent for this application to the
 overloaded realm.

Korhonen, et al. Standards Track [Page 9] RFC 7683 DOIC October 2015

 This document assumes that there is a single source for realm reports
 for a given realm, or that if multiple nodes can send realm reports,
 that each such node has full knowledge of the overload state of the
 entire realm.  A reacting node cannot distinguish between receiving
 realm reports from a single node or from multiple nodes.
    Note: Known issues exist if there are multiple sources for
    overload reports that apply to the same Diameter entity.  Reacting
    nodes have no way of determining the source and, as such, will
    treat them as coming from a single source.  Variance in sequence
    numbers between the two sources can then cause incorrect overload
    abatement treatment to be applied for indeterminate periods of
    time.
 Reporting nodes are responsible for determining the need for a
 reduction of traffic.  The method for making this determination is
 implementation specific and 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

Korhonen, et al. Standards Track [Page 10] RFC 7683 DOIC October 2015

 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.
 Note that erroneous overload reports can be used for DoS attacks.
 This includes the ability to indicate that a significant reduction in
 traffic, up to and including a request for no traffic, should be sent
 to a reporting node.  As such, care should be taken to verify the
 sender of overload reports.

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.

Korhonen, et al. Standards Track [Page 11] RFC 7683 DOIC October 2015

4.5. Simplified Example Architecture

 Figure 1 illustrates the simplified architecture for Diameter
 overload information conveyance.
  Realm X                                  Same or other Realms
 <--------------------------------------> <---------------------->
    +--------+                 : (optional) :
    |Diameter|                 :            :
    |Server A|--+     .--.     : +--------+ :     .--.
    +--------+  |   _(    `.   : |Diameter| :   _(    `.   +--------+
                +--(        )--:-|  Agent |-:--(        )--|Diameter|
    +--------+  | ( `  .  )  ) : +--------+ : ( `  .  )  ) | Client |
    |Diameter|--+  `--(___.-'  :            :  `--(___.-'  +--------+
    |Server B|                 :            :
    +--------+                 :            :
                        End-to-end Overload Indication
           1)  <----------------------------------------------->
                           Diameter Application Y
                Overload Indication A    Overload Indication A'
           2)  <----------------------> <---------------------->
               Diameter Application Y   Diameter Application Y
   Figure 1: Simplified Architecture Choices for Overload Indication
                               Delivery
 In Figure 1, the Diameter overload indication can be conveyed (1)
 end-to-end between servers and clients or (2) between servers and the
 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

Korhonen, et al. Standards Track [Page 12] RFC 7683 DOIC October 2015

    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
    reporting node to select different features on a per-transaction
    basis.

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
 AVP.
    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.

Korhonen, et al. Standards Track [Page 13] RFC 7683 DOIC October 2015

 A reporting node MUST NOT include the OC-Supported-Features AVP,
 OC-OLR AVP, or any other overload control AVPs defined in extension
 documents 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 select a single 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 the OC-Feature-Vector AVP.  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 documents 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 policy of the
    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
 message.

Korhonen, et al. Standards Track [Page 14] RFC 7683 DOIC October 2015

 For a Diameter Agent to be a reacting node for a non-supporting
 Diameter endpoint, the Diameter Agent MUST include the OC-Supported-
 Features AVP in request messages it 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.
    Example: 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
 decision.

Korhonen, et al. Standards Track [Page 15] RFC 7683 DOIC October 2015

5.2.1.1. Overload Control State for Reacting Nodes

 A reacting node maintains the following OCS per supported Diameter
 application:
 o  a host-type OCS entry for each Destination-Host to which it sends
    host-type requests and
 o  a realm-type OCS entry for each Destination-Realm to which it
    sends realm-type requests.
 A host-type OCS entry is identified by the pair of Application-ID 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
 decision):
 o  Sequence number (as received in OC-OLR; see Section 7.3)
 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  Input data that is abatement algorithm specific (as received in
    the OC-OLR AVP -- for example, OC-Reduction-Percentage for the
    loss abatement algorithm)

5.2.1.2. 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 it includes the following
 information (the actual information stored is an implementation
 decision):
 o  Sequence number
 o  Validity duration

Korhonen, et al. Standards Track [Page 16] RFC 7683 DOIC October 2015

 o  Expiration time
 o  Input data that is algorithm specific (for example, the reduction
    percentage for the loss abatement algorithm)

5.2.1.3. Reacting Node's 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
 OLR.
 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 reacting node determines that the sequence number has rolled
 over, then the reacting node MUST update the matching OCS entry.
 This can be determined by recognizing that the number has changed
 from a value within 1% of the maximum value in the OC-Sequence-Number
 AVP to a value within 1% of the minimum value in the OC-Sequence-
 Number AVP.

Korhonen, et al. Standards Track [Page 17] RFC 7683 DOIC October 2015

 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 an OCS entry
 with the Application-ID in the received message and DiameterIdentity
 of the Origin-Host in the received message.
    Note: This solution assumes that the Origin-Host AVP in the answer
    message included by the reporting node is not changed along the
    path to the reacting node.
 For a realm report, this means a reacting node creates an 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 the recommended behavior is 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").

5.2.1.4. Reporting Node's 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.

Korhonen, et al. Standards Track [Page 18] RFC 7683 DOIC October 2015

    Note: One way of addressing this over a reboot of a reporting node
    is to use a timestamp 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.
    Example: If a reporting node wishes to instruct reacting nodes to
    continue overload abatement for a longer period of time 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 parameters specific to the abatement algorithm, including, for
 example, the reduction percentage used for the loss abatement
 algorithm.
    Example: 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 them 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
 unexpired 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.

Korhonen, et al. Standards Track [Page 19] RFC 7683 DOIC October 2015

 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.
 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
 applied.
    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 define its
    interaction with existing treatments.
 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 1) if the Application-ID in the request
    matches the Application-ID in any active OCS entry and 2) 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.

Korhonen, et al. Standards Track [Page 20] RFC 7683 DOIC October 2015

 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
    be able to guarantee that the reacting node has received the
    report.
 A reporting node MUST NOT send overload reports of a type that has
 not been advertised as supported by the reacting node.
    Note: 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 cleanup of overload control state 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
    expired.
 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

Korhonen, et al. Standards Track [Page 21] RFC 7683 DOIC October 2015

 for reasons other than overload.  For example, an agent or server
 might have a configured rate limit for each client and might 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.
    Example: A reporting node 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
 AVP.  This feature bit is used to communicate support for the new
 feature.
 The extension may define new AVPs for use in the 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.
 The Grouped AVP extension mechanisms defined in [RFC6733] 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.

Korhonen, et al. Standards Track [Page 22] RFC 7683 DOIC October 2015

 As with any Diameter specification, RFC 6733 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
 algorithm.

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 DOIC 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
     entry.
 4.  The reacting node determines if overload abatement treatment
     should be applied to the request.  One approach that could be
     taken for each request is to select a uniformly selected random
     number between 1 and 100.  If the random number is less than or

Korhonen, et al. Standards Track [Page 23] RFC 7683 DOIC October 2015

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

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.
 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 handling 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
    treatment.
 If the reacting node comes out of the 100% traffic reduction
 (meaning, it has received an OLR indicating that no traffic should be
 sent, 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%
 reduction.

Korhonen, et al. Standards Track [Page 24] RFC 7683 DOIC October 2015

    Note: 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
 document.
 Refer to Section 4 of [RFC6733] for more information on AVPs and AVP
 data types.

7.1. OC-Supported-Features AVP

 The OC-Supported-Features AVP (AVP Code 621) 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: 621 >
                              [ OC-Feature-Vector ]
                            * [ AVP ]

7.2. OC-Feature-Vector AVP

 The OC-Feature-Vector AVP (AVP Code 622) 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.

Korhonen, et al. Standards Track [Page 25] RFC 7683 DOIC October 2015

 The following capability is 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 623) 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 identified by the Application-ID found in the Diameter
 message header.  The host or realm the OC-OLR AVP concerns is
 determined from the Origin-Host AVP and/or Origin-Realm AVP found in
 the encapsulating Diameter command.  The OC-OLR AVP is intended to be
 sent only by a reporting node.
    OC-OLR ::= < AVP Header: 623 >
               < 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 624) 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 nonvolatile increasing counter for a sequence of overload
 reports between two DOIC nodes for the same overload occurrence.
 Sequence numbers are treated in a unidirectional manner, i.e., two
 sequence numbers in each direction between two DOIC nodes are not
 related or correlated.

7.5. OC-Validity-Duration AVP

 The OC-Validity-Duration AVP (AVP Code 625) 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

Korhonen, et al. Standards Track [Page 26] RFC 7683 DOIC October 2015

 86,400 seconds (24 hours).  If the value received in the OC-Validity-
 Duration is greater than the maximum value, then the default value
 applies.

7.6. OC-Report-Type AVP

 The OC-Report-Type AVP (AVP Code 626) 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.
 The values 2-4294967295 are unassigned.

7.7. OC-Reduction-Percentage AVP

 The OC-Reduction-Percentage AVP (AVP Code 627) 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
 algorithm.
 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.

Korhonen, et al. Standards Track [Page 27] RFC 7683 DOIC October 2015

7.8. AVP Flag Rules

                                                       +---------+
                                                       |AVP flag |
                                                       |rules    |
                                                       +----+----+
                            AVP   Section              |    |MUST|
     Attribute Name         Code  Defined  Value Type  |MUST| NOT|
    +--------------------------------------------------+----+----+
    |OC-Supported-Features  621   7.1      Grouped     |    | V  |
    +--------------------------------------------------+----+----+
    |OC-Feature-Vector      622   7.2      Unsigned64  |    | V  |
    +--------------------------------------------------+----+----+
    |OC-OLR                 623   7.3      Grouped     |    | V  |
    +--------------------------------------------------+----+----+
    |OC-Sequence-Number     624   7.4      Unsigned64  |    | V  |
    +--------------------------------------------------+----+----+
    |OC-Validity-Duration   625   7.5      Unsigned32  |    | V  |
    +--------------------------------------------------+----+----+
    |OC-Report-Type         626   7.6      Enumerated  |    | V  |
    +--------------------------------------------------+----+----+
    |OC-Reduction                                      |    |    |
    |  -Percentage          627   7.7      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.

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, the DIAMETER_UNABLE_TO_COMPLY error
 response SHOULD be used.  Retrying would consume valuable resources
 during an occurrence of overload.

Korhonen, et al. Standards Track [Page 28] RFC 7683 DOIC October 2015

    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 "AVP Codes" sub-registry under the
 "Authentication, Authorization, and Accounting (AAA) Parameters"
 registry.

9.2. New Registries

 Two new registries have been created in the "AVP Specific Values"
 sub-registry under the "Authentication, Authorization, and Accounting
 (AAA) Parameters" registry.
 A new "OC-Feature-Vector AVP Values (code 622)" registry has been
 created.  This registry contains the following:
    Feature Vector Value Name
    Feature Vector Value
    Specification defining the new value
 See Section 7.2 for the initial Feature Vector Value in the registry.
 This specification defines the value.  New values can be added to the
 registry using the Specification Required policy [RFC5226].

Korhonen, et al. Standards Track [Page 29] RFC 7683 DOIC October 2015

 A new "OC-Report-Type AVP Values (code 626)" registry has been
 created.  This registry contains the following:
    Report Type Value Name
    Report Type Value
    Specification defining 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.  For
 instance, a series of injected realm OLRs with a requested reduction
 percentage of 100% could be used to completely eliminate any traffic
 from being sent to that realm.
 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 their
 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.

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.

Korhonen, et al. Standards Track [Page 30] RFC 7683 DOIC October 2015

 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 occur 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 "example.com" might send an overload report indicating
 that a competitor's realm "example.net" is overloaded.  If other
 nodes act on the report, they may falsely believe that "example.net"
 is overloaded, effectively reducing that realm's capacity.
 Therefore, it's critical that nodes validate that an overload report
 received 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.  This may require out-of-band,
 non-Diameter agreements and/or mechanisms.
    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

Korhonen, et al. Standards Track [Page 31] RFC 7683 DOIC October 2015

 protocols, a DoS attack on Diameter is likely to impact those
 protocols as well.  In the worst case, where the Diameter application
 is being used for access control into an IP network, a coordinated
 DoS attack could result in the blockage of all traffic into that
 network.  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. Noncompliant 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
 noncompliant node might continue to send requests with no reduction
 in load.  Such noncompliance could be done accidentally or
 maliciously to gain an unfair advantage over compliant nodes.
 Requirement 28 in [RFC7068] indicates that the overload control
 solution cannot assume that all Diameter nodes in a network are
 trusted.  It also requires that malicious nodes not be allowed to
 take advantage of the overload control mechanism to get more than
 their fair share of service.

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

Korhonen, et al. Standards Track [Page 32] RFC 7683 DOIC October 2015

 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.
 It is expected that work on end-to-end Diameter security 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 allows Diameter Agents to modify AVPs in,
 or insert additional AVPs into, existing messages that are originated
 by other nodes.  If end-to-end security is enabled, there is a risk
 that such modification could violate integrity protection.  The
 details of using any future Diameter end-to-end security mechanism
 with overload control will require careful consideration, and are
 beyond the scope of this document.

Korhonen, et al. Standards Track [Page 33] RFC 7683 DOIC October 2015

11. References

11.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.
 [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
            Ed., "Diameter Base Protocol", RFC 6733,
            DOI 10.17487/RFC6733, October 2012,
            <http://www.rfc-editor.org/info/rfc6733>.

11.2. Informative References

 [Cx]       3GPP, "Cx and Dx interfaces based on the Diameter
            protocol; Protocol details", 3GPP TS 29.229 12.7.0,
            September 2015.
 [PCC]      3GPP, "Policy and charging control architecture", 3GPP
            TS 23.203 12.10.0, September 2015.
 [RFC4006]  Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
            Loughney, "Diameter Credit-Control Application", RFC 4006,
            DOI 10.17487/RFC4006, August 2005,
            <http://www.rfc-editor.org/info/rfc4006>.
 [RFC7068]  McMurry, E. and B. Campbell, "Diameter Overload Control
            Requirements", RFC 7068, DOI 10.17487/RFC7068, November
            2013, <http://www.rfc-editor.org/info/rfc7068>.
 [S13]      3GPP, "Evolved Packet System (EPS); Mobility Management
            Entity (MME) and Serving GPRS Support Node (SGSN) related
            interfaces based on Diameter protocol", 3GPP TS 29.272
            12.8.0, September 2015.

Korhonen, et al. Standards Track [Page 34] RFC 7683 DOIC October 2015

Appendix A. Issues Left for Future Specifications

 The base solution for 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 subsections
 define some of the potential extensions to the DOIC solution.

A.1. Additional Traffic Abatement Algorithms

 This specification describes only means for a simple loss-based
 algorithm.  Future algorithms can be added using the designed
 solution extension mechanism.  The new algorithms need to be
 registered with IANA.  See Sections 7.2 and 9 for the required IANA
 steps.

A.2. Agent Overload

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

A.3. New Error Diagnostic AVP

 This specification indicates the use of existing error messages when
 nodes reject requests due to overload.  There is an expectation that
 additional error codes or AVPs will be defined in a separate
 specification to indicate that overload was the reason for the
 rejection of the message.

Appendix B. Deployment Considerations

 Non-supporting Agents
    Due to the way that realm-routed requests are handled in Diameter
    networks with the server selection for the request done by an
    agent, network operators should enable DOIC at agents that perform
    server selection first.
 Topology-Hiding Interactions
    There exist proxies that implement what is referred to as Topology
    Hiding.  This can include cases where the agent modifies the
    Origin-Host in answer messages.  The behavior of the DOIC solution
    is not well understood when this happens.  As such, the DOIC
    solution does not address this scenario.

Korhonen, et al. Standards Track [Page 35] RFC 7683 DOIC October 2015

 Inter-Realm/Administrative Domain Considerations
    There are likely to be special considerations for handling DOIC
    signaling across administrative boundaries.  This includes
    considerations for whether or not information included in the DOIC
    signaling should be sent across those boundaries.  In addition,
    consideration should be taken as to whether or not a reacting node
    in one realm can be trusted to implement the requested overload
    abatement handling for overload reports received from a separately
    administered realm.

Appendix C. Considerations for Applications Integrating the DOIC

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

C.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 entity 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.

Korhonen, et al. Standards Track [Page 36] RFC 7683 DOIC October 2015

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

C.2. Implications of Application Type Overload

 This section discusses considerations for mitigating overload
 reported by a Diameter entity.  This discussion focuses on the type
 of application.  Appendix C.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 it 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.

Korhonen, et al. Standards Track [Page 37] RFC 7683 DOIC October 2015

 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
    repeated.
 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.

C.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.

Korhonen, et al. Standards Track [Page 38] RFC 7683 DOIC October 2015

 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 Policy and Charging Control (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 as 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:
    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 exist 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.

C.4. Request Type Overload Implications

 The request classes identified in Appendix C.3 have implications on
 decisions about which requests should be throttled first.  The
 following list of request treatments 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.

Korhonen, et al. Standards Track [Page 39] RFC 7683 DOIC October 2015

 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 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, it represents more work load than other requests.  As
    such, these requests might be throttled more frequently than other
    request types.
 Pseudo-session Requests:
    Throttling decisions for pseudo-session requests can take into
    consideration where individual requests fit into the overall
    sequence of requests within the pseudo-session.  Requests that are
    earlier in the sequence might be throttled more aggressively than
    requests that occur later in the sequence.
 Intra-session Requests:
    There are two 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.

Korhonen, et al. Standards Track [Page 40] RFC 7683 DOIC October 2015

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

Korhonen, et al. Standards Track [Page 41] RFC 7683 DOIC October 2015

Authors' Addresses

 Jouni Korhonen (editor)
 Broadcom Corporation
 3151 Zanker Road
 San Jose, CA  95134
 United States
 Email: jouni.nospam@gmail.com
 Steve Donovan (editor)
 Oracle
 7460 Warren Parkway
 Frisco, Texas  75034
 United States
 Email: srdonovan@usdonovans.com
 Ben Campbell
 Oracle
 7460 Warren Parkway
 Frisco, Texas  75034
 United States
 Email: ben@nostrum.com
 Lionel Morand
 Orange Labs
 38/40 rue du General Leclerc
 Issy-Les-Moulineaux Cedex 9  92794
 France
 Phone: +33145296257
 Email: lionel.morand@orange.com

Korhonen, et al. Standards Track [Page 42]

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