RFC 3181 (rfc3181) - Page 2 of 12

Signaled Preemption Priority Policy Element

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