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Versions: (draft-docdt-dime-ovli) 00 01 02 03 04 05 06 07 08 09 10 RFC 7683

Diameter Maintenance and Extensions (DIME)              J. Korhonen, Ed.
Internet-Draft                                                  Broadcom
Intended status: Standards Track                         S. Donovan, Ed.
Expires: January 4, 2015                                     B. Campbell
                                                                  Oracle
                                                               L. Morand
                                                             Orange Labs
                                                            July 3, 2014


                Diameter Overload Indication Conveyance
                      draft-ietf-dime-ovli-03.txt

Abstract

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

Requirements

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

Status of This Memo

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

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

   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 January 4, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   (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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Abbreviations . . . . . . . . . . . . . . . .   4
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Overload Control Endpoints (Non normative)  . . . . . . .   6
     3.2.  Piggybacking Principle (Non normative)  . . . . . . . . .  10
     3.3.  DOIC Capability Announcement (Non normative)  . . . . . .  11
     3.4.  DOIC Overload Condition Reporting (Non normative) . . . .  12
     3.5.  DOIC Extensibility (Non normative)  . . . . . . . . . . .  13
     3.6.  Simplified Example Architecture (Non normative) . . . . .  14
     3.7.  Considerations for Applications Integrating the DOIC
           Solution (Non normative)  . . . . . . . . . . . . . . . .  15
       3.7.1.  Application Classification  (Non normative) . . . . .  15
       3.7.2.  Application Type Overload Implications  (Non
               normative)  . . . . . . . . . . . . . . . . . . . . .  16
       3.7.3.  Request Transaction Classification  (Non normative) .  18
       3.7.4.  Request Type Overload Implications  (Non normative) .  18
   4.  Solution Procedures (Normative) . . . . . . . . . . . . . . .  20
     4.1.  Capability Announcement (Normative) . . . . . . . . . . .  20
       4.1.1.  Reacting Node Behavior (Normative)  . . . . . . . . .  20
       4.1.2.  Reporting Node Behavior  (Normative)  . . . . . . . .  21
       4.1.3.  Agent Behavior  (Normative) . . . . . . . . . . . . .  22
     4.2.  Overload Report Processing (Normative)  . . . . . . . . .  22
       4.2.1.  Overload Control State (Normative)  . . . . . . . . .  22
       4.2.2.  Reacting Node Behavior  (Normative) . . . . . . . . .  24
       4.2.3.  Reporting Node Behavior  (Normative)  . . . . . . . .  26
       4.2.4.  Agent Behavior  (Normative) . . . . . . . . . . . . .  26
     4.3.  Protocol Extensibility (Normative)  . . . . . . . . . . .  27
   5.  Loss Algorithm (Normative)  . . . . . . . . . . . . . . . . .  28
     5.1.  Overview (Non normative)  . . . . . . . . . . . . . . . .  28
     5.2.  Use of OC-Reduction-Percentage AVP  . . . . . . . . . . .  29
     5.3.  Reporting Node Behavior (Normative) . . . . . . . . . . .  29
     5.4.  Reacting Node Behavior (Normative)  . . . . . . . . . . .  29
   6.  Attribute Value Pairs (Normative) . . . . . . . . . . . . . .  30
     6.1.  OC-Supported-Features AVP . . . . . . . . . . . . . . . .  31
     6.2.  OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . .  31
     6.3.  OC-OLR AVP  . . . . . . . . . . . . . . . . . . . . . . .  32
     6.4.  OC-Sequence-Number AVP  . . . . . . . . . . . . . . . . .  33
     6.5.  OC-Validity-Duration AVP  . . . . . . . . . . . . . . . .  33



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     6.6.  OC-Report-Type AVP  . . . . . . . . . . . . . . . . . . .  34
     6.7.  OC-Reduction-Percentage AVP . . . . . . . . . . . . . . .  35
     6.8.  Attribute Value Pair flag rules . . . . . . . . . . . . .  35
   7.  Error Response Codes  . . . . . . . . . . . . . . . . . . . .  36
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  36
     8.1.  AVP codes . . . . . . . . . . . . . . . . . . . . . . . .  36
     8.2.  New registries  . . . . . . . . . . . . . . . . . . . . .  37
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  37
     9.1.  Potential Threat Modes  . . . . . . . . . . . . . . . . .  37
     9.2.  Denial of Service Attacks . . . . . . . . . . . . . . . .  38
     9.3.  Non-Compliant Nodes . . . . . . . . . . . . . . . . . . .  39
     9.4.  End-to End-Security Issues  . . . . . . . . . . . . . . .  39
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  40
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  40
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  40
     11.2.  Informative References . . . . . . . . . . . . . . . . .  41
   Appendix A.  Issues left for future specifications  . . . . . . .  41
     A.1.  Additional traffic abatement algorithms . . . . . . . . .  41
     A.2.  Agent Overload  . . . . . . . . . . . . . . . . . . . . .  41
     A.3.  DIAMETER_TOO_BUSY clarifications  . . . . . . . . . . . .  42
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  42
     B.1.  Mix of Destination-Realm routed requests and Destination-
           Host routed requests  . . . . . . . . . . . . . . . . . .  42
   Appendix C.  Restructuring of -02 version of the draft  . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  48

1.  Introduction

   This specification defines a base solution for Diameter Overload
   Control (DOC), refered to as Diameter Overload Indication Conveyance
   (DOIC).  The requirements for the solution are described and
   discussed in the corresponding design requirements document
   [RFC7068].  Note that the overload control solution defined in this
   specification does not address all the requirements listed in
   [RFC7068].  A number of overload control related features are left
   for the future specifications.

   The solution defined in this specification addresses Diameter
   overload control between two endpoints (see Section 3.1).
   Furthermore, the solution is designed to apply to existing and future
   Diameter applications, requires no changes to the Diameter base
   protocol [RFC6733] and is deployable in environments where some
   Diameter nodes do not implement the Diameter overload control
   solution defined in this specification.







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2.  Terminology and Abbreviations

   Abatement Algorithm

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

   Throttling

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

      Editor's note: Propose to add a definition of Abatement to include
      both throttling and diversion (redirecting of messages) actions.
      Then to modify this definition to include just the rejecting of
      requests and adding a definition of diversion.

   Reporting Node

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

   Reacting Node

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

   Overload Control State (OCS)

      State describing an occurrence of overload control maintained by
      reporting and reacting nodes.

   Overload Report (OLR)

      A set of AVPs sent by a reporting node indicating the start or
      continuation of an occurrence of overload control.

3.  Solution Overview

   The Diameter Overload Information Conveyance (DOIC) mechanism allows
   Diameter nodes to request other nodes to perform overload abatement




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

   A reacting node consumes 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 (typically upstream) nodes.  Likewise, a reacting node may
   perform overload abatement on its own behalf, or on behalf of other
   (typically downstream) nodes.

   A node's role as a DOIC endpoint is independent of its Diameter role.
   For example, Diameter relay and proxy agents may act as DOIC
   endpoints, 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 a reporting node and a reacting node.

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

   DOIC endpoints 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 6.2) into existing requests and responses.  Reporting nodes
   send OLRs by inserting OC-OLR AVPs (Section 6.3).

   A given OLR applies to the Diameter realm and application of the
   Diameter message that carries it.  If a reporting node supports more
   than one realm and/or application, it reports independently for each
   combination of realm and application.  Similarly, OC-Feature-Vector
   AVPs apply 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
   the parameters of an OLR, and the procedures required for overload



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   abatement.  This document specifies a single must-support algorithm,
   namely the "loss" algorithm Section 5).  Future specifications may
   introduce new algorithms.

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

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

3.1.  Overload Control Endpoints (Non normative)

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

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

   C  Diameter client as defined in [RFC6733].

   S  Diameter server as defined in [RFC6733].



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

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

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

   DOIC Association  A DOIC association exists between two Diameter
      Overload Endpoints.  One of the endpoints is the overload reporter
      and the other is the overload reactor.

   Figure 1 illustrates the most basic configuration where a client is
   connected directly to a server.  In this case, the Diameter session
   and the DOIC association are both between the client and server.

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


                      Figure 1: Basic DOIC deployment

   In Figure 2 there is an agent that is not participating directly in
   the exchange of overload reports.  As a result, the Diameter session
   and the DOIC association are still established between the client and
   the server.















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


          Figure 2: DOIC deployment with non participating agent

   Figure 3 illustrates the case where the client does not support
   Diameter overload.  In this case, the DOIC association is between the
   agent and the server.  The agent handles the role of the reactor for
   overload reports generated by the server.

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


   Figure 3: DOIC deployment with non-DOIC client and DOIC enabled agent

   In Figure 4 there is a DOIC association between the client and the
   agent and a second DOIC association between the agent and the server.
   One use case requiring this configuration is when the agent is
   serving as a SFE for a set of servers.












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


            Figure 4: A deployment where all nodes support DOIC

   Figure 5 illustrates a deployment where some clients support Diameter
   overload control and some do not.  In this case the agent must
   support Diameter overload control for the non supporting client.  It
   might also need to have a DOIC association with the server, as shown
   here, to handle overload for a server farm and/or for managing Realm
   overload.

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


     Figure 5: A deployment with DOIC and non-DOIC supporting clients

   Editor's note: Propose to remove C1, which is already shown in a
   previous figure.  Have this focus just on the non supporting client
   scenario.





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   Figure 6 illustrates a deployment where some agents support Diameter
   overload control and others do not.

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


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

   Editor's note: Propose to add a non supporting server scenario.

3.2.  Piggybacking Principle (Non normative)

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

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

   Reporting nodes indicate support for DOIC by including the OC-
   Supported-Features AVP in all answer messages originated or relayed
   by the Diameter node.  Reporting nodes also include overload reports
   using the OC-OLR AVP in answer messages.

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

   Note that the overload control solution does not have fixed server
   and client roles.  The endpoint role is determined based on the



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   message type: whether the message is a request (i.e. sent by a
   "reacting node") or an answer (i.e. send by a "reporting node").
   Therefore, in a typical "client-server" deployment, the "client" MAY
   report its overload condition to the "server" for any server
   initiated message exchange.  An example of such is the server
   requesting a re-authentication from a client.

3.3.  DOIC Capability Announcement (Non normative)

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

   The DCA mechanism is built around the piggybacking principle used for
   transporting Diameter overload AVPs.  This includes both DCA AVPs and
   AVPs associated with Diameter overload reports.  This allows for the
   DCA AVPs to be carried across Diameter nodes that do not support the
   DOIC solution.

   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-Feature AVP in the request
   message.  This includes an indication that it supports the loss
   overload abatement algorithm defined in this specification (see
   Section 5).  This insures that there is at least one commonly
   supported overload abatement algorithm between the reporting node and
   the reacting nodes in the path of the request.

      DOIC must support deployments where Diameter Clients and/or
      Diameter servers do not support the DOIC solution.  In this
      scenario, it is assumed that Diameter Agents that support the DOIC
      solution will handle overload abatement for the non supporting
      clients.  In this case the DOIC agent will insert the OC-
      Supporting-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.

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

   The reporting node only includes an indication of support for one
   overload abatement algorithm.  This is the algorithm that the



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   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.

      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 to insure that overload reports can be
      properly handled.

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

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

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

3.4.  DOIC Overload Condition Reporting (Non normative)

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

   The OC-OLR AVP is referred to as an overload report.  The OC-OLR AVP
   includes the type of report, an overload report ID, 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.

   Host reports apply to traffic that is sent to a specific Diameter
   host.  The applies to requests that contain the Destination-Host AVP
   that contains a DiameterIdentity that matches that of the overload
   report.  These requests are referred to as host-routed requests.  A
   host report also applies to realm-routed requests, requests that do
   not have a Destination-Host AVP, when the selected route for the
   request is a connection to the impacted host.



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   Realm reports apply to realm-routed requests for a specific realm as
   indicated in the Destination-Realm AVP.

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

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

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

   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 overlaod condition has
   ended and use of the abatement algorithm is no longer needed.

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

3.5.  DOIC Extensibility (Non normative)

   The DOIC solutions is designed to be extensible.  This extensibility
   is based on existing Diameter based extensibility mechanisms.

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



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   The DOIC solution uses the OC-Supported-Features AVP for DOIC nodes
   to communicate supported features.  The specific features supported
   by the DOIC node are indicated in the OC-Feature-Vector AVP.  DOIC
   extensions must 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 to be communicate.

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

   If necessary, new extensions can also define new top level AVPs.  It
   is, however, recommended that DOIC extensions use the OC-Supported-
   Features and OC-OLR to carry all DOIC related AVPs.

3.6.  Simplified Example Architecture (Non normative)

   Figure 7 illustrates the simplified architecture for Diameter
   overload information conveyance.  See Section 3.1 for more discussion
   and details how different Diameter nodes fit into the architecture
   from the DOIC point of view.




























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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)  <----------------------> <---------------------->
                 standard base protocol   standard base protocol



     Figure 7: Simplified architecture choices for overload indication
                                 delivery

   In Figure 7, the Diameter overload indication can be conveyed (1)
   end-to-end between servers and clients or (2) between servers and
   Diameter agent inside the realm and then between the Diameter agent
   and the clients when the Diameter agent acting as back-to-back-agent
   for DOIC purposes.

3.7.  Considerations for Applications Integrating the DOIC Solution (Non
      normative)

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

3.7.1.  Application Classification (Non normative)

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

   Section 8.1 of [RFC6733] defines two state machines that imply two
   types of applications, session-less and session-based applications.



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   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.

   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.

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

   The handling of overload reports must take the type of application
   into consideration, as discussed in Section 3.7.2.

3.7.2.  Application Type Overload Implications (Non normative)

   This section discusses considerations for mitigating overload
   reported by a Diameter entity.  This discussion focuses on the type
   of application.  Section 3.7.3 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



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   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
      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 clean-up procedures.




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3.7.3.  Request Transaction Classification (Non normative)

   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 requests.

   Pseudo-Session Requests:

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

3.7.4.  Request Type Overload Implications (Non normative)

   The request classes identified in Section 3.7.3 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




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   exact behavior regarding throttling is a matter of local policy,
   unless specifically defined for the application.

   Independent requests:

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

   Session-initiating requests:

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

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

   Intra-session requests

      There are two classes of intra-sessions requests.  The first class
      consists of requests that terminate a session.  The second one
      contains the set of requests that are used by the Diameter client
      and server to maintain the ongoing session state.  Session
      terminating requests should be throttled less aggressively in
      order to gracefully terminate sessions, allow clean-up of the
      related resources (e.g. session state) and get rid of the need for
      other intra-session requests, reducing the session management
      impact on the overloaded entity.  The default handling of other
      intra-session requests might be to treat them equally when making



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      throttling decisions.  There might also be application level
      considerations whether some request types are favored over others.

4.  Solution Procedures (Normative)

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

4.1.  Capability Announcement (Normative)

   This section defines DOIC Capability Announcement (DCA) behavior.

   The DCA procedures are used to indicate support for DOIC and support
   for DOIC features.  The DOIC features include overload abatement
   algorithms supported.  It might also include new report types or
   other extensions documented in the future.

   Diameter nodes indicate support for DOIC by including the OC-
   Supported-Features AVP in messages sent or handled by the node.

   Diameter agents that support DOIC MUST ensure that all messages have
   the OC-Supporting-Features AVP.  If a message handled by the DOIC
   agent does not include the OC-Supported-Features AVP then the DOIC
   agent inserts the AVP.  If the message already has the AVP then the
   agent either leaves it unchanged in the relayed message or modifies
   it to reflect a mixed set of DOIC features.

4.1.1.  Reacting Node Behavior (Normative)

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

   A reacting node MUST include the OC-Feature-Vector AVP with an
   indication of the loss algorithm.

   A reacting node SHOULD indicate support for all other DOIC features
   it supports.

   An OC-Supported-Features AVP in answer messages indicates there is a
   reporting node for the transaction.  The reacting node MAY take
   action based on the features indicated in the OC-Feature-Vector AVP.

      Note that the loss abatement algorithm is the only feature
      described in this document and it does not require action to be
      taken by the reacting node except when the answer message also has
      an overload report.  This behavior is described in Section 4.2 and
      Section 5.




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4.1.2.  Reporting Node Behavior (Normative)

   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.

   Based on the content of the OC-Supported-Features AVP in the request
   message, the reporting node knows what overload control functionality
   supported by reacting node(s).  The reporting node then acts
   accordingly for the subsequent answer messages it initiates.

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

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

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

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

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

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

   An agent MAY modify the OC-Supported-Features AVP carried in answer
   messages.








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4.1.3.  Agent Behavior (Normative)

   Editor's note -- Need to add this section.

4.2.  Overload Report Processing (Normative)

4.2.1.  Overload Control State (Normative)

   Both reacting and reporting nodes maintain an overload control state
   (OCS) for each endpoint (a host or a realm) they communicate with and
   both endpoints have announced support for DOIC.  See Sections 6.1 and
   4.1 for discussion about how the support for DOIC is determined.

4.2.1.1.  Overload Control State for Reacting Nodes

   A reacting node maintains the following OCS per supported Diameter
   application:

   o  A host-type Overload Control State for each Destination-Host
      towards which it sends host-type requests and

   o  A realm-type Overload Control State for each Destination-Realm
      towards which it sends realm-type requests.

   A host-type Overload Control State may be identified by the pair of
   Application-Id and Destination-Host.  A realm-type Overload Control
   State may be identified by the pair of Application-Id and
   Destination-Realm.  The host-type/realm-type Overload Control State
   for a given pair of Application and Destination-Host / Destination-
   Realm could include the following information:

   o  Sequence number (as received in OC-OLR)

   o  Time of expiry (deviated from validity duration as received in OC-
      OLR and time of reception)

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

   o  Algorithm specific input data (as received within OC-OLR, e.g.
      Reduction Percentage for Loss)

4.2.1.2.  Overload Control States for Reporting Nodes

   A reporting node maintains per supported Diameter application and per
   supported (and eventually selected) Abatement Algorithm an Overload
   Control State.




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   An Overload Control State may be identified by the pair of
   Application-Id and supported Abatement Algorithm.

   The Overload Control State for a given pair of Application and
   Abatement Algorithm could include the information:

   o  Sequence number

   o  Validity Duration and Expiry Time

   o  Algorithm specific input data (e.g.  Reduction Percentage for
      Loss)

   Overload Control States for reporting nodes containing a validity
   duration of 0 sec. should not expire before any previously sent
   (stale) OLR has timed out at any reacting node.

   Editor's note: This statement is unclear and contradictory with other
   statements.  A validity timer of zero seconds indicates that the
   overload condition has ended and abatement is no longer requested.

4.2.1.3.  Maintaining Overload Control State

   Reacting nodes create a host-type OCS identified by OCS-Id = (app-
   id,host-id) when receiving an answer message of application app-id
   containing an Orig-Host of host-id and a host-type OC-OLR AVP unless
   such host-type OCS already exists.

   Reacting nodes create a realm-type OCS identified by OCS-Id = (app-
   id,realm-id) when receiving an answer message of application app-id
   containing an Orig-Realm of realm-id and a realm-type OC-OLR AVP
   unless such realm type OCS already exists.

   Reacting nodes delete an OCS when it expires (i.e. when current time
   minus reception time is greater than validity duration).

   Editor's note: Reacting nodes also delete on OCS with an updated OLR
   is received with a validity duration of zero.

   Reacting nodes update the host-type OCS identified by OCS-Id = (app-
   id,host-id) when receiving an answer message of application app-id
   containing an Orig-Host of host-id and a host-type OC-OLR AVP with a
   sequence number higher than the stored sequence number.

   Reacting nodes update the realm-type OCS identified by OCS-Id = (app-
   id,realm-id) when receiving an answer message of application app-id
   containing an Orig-Realm of realm-id and a realm-type OC-OLR AVP with
   a sequence number higher than the stored sequence number.



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   Reacting nodes do 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 nodes create an OCS identified by OCS-Id = (app-id,Alg)
   when receiving a request of application app-id containing an OC-
   Supported-Features AVP indicating support of the Abatement Algorithm
   Alg (which the reporting node selects) while being overloaded, unless
   such OCS already exists.

   Reporting nodes delete an OCS when it expires.

   Editor's note: Reporting nodes should send updated overload reports
   with a validity duration of zero for a period of time after an OCS
   expires or is removed due to the overload condition ending.

   Reporting nodes update the OCS identified by OCS-Id = (app-id,Alg)
   when they detect the need to modify the requested amount of
   application app-id traffic reduction.

4.2.2.  Reacting Node Behavior (Normative)

   Once a reacting node receives an OC-OLR AVP from a reporting node, it
   applies traffic abatement based on the selected algorithm with the
   reporting node and the current overload condition.  The reacting node
   learns the reporting node supported abatement algorithms directly
   from the received answer message containing the OC-Supported-Features
   AVP.

   The received OC-Supported-Features AVP does not change the existing
   overload condition and/or traffic abatement algorithm settings if the
   OC-Sequence-Number AVP contains a value that is equal to the
   previously received/recorded value.  If the OC-Supported-Features AVP
   is received for the first time for the reporting node or the OC-
   Sequence-Number AVP value is less than the previously received/
   recorded value (and is outside the valid overflow window), then the
   sequence number is stale (e.g. an intentional or unintentional
   replay) and SHOULD be silently discarded.

   As described in Section 6.3, the OC-OLR AVP contains the necessary
   information for the overload condition on the reporting node.

   From the OC-Report-Type AVP contained in the OC-OLR AVP, the reacting
   node learns whether the overload condition report concerns a specific
   host (as identified by the Origin-Host AVP of the answer message
   containing the OC-OLR AVP) or the entire realm (as identified by the
   Origin-Realm AVP of the answer message containing the OC-OLR AVP).
   The reacting node learns the Diameter application to which the



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   overload report applies from the Application-ID of the answer message
   containing the OC-OLR AVP.  The reacting node MUST use this
   information as an input for its traffic abatement algorithm.  The
   idea is that the reacting node applies different handling of the
   traffic abatement, whether sent request messages are targeted to a
   specific host (identified by the Diameter-Host AVP in the request) or
   to any host in a realm (when only the Destination-Realm AVP is
   present in the request).  Note that future specifications MAY define
   new OC-Report-Type AVP values that imply different handling of the
   OC-OLR AVP.  For example, in a form of new additional AVPs inside the
   Grouped OC-OLR AVP that would define report target in a finer
   granularity than just a host.

      Editor's note: The above behavior for Realm reports is
      inconsistent with the definition of realm reports in section
      Section 6.6.

   If the OC-OLR AVP is received for the first time, the reacting node
   MUST create overload control state associated with the related realm
   or a specific host in the realm identified in the message carrying
   the OC-OLR AVP, as described in Section 4.2.1.

   If the value of the OC-Sequence-Number AVP contained in the received
   OC-OLR AVP is equal to or less than the value stored in an existing
   overload control state, the received OC-OLR AVP SHOULD be silently
   discarded.  If the value of the OC-Sequence-Number AVP contained in
   the received OC-OLR AVP is greater than the value stored in an
   existing overload control state or there is no previously recorded
   sequence number, the reacting node MUST update the overload control
   state associated with the realm or the specific node in the realm.

   When an overload control state is created or updated, the reacting
   node MUST apply the traffic abatement requested in the OC-OLR AVP
   using the algorithm announced in the OC-Supported-Features AVP
   contained in the received answer message along with the OC-OLR AVP.

   The validity duration of the overload information contained in the
   OC-OLR AVP is either explicitly indicated in the OC-Validity-Duration
   AVP or is implicitly equals to the default value (5 seconds) if the
   OC-Validity-Duration AVP is absent.  The reacting node MUST maintain
   the validity duration in the overload control state.  Once the
   validity duration times out, the reacting node MUST assume the
   overload condition reported in a previous OC-OLR AVP has ended.

   A value of zero ("0") received in the OC-Validity-Duration in an
   updated overload report indicates that the overload condition has
   ended and that the overload state is no longer valid.




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   In the case that the validity duration expires or is explicitly
   signaled as being no longer valid the state associated with the
   overload report MUST be removed and any abatement associated with the
   overload report MUST be ended in a controlled fashion.  After
   removing the overload state the sequence number MUST NOT be used for
   future comparisons of sequence numbers.

4.2.3.  Reporting Node Behavior (Normative)

   A reporting node is a Diameter node inserting an OC-OLR AVP in a
   Diameter message in order to inform a reacting node about an overload
   condition and request Diameter traffic abatement.

   The operation on the reporting node is straight forward.  The
   reporting node learns the capabilities of the reacting node when it
   receives the OC-Supported-Features AVP as part of any Diameter
   request message.  If the reporting node shares at least one common
   feature with the reacting node, then the DOIC can be enabled between
   these two endpoints.  See Section 4.1 for further discussion on the
   capability and feature announcement between two endpoints.

   When a traffic reduction is required due to an overload condition and
   the overload control solution is supported by the sender of the
   Diameter request, the reporting node MUST include an OC-Supported-
   Features AVP and an OC-OLR AVP in the corresponding Diameter answer.
   The OC-OLR AVP contains the required traffic reduction and the OC-
   Supported-Features AVP indicates the traffic abatement algorithm to
   apply.  This algorithm MUST be one of the algorithms advertised by
   the request sender.

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

   The reporting node SHOULD 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 insure that all reacting nodes
   receive the updated overload report.

4.2.4.  Agent Behavior (Normative)

   Editor's note -- Need to add this section.








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4.3.  Protocol Extensibility (Normative)

   The overload control solution can be extended, e.g. with new traffic
   abatement algorithms, new report types or other new functionality.

   When defining a new extension a new feature bit MUST be defined for
   the OC-Feature-Vector.  This feature bit is used to communicate
   support for the new feature.

   The extention may also define new AVPs for use in DOIC Capability
   Anouncement and for use in DOIC Overload reporting.  These new AVP
   should be defined to be extensions to the OC-Supported-Features and
   OC-OLR AVPs defined in this document.

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

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

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

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

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








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5.  Loss Algorithm (Normative)

   This section documents the Diameter overload loss abatement
   algorithm.

5.1.  Overview (Non normative)

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

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

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

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

   From a conceptual level, the logic at the reacting node could be
   outlined as follows.  In this discussion assume that the reacting
   node is also the sending node.

   1.  An overload report is received and the associated overload state
       is saved 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.

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






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5.2.  Use of OC-Reduction-Percentage AVP

   A reporting node using the loss algorithm must use the OC-Reduction-
   Percentage AVP (Section 6.7 to indicated the desired percentage of
   traffic reduction.)

      Editor's note: The above duplicates what is in the OC-Reduction-
      Percentage AVP section can probably be removed.

5.3.  Reporting Node Behavior (Normative)

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

   When a reporting node that has selected the loss abatement algorithm
   determines the need to request a traffic reduction it must include an
   OC-OLR AVP in all response messages.

   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 4.2.3.

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

5.4.  Reacting Node Behavior (Normative)

   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 attempt to 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.





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

      Editor's note: Need to add additional guidance to slowly increase
      the rate of traffic sent to avoid a sudden spike in traffic, as
      the spike in traffic could result in oscillation of the need for
      overload control.

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

   It is suggested that the reacting node decrease the amount of traffic
   given abatement treatment by 20% each second until the reduction is
   completely removed and no traffic is given abatement treatment.

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

6.  Attribute Value Pairs (Normative)

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

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

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






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6.1.  OC-Supported-Features AVP

   The OC-Supported-Features AVP (AVP code TBD1) is type of Grouped and
   serves for two purposes.  First, it announces a node's support for
   the DOIC 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 message a DOIC
   supporting node sends.

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


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

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

   During the message exchange the overload control endpoints express
   their common set of supported capabilities.  The reacting node
   includes the OC-Supported-Features AVP that announces what it
   supports.  The reporting node that sends the answer also includes the
   OC-Supported-Features AVP that describes the capabilities it
   supports.  The set of capabilities advertised by the reporting node
   depends on local policies.  At least one of the announced
   capabilities MUST match.  If there is no single matching capability
   the reacting node MUST act as if it does not implement DOIC and cease
   inserting any DOIC related AVPs into any Diameter messages with this
   specific reacting node.

      Editor's note: The last sentence conflicts with the last sentence
      two paragraphs up.  In reality, there will always be at least one
      matching capability as all nodes supporting DOIC must support the
      loss algorithm.  Suggest removing the last sentence.

6.2.  OC-Feature-Vector AVP

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



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   The following capabilities are defined in this document:

   OLR_DEFAULT_ALGO (0x0000000000000001)

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

6.3.  OC-OLR AVP

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

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


   The OC-Validity-Duration AVP indicates the validity time of the
   overload report associated with a specific sequence number, measured
   after reception of the OC-OLR AVP.  The validity time MUST NOT be
   updated after reception of subsequent OC-OLR AVPs with the same
   sequence number.  The default value for the OC-Validity-Duration AVP
   value is 5 (i.e., 5 seconds).  When the OC-Validity-Duration AVP is
   not present in the OC-OLR AVP, the default value applies.

   Note that if a Diameter command were to contain multiple OC-OLR AVPs
   they all MUST have different OC-Report-Type AVP value.  OC-OLR AVPs
   with unknown values SHOULD be silently discarded and the event SHOULD
   be logged.

      Editor's note: Need to specify what happens when two reports of
      the same type are received.






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6.4.  OC-Sequence-Number AVP

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

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

   When generating sequence numbers, the new sequence number MUST be
   greater than any sequence number in an active overload report
   previously sent by the reporting node.  This property MUST hold over
   a reboot of the reporting node.

6.5.  OC-Validity-Duration AVP

   The OC-Validity-Duration AVP (AVP code TBD4) is type of 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 5 (i.e., 5 seconds).  When the
   OC-Validity-Duration AVP is not present in the OC-OLR AVP, the
   default value applies.  Validity duration with values above 86400
   (i.e.; 24 hours) MUST NOT be used.  Invalid duration values are
   treated as if the OC-Validity-Duration AVP were not present and
   result in the default value being used.

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

   When a reporting node has recovered from overload, it SHOULD
   invalidate any existing overload reports in a timely matter.  This
   can be achieved by sending an updated overload report (meaning the
   OLR contains a new sequence number) with the OC-Validity-Duration AVP
   value set to zero ("0").  If the overload report is about to expire
   naturally, the reporting node MAY choose to simply let it do so.

   A reacting node MUST invalidate and remove an overload report that
   expires without an explicit overload report containing an OC-
   Validity-Duration value set to zero ("0").





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6.6.  OC-Report-Type AVP

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

   0  A host report.  The overload treatment should apply to requests
      for which all of the following conditions are true:

      Either the Destination-Host AVP is present in the request and its
      value matches the value of the Origin-Host AVP of the received
      message that contained the OC-OLR AVP; or the Destination-Host is
      not present in the request but the value of peer identity
      associated with the connection used to send the request matches
      the value of the Origin-Host AVP of the received message that
      contained the OC-OLR AVP.

      The value of the Destination-Realm AVP in the request matches the
      value of the Origin-Realm AVP of the received message that
      contained the OC-OLR AVP.

      The value of the Application-ID in the Diameter Header of the
      request matches the value of the Application-ID of the Diameter
      Header of the received message that contained the OC-OLR AVP.

   1  A realm report.  The overload treatment should apply to requests
      for which all of the following conditions are true:

      The Destination-Host AVP is absent in the request.

      The value of the Destination-Realm AVP in the request matches the
      value of the Origin-Realm AVP of the received message that
      contained the OC-OLR AVP.

      The value of the Application-ID in the Diameter Header of the
      request matches the value of the Application-ID of the Diameter
      Header of the received message that contained the OC-OLR AVP.

      Editor's note: There is still an open issue on the definition of
      Realm reports and whether what report types should be supported.
      There is consensus that host reports should be supported.  There
      is discussion on Realm reports and Realm-Routed-Request reports.
      The above definition applies to Realm-Routed-Request reports where
      Realm reports are defined to apply to all requests that match the
      realm, independent of the presence, absence or value of the
      Destination-Host AVP.





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

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

6.7.  OC-Reduction-Percentage AVP

   The OC-Reduction-Percentage AVP (AVP code TBD8) is type of Unsigned32
   and describes the percentage of the traffic that the sender is
   requested to reduce, compared to what it otherwise would 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 other endpoint to apply any traffic abatement.
   The default value of the OC-Reduction-Percentage AVP is 0.  When the
   OC-Reduction-Percentage AVP is not present in the overload report,
   the default value applies.

6.8.  Attribute Value Pair flag rules



















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


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

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

7.  Error Response Codes

   Editor's note: This section depends on resolution of issue #27.

8.  IANA Considerations

8.1.  AVP codes

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






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8.2.  New registries

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

   Section 6.2 defines a new "Overload Control Feature Vector" registry
   including the initial assignments.  New values can be added into the
   registry using the Specification Required policy [RFC5226].  See
   Section 6.2 for the initial assignment in the registry.

   Section 6.6 defines a new "Overload Report Type" registry with its
   initial assignments.  New types can be added using the Specification
   Required policy [RFC5226].

9.  Security Considerations

   This mechanism gives Diameter nodes the ability to request that
   downstream nodes send fewer Diameter requests.  Nodes do this by
   exchanging overload reports that directly affect 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.

9.1.  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 hop-by-hop
   trust model.  That is, a Diameter client or server can authorize an



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   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 a response.  Therefore, implementations SHOULD
   validate that an answer containing an overload report is a properly
   constructed response to a pending request prior to acting on the
   overload report.

   A similar attack involves an otherwise authorized Diameter 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 an peer that applies to a realm not
   handled by that peer is suspect.

   An attacker might use the information in an overload report to assist
   in certain attacks.  For example, an attacker could use information
   about current overload conditions to time a DoS attack for maximum
   effect, or use subsequent overload reports as a feedback mechanism to
   learn the results of a previous or ongoing attack.

9.2.  Denial of Service Attacks

   Diameter overload 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 tacks.  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 overload reports from unauthorized or
   otherwise untrusted sources.




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9.3.  Non-Compliant Nodes

   When a Diameter node sends an overload report, it cannot assume that
   all nodes will comply.  A non-compliant node might continue to send
   requests with no reduction in load.  Requirement 28 [RFC7068]
   indicates that the overload control solution cannot assume that all
   Diameter nodes in a network are necessarily 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.

   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 reject 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.

9.4.  End-to End-Security Issues

   The lack of end-to-end security features makes it far more difficult
   to establish trust in overload reports that originate from non-
   adjacent nodes.  Any agents in the message path may insert or modify
   overload reports.  Nodes must 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.

   The lack of end-to-end confidentiality protection means that any
   Diameter agent in the path of an overload report can view the
   contents of that report.  In addition to the requirement to select
   which peers are trusted to send overload reports, operators MUST be
   able to select which peers are authorized to receive reports.  A node
   MUST not send an overload report to a peer not authorized to receive
   it.  Furthermore, an agent MUST remove any overload reports that
   might have been inserted by other nodes before forwarding a Diameter
   message to a peer that is not authorized to receive overload reports.

   At the time of this writing, the DIME working group is studying
   requirements for adding end-to-end security



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   [I-D.ietf-dime-e2e-sec-req] features to Diameter.  These features,
   when they become available, might make it easier to establish trust
   in non-adjacent nodes for overload control purposes.  Readers should
   be reminded, however, that the overload control mechanism encourages
   Diameter agents to modify AVPs in, or insert additional AVPs into,
   existing messages that are originated by other nodes.  If end-to-end
   security is enabled, there is a risk that such modification could
   violate integrity protection.  The details of using any future
   Diameter end-to-end security mechanism with overload control will
   require careful consideration, and are beyond the scope of this
   document.

10.  Contributors

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

   o  Eric McMurry

   o  Hannes Tschofenig

   o  Ulrich Wiehe

   o  Jean-Jacques Trottin

   o  Maria Cruz Bartolome

   o  Martin Dolly

   o  Nirav Salot

   o  Susan Shishufeng

11.  References

11.1.  Normative References

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

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.




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

11.2.  Informative References

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

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

   [PCC]      3GPP, , "ETSI TS 123 203 V11.12.0", December 2013.

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

   [RFC5729]  Korhonen, J., Jones, M., Morand, L., and T. Tsou,
              "Clarifications on the Routing of Diameter Requests Based
              on the Username and the Realm", RFC 5729, December 2009.

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

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

Appendix A.  Issues left for future specifications

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

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 6.1 and 8 for the required IANA
   steps.

A.2.  Agent Overload

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




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A.3.  DIAMETER_TOO_BUSY clarifications

   The current [RFC6733] behavior in a case of DIAMETER_TOO_BUSY is
   somewhat under specified.  For example, there is no information how
   long the specific Diameter node is willing to be unavailable.  A
   specification updating [RFC6733] should clarify the handling of
   DIAMETER_TOO_BUSY from the error answer initiating Diameter node
   point of view and from the original request initiating Diameter node
   point of view.  Further, the inclusion of possible additional
   information providing AVPs should be discussed and possible be
   recommended to be used.

Appendix B.  Examples

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

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

   Clients commonly send mixtures of Destination-Host and Destination-
   Realm routed requests.  For example, in an application that uses user
   sessions, a client typically won't care which server handles a
   session-initiating requests.  But once the session is initiated, the
   client will send all subsequent requests in that session to the same
   server.  Therefore it would send the initial request with no
   Destination-Host AVP.  If it receives a successful answer, the client
   would copy the Origin-Host value from the answer message into a
   Destination-Host AVP in each subsequent request in the session.

   An agent has very limited options in applying overload abatement to
   requests that contain Destination-Host AVPs.  It typically cannot
   route the request to a different server than the one identified in
   Destination-Host.  It's only remaining options are to throttle such
   requests locally, or to send an overload report back towards the
   client so the client can throttle the requests.  The second choice is
   usually more efficient, since it prevents any throttled requests from
   being sent in the first place, and removes the agent's need to send
   errors back to the client for each dropped request.

   On the other hand, an agent has much more leeway to apply overload
   abatement for requests that do not contain Destination-Host AVPs.  If
   the agent has multiple servers in its peer table for the given realm



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   and application, it can route such requests to other, less overloaded
   servers.

   If the overload severity increases, the agent may reach a point where
   there is not sufficient capacity across all servers to handle even
   realm-routed requests.  In this case, the realm itself can be
   considered overloaded.  The agent may need the client to throttle
   realm-routed requests in addition to Destination-Host routed
   requests.  The overload severity may be different for each server,
   and the severity for the realm at is likely to be different than for
   any specific server.  Therefore, an agent may need to forward, or
   originate, multiple overload reports with differing ReportType and
   Reduction-Percentage values.

   Figure 8 illustrates such a mixed-routing scenario.  In this example,
   the servers S1, S2, and S3 handle requests for the realm "realm".
   Any of the three can handle requests that are not part of a user
   session (i.e. routed by Destination-Realm).  But once a session is
   established, all requests in that session must go to the same server.

        Client     Agent      S1        S2        S3
           |         |         |         |         |
           |(1) Request (DR:realm)       |         |
           |-------->|         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |Agent selects S1   |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |(2) Request (DR:realm)       |
           |         |-------->|         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |S1 overloaded, returns OLR
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |(3) Answer (OR:realm,OH:S1,OLR:RT=DH)
           |         |<--------|         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |sees OLR,routes DR traffic to S2&S3
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |(4) Answer (OR:realm,OH:S1, OLR:RT=DH) |
           |<--------|         |         |         |



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           |         |         |         |         |
           |         |         |         |         |
           |Client throttles requests with DH:S1   |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |(5) Request (DR:realm)       |         |
           |-------->|         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |Agent selects S2   |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |(6) Request (DR:realm)       |
           |         |------------------>|         |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |S2 is overloaded...
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |(7) Answer (OH:S2, OLR:RT=DH)|
           |         |<------------------|         |
           |         |         |         |         |
           |         |         |         |         |
           |         |Agent sees OLR, realm now overloaded
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |(8) Answer (OR:realm,OH:S2, OLR:RT=DH, OLR: RT=R)
           |<--------|         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |Client throttles DH:S1, DH:S2, and DR:realm
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |
           |         |         |         |         |



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

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



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

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

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

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

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

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

   8.  The agent sees that S2 is also overloaded by the value in
       Reduction-Percentage.  This value is probably different than the
       value from S1's report.  The agent diverts the remaining traffic
       to S3 as best as it can, but it calculates that the remaining
       capacity across all three servers is no longer sufficient to
       handle all of the realm-routed traffic.  This means the realm
       itself is overloaded.  The realm's overload percentage is most
       likely different than that for either S1 or S2.  The agent
       forward's S2's report back to the client in the Diameter answer.
       Additionally, the agent generates a new report for the realm of
       "realm", and inserts that report into the answer.  The client
       throttles requests with Destination-Host:S1 at one rate, requests
       with Destination-Host:S2 at another rate, and requests with no
       Destination-Host AVP at yet a third rate.  (Since S3 has not
       indicated overload, the client does not throttle requests with
       Destination-Host:S3.)

Appendix C.  Restructuring of -02 version of the draft

   This section captures the initial plan for restructuring the DOIC
   specification from the -02 version to the new -03 version.

   1. Introduction (non normative)



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      -- Existing Text from section 1. --
   2. Terminology and Abbreviations (non normative)
      -- Existing Text from section 2. --
   3. Solution Overview (Non normative)
      -- Existing text from section 3. --
     3.1 Overload Control Endpoints (Non normative)
         -- New text leveraging text from existing section 5.1 --
     3.2 Piggybacking Principle (Non normative)
         -- Existing text from existing section 5.2, with enhancements --
     3.3 DOIC Capability Discovery (Non normative)
         -- New text leveraging text from existing section 5.3 --
     3.4 DOIC Overload Condition Reporting (Non normative)
         -- New text --
     3.5 DOIC Extensibility (Non normative)
         -- New text leveraging text from existing Section 5.4 --
     3.5 Simplified Example Architecture (Non normative)
         -- Existing text from section 3.1.6, with enhancements --
     3.6 Considerations for Applications Integrating the DOIC Solution (Non normative)
         -- New text --
       3.6.1. Application Classification  (Non normative)
              -- Existing text from section 3.1.1 --
       3.6.2. Application Type Overload Implications  (Non normative)
              -- Existing text from section 3.1.2 --
       3.6.3. Request Transaction Classification  (Non normative)
              -- Existing text from section 3.1.3 --
       3.6.4. Request Type Overload Implications  (Non normative)
              -- Existing text from section 3.1.4 --
   4. Solution Procedures (Normative)
     4.1 Capability Announcement (Normative)
        -- Existing text from section 5.3 --
       4.1.1. Reacting Node Behavior (Normative)
            -- Existing text from section 5.3.1 --
       4.1.2. Reporting Node Behavior  (Normative)
            -- Existing text from section 5.3.2 --
       4.1.3. Agent Behavior  (Normative)
            -- Existing text from section 5.3.3 --
     4.2. Overload Report Processing (Normative)
       4.2.1. Overload Control State (Normative)
            -- Existing text from section 5.5.1 --
       4.2.2. Reacting Node Behavior  (Normative)
            -- Existing text from section 5.5.2 --
       4.2.3. Reporting Node Behavior  (Normative)
            -- Existing text from section 5.5.3 --
       4.2.4. Agent Behavior  (Normative)
            -- Existing text from section 5.5.4 --
     4.3. Protocol Extensibility (Normative)
        -- Existing text from section 5.4 --
   5. Loss Algorithm (Normative)



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      -- New text pulling from information spread through the document --
     5.1. Overview (Non normative)
          -- New text pulling from information spread through the document --
     5.2. Reporting Node Behavior (Normative)
          -- New text pulling from information spread through the document --
     5.3. Reacting Node Behavior (Normative)
          -- New text pulling from information spread through the document --
   6. Attribute Value Pairs (Normative)
      -- Existing text from section 4. --
     6.1. OC-Supported-Features AVP
          -- Existing text from section 4.1 --
     6.2. OC-Feature-Vector AVP
          -- Existing text from section 4.2 --
     6.3. OC-OLR AVP
          -- Existing text from section 4.3 --
     6.4. OC-Sequence-Number AVP
          -- Existing text from section 4.4 --
     6.5. OC-Validity-Duration AVP
          -- Existing text from section 4.5 --
     6.6. OC-Report-Type AVP
          -- Existing text from section 4.6 --
     6.7. OC-Reduction-Percentage AVP
          -- Existing text from section 4.7 --
     6.8. Attribute Value Pair flag rules
          -- Existing text from section 4.8 --
   7. Error Response Codes
          -- New text based on resolution of issue --
   8. IANA Considerations
      -- Existing text from section 7. --
     8.1. AVP codes
          -- Existing text from section 7.1 --
     8.2. New registries
          -- Existing text from section 7.2 --
   9. Security Considerations
       -- Existing text from section 8. --
     9.1. Potential Threat Modes
           -- Existing text from section 8.1 --
     9.2. Denial of Service Attacks
           -- Existing text from section 8.2 --
     9.3. Non-Compliant Nodes
           -- Existing text from section 8.3 --
     9.4. End-to End-Security Issues
           -- Existing text from section 8.4 --
   10. Contributors
   11. References
     11.1. Normative References
     11.2. Informative References
   Appendix A. Issues left for future specifications



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     A.1. Additional traffic abatement algorithms
     A.2. Agent Overload
     A.3. DIAMETER_TOO_BUSY clarifications
     A.4. Per reacting node reports
   Appendix B. Examples
     B.1. Mix of Destination-Realm routed requests and Destination-
           Host routed requests
   Authors' Addresses


Authors' Addresses

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

   Email: jouni.nospam@gmail.com


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

   Email: srdonovan@usdonovans.com


   Ben Campbell
   Oracle
   7460 Warren Parkway
   Frisco, Texas  75034
   United States

   Email: ben@nostrum.com


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

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




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