An Extension to Session Initiation Protocol (SIP) Events for Conditional Event Notification
RFC 5839

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Internet Engineering Task Force (IETF)                          A. Niemi
Request for Comments: 5839                                         Nokia
Category: Standards Track                                 D. Willis, Ed.
ISSN: 2070-1721                                        Softarmor Systems
                                                                May 2010

        An Extension to Session Initiation Protocol (SIP) Events
                   for Conditional Event Notification

Abstract

   The Session Initiation Protocol (SIP) events framework enables
   receiving asynchronous notification of various events from other SIP
   user agents.  This framework defines the procedures for creating,
   refreshing, and terminating subscriptions, as well as fetching and
   periodic polling of resource state.  These procedures provide no
   tools to avoid replaying event notifications that have already been
   received by a user agent.  This memo defines an extension to SIP
   events that allows the subscriber to condition the subscription
   request to whether the state has changed since the previous
   notification was received.  When such a condition is true, either the
   body of a resulting event notification or the entire notification
   message is suppressed.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5839.

Niemi & Willis               Standards Track                    [Page 1]
RFC 5839               Entity-Tags for SIP Events               May 2010

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Niemi & Willis               Standards Track                    [Page 2]
RFC 5839               Entity-Tags for SIP Events               May 2010

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Document Conventions . . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Motivations and Background . . . . . . . . . . . . . . . . . .  5
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Problem Description  . . . . . . . . . . . . . . . . . . .  5
     2.3.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .  7
   4.  Resource Model for Entity-Tags . . . . . . . . . . . . . . . . 10
   5.  Subscriber Behavior  . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  Detecting Support for Conditional Notification . . . . . . 13
     5.2.  Generating SUBSCRIBE Requests  . . . . . . . . . . . . . . 13
     5.3.  Receiving NOTIFY Requests  . . . . . . . . . . . . . . . . 14
     5.4.  Polling or Fetching Resource State . . . . . . . . . . . . 15
     5.5.  Resuming a Subscription  . . . . . . . . . . . . . . . . . 17
     5.6.  Refreshing a Subscription  . . . . . . . . . . . . . . . . 18
     5.7.  Terminating a Subscription . . . . . . . . . . . . . . . . 18
     5.8.  Handling Transient Errors  . . . . . . . . . . . . . . . . 19
   6.  Notifier Behavior  . . . . . . . . . . . . . . . . . . . . . . 20