Signaled Preemption Priority Policy Element
RFC 3181

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Network Working Group                                          S. Herzog
Request for Comments: 3181                          PolicyConsulting.Com
Obsoletes: 2751                                             October 2001
Category: Standards Track

              Signaled Preemption Priority Policy Element

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document describes a preemption priority policy element for use
   by signaled policy based admission protocols (such as the Resource
   ReSerVation Protocol (RSVP) and Common Open Policy Service (COPS).

   Preemption priority defines a relative importance (rank) within the
   set of flows competing to be admitted into the network. Rather than
   admitting flows by order of arrival (First Come First Admitted)
   network nodes may consider priorities to preempt some previously
   admitted low priority flows in order to make room for a newer, high-
   priority flow.

   This memo corrects an RSVP POLICY_DATA P-Type codepoint assignment
   error in RFC 2751.

Herzog                      Standards Track                     [Page 1]
RFC 3181      Signaled Preemption Priority Policy Element   October 2001

Table of Contents

   1 Introduction .....................................................2
   2 Scope and Applicability ..........................................3
   3 Stateless Policy .................................................3
   4 Policy Element Format ............................................4
   5 Priority Merging Issues ..........................................5
   5.1  Priority Merging Strategies ...................................6
   5.1.1 Take priority of highest QoS .................................6
   5.1.2 Take highest priority ........................................7
   5.1.3 Force error on heterogeneous merge ...........................7
   5.2  Modifying Priority Elements ...................................7
   6 Error Processing .................................................8
   7 IANA Considerations ..............................................8
   8 Security Considerations ..........................................8
   9 References .......................................................9
   10  Author's Address ...............................................9
   Appendix A: Example ...............................................10
   A.1  Computing Merged Priority ....................................10
   A.2  Translation (Compression) of Priority Elements ...............11
   Full Copyright Statement ..........................................12

1  Introduction

   This document describes a preemption priority policy element for use
   by signaled policy based admission protocols (such as [RSVP] and
   [COPS]).

   Traditional Capacity based Admission Control (CAC) indiscriminately
   admits new flows until capacity is exhausted (First Come First
   Admitted).  Policy based Admission Control (PAC) on the other hand
   attempts to minimize the significance of order of arrival and use
   policy based admission criteria instead.

   One of the more popular policy criteria is the rank of importance of
   a flow relative to the others competing for admission into a network
   node.  Preemption Priority takes effect only when a set of flows
   attempting admission through a node represents overbooking of
   resources such that based on CAC some would have to be rejected.
   Preemption priority criteria help the node select the most important
   flows (highest priority) for admission, while rejecting the low
   priority ones.

   Network nodes which support preemption should consider priorities to
   preempt some previously admitted low-priority flows in order to make
   room for a newer, high-priority flow.

Herzog                      Standards Track                     [Page 2]
RFC 3181      Signaled Preemption Priority Policy Element   October 2001

   This document describes the format and applicability of the
   preemption priority represented as a policy element in [RSVP-EXT].

2  Scope and Applicability

   The Framework document for policy-based admission control [RAP]
   describes the various components that participate in policy decision
   making (i.e., PDP, PEP and LDP).  The emphasis of PREEMPTION_PRI
   elements is to be simple, stateless, and light-weight such that they
   could be implemented internally within a node's LDP (Local Decision
   Point).

   Certain base assumptions are made in the usage model for
   PREEMPTION_PRI elements:

   -  They are created by PDPs