Network Performance, Reliability, and Quality of Service Committee
Reliability and QoS Task Forces

Denver, CO; April 11-15, 2005

CONTRIBUTION PRQC-2005-059

CONTRIBUTION PTSC-SAC-2005-100

TITLE: Interpretation of User Plane Priority Classes in IP Networks

SOURCE*: AT&T (P. S. Tarapore, M. Dolly, S. Sayers)

ISSUE: Proposed New Issue: Vertical Signaling Interface to Communicate QoS and Reliability/Priority Parameters Between the Application Layer and the User Plane in IP Networks

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ABSTRACT

This contribution begins the process of interpreting the defined User Plane priority classes for appropriate action in the User Plane. An illustrative example of an MPLS-enabled IP backbone is used to demonstrate how the priority levels can be mapped into appropriate DiffServ Code Points for different traffic types.

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NOTICE

This contribution has been prepared to assist Accredited Standards Committee ATIS/PRQC. This document is offered to the Committee as a basis for discussion and is not a binding proposal on AT&T. The requirements presented in this document are subject to change in form and numerical value after more study. AT&T specifically reserves the right to add to, or amend, the statements contained herein.

CONTACT: Percy S. Tarapore; email: ; Tel: 732-420-4172

I. Introduction

Priority classes in the User Plane for the purpose of admission and bandwidth reservation have been described in a recently approved ATIS/PRQC Technical Report [1]. In addition, work has commenced in the ATIS/PTSC-SAC Sub-Committee [2] that associates signaling messages related to call flows with the same User Plane priority as the traffic itself. For example, SIP signaling messages related to a High Priority ETS call would be assigned High Priority in the User Plane. Similarly, SIP messages related to a Normal Priority VoIP call would be assigned Normal Priority in the User Plane.

This contribution provides initial discussion on how the priority classes need to be considered for appropriate action in the User Plane. An illustrative example of an MPLS-enabled IP backbone is used to stimulate the discussion.

II. User Plane Priority Class Interpretation – Illustrative Example

The recently approved Technical Report from ATIS/PRQC [1] proposes three broad User Plane classes of traffic from the perspective of bandwidth allocation as follows:

·  High: Reserved for Emergency Services such as ETS and E-911 (high probability of bandwidth allocation per SLA agreements between customers and service providers). It is assumed that emergency services represent a very small percentage of total network traffic (~<5%) and bandwidth allocation schemes for this class can be done to give this traffic class high priority treatment.

·  Normal: Real-time and Data services that require better than “Best Effort” (“reasonable” probability of bandwidth allocation per SLA agreements between customers and service providers). Bandwidth allocation for this substantial class of traffic can be done such that successful transmission of this class of traffic is enhanced.

·  Best Effort: No bandwidth guarantee for these services. In other words, bandwidth for this substantial class of traffic is tightly controlled. In the event of network outages or overloads, this class of service could be negatively impacted.

The guiding rationale underlying the creation of three classes is that given a large amount of available bandwidth in the User Plane, emergency services require strong guarantees for bandwidth reservation, best effort services by definition require no guarantees, and normal services fit in between these two extremes.

Assume that the IP backbone is MPLS-enabled and that DiffServ Code Points (DSCP) need to be assigned to traffic flows for ultimate action in router queues. Assume further that for real-time traffic flows, there are two DSCP points available to distinguish two Expedited Forwarding DSCP Per Hop Behavior treatments [3] – EF(1) for High Priority emergency flows and EF(2) for Normal Priority VoIP calls[1]. The underlying rationale is that the bandwidth requirements for emergency flows are small (< 5%) when compared to the total traffic in the User Plane.

An initial proposed mapping of the User Plane traffic priority classes to DSCP points is as follows. This proposal is intended to stimulate further discussions on this topic.

Traffic Type / DSCP
High Priority
Voice Call (ETS/WPS) / EF(1)
(See Footnote 1)
Normal Priority
Voice Call / EF(2)
(See Footnote 1)
High Priority
Data (ETS) / AF(1)
Normal Priority
Data / AF(2), AF(3), AF(4)
Best Effort
Traffic / BE

III.  Proposal

This contribution provides initial discussion on how to interpret User Plane priority classes. Specifically, an initial mapping between the priority classes and the DSCP values is presented for discussion. It is critical that all possible mappings are ultimately determined such that appropriate action can be taken in the User Plane [4]. This work will also be crucial in shaping discussion on the development of the requirements for the vertical signaling interface between the application layer and the User Plane [5].

IV.  References

[1] “User Plane Priority Levels for IP-Based Networks and Services”, ATIS/PRQC Draft Technical Report (pre-publication), ATIS Contribution T1A1/2003-196 R2, October 2004.

[2] “Discussion on Associating Control Signaling Messages with Media Priority Levels”, ATIS Contribution T1S1.7/2003-577, October 2004.

[3] “Multi-Level Expedited Forwarding Per Hop Behavior (MLEF PHB)”, M. Pierce and S. Silverman, IETF I-D, February 2005.

[4]”Output Baseline Text – Support of ETS in IP Networks”, ATIS Contribution PTSC-SAC-2005-076 R1, February 2005.

[5] “Proposal to Develop Requirements for a Vertical Signaling Interface Between the User Plane and Application Layer in IP Networks”, ATIS Contribution PRQC-2005-xxx, April 2005.

2

[1] Currently, a single EF queue is available for all real-time traffic. In that case, a drop precedence is desirable to ensure that High Priority ETS calls are not dropped in the EF queue.