RFC 3856 (rfc3856) - Page 2 of 27

A Presence Event Package for the Session Initiation Protocol (SIP)

RFC 3856                      SIP Presence                   August 2004


       6.8.  Subscriber Processing of NOTIFY Requests ..............  13
       6.9.  Handling of Forked Requests ...........................  13
       6.10. Rate of Notifications .................................  14
       6.11. State Agents ..........................................  14
             6.11.1. Aggregation, Authentication, and Authorization.  14
             6.11.2. Migration .....................................  15
   7.  Learning Presence State .....................................  16
       7.1.  Co-location ...........................................  16
       7.2.  REGISTER ..............................................  16
       7.3.  Uploading Presence Documents ..........................  17
   8.  Example Message Flow ........................................  17
   9.  Security Considerations .....................................  20
       9.1.  Confidentiality .......................................  20
       9.2.  Message Integrity and Authenticity ....................  21
       9.3.  Outbound Authentication ...............................  22
       9.4.  Replay Prevention .....................................  22
       9.5.  Denial of Service Attacks Against Third Parties .......  22
       9.6.  Denial Of Service Attacks Against Servers .............  23
   10. IANA Considerations .........................................  23
   11. Contributors ................................................  24
   12. Acknowledgements ............................................  25
   13. Normative References ........................................  25
   14. Informative References ......................................  26
   15. Author's Address ............................................  26
   16. Full Copyright Statement ....................................  27

1.  Introduction

   Presence, also known as presence information, conveys the ability and
   willingness of a user to communicate across a set of devices.  RFC
   2778 [10] defines a model and terminology for describing systems that
   provide presence information.  In that model, a presence service is a
   system that accepts, stores, and distributes presence information to
   interested parties, called watchers.  A presence protocol is a
   protocol for providing a presence service over the Internet or any IP
   network.

   This document proposes the usage of the Session Initiation Protocol
   (SIP) [1] as a presence protocol.  This is accomplished through a
   concrete instantiation of the general event notification framework
   defined for SIP [2], and as such, makes use of the SUBSCRIBE and
   NOTIFY methods defined there.  Specifically, this document defines an
   event package, as described in RFC 3265 [2].  SIP is particularly
   well suited as a presence protocol.  SIP location services already
   contain presence information, in the form of registrations.
   Furthermore, SIP networks are capable of routing requests from any
   user on the network to the server that holds the registration state
   for a user.  As this state is a key component of user presence, those



Rosenberg                   Standards Track