http://www.rfc-editor.org/rfc/rfc4661.txt
RFC 4661: An Extensible Markup Language (XML)-Based Format for Event Notification Filtering, H. Khartabil, E. Leppanen, M. Lonnfors, J. Costa-Requena2006-09-01T23:00:00-00:00The SIP event notification framework describes the usage of the Session Initiation Protocol (SIP) for subscriptions and notifications of changes to a state of a resource. The document does not describe a mechanism whereby filtering of event notification information can be achieved. Filtering is a mechanism for defining the preferred notification information to be delivered and for specifying triggers that cause that information to be delivered. In order to enable this, a format is needed to enable the subscriber to describe the state changes of a resource that cause notifications to be sent to it and what those notifications are to contain. This document presents a format in the form of an XML document. [STANDARDS-TRACK]