A Watcher Information Event Template-Package for the Session Initiation Protocol (SIP)
RFC 3857

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Network Working Group                                       J. Rosenberg
Request for Comments: 3857                                   dynamicsoft
Category: Standards Track                                    August 2004

           A Watcher Information Event Template-Package 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 (2004).

Abstract

   This document defines the watcher information template-package for
   the Session Initiation Protocol (SIP) event framework.  Watcher
   information refers to the set of users subscribed to a particular
   resource within a particular event package.  Watcher information
   changes dynamically as users subscribe, unsubscribe, are approved, or
   are rejected.  A user can subscribe to this information, and
   therefore learn about changes to it.  This event package is a
   template-package because it can be applied to any event package,
   including itself.

Rosenberg                   Standards Track                     [Page 1]
RFC 3857                  Watcher Information                August 2004

Table of Contents

   1.   Introduction ........................................    2
   2.   Terminology .........................................    3
   3.   Usage Scenarios .....................................    3
        3.1.  Presence Authorization ........................    4
        3.2.  Blacklist Alerts ..............................    5
   4.   Package Definition ..................................    5
        4.1.  Event Package Name ............................    5
        4.2.  Event Package Parameters ......................    5
        4.3.  SUBSCRIBE Bodies ..............................    6
        4.4.  Subscription Duration .........................    6
        4.5.  NOTIFY Bodies .................................    7
        4.6.  Notifier Processing of SUBSCRIBE Requests......    7
        4.7.  Notifier Generation of NOTIFY Requests ........    8
              4.7.1.  The Subscription State Machine.........    9
              4.7.2.  Applying the State Machine.............   11
        4.8.  Subscriber Processing of NOTIFY Requests ......   12
        4.9.  Handling of Forked Requests ...................   12
        4.10. Rate of Notifications .........................   13
        4.11. State Agents ..................................   13
   5.   Example Usage .......................................   14
   6.   Security Considerations .............................   17
        6.1.  Denial of Service Attacks .....................   17
        6.2.  Divulging Sensitive Information ...............   17
   7.   IANA Considerations .................................   18
   8.   Acknowledgements ....................................   18
   9.   Normative References ................................   18
   10.  Informative References ..............................   19
   11.  Author's Address ....................................   19
   12.  Full Copyright Statement ............................   20

1.  Introduction

   The Session Initiation Protocol (SIP) event framework is described in
   RFC 3265 [1].  It defines a generic framework for subscription to,
   and notification of, events related to SIP systems.  The framework
   defines the methods SUBSCRIBE and NOTIFY, and introduces the notion
   of a package.  A package is a concrete application of the event
   framework to a particular class of events.  Packages have been
   defined for user presence [5], for example.

   This document defines a "template-package" within the SIP event
   framework.  A template-package has all the properties of a regular
   SIP event package.  However, it is always associated with some other
   event package, and can always be applied to any event package,
   including the template-package itself.

Rosenberg                   Standards Track                     [Page 2]
RFC 3857                  Watcher Information                August 2004

   The template-package defined here is for watcher information, and is
   denoted with the token "winfo".  For any event package, such as
   presence, there exists a set (perhaps an empty set) of subscriptions
   that have been created or requested by users trying to ascertain the
   state of a resource in that package.  This set of subscriptions
   changes over time as new subscriptions are requested by users, old
   subscriptions expire, and subscriptions are approved or rejected by
   the owners of that resource.  The set of users subscribed to a