Internet Engineering Task Force (IETF) K. Carlberg, Ed.

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.

Copyright Notice

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

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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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RFC 6735 Resource Priorities AVPs October 2012

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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: [email protected]

Tom Taylor
PT Taylor Consulting
1852 Lorraine Ave
Ottawa
Canada

EMail: [email protected]

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