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Diameter Maintenance and Extensions                       L. Morand, Ed.
(DIME)                                                       Orange Labs
Internet-Draft                                                V. Fajardo
Intended status: Informational
Expires: October 3, 2012                                   H. Tschofenig
                                                  Nokia Siemens Networks
                                                           April 1, 2012


                Diameter Applications Design Guidelines
                  draft-ietf-dime-app-design-guide-14

Abstract

   The Diameter Base protocol provides facilities for protocol
   extensibility enabling to define new Diameter applications or modify
   existing applications.  This document is a companion document to the
   Diameter Base protocol that further explains and clarifies the rules
   to extend the Diameter Base protocol.  It is meant as a guidelines
   document and therefore it does not add, remove or change existing
   rules.






























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Requirements Language

   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 [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 October 3, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.














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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Reusing existing Diameter applications . . . . . . . . . . . .  8
     4.1.  Adding a new command . . . . . . . . . . . . . . . . . . .  8
     4.2.  Deleting a command . . . . . . . . . . . . . . . . . . . .  9
     4.3.  Reusing existing commands  . . . . . . . . . . . . . . . .  9
       4.3.1.  Adding AVPs to a command . . . . . . . . . . . . . . . 10
       4.3.2.  Deleting AVPs from a Command . . . . . . . . . . . . . 11
     4.4.  Reusing existing AVPs  . . . . . . . . . . . . . . . . . . 12
       4.4.1.  Setting of the AVP flags . . . . . . . . . . . . . . . 12
       4.4.2.  Reuse of AVP of type Enumerated  . . . . . . . . . . . 12
   5.  Rules for new Applications . . . . . . . . . . . . . . . . . . 13
     5.1.  Use of Application-Id in a Message . . . . . . . . . . . . 13
     5.2.  Application Specific Session State Machine . . . . . . . . 14
   6.  End-to-End Applications Capabilities Exchange  . . . . . . . . 15
   7.  Diameter Accounting Support  . . . . . . . . . . . . . . . . . 16
   8.  Generic Diameter Extensions  . . . . . . . . . . . . . . . . . 18
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 23
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 24
     13.2. Informative References . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26























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1.  Introduction

   The Diameter Base protocol provides facilities to extend the Diameter
   Base protocol (see Section 1.3 of [I-D.ietf-dime-rfc3588bis]) for
   supporting new functionalities.  In the context of this document,
   extending Diameter means one of the following:


   1.  Addition of a new functionality to an existing Diameter
       application without defining a new application.


   2.  Addition of a new functionality to an existing Diameter
       application that requires the definition of a new application.


   3.  The definition of a new Diameter application to provide a set of
       functionalities not supporting by existing applications.


   4.  The definition of a new generic functionality that can be reused
       across different applications.


   All of these choices are design decisions that can done by any
   combination of reusing existing or defining new commands, AVPs or AVP
   values.  Protocol designers do, however, not have total freedom when
   making their design.  A number of rules defined in
   [I-D.ietf-dime-rfc3588bis] place constraints on when an extension
   demands a new Diameter application to be defined or a new command
   code to be registered.  The objective of this document is the
   following:


   o  Clarify updated Diameter extensibility rules in the Diameter Base
      Protocol.


   o  Clarify usage of certain Diameter functionalities that are not
      explicitly described in the Diameter Base specification.


   o  Discuss design choices and provide guidelines when defining
      applications.


   o  Present tradeoffs of design choices.




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2.  Terminology

   This document reuses the terminology used in
   [I-D.ietf-dime-rfc3588bis].















































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3.  Overview

   As designed, the Diameter Base protocol can be seen as a two-layer
   protocol.  The lower layer is mainly responsible for managing
   connections between neighboring peers and for message routing.  The
   upper layer is where the Diameter applications reside.  This model is
   in line with a Diameter node having an application layer and a peer-
   to-peer delivery layer.  The Diameter Base protocol document
   completely defines the architecture and behavior of the message
   delivery layer and then provides the framework for designing Diameter
   applications on the application layer.  This framework includes
   definitions of application sessions and accounting support (see
   Section 8 and 9 of [I-D.ietf-dime-rfc3588bis]).  The remainder of
   this document also treats a Diameter node as a single instance of a
   Diameter message delivery layer and one or more Diameter applications
   using it.

   The Diameter protocol is designed to be extensible and the principles
   are descibed in the section 1.3 of [I-D.ietf-dime-rfc3588bis].
   Extending Diameter can mean the definition of a new Diameter
   application and/or the reuse of commands, AVPs and AVP values in any
   combination for the purpose of inheriting the features of an existing
   Diameter application.  The reuse recommendation is meaningful as most
   of the requirements defined for a new application are likely already
   fulfilled by an existing application.

   However, when reusing existing applications, there is a greater
   likelihood of ambiguity on how much of the existing application can
   be enhanced without being distorted too much and therefore requiring
   the definition of a new application.

   The impacts of extending existing applications can be categorized as
   follow:

   Minor Extension:  Enhancing the functional scope of an existing
      application by the addition of optional features to support.  Such
      enhancement has no backward compatibility issue with the existing
      application.  A typical example would be the definition of a new
      optional AVP to use in an existing command.  In general, this
      includes everything that is not covered by the next category.  The
      standardization effort will be fairly small.


   Major Extension:  Enhancing the functional scope of an existing
      application in such a way that this implies backward compatible
      change to the existing application and then requires the
      definition of a new Diameter application.  A typical example would
      be the creation of a new command for providing functionality not



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      supported by existing applications.  For such extension, a
      significant specification effort is required and a carefull
      approach is recommended.

   The rules outlined in the section 1.3 of [I-D.ietf-dime-rfc3588bis]
   indicate when an extension requires a new command code to be
   registered and when new Diameter applications have to be defined.
   The subsequent sections further explain and clarify the rules to
   extend the Diameter Base protocol.  It is meant as a guidelines
   document and therefore it does not add, remove or change existing
   rules.








































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4.  Reusing existing Diameter applications

   When selecting the Diameter Base protocol to support new
   functionalities, protocol designers are advised to try to re-use as
   much as possible existing Diameter applications to simplify
   standardization, implementation and avoid potential interoperability
   issues.  However, existing application needs to be adapted to support
   new requirements and these modifications can be at the command level
   and/or at the AVP level.  The following sections describe the
   possible modifications that can be performed on existing applications
   and their related impacts.

4.1.  Adding a new command

   Adding a new command is considered as a major extension and requires
   a new Diameter application to be defined.  Adding a new command to an
   application means either defining a completely new command or
   importing the command's CCF syntax specification from another
   application whereby the new application inherits some or all of the
   functionality of the application where the command came from.  In the
   former case, the decision to create an new application is
   straightforward since this is typically a result of adding a new
   functionality that does not exist yet.  For the latter, the decision
   to create a new application will depend on whether importing the
   command in a new application is more suitable than simply using the
   existing application as it is in conjunction with any other
   application.  Therefore, a case by case study of each application
   requirement should be applied.

   An illustrative example is the command pair defined in Diameter EAP
   application [RFC4072] that can be re-used conjointly with any other
   application (e.g. the Diameter NASREQ application [RFC4005]) as soon
   as standard EAP-based authentication procedures need to be supported
   by the implementation.  It may therefore not be required to import
   the command pair in the new defined application.

   However, in general, it is difficult to come to a hard guideline, and
   so a case by case study of each application requirement should be
   applied.  Before adding or importing a command, application designers
   should consider the following:


   o  Can the new functionality be fulfilled by creating a new command
      independent from any existing command?  In this case, the
      resulting new application and the existing application can work
      independent of, but cooperating with each other.





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   o  Can the existing command be reused without major extensions and
      therefore without the need for the definition of a new
      application, e.g. new funtionality introduced by the creation of
      new optional AVPs.


   o  Care should be taken to avoid a liberal method of importing
      existing command's CCF syntax specification.  This would result in
      a monolithic and hard to manage applications supporting too many
      different functionalities and can cause interoperability issues
      between the different applications. .



4.2.  Deleting a command

   Although this process is not typical, removing a command to an
   application requires a new Diameter application to be defined. this
   is due to the fact that the reception of the deleted command would
   systematically result in a protocol error
   (DIAMETER_COMMAND_UNSUPPORTED).

   It is unusual to delete an existing command from an application for
   the sake of deleting it or the functionality it represents.  This
   normally indicates of a flawed design.  An exception might be if the
   intent of the deletion is to create a newer version of the same
   application which is somehow simpler than the previous version.

4.3.  Reusing existing commands

   This section discusses rules in adding and/or deleting AVPs from an
   existing command of an existing application.  The cases described in
   this section may not necessarily result in the creation of new
   applications.

   It is worth to note that the strong recommendation to re-use existing
   commands in the [RFC3588] was to prevent rapid scarcity of code
   values available for vendor-specific commands.
   [I-D.ietf-dime-rfc3588bis] relaxes the policy with respect to the
   allocation of command codes for vendor-specific uses and enlarges the
   range of available code values for vendor-specific applications.
   Therefore, if it is still recommended to re-use as much as possible
   existing commands, protocol designers can consider more easily the
   definition of a new command when it is a solution more suitable than
   twisting existings command use and applications.






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4.3.1.  Adding AVPs to a command

   Based on the rules in [I-D.ietf-dime-rfc3588bis], AVPs that are added
   to an existing command can be categorized into:


   o  Mandatory (to understand) AVPs.  As defined in
      [I-D.ietf-dime-rfc3588bis], these are AVPs with the M-bit flag
      set, which means that a Diameter node receiving are required to
      understand not only their values but their semantics.  Failure to
      do so will cause an message handling error.  This is regardless of
      whether these AVPs are required or optional as specified by the
      command's CCF syntax specification.


   o  Optional (to understand) AVPs.  As defined in
      [I-D.ietf-dime-rfc3588bis], these are AVPs with the M-bit flag
      cleared, which mean that a Diameter node receiving these AVP can
      simply ignore them if not supported in the process of the received
      command.

   The rules are strict in the case where the AVPs to be added are
   mandatory to understand i.e. with the M-bit set.  A mandatory AVP
   cannot be added to an existing command without defining a new
   Diameter application, as stated in [I-D.ietf-dime-rfc3588bis].  This
   falls into the "Major Extensions" category.  Despite the clarity of
   the rule, ambiguity still arises when evaluating whether a new AVP
   being added should be mandatory to begin with.  Here is a list of few
   common questions that application designers should wonder when trying
   to decide:


   o  Would it be required for the receiving side to be able to process
      and understand the AVP and its content?


   o  Would the new AVPs change the state machine of the application?


   o  Would the presence of the new AVP lead to a different number of
      roundtrips, effectively changing the state machine of the
      application?


   o  Would the new AVP be used to differentiate between old and new
      versions of the same application whereby the two versions are not
      backward compatible?




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   o  Would the new AVP have duality in meaning i.e. be used to carry
      application related information as well as be used to indicate
      that the message is for a new application?

   When one of the above questions can be answered in the affirmative
   then the M-bit has to be set for the new AVP.

   If application designers are instead contemplating on the use of
   optional AVPs i.e. with the M-bit cleared, then the following are
   some of the pitfalls that should be avoided:


   o  Use of optional AVPs with intersecting meaning.  One AVP has
      partially the same usage and meaning as another AVP.  The presence
      of both can lead to confusion.


   o  An optional AVPs with dual purpose, i.e. to carry applications
      data as well as to indicate support for one or more features.
      This has a tendency to introduce interpretation issues.


   o  Adding one or more optional AVPs and indicating (usually within
      descriptive text for the command) that at least one of them has to
      be present in the command.  This essentially circumventing the
      ABNF and is equivalent to adding a mandatory AVPs to the command.


   These practices generally result in interoperability issues and
   should be avoided as much as possible.

4.3.2.  Deleting AVPs from a Command

   When deleting an AVP from a command, the following cases need to be
   differentiated:


   o  Deleting an AVP that is indicated as { AVP } in the command's CCF
      syntax specification, whatever the setting of the M-bit set.  This
      means the definition of a new command.  In this case, a new
      command code and subsequently a new Diameter application have to
      be specified.


   o  Deleting an AVP with M-bit set that is indicated as [ AVP ] in the
      command's CCF syntax specification.  No new command code has to be
      specified but the definition of a new Diameter application is
      required.



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   o  Deleting an AVP with the M-bit cleared that is indicated as [ AVP
      ] in the command's CCF syntax specification.  In this case, the
      AVP can be deleted without consequences.


   If possible application designers should attempt the reuse the
   command's CCF syntax specification without modification and simply
   ignore (but not delete) any optional AVP that will not be used.  This
   is to maintain compatibility with existing applications that will not
   know about the new functionality as well as maintain the integrity of
   existing dictionaries.

4.4.  Reusing existing AVPs

   This section discusses rules in reusing existing AVP when reusing an
   existing command or defining a new command in a new application.

4.4.1.  Setting of the AVP flags

   When reusing AVPs in a new application, the AVP flag setting, such as
   the mandatory flag ('M'-bit), has to be re-evaluated for a new
   Diameter application and, if necessary, even for every command within
   the application.  In general, for AVPs defined outside of the base
   protocol, its mandatory characteristics are tied to its role within
   an application and command.

   All other AVP flags shall remain unchanged

4.4.2.  Reuse of AVP of type Enumerated

   When modifying the set of values supported by an AVP of type
   Enumerated, this means defining a new AVP.  Modifying the set of
   Enumerated values includes adding a value or deprecating the use of a
   value defined initially for the AVP.  Defining a new AVP will avoid
   interoperability issues.
















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5.  Rules for new Applications

   The general recommendation for Diameter extensibility is to reuse
   commands, AVPs and AVP values as much as possible.  However, some of
   the extensibility rules described in the previous section also apply
   to scenarios where a designer is trying to define a completely new
   Diameter application.

   This section discusses the case where new applications have
   requirements that cannot be filled by existing applications and would
   require definition of completely new commands, AVPs and/or AVP
   values.  Typically, there is little ambiguity about the decision to
   create these types of applications.  Some examples are the interfaces
   defined for the IP Multimedia Subsystem of 3GPP, i.e.  Cx/Dx
   ([TS29.228] and [TS29.229]), Sh ([TS29.328] and [TS29.329]) etc.

   Application designers should also follow the theme of Diameter
   extensibility which in this case means to import existing AVPs and
   AVP values for any newly defined commands.  In certain cases where
   accounting will be used, the models described in Section 7 should
   also be considered.  Though some decisions may be clear, designers
   should also consider certain aspects of defining a new application.
   Some of these aspects are described in following sections.

5.1.  Use of Application-Id in a Message

   When designing new applications, designers should specify that the
   application ID carried in all session level messages must be the
   application ID of the application using those messages.  This
   includes the session level messages defined in base protocol, i.e.,
   RAR/RAA, STR/STA, ASR/ASA and possibly ACR/ACA in the coupled
   accounting model, see Section 7.  Existing specifications may not
   adhere to this rule for historical or other reasons.  However, this
   scheme should be followed to avoid possible routing problems for
   these messages.

   In general, when a new application has been allocated with a new
   application id and it also reuses existing commands with or without
   modifications (Sec 4.1), it must use the newly allocated application
   id in the header and in all relevant application id AVPs (Auth-
   Application-Id or Acct-Application-Id) present in the commands
   message body.

   Additionally, application designs using
   Vendor-Specific-Application-Id AVP should not use the Vendor-Id AVP
   to further dissect or differentiate the vendor-specification
   application id.  Diameter routing is not based on the Vendor-Id.  As
   such, the Vendor-ID should not be used as an additional input for



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   routing or delivery of messages.  In general, the Vendor-Id AVP is an
   informational AVP only and kept for backward compatibility reasons.

5.2.  Application Specific Session State Machine

   Section 8 of [I-D.ietf-dime-rfc3588bis] provides session state
   machines for authentication, authorization and accounting (AAA)
   services.  When a new application is being defined that cannot
   clearly be categorized into any of these services it is recommended
   that the application itself define its own session state machine.
   The existing session state machines defined by
   [I-D.ietf-dime-rfc3588bis] is not intended for general use beyond AAA
   services, therefore any behavior not covered by that category would
   not fit well.  Support for server initiated request is a clear
   example where an application specific session state machine would be
   needed, for example, the Rw interface for ITU-T push model (
   cf.[Q.3303.3]).


































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6.  End-to-End Applications Capabilities Exchange

   It is also possible that applications can use optional AVPs to
   exchange application specific capabilities and features.  These AVPs
   are exchanged on an end-to-end basis.  Examples of this can be found
   in [I-D.ietf-dime-mip6-integrated] and
   [I-D.ietf-dime-qos-attributes].

   The end-to-end capabilities AVPs can aid in the following cases:


   o  Formalizing the way new functionality is added to existing
      applications by announcing support for it.


   o  Applications that do not understand these AVP can discard it upon
      receipt.  In such case, senders of the AVP can also safely assume
      the receiving end-point does not support any functionality carried
      by the AVP if it is not present in subsequent responses.


   o  Useful in cases where deployment choices are offered and the
      generic design can be made available for a number of applications.


   Note that this list is not meant to be comprehensive.

   When used in a new application, protocol designers should clearly
   specify this end-to-end capabilities exchange and the corresponding
   behaviour of the Diameter nodes supporting the application.





















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7.  Diameter Accounting Support

   Accounting can be treated as an auxiliary application which is used
   in support of other applications.  In most cases, accounting support
   is required when defining new applications.  This document provides
   two(2) possible models for using accounting:


   Split Accounting Model

      In this model, the accounting messages will use the Diameter base
      accounting application ID (value of 3).  The design implication
      for this is that the accounting is treated as an independent
      application, especially during Diameter routing.  This means that
      accounting commands emanating from an application may be routed
      separately from the rest of the other application messages.  This
      may also imply that the messages generally end up in a central
      accounting server.  A split accounting model is a good design
      choice when:


      *  The application itself will not define its own unique
         accounting commands.


      *  The overall system architecture permits the use of centralized
         accounting for one or more Diameter applications.


      Centralizing accounting may have advantages but there are also
      drawbacks.  The model assumes that the accounting server can
      somehow differentiate received accounting messages.  Since the
      received accounting messages can be for any application and/or
      service, the accounting server has to be have a method to uniquely
      match accounting messages with applications and/or services being
      accounted for.  This may mean defining new AVPs, checking the
      presence, absence or contents of existing AVPs or checking the
      contents of the accounting records itself.  But in general, there
      is no clean and generic scheme for sorting these messages.
      Therefore, the use of this model is recommended only when all
      received accounting messages can be clearly identified and sorted.
      For most cases, the use of Coupled Accounting Model is
      recommended.








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   Coupled Accounting Model

      In this model, the accounting messages will use the application ID
      of the application using the accounting service.  The design
      implication for this is that the accounting messages are tightly
      coupled with the application itself; meaning that accounting
      messages will be routed like any other application messages.  It
      would then be the responsibility of the application server
      (application entity receiving the ACR message) to send the
      accounting records carried by the accounting messages to the
      proper accounting server.  The application server is also
      responsible for formulating a proper response (ACA).  A coupled
      accounting model is a good design choice when:


      *  The system architecture or deployment will not provide an
         accounting server that supports Diameter.


      *  The system architecture or deployment requires that the
         accounting service for the specific application should be
         handled by the application itself.


      *  The application server is provisioned to use a different
         protocol to access the accounting server; e.g., via LDAP, SOAP
         etc.  This includes attempting to support older accounting
         systems that are not Diameter aware.


      In all cases above, there will generally be no direct Diameter
      access to the accounting server.


   These models provide a basis for using accounting messages.
   Application designers may obviously deviate from these models
   provided that the factors being addressed here have also been taken
   into account.  Though it is not recommended, examples of other
   methods might be defining a new set of commands to carry application
   specific accounting records.











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8.  Generic Diameter Extensions

   Generic Diameter extensions are AVPs, commands or applications that
   are designed to support other Diameter applications.  They are
   auxiliary applications meant to improve or enhance the Diameter
   protocol itself or Diameter applications/functionality.  Some
   examples include the extensions to support auditing and redundancy
   (see [I-D.calhoun-diameter-res-mgmt]), improvements in duplicate
   detection scheme (see [I-D.asveren-dime-dupcons]), and piggybacking
   of QoS attributes (see [I-D.ietf-dime-qos-attributes]).

   Since generic extensions can cover many aspects of Diameter and
   Diameter applications, it is not possible to enumerate all the
   probable scenarios in this document.  However, some of the most
   common considerations are as follows:


   o  Backward compatibility: Dealing with existing applications that do
      not understand the new extension.  Designers also have to make
      sure that new extensions do not break expected message delivery
      layer behavior.


   o  Forward compatibility: Making sure that the design will not
      introduce undue restrictions for future applications.  Future
      applications attempting to support this feature should not have to
      go through great lengths to implement any new extensions.


   o  Tradeoffs in signaling: Designers may have to choose between the
      use of optional AVPs piggybacked onto existing commands versus
      defining new commands and applications.  Optional AVPs are simpler
      to implement and may not need changes to existing applications;
      However, the drawback is that the timing of sending extension data
      will be tied to when the application would be sending a message.
      This has consequences if the application and the extensions have
      different timing requirements.  The use of commands and
      applications solves this issue but the tradeoff is the additional
      complexity of defining and deploying a new application.  It is
      left up to the designer to find a good balance among these
      tradeoffs based on the requirements of the extension.


   In practice, it is often the case that the generic extensions use
   optional AVPs because it's simple and not intrusive to the
   application that would carry it.  Peers that do not support the
   generic extensions need not understand nor recognize these optional
   AVPs.  However, it is recommended that the authors of the extension



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   specify the context or usage of the optional AVPs.  As an example, in
   the case that the AVP can be used only by a specific set of
   applications then the specification must enumerate these applications
   and the scenarios when the optional AVPs will be used.  In the case
   where the optional AVPs can be carried by any application, it is
   should be sufficient to specify such a use case and perhaps provide
   specific examples of applications using them.

   In most cases, these optional AVPs piggybacked by applications would
   be defined as a Grouped AVP and it would encapsulate all the
   functionality of the generic extension.  In practice, it is not
   uncommon that the Grouped AVP will encapsulate an existing AVP that
   has previously been defined as mandatory ('M'-bit set) e.g., 3GPP IMS
   Cx / Dx interfaces ([TS29.228] and [TS29.229]).





































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9.  IANA Considerations

   This document does not require actions by IANA.
















































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10.  Security Considerations

   This document does provides guidelines and considerations for
   extending Diameter and Diameter applications.  It does not define nor
   address security related protocols or schemes.














































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11.  Contributors

   The content of this document was influenced by a design team created
   to revisit the Diameter extensibility rules.  The team consisting of
   the members listed below was formed in February 2008 and finished its
   work in June 2008.


   o  Avi Lior

   o  Glen Zorn

   o  Jari Arkko

   o  Lionel Morand

   o  Mark Jones

   o  Victor Fajardo

   o  Tolga Asveren

   o  Jouni Korhonen

   o  Glenn McGregor

   o  Hannes Tschofenig

   o  Dave Frascone

   We would like to thank Tolga Asveren, Glenn McGregor, and John
   Loughney for their contributions as co-authors to earlier versions of
   this document.


















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12.  Acknowledgments

   We greatly appreciate the insight provided by Diameter implementers
   who have highlighted the issues and concerns being addressed by this
   document.














































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13.  References

13.1.  Normative References

   [I-D.ietf-dime-rfc3588bis]
              Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", draft-ietf-dime-rfc3588bis-31
              (work in progress), March 2012.

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

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

13.2.  Informative References

   [I-D.asveren-dime-dupcons]
              Asveren, T., "Diameter Duplicate Detection Cons.",
              draft-asveren-dime-dupcons-00 (work in progress),
              August 2006.

   [I-D.calhoun-diameter-res-mgmt]
              Calhoun, P., "Diameter Resource Management Extensions",
              draft-calhoun-diameter-res-mgmt-08.txt (work in progress),
              March 2001.

   [I-D.ietf-dime-mip6-integrated]
              Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C.,
              and K. Chowdhury, "Diameter Mobile IPv6: Support for
              Network Access Server to Diameter Server Interaction",
              draft-ietf-dime-mip6-integrated-12 (work in progress),
              January 2009.

   [I-D.ietf-dime-qos-attributes]
              Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,
              and A. Lior, "Traffic Classification and Quality of
              Service Attributes for Diameter",
              draft-ietf-dime-qos-attributes-15 (work in progress),
              December 2009.

   [Q.3303.3]
              3rd Generation Partnership Project, "ITU-T Recommendation
              Q.3303.3, "Resource control protocol no. 3 (rcp3):
              Protocol at the Rw interface between the Policy Decision
              Physical Entity (PD-PE) and the Policy Enforcement
              Physical Entity (PE-PE): Diameter"", 2008.




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   [RFC4005]  Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
              "Diameter Network Access Server Application", August 2005,
              <http://www.rfc-editor.org/rfc/rfc4005.txt>.

   [RFC4072]  Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application", August 2005,
              <http://www.rfc-editor.org/rfc/rfc4072.txt>.

   [TS29.228]
              3rd Generation Partnership Project, "3GPP TS 29.228;
              Technical Specification Group Core Network and Terminals;
              IP Multimedia (IM) Subsystem Cx and Dx Interfaces;
              Signalling flows and message contents",
              <http://www.3gpp.org/ftp/Specs/html-info/29272.htm>.

   [TS29.229]
              3rd Generation Partnership Project, "3GPP TS 29.229;
              Technical Specification Group Core Network and Terminals;
              Cx and Dx interfaces based on the Diameter protocol;
              Protocol details",
              <http://www.3gpp.org/ftp/Specs/html-info/29229.htm>.

   [TS29.328]
              3rd Generation Partnership Project, "3GPP TS 29.328;
              Technical Specification Group Core Network and Terminals;
              IP Multimedia (IM) Subsystem Sh interface; signalling
              flows and message content",
              <http://www.3gpp.org/ftp/Specs/html-info/29328.htm>.

   [TS29.329]
              3rd Generation Partnership Project, "3GPP TS 29.329;
              Technical Specification Group Core Network and Terminals;
              Sh Interface based on the Diameter protocol; Protocol
              details",
              <http://www.3gpp.org/ftp/Specs/html-info/29329.htm>.
















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Authors' Addresses

   Lionel Morand (editor)
   Orange Labs


   Phone: +33 1 4529 6257
   Email: lionel.morand@orange.com


   Victor Fajardo


   Email: vf0213@gmail.com


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


























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