Communications Resource Priority for the Session Initiation Protocol (SIP)
RFC 4412

Network Working Group                                     H. Schulzrinne
Request for Comments: 4412                                   Columbia U.
Category: Standards Track                                        J. Polk
                                                           Cisco Systems
                                                           February 2006

                 Communications Resource Priority for
                 the Session Initiation Protocol (SIP)

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 (2006).

Abstract

   This document defines two new Session Initiation Protocol (SIP)
   header fields for communicating resource priority, namely,
   "Resource-Priority" and "Accept-Resource-Priority".  The
   "Resource-Priority" header field can influence the behavior of SIP
   user agents (such as telephone gateways and IP telephones) and SIP
   proxies.  It does not directly influence the forwarding behavior of
   IP routers.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................6
   3. The Resource-Priority and Accept-Resource-Priority SIP
      Header Fields ...................................................6
      3.1. The 'Resource-Priority' Header Field .......................6
      3.2. The 'Accept-Resource-Priority' Header Field ................8
      3.3. Usage of the 'Resource-Priority' and
           'Accept-Resource-Priority' .................................8
      3.4. The 'resource-priority' Option Tag .........................9
   4. Behavior of SIP Elements That Receive Prioritized Requests ......9
      4.1. Introduction ...............................................9
      4.2. General Rules ..............................................9
      4.3. Usage of Require Header with Resource-Priority ............10
      4.4. OPTIONS Request with Resource-Priority ....................10

Schulzrinne & Polk          Standards Track                     [Page 1]
RFC 4412                 SIP Resource Priority             February 2006

      4.5. Approaches for Preferential Treatment of Requests .........11
           4.5.1. Preemption .........................................11
           4.5.2. Priority Queueing ..................................12
      4.6. Error Conditions ..........................................12
           4.6.1. Introduction .......................................12
           4.6.2. No Known Namespace or Priority Value ...............13
           4.6.3. Authentication Failure .............................13
           4.6.4. Authorization Failure ..............................14
           4.6.5. Insufficient Resources .............................14
           4.6.6. Busy ...............................................14
      4.7. Element-Specific Behaviors ................................15
           4.7.1. User Agent Client Behavior .........................15
           4.7.2. User Agent Server Behavior .........................15
           4.7.3. Proxy Behavior .....................................16
   5. Third-Party Authentication .....................................17
   6. Backwards Compatibility ........................................17
   7. Examples .......................................................17
      7.1. Simple Call ...............................................18
      7.2. Receiver Does Not Understand Namespace ....................19
   8. Handling Multiple Concurrent Namespaces ........................21
      8.1. General Rules .............................................21
      8.2. Examples of Valid Orderings ...............................21
      8.3. Examples of Invalid Orderings .............................22
   9. Registering Namespaces .........................................23
   10. Namespace Definitions .........................................24
      10.1. Introduction .............................................24
      10.2. The "DSN" Namespace ......................................24
      10.3. The "DRSN" Namespace .....................................25
      10.4. The "Q735" Namespace .....................................25
      10.5. The "ETS" Namespace ......................................26
      10.6. The "WPS" Namespace ......................................26