Diameter Priority Attribute-Value Pairs
RFC 6735

Internet Engineering Task Force (IETF)                  K. Carlberg, Ed.
Request for Comments: 6735                                           G11
Category: Standards Track                                      T. Taylor
ISSN: 2070-1721                                     PT Taylor Consulting
                                                            October 2012

                Diameter Priority Attribute-Value Pairs

Abstract

   This document defines Attribute-Value Pair (AVP) containers for
   various priority parameters for use with Diameter and the
   Authentication, Authorization, and Accounting (AAA) framework.  The
   parameters themselves are defined in several different protocols that
   operate at either the network or application layer.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by
   the Internet Engineering Steering Group (IESG).  Further
   information on Internet Standards is available in Section 2 of
   RFC 5741.

   Information about the current status of this document, any
   errata, and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6735.

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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   This document may contain material from IETF Documents or IETF
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   material may not have granted the IETF Trust the right to allow
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   Without obtaining an adequate license from the person(s) controlling
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   than English.

1.  Introduction

   This document defines a number of Attribute-Value Pairs (AVP) that
   can be used within the Diameter protocol [RFC6733] to convey a
   specific set of priority parameters.  These parameters are specified
   in other documents, but are briefly described below.  The
   corresponding AVPs defined in Section 3 are extensions to those
   defined in [RFC5866].  We note that all the priority fields
   associated with the AVPs defined in this document are extensible and
   allow for additional values beyond what may have already been defined
   or registered with IANA.

   Priority influences the distribution of resources and, in turn, the
   QoS associated with that resource.  This influence may be
   probabilistic, ranging between (but not including) 0% and 100%, or it
   may be in the form of a guarantee to either receive or not receive
   the resource.

   Another example of how prioritization can be realized is articulated
   in Appendix A.3 (the Priority Bypass Model) of [RFC6401].  In this
   case, prioritized flows may gain access to resources that are never
   shared with non-prioritized flows.

1.1.  Other Priority-Related AVPs

   The 3rd Generation Partnership Project (3GPP) has defined several
   Diameter AVPs that support prioritization of sessions.  The following
   AVPs are intended to be used for priority services (e.g., Multimedia
   Priority Service):

      -  Reservation-Priority AVP as defined in [ETSI]
      -  MPS-Identifier AVP as defined in [3GPPa]
      -  Priority-Level AVP (as part of the Allocation Retention
         Priority AVP) as defined in [3GPPb]
      -  Session-Priority AVP as defined in [3GPPc] and [3GPPd]

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   Both the Reservation-Priority AVP and the Priority-Level AVP can
   carry priority levels associated with a session initiated by a user.
   We note that these AVPs are defined from the allotment set aside for
   3GPP for Diameter-based interfaces, and they are particularly aimed
   at IP Multimedia Subsystem (IMS) deployment environments.  The above
   AVPs defined by 3GPP are to be viewed as private implementations
   operating within a walled garden.  In contrast, the priority-related
   AVPs defined below in Section 3 are not constrained to IMS
   environments.  The potential applicability or use-case scenarios that
   involve coexistence between the above 3GPP-defined priority-related
   AVPs and those defined below in Section 3 is for further study.

2.  Terminology and Abbreviations

   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].

3.  Priority Parameter Encoding

   This section defines a set of AVPs that correlates to priority fields
   defined in other protocols.  This set of priority-related AVPs is for
   use with the Diameter QoS application [RFC5866] and represents a
   continuation of the list of AVPs defined in [RFC5624].  The syntax
   notation used is that of [RFC6733].  We note that the following
   subsections describe the prioritization field of a given protocol as
   well as the structure of the AVP corresponding to that field.

   We stress that neither the priority-related AVPs, nor the Diameter
   protocol, perform or realize the QoS for a session or flow of
   packets.  Rather, these AVPs are part of a mechanism to determine
   validation of the priority value.

3.1.  Dual-Priority AVP

   The Dual-Priority AVP (AVP Code 608) is a grouped AVP consisting of
   two AVPs, the Preemption-Priority and the Defending-Priority AVP.
   These AVPs are derived from the corresponding priority fields
   specified in the "Signaled Preemption Priority Policy Element"
   [RFC3181] of RSVP [RFC2205].

   In [RFC3181], the Defending-Priority value is set when the
   reservation has been admitted by the RSVP protocol.  The Preemption-
   Priority field (described in [RFC3181]) of a newly requested
   reservation is compared with the Defending-Priority value of a
   previously admitted flow.  The actions taken based upon the result of
   this comparison are a function of local policy.

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     Dual-Priority  ::= < AVP Header: 608 >
                 { Preemption-Priority }
                 { Defending-Priority }

3.1.1.  Preemption-Priority AVP

   The Preemption-Priority AVP (AVP Code 609) is of type Unsigned16.
   Higher values represent higher priority.  The value encoded in this
   AVP is the same as the preemption-priority value that would be
   encoded in the signaled preemption priority policy element.

3.1.2.  Defending-Priority AVP

   The Defending-Priority AVP (AVP Code 610) is of type Unsigned16.
   Higher values represent higher priority.  The value encoded in this
   AVP is the same as the defending-priority value that would be encoded
   in the signaled preemption priority policy element.

3.2.  Admission-Priority AVP

   The Admission-Priority AVP (AVP Code 611) is of type Unsigned8.  The
   admission priority associated with an RSVP flow is used to increase
   the probability of session establishment for selected RSVP flows.
   Higher values represent higher priority.  A given admission priority
   is encoded in this information element using the same value as when
   encoded in the admission-priority parameter defined in Section 5.1 of
   [RFC6401].

3.3.  SIP-Resource-Priority AVP

   The SIP-Resource-Priority AVP (AVP Code 612) is a grouped AVP
   consisting of two AVPs, the SIP-Resource-Priority-Namespace and the
   SIP-Resource-Priority-Value AVP, which are derived from the
   corresponding optional header fields in [RFC4412].

     SIP-Resource-Priority ::= < AVP Header: 612 >
                    { SIP-Resource-Priority-Namespace }
                    { SIP-Resource-Priority-Value }

3.3.1.  SIP-Resource-Priority-Namespace AVP

   The SIP-Resource-Priority-Namespace AVP (AVP Code 613) is of type
   UTF8String.  This AVP contains a string that identifies a unique
   ordered set of priority values as described in [RFC4412].

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3.3.2.  SIP-Resource-Priority-Value AVP

   The SIP-Resource-Priority-Value AVP (AVP Code 614) is of type
   UTF8String.  This AVP contains a string (i.e., a namespace entry)
   that identifies a member of a set of priority values unique to the
   namespace.  Examples of namespaces and corresponding sets of priority
   values are found in [RFC4412].

3.4.  Application-Level-Resource-Priority AVP

   The Application-Level-Resource-Priority (ALRP) AVP (AVP Code 615) is
   a grouped AVP consisting of two AVPs, the ALRP-Namespace AVP and the
   ALRP-Value AVP.

     Application-Level-Resource-Priority  ::= < AVP Header: 615 >
                                     { ALRP-Namespace }
                                     { ALRP-Value }

   A description of the semantics of the parameter values can be found
   in [RFC4412] and in [RFC6401].  The registry set up by [RFC4412]
   provides string values for both the priority namespace and the
   priority values associated with that namespace.  [RFC6401] modifies
   that registry to assign numerical values to both the namespace
   identifiers and the priority values within them.  Consequently, SIP-
   Resource-Priority and Application-Level-Resource-Priority AVPs convey
   the same priority semantics, but with differing syntax.  In the
   former case, an alpha-numeric encoding is used, while the latter case
   is constrained to a numeric-only value.

3.4.1.  ALRP-Namespace AVP

   The ALRP-Namespace AVP (AVP Code 616) is of type Unsigned16.  This
   AVP contains a numerical value identifying the namespace of the
   application-level resource priority as described in [RFC6401].

3.4.2.  ALRP-Value AVP

   The ALRP-Value AVP (AVP Code 617) is of type Unsigned8.  This AVP
   contains the priority value within the ALRP-Namespace, as described
   in [RFC6401].

4.  Examples of Usage

   Usage of the Dual-Priority, Admission-Priority, and Application-
   Level-Resource-Priority AVPs can all be illustrated by the same
   simple network scenario, although they would not all typically be
   used in the same network.  The scenario is as follows:

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   A user with special authorization is authenticated by a Network
   Access Server (NAS), which acts as a client to a Diameter Server
   supporting the user's desired application.  Once the user has
   authenticated, the Diameter Server provides the NAS with information
   on the user's authorized QoS, including instances of the Dual-
   Priority, Admission-Priority, and/or Application-Level-Resource-
   Priority AVPs.

   Local policy governs the usage of the values conveyed by these AVPs
   at the NAS to decide whether the flow associated with the user's
   application can be admitted.  If the decision is positive, the NAS
   forwards the authorized QoS values as objects in RSVP signaling.  In
   particular, the values in the Dual-Priority AVP would be carried in
   the "Signaled Preemption Priority Policy Element" defined in
   [RFC3181], and the values contained in the Admission-Priority and
   Application-Level-Resource-Priority AVPs would be carried in the
   corresponding policy objects defined in [RFC6401].  Each subsequent
   node would make its own decision taking account of the authorized QoS
   objects including the priority-related objects, again governed by
   local policy.  The example assumes that the user session terminates
   on a host or server in the same administrative domain as the NAS to
   avoid complications due to the restricted applicability of [RFC3181]
   and [RFC6401].

   Local policy might for example indicate:

      -  which value to take if both Admission-Priority and Application-
         Level-Resource-Priority are present;

      -  which namespace or namespaces are recognized for use in
         Application-Level-Resource-Priority;

      -  which resources are subject to preemption if the values in
         Dual-Priority are high enough to allow it.

   A scenario for the use of the SIP-Resource-Priority AVP will differ
   slightly from the previous one, in that the initial decision point
   would typically be a SIP proxy receiving a session initiation request
   containing a Resource-Priority header field and deciding whether to
   admit the session to the domain.  Like the NAS, the SIP proxy would
   serve as client to a Diameter Server during the process of user
   authentication, and upon successful authentication would receive back
   from the Diameter Server AVPs indicating authorized QoS.  Among these
   might be the SIP-Resource-Priority AVP, the contents of which would
   be compared with the contents of the Resource-Priority header field.
   Again, local policy would determine which namespaces to accept and
   the effect of a given priority level on the admission decision.

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   For the sake of our example, suppose now that the SIP proxy signals
   using RSVP to the border router that will be admitting the media
   flows associated with the session.  (This, of course, makes a few
   assumptions on routing and knowledge of that routing at the proxy.)
   The SIP proxy can indicate authorized QoS using various objects.  In
   particular, it can map the values from the Resource-Priority header
   field to the corresponding numeric values as defined by [RFC6401] and
   send it using the Application-Level Resource Priority Policy Element.

5.  IANA Considerations

5.1.  AVP Codes

   IANA has allocated AVP codes for the following AVPs that are defined
   in this document.

    +------------------------------------------------------------------+
    |                                       AVP  Section               |
    |AVP Name                               Code Defined   Data Type   |
    +------------------------------------------------------------------+
    |Dual-Priority                          608  3.1       Grouped     |
    |Preemption-Priority                    609  3.1.1     Unsigned16  |
    |Defending-Priority                     610  3.1.2     Unsigned16  |
    |Admission-Priority                     611  3.2       Unsigned8   |
    |SIP-Resource-Priority                  612  3.3       Grouped     |
    |SIP-Resource-Priority-Namespace        613  3.3.1     UTF8String  |
    |SIP-Resource-Priority-Value            614  3.3.2     UTF8String  |
    |Application-Level-Resource-Priority    615  3.4       Grouped     |
    |ALRP-Namespace                         616  3.4.1     Unsigned32  |
    |ALRP-Value                             617  3.4.2     Unsigned32  |
    +------------------------------------------------------------------+

5.2.  QoS Profile

   IANA has allocated a new value from the "QoS Profiles" subregistry of
   the "Authentication, Authorization, and Accounting (AAA) Parameters"
   defined in [RFC5624] for the QoS profile defined in this document.
   The name of the profile is "Resource priority parameters" (1).

6.  Security Considerations

   This document describes an extension for conveying quality-of-service
   information, and therefore follows the same security considerations
   of the Diameter QoS Application [RFC5866].  The values placed in the
   AVPs are not changed by this document, nor are they changed in the
   Diameter QoS application.  We recommend the use of mechanisms to
   ensure integrity when exchanging information from one protocol to an
   associated DIAMETER AVP.  Examples of these integrity mechanisms

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   would be use of S/MIME with the SIP Resource Priority Header (RPH),
   or an INTEGRITY object within a POLICY_DATA object within the context
   of RSVP.  The consequences of changing values in the Priority AVPs
   may result in an allocation of additional or less resources.

   Changes in integrity-protected values SHOULD NOT be ignored, and
   appropriate protocol-specific error messages SHOULD be sent back
   upstream.  Note that we do not use the term "MUST NOT be ignored"
   because the local policy of an administrative domain associated with
   other protocols acts as the final arbiter.  In addition, some
   protocols associated with the AVPs defined in this document may be
   deployed within a single administrative domain or "walled garden";
   thus, possible changes in values would reflect policies of that
   administrative domain.

   The security considerations of the Diameter protocol itself are
   discussed in [RFC6733].  Use of the AVPs defined in this document
   MUST take into consideration the security issues and requirements of
   the Diameter base protocol.

   The authors also recommend that readers familiarize themselves with
   the security considerations of the various protocols listed in the
   Normative References.  This is because values placed in the AVPs
   defined in this document are set/changed by other protocols.

7.  Acknowledgements

   We would like to thank Lionel Morand, Janet Gunn, Piers O'Hanlon,
   Lars Eggert, Jan Engelhardt, Francois LeFaucheur, John Loughney, An
   Nguyen, Dave Oran, James Polk, Martin Stiemerling, Magnus Westerlund,
   David Harrington, Robert Sparks, and Dan Romascanu for their review
   and/or comments on previous draft versions of this document.

8.  References

8.1.  Normative References

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

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC3181]  Herzog, S., "Signaled Preemption Priority Policy Element",
              RFC 3181, October 2001.

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   [RFC4412]  Schulzrinne, H. and J. Polk, "Communications Resource
              Priority for the Session Initiation Protocol (SIP)", RFC
              4412, February 2006.

   [RFC5624]  Korhonen, J., Ed., Tschofenig, H., and E. Davies, "Quality
              of Service Parameters for Usage with Diameter", RFC 5624,
              August 2009.

   [RFC5866]  Sun, D., Ed., McCann, P., Tschofenig, H., Tsou, T., Doria,
              A., and G. Zorn, Ed., "Diameter Quality-of-Service
              Application", RFC 5866, May 2010.

   [RFC6401]  Le Faucheur, F., Polk, J., and K. Carlberg, "RSVP
              Extensions for Admission Priority", RFC 6401, October
              2011.

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

8.2.  Informative References

   [3GPPa]   "TS 29.214: Policy and charging control over Rx reference
              point", 3GPP, March, 2011

   [3GPPb]   "TS 29.212: Policy and charging control over Gx reference
              point", 3GPP, October, 2010

   [3GPPc]   "TS 29.229: Cx and Dx interfaces based on the Diameter
              protocol; Protocol details", 3GPP, September, 2010

   [3GPPd]   "TS 29.329: Sh interface based on the Diameter protocol;
              Protocol details", 3GPP, September, 2010

   [ETSI]    "TS 183 017: Telecommunications and Internet Converged
              Services and Protocols for Advanced Networking (TISPAN);
              Resource and Admission Control", ETSI

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Authors' Addresses

   Ken Carlberg (editor)
   G11
   1601 Clarendon Dr
   Arlington, VA 22209
   United States

   EMail: carlberg@g11.org.uk

   Tom Taylor
   PT Taylor Consulting
   1852 Lorraine Ave
   Ottawa
   Canada

   EMail: tom.taylor.stds@gmail.com

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