Diameter Overload Indication Conveyance
draft-docdt-dime-ovli-00

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Document Type Active Internet-Draft (individual)
Authors Jouni Korhonen  , Steve Donovan  , Ben Campbell 
Last updated 2013-10-21
Replaced by draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, draft-ietf-dime-ovli, RFC 7683, RFC 7683, RFC 7683
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Diameter Maintenance and Extensions (DIME)              J. Korhonen, Ed.
Internet-Draft                                   Broadcom Communications
Intended status: Standards Track                              S. Donovan
Expires: April 24, 2014                                      B. Campbell
                                                                  Oracle
                                                        October 21, 2013

                Diameter Overload Indication Conveyance
                      draft-docdt-dime-ovli-00.txt

Abstract

   This specification documents a Diameter Overload Information
   Conveyance (DOIC) 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
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   This Internet-Draft will expire on April 24, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of

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   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 . . . . . . . . . . . . . . . .   3
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Architectural Assumptions . . . . . . . . . . . . . . . .   6
       3.1.1.  Application Classification  . . . . . . . . . . . . .   6
       3.1.2.  Application Type Overload Implications  . . . . . . .   7
       3.1.3.  Request Transaction Classification  . . . . . . . . .   8
       3.1.4.  Request Type Overload Implications  . . . . . . . . .   9
       3.1.5.  Diameter Deployment Scenarios . . . . . . . . . . . .  10
       3.1.6.  Diameter Agent Behaviour  . . . . . . . . . . . . . .  11
       3.1.7.  Simplified Example Architecture . . . . . . . . . . .  12
     3.2.  Conveyance of the Overload Indication . . . . . . . . . .  13
       3.2.1.  Negotiation and Versioning  . . . . . . . . . . . . .  13
       3.2.2.  Transmission of the Attribute Value Pairs . . . . . .  13
     3.3.  Overload Condition Indication . . . . . . . . . . . . . .  14
   4.  Attribute Value Pairs . . . . . . . . . . . . . . . . . . . .  14
     4.1.  OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . .  14
     4.2.  OC-OLR AVP  . . . . . . . . . . . . . . . . . . . . . . .  16
     4.3.  TimeStamp AVP . . . . . . . . . . . . . . . . . . . . . .  16
     4.4.  ValidityDuration AVP  . . . . . . . . . . . . . . . . . .  17
     4.5.  ReportType AVP  . . . . . . . . . . . . . . . . . . . . .  17
     4.6.  OC-Algorithm AVP  . . . . . . . . . . . . . . . . . . . .  18
     4.7.  Algorithm-ID AVP  . . . . . . . . . . . . . . . . . . . .  18
     4.8.  Reduction-Percentage AVP  . . . . . . . . . . . . . . . .  19
     4.9.  Attribute Value Pair flag rules . . . . . . . . . . . . .  19
   5.  Overload Control Operation  . . . . . . . . . . . . . . . . .  20
     5.1.  Overload Control Endpoints  . . . . . . . . . . . . . . .  20
     5.2.  Piggybacking Principle  . . . . . . . . . . . . . . . . .  20
     5.3.  Capability Negotiation  . . . . . . . . . . . . . . . . .  21
       5.3.1.  Request Message Initiator Endpoint Considerations . .  21
       5.3.2.  Answer Message Initiating Endpoint Considerations . .  22
     5.4.  Protocol Extensibility  . . . . . . . . . . . . . . . . .  23
     5.5.  Overload Report Processing  . . . . . . . . . . . . . . .  23
       5.5.1.  Sender Endpoint Considerations  . . . . . . . . . . .  23
       5.5.2.  Receiver Endpoint Considerations  . . . . . . . . . .  23
   6.  Transport Considerations  . . . . . . . . . . . . . . . . . .  23
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     7.1.  AVP codes . . . . . . . . . . . . . . . . . . . . . . . .  24
     7.2.  New registries  . . . . . . . . . . . . . . . . . . . . .  24

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   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
     8.1.  Potential Threat Modes  . . . . . . . . . . . . . . . . .  25
     8.2.  Denial of Service Attacks . . . . . . . . . . . . . . . .  26
     8.3.  Non-Compliant Nodes . . . . . . . . . . . . . . . . . . .  26
     8.4.  End-to End-Security Issues  . . . . . . . . . . . . . . .  26
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  28
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     11.2.  Informative References . . . . . . . . . . . . . . . . .  29
   Appendix A.  Issues left for future specifications  . . . . . . .  29
     A.1.  Additional traffic abatement algorithms . . . . . . . . .  29
     A.2.  Agent Overload  . . . . . . . . . . . . . . . . . . . . .  29
     A.3.  DIAMETER_TOO_BUSY clarifications  . . . . . . . . . . . .  29
     A.4.  Load  . . . . . . . . . . . . . . . . . . . . . . . . . .  30
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  30
     B.1.  3GPP S6a interface overload indication  . . . . . . . . .  30
     B.2.  3GPP PCC interfaces overload indication . . . . . . . . .  30
     B.3.  Mix of Destination-Realm routed requests and Destination-
           Host reouted requests . . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

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

2.  Terminology and Abbreviations

   Server Farm

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

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

   Server Front End

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      A Server Front End (SFE) is a role that can be performed by a
      Diameter agent -- either a relay or a proxy -- that sits between
      Diameter clients and a Server Farm.  An SFE can perform various
      functions for the server farm it sits in front of.  This includes
      some or all of the following functions:

      *  Diameter Routing

      *  Diameter layer load balancing

      *  Load Management

      *  Overload Management

      *  Topology Hiding

      *  Server Farm Identity Management

      [OpenIssue: We used the concept of a server farm and SFE for
      internal discussions.  Do we still need those concepts to explain
      the mechanism?  It doesn't seem like we use them much.]

   Diameter Routing:

      Diameter Routing determines the destination of Diameter messages
      addressed to either a Diameter Realm and Application in general,
      or to a specific server using Destination-Host.  This function is
      defined in [RFC6733].  Application level routing specifications
      that expand on [RFC6733] also exist.

   Diameter-layer Load Balancing:

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

   Load Management:

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

   Overload Management:

      The SFE is the entity that understands the consolidated overload
      state for the server farm.  Just as it is outside the scope of

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

      [OpenIssue: Does this mean the way servers communicate overload
      info to an SFE is also out of scope?  It would be nice if the
      mechanism is useful for that purpose.]

   Topology Hiding:

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

   Server Farm Identity Management:

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

   Throttling:

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

   Reporting Node

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

   Reacting Node

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      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".

3.  Solution Overview

3.1.  Architectural Assumptions

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

3.1.1.  Application Classification

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

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

   The 3GPP-defined S6a application is an example of a session-less
   application.  The following, copied from section 7.1.4 of 29.272,
   explicitly states that sessions are implicitly terminated and that
   the server does not maintain session state:

      "Between the MME and the HSS and between the SGSN and the HSS and
      between the MME and the EIR, Diameter sessions shall be implicitly
      terminated.  An implicitly terminated session is one for which the
      server does not maintain state information.  The client shall not
      send any re-authorization or session termination requests to the
      server.

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

      The client (server) shall include in its requests (responses) the
      Auth-Session-State AVP set to the value NO_STATE_MAINTAINED (1),

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      as described in [RFC6733].  As a consequence, the server shall not
      maintain any state information about this session and the client
      shall not send any session termination request.  Neither the
      Authorization-Lifetime AVP nor the Session-Timeout AVP shall be
      present in requests or responses."

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

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

   Pseudo-session applications:  While this class of application does
      not use the Diameter Session-ID AVP to correlate requests, there
      is an implied ordering of transactions defined by the application.
      Transactions in a pseudo-session typically need to be handled by
      the same server.  The 3GPP defined Cx application [reference] is
      an example of a pseudo-session application.

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

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

3.1.2.  Application Type Overload Implications

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

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

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   requesting the Diameter service that the network is busy and to try
   again later.

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

   Pseudo-stateful applications:  Pseudo stateful applications are also
      stateless applications in that there is no session Diameter state
      maintained between transactions.  There is, however, an implied
      ordering of requests.  As a result, decisions about which
      transactions to reject as a result of an overloaded entity 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.

   Stateful applications:  Overload handling for stateful applications
      must take into consideration the work associated with setting up
      an maintaining a session.  As such, the Diameter entity handling
      overload for a stateful application might tend to reject new
      session requests before rejecting intra-session requests.  In
      addition, session ending requests might be given a lower chance of
      being rejected, since rejecting session ending requests could
      result in session status being out of sync between the Diameter
      clients and servers, while successful execution might actually
      free up resources.  Nodes that reject mid-session requests will
      need to consider whether the rejection invalidates the session,
      and any session clean-up that may be required.

3.1.3.  Request Transaction Classification

   Independent Request:  An independent request is not a part of a
      Diameter session 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.

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   Correlated Session-Initiating Request:  There are cases, most notably
      in the 3GPP PCC architecture, where multiple Diameter sessions are
      correlated and must be handled by the same Diameter server.  This
      is a special case of a Session-Initiating Request.  Gx CCR-I
      requests and Rx AAR messages are examples of correlated session-
      initiating requests.

      [OpenIssue: The previous paragraph needs references.]

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

   Pseudo-Session Requests:  Pseudo session requests are independent
      requests and, as such, the request transactions are not tied
      together using the Diameter session-id.  There exist Diameter
      applications that define an expected ordering of transactions.
      This sequencing of independent transactions results in a pseudo
      session.  The AIR, MAR and SAR requests in the 3GPP defined Cx
      application are examples of pseudo-session requests.

   [OpenIssue: This section offers discusses priorities around
   throttling of requests.  Should we also discuss considerations for
   diverting requests non-overloaded destinations?]

3.1.4.  Request Type Overload Implications

   The request classes identified in Section 3.1.3 have implications on
   decisions about which requests should be throttled first.

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

   Session-creating requests:  Session-creating requests represent more
      work than independent or intra-session requests.  As such,
      throttling decisions might favor intra-session requests over
      session-creating requests.  Individual session-creating requests
      can be given equal treatment when making throttling decisions.

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

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

   Intra-session requests  There are two classes of intra-sessions
      requests.  The first is a request that ends a session.  The second
      is a request that is used to convey session related state between
      the Diameter client and server.  Session ending request should be
      throttled less aggressively in order to keep session state
      consistent between the client and server, and possibly reduce the
      sessions impact on the overloaded entity.  The default handling of
      other intra-session requests might be to treat them equally when
      making throttling decisions.  There might also be application
      level considerations whether some request types are favored over
      others.

3.1.5.  Diameter Deployment Scenarios

   This section discusses various Diameter network deployment scenarios
   and the implications of those deployment models on handling of
   overload reports.

   The scenarios vary based on the following:

   o  The presence or absence of Diameter agents

   o  Which Diameter entities support the DOIC extension

   o  The amount of the network topology understood by Diameter clients

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

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

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

   o  Client --- Server

   o  Client --- Multiple equivalent servers

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

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

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

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

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

   The following is a list of representative DOIC deployment scenarios:

   o  Direct connection between a DOIC client and a DOIC server

   o  DOIC client --- one or more non-DOIC agent(s) --- DOIC server

   o  DOIC client --- DOIC agent --- DOIC server

   o  Non-DOIC client --- DOIC agent --- DOIC server

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

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

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

   o  DOIC client --- DOIC edge agent --- DOIC edge agent --- DOIC
      server

3.1.6.  Diameter Agent Behaviour

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

   Since the solution defined in this specification must not break the
   Diameter base protocol assumptions at any time, great care has to be

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   taken not to assume functionality from the Diameter agents that would
   break base protocol behavior, or to assume agent functionality beyond
   the Diameter base protocol.  Effectively this means the following
   from a Diameter agent:

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

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

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

3.1.7.  Simplified Example Architecture

    Realm X                                  Other Realms
   <--------------------------------------> <---------------------->

   +--^-----+                 : (optional) :
   |Diameter|                 :            :
   |Server A|--+     .--.     : +---^----+ :     .--.
   +--------+  |   _(    `.   : |Diameter| :   _(    `.   +---^----+
               +--(        )--:-|  Agent |-:--(        )--|Diameter|
   +--------+  | ( `  .  )  ) : +-----^--+ : ( `  .  )  ) | Client |
   |Diameter|--+  `--(___.-'  :            :  `--(___.-'  +-----^--+
   |Server B|                 :            :
   +---^----+                 :            :
               Overload Indication A    Overload Indication A'
          1)  <----------------------> <---------------------->

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              standard base protocol   standard base protocol

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

     Simplified architecture choices for overload indication delivery

   [OpenIssue: Need to clarify the meaning of option 2 with the agent in
   place.  Does this mean the agent is not an Overload Endpoint?]

3.2.  Conveyance of the Overload Indication

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

3.2.1.  Negotiation and Versioning

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

3.2.2.  Transmission of the Attribute Value Pairs

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

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   From the Diameter overload control functionality point of view, the
   "Reacting node" is always the requester of the overload report
   information and the "Reporting node" is the provider of the overload
   report.  The overload report or the capability information in the
   request message is always interpreted as an announcement of a
   "capability".  The capability information and the overload report in
   the answer is always interpreted respectively as a report of
   supported common functionality and as a status report of an overload
   condition.

3.3.  Overload Condition Indication

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

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

4.  Attribute Value Pairs

   This section describes the encoding and semantics of Overload
   Indication Attribute Value Pairs (AVPs).

4.1.  OC-Feature-Vector AVP

   The OC-Feature-Vector AVP (AVP code TBD1) is type of Unsigned64 and
   contains a 64 bit flags field of supported capabilities of an
   overload control endpoint.  Receiving the OC-Feature-Vector AVP with
   the value 0 indicates that two endpoints do not share a single common
   capability (or a capability they could agree based on the local
   policy and/or configuration).  A request message initiating endpoint
   (a reacting node) MUST NOT send the OC-Feature-Vector AVP with the
   value 0.

   [OpenIssue: We need further discussion on whether the "no shared
   capability" case is allowed, or if we guarantee certain basic levels
   of compatibility by using mandatory-to-support defaults.]

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

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   [OpenIssue: There is an ongoing discussion as to whether the OC-
   Feature-Vector AVP should be an optional (MAY vs MUST) way to declare
   support, where new Diameter applications could define other ways, or
   whether this should be the "one true" way.  The latter approach
   prevents agents that are not application aware from supporting DOIC,
   but the latter may reduce the flexibility for defining new
   applications.]

   During the message exchange the overload control endpoints express
   their common set of supported capabilities.  The endpoint sending a
   request (the reacting node) includes the OC-Feature-Vector AVP with
   those flags set that correspond what it supports.  The endpoint that
   sends the answer (the reporting node) also includes the OC-Feature-
   Vector AVP with flags set to describe the capabilities it both
   supports and agrees with the request sender (e.g., based on the local
   policy and/or configuration).  The answer sending endpoint (the
   reporting node) does not need to advertise those capabilities it is
   not going to use with the request sending endpoint (the reacting
   node).

   Note that when the OC-Feature-Vector AVP is used together with the
   OC-OLR AVPs, the contents of the announced features and the contents
   of the OC-OLR AVPs MUST NOT contradict each other.  In a case they
   do, the receiver of contradicting information SHOULD discard the AVPs
   as if they were not present to start with and log the event.

   In some cases a single flag bit in the OC-Feature-Vector AVP is not
   verbose enough to describe all of the advertised capability.  This
   concerns the situation where the OC-Feature-Vector AVP is sent in a
   request message.  In this particular case, the OC-OLR AVP MUST
   contain the rest of the required parameters.  For example, if the
   advertised capability concerns an abatement algorithm that needs more
   algorithm specific parameters to agree on, then the OC-OLR abatement
   algorithm specific AVPs MUST contain the rest of the parameter
   information.

   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.

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4.2.  OC-OLR AVP

   The OC-OLR AVP (AVP code TBD2) is type of Grouped and contains the
   necessary information to convey an overload report.  OC-OLR may also
   be used to convey additional information about an extension that is
   declared in the OC-Feature-Vector AVP.

   Since the OC-OLR AVP contains information that may be critical for
   handling overload conditions, reporting nodes SHOULD place the AVP as
   early in the Diameter message as possible.

   The OC-OLR AVP does not contain explicit information to which
   application it applies to and who inserted the AVP or whom the
   specific OC-OLR AVP concerns to.  Both these information is
   implicitly learned from the encapsulating Diameter message/command.
   The application the OC-OLR AVP applies to is the same as the
   Application-Id found in the Diameter message header.  The identity
   the OC-OLR AVP concerns is determined from the Origin-Host AVP found
   from the encapsulating Diameter message.

   [OpenIssue: There is ongoing discussion on whether it's best to infer
   information like application, realm, reporting node identity, etc,
   from the enclosing Diameter message vs making the overload reports
   self-contained.]

   OC-OLR ::= < AVP Header: TBD2 >
              < TimeStamp >
              [ ValidityDuration ]
              [ ReportType ]
            * [ OC-Algorithm ]
            * [ AVP ]

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

   [OpenIssue: Is this necessarily a timestamp, or is it just a sequence
   number that can be implemented as a timestamp?  We should also
   consider whether either a timestamp or sequence number is needed for
   protection against replay attacks.]

4.3.  TimeStamp AVP

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   The TimeStamp AVP (AVP code TBD3) is type of Time.  Its usage in the
   context of the overload control is described in Section 4.2.  From
   the functionality point of view, the TimeStamp AVP is merely used as
   a non-volatile increasing counter between two overload control
   endpoints.

4.4.  ValidityDuration AVP

   The ValidityDuration AVP (AVP code TBD4) is type of Unsigned32 and
   describes the number of seconds the OC-OLR AVP and its content is
   valid since the creation of the OC-OLR AVP (as indicated by the
   TimeStamp AVP).

   A timeout of the overload report has specific concerns that need to
   be taken into account by the endpoint acting on the earlier received
   overload report(s).  Section 4.8 discusses the impacts of timeout in
   the scope of the traffic abatement algorithms.

   As a general guidance for implementations it is RECOMMENDED never to
   let any overload report to timeout.  Rather, an overload endpoint
   should explicitly signal either the continuance of the overload
   condition by sending an new overload report.  This new report would
   indicate a continuance of the overload condition by including a non-
   zero ValidityDuration value, or indicate the end of the condition by
   including a zero value.  This approach leaves no need for the
   reacting node to reason or guess the current condition of the
   reporting node.

4.5.  ReportType AVP

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

   0  Reserved.

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

   2  Realm (aggregated) report.  The overload treatment should apply to
      all requests bound for the overloaded realm.

   The ReportType 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 requests that are targeted to a specific

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   server by the presence of a Destination-Host AVP than for requests
   that can be handled by any server in a realm.  The example in
   Appendix B.3 illustrates this usage.

   [OpenIssue: There is an ongoing discussion about whether the
   ReportType AVP is the right way to solve that issue, and whether it's
   needed at all.]

   [OpenIssue: ReportType should probably be extensible, and have its
   own IANA table.]

4.6.  OC-Algorithm AVP

   The OC-Algorithm AVP (AVP code TBD6) is type of Grouped.  The AVP
   contains the necessary sub-AVPs and information for the use for the
   traffic abatement algorithm.  The OC-Algorithm AVP serves as a
   generic template for all future traffic abatement algorithms.

   This specification defines an identifier for the default (loss)
   algorithm (see Section 4.1 for the OC-Feature-Vector flag
   corresponding to the algorithm), as well as the format and meaning of
   that algorithm's input parameter.

   OC-Algorithm ::= < AVP Header: TBD6 >
                    < Algorithm-ID >
                    [ Reduction-Percentage ]
                  * [ AVP ]

   As already discussed in Section 4.1 in certain cases, the Algorithm
   AVP MAY be used in a request message together with the OC-Feature-
   Vector AVP to describe the detailed parameterization of the abatement
   algorithm to the other endpoint (i.e. to the reporting node).  This
   implies, the possible future algorithms and their sub-AVPs must be
   designed accordingly.

4.7.  Algorithm-ID AVP

   The Algorithm-ID AVP (AVP code TBD7) is type of Enumerated and
   identifies the traffic abatement algorithm the OC-Algorithm AVP
   "describes" and implements.  This specification defines the following
   algorithms:

   0  Reserved.

   1  Default (loss) algorithm.

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4.8.  Reduction-Percentage AVP

   The Reduction-Percentage AVP (AVP code TBD8) is type of Unsigned32
   and describes the percentage of the traffic that the sender is
   requested to reduce, compared to what it otherwise would have sent.

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

   [OpenIssue: We should consider an algorithm independent way to end an
   overload condition.  Perhaps setting the validitytime to zero?
   Counter comment; since the abatement is based on a specific
   algorithm, it is natural to indicate that from the abatement
   algorithm point of view status quo has been reached.]

   Since a Reduction-Percentage of 100% prevents the reporting node from
   explicitly ending the overload condition, such a condition can only
   end due to a report timeout.  When an overload control endpoint comes
   out of the 100 percent traffic reduction as a result, the following
   concerns are RECOMMENDED to be applied.  The endpoint sending the
   traffic should be conservative and, for example, first send few
   "probe" messages to learn the overload condition of the other
   endpoint before converging to any traffic level decided by the
   sender.  Similar concerns actually apply in all cases when the
   overload report times out unless the previous overload report stated
   0 percent reduction.

4.9.  Attribute Value Pair flag rules

                                                      +---------+
                                                      |AVP flag |
                                                      |rules    |
                                                      +----+----+
                      AVP   Section                   |    |MUST|
    Attribute Name    Code  Defined  Value Type       |MUST| NOT|
   +--------------------------------------------------+----+----+
   |OC-Feature-Vector TBD1  x.x      Unsigned64       |    | V  |
   +--------------------------------------------------+----+----+
   |OC-OLR            TBD2  x.x      Grouped          |    | V  |
   +--------------------------------------------------+----+----+
   |TimeStamp         TBD3  x.x      Time             |    | V  |
   +--------------------------------------------------+----+----+
   |ValidityPeriod    TBD4  x.x      Unsigned32       |    | V  |

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   +--------------------------------------------------+----+----+
   |ReportType        TBD5  x.x      Enumerated       |    | V  |
   +--------------------------------------------------+----+----+
   |OC-Algorithm      TBD6  x.x      Grouped          |    | V  |
   +--------------------------------------------------+----+----+
   |Algorithm-ID      TBD7  x.x      Enumerated       |    | V  |
   +--------------------------------------------------+----+----+
   |Reduction                                         |    |    |
   |  -Percentage     TBD8  x.x      Unsigned32       |    | V  |
   +--------------------------------------------------+----+----+

5.  Overload Control Operation

5.1.  Overload Control Endpoints

   The overload control solution can be considered as an overlay on top
   of an arbitrary Diameter network.  An overload control "association"
   exists between two Diameter nodes that exchanging overload control
   information.  These nodes are called "overload control endpoints".
   These endpoints, namely the "reacting node" and the "reporting node"
   do not need to be adjacent Diameter peer nodes, nor do 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 endpoint 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.

      [Editor's note: a picture illustrating the endpoint concept would
      be useful.]

5.2.  Piggybacking Principle

   The overload control solution defined AVPs are essentially
   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-Feature-Vector AVP into existing commands (this
   has an assumption that the application CCF allows adding new AVPs
   into the Diameter messages.

   In a case of newly defined Diameter applications, it is RECOMMENDED
   to add and define how overload control mechanisms works on that
   application.  Using OC-Feature-Vector and OC-OLR AVPs is optional,
   and is intended only existing applications.

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   [OpenIssue: The guidance in the previous paragraph depends on the
   outcome of the open issue mentioned at the definition of OC-Feature-
   Vector.]

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

5.3.  Capability Negotiation

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

   [OpenIssue: Some of the guidance in the previous paragraph depends on
   the outcome of the open issue mentioned at the definition of OC-
   Feature-Vector.]

   [OpenIssue: We need to think more about the general flow for
   capabilities negotiation.  Call flows would be helpful here.  A
   counter comment: the text in Section 4.1 should be rather clear now
   regarding the capability negotiation.]

5.3.1.  Request Message Initiator Endpoint Considerations

   The basic principle is that the request message initiating endpoint
   (i.e. the "reacting node") announces its support for the overload
   control mechanism by including in a Diameter request message the OC-
   Feature-Vector AVP with those capability flag bits set that it
   supports and is willing to use for this Diameter session (or
   transaction in a case of a non-session state maintaining

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   applications).  In a case of session maintaining applications the
   request message initiating endpoint does not need to do the
   capability announcement more than once for the lifetime of the
   Diameter session.  In a case of non-session maintaining applications,
   it is RECOMMENDED that the request message initiating endpoint
   includes the capability announcement into every request regardless it
   has had prior message exchanges with the give remote endpoint.

   [OpenIssue: We need to think about the lifetime of a capabilities
   declaration.  It's probably not the same as for a session.  We have
   had proposals that the feature vector needs to go into every request
   sent by an OC node.  For peer to peer cases, this can be associated
   with connection lifetime, but it's more complex for non-adjacent OC
   support.]

   If the OC-Feature-Vector AVP does not have enough information about
   the supported feature or the traffic abatement algorithm, then the
   request message initiating endpoint MUST also include the OC-OLR AVP
   with an appropriate content in it (such as a rate based abatement
   algorithm would include the desired rate information AVPs inside the
   OC-OLR AVP).  See the discussion in Section 4.1 and in Section 4.6.

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

5.3.2.  Answer Message Initiating Endpoint Considerations

   When a remote endpoint (i.e. a "reporting node") receives a request
   message in can detect whether the request message initiating endpoint
   has support for the overload control solution based on the presence
   of the OC-Feature-Vector AVP and possibly the OC-OLR AVP.  For the
   newly defined applications the overload control solution support can
   be part of the application specification.  Based on the content of
   the OC-Feature-Vector AVP and optionally the contents of the OC-OLR
   AVP, the request message receiving endpoint knows what overload
   control functionality the other endpoint supports and then act
   accordingly for the subsequent answer messages it initiates.  It is
   RECOMMENDED that the answer message initiating endpoint selects one

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

5.4.  Protocol Extensibility

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

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

5.5.  Overload Report Processing

5.5.1.  Sender Endpoint Considerations

5.5.2.  Receiver Endpoint Considerations

   [OpenIssue: did we now agree that e.g. a server can refrain sending
   OLR in answers based on some magical algorithm?  (Note: We seem to
   have consensus that a server MAY repeat OLRs in subsequent messages,
   but is not required to do so, based on local policy.)]

   [OpenIssue: We need to define some rules about throttling at an
   agent.  In particular, that the agent needs to send errors back
   downstream if it drops requests, and propose a specific error code
   for this purpose.]

6.  Transport Considerations

   In order to reduce overload control introduced additional AVP and
   message processing it might be desirable/beneficial to signal whether
   the Diameter command carries overload control information that should
   be of interest of an overload aware Diameter node.

   Should such indication be include is not part of this specification.
   It has not either been concluded at what layer such possible

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   indication should be.  Obvious candidates include transport layer
   protocols (e.g., SCTP PPID or TCP flags) or Diameter command header
   flags.

7.  IANA Considerations

7.1.  AVP codes

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

7.2.  New registries

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

   Section 4.1 defines a new "Overload Control Feature Vector" registry
   including the initial assignments.  New values can be added into the
   registry using the Specification Required policy [RFC5226].

   Section 4.5 defines a new "Overload Report Type" registry with its
   initial assignments.  New types can be added using the Specification
   Required policy [RFC5226].

   Section 4.7 defines a new "Overload Control Algorithm" registry with
   its initial assignments.  New types can be added using the
   Specification Required policy [RFC5226].

8.  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 currently include features to provide end-to-end
   authentication, integrity protection, or confidentiality.  This may
   cause complications when sending overload reports between non-
   adjacent nodes.

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8.1.  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
   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

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   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.

8.2.  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.

8.3.  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
   [I-D.ietf-dime-overload-reqs] 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.

8.4.  End-to End-Security Issues

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

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   reports, and whether they are trusted to forward overload reports
   from non-adjacent nodes.

   [OpenIssue: This requires that a responding node be able to tell a
   peer-generated OLR from one generated by a non-adjacent node.  One
   way of doing this would be to include the identity of the node that
   generated the report as part of the OLR]

   [OpenIssue: Do we need further language about what rules an agent
   should apply before forwarding an OLR?]

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

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

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

      At the time of this writing, the DIME working group is studying
      requirements for adding end-to-end security
      [I-D.ietf-dime-e2e-sec-req] features to Diameter.  These features,
      when they become available, might make it easier to establish
      trust in non-adjacent nodes for overload control purposes.
      Readers should be reminded, however, that the overload control
      mechanism encourages Diameter agents to modify AVPs in, or insert

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      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.

9.  Contributors

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

   o  Eric McMurry

   o  Hannes Tschofenig

   o  Ulrich Wiehe

   o  Jean-Jacques Trottin

   o  Lionel Morand

   o  Maria Cruz Bartolome

   o  Martin Dolly

   o  Nirav Salot

   o  Susan Shishufeng

10.  Acknowledgements

   ...

11.  References

11.1.  Normative References

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

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

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

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11.2.  Informative References

   [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.

   [I-D.ietf-dime-overload-reqs]
              McMurry, E. and B. Campbell, "Diameter Overload Control
              Requirements", draft-ietf-dime-overload-reqs-13 (work in
              progress), September 2013.

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

Appendix A.  Issues left for future specifications

   The base solution for 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 4.1, 4.7 and 7 for the required
   IANA steps.

A.2.  Agent Overload

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

A.3.  DIAMETER_TOO_BUSY clarifications

   The current [RFC6733] behaviour in a case of DIAMETER_TOO_BUSY is
   somewhat underspecified.  For example, there is no information how
   long the specific Diameter node is willing to 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 APVs should be discussed and possible be
   recommended to be used.

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A.4.  Load

   This specification defines the mechanism for a Diameter end-point to
   request a reduction in traffic.  The full solution envisioned by the
   Diameter overload requirements also included a mechanism to
   communicate load that a Diameter node is able to handle.  This
   capability is expected to help to decrease the oscillation of
   overload events.  This load capability has been left for follow on
   work.

Appendix B.  Examples

B.1.  3GPP S6a interface overload indication

   [TBD: Would cover S6a MME-HSS communication with several topology
   choices (such as with or without DRA, and with "generic" agents).]

B.2.  3GPP PCC interfaces overload indication

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

B.3.  Mix of Destination-Realm routed requests and Destination-Host
      reouted requests

   [TBD: Add example showing the use of Destination-Host type OLRs and
   Realm type OLRs.]

Authors' Addresses

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

   Email: jouni.nospam@gmail.com

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

   Email: srdonovan@usdonovans.com

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

   Email: ben@nostrum.com

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