RFC 3858 (rfc3858) - Page 2 of 13

An Extensible Markup Language (XML) Based Format for Watcher Information

Alternative Format: Original Text Document
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RFC 3858                      Watcher Info                   August 2004


   11. Acknowledgements ...........................................   11
   12. Contributors ...............................................   12
   13. Author's Address ...........................................   13
   14. Full Copyright Statement ...................................   14

1. Introduction

   Watchers are defined as entities that request (i.e., subscribe to)
   information about a resource, using the SIP event framework, RFC 3265
   [1].  There is fairly complex state associated with these
   subscriptions.  This state includes the identity of the subscriber,
   the state of the subscription, and so on.  The union of the state for
   all subscriptions to a particular resource is called the watcher
   information for that resource.  This state is dynamic, changing as
   subscribers come and go.  As a result, it is possible, and indeed
   useful, to subscribe to the watcher information for a particular
   resource.  An important application of this is the ability for a user
   to find out the set of subscribers to their presentity [11].  This
   would allow the user to provide an authorization decision for the
   subscription.

   To support subscriptions to watcher information, two components are
   needed.  The first is the definition of a SIP event template-package
   for watcher information.  The other is the definition of a data
   format to represent watcher information.  The former is specified in
   [2], and the latter is specified here.

2. Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
   [3] and indicate requirement levels for compliant implementations.

   This document also uses the terms subscriber, watcher, subscription,
   notification, watcherinfo subscription, watcherinfo subscriber, and
   watcherinfo notification with the meanings described in [2].

3.  Structure of Watcher Information

   Watcher information is an XML document [4] that MUST be well-formed
   and SHOULD be valid.  Watcher information documents MUST be based on
   XML 1.0 and MUST be encoded using UTF-8.  This specification makes
   use of XML namespaces for identifying watcherinfo documents and
   document fragments.  The namespace URI for elements defined by this
   specification is a URN [5], using the namespace identifier 'ietf'
   defined by [6] and extended by [7].  This URN is:




Rosenberg                   Standards Track
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