Technical Summary
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 SIP Events Framework
procedures have a serious deficiency in that they provide no tools to
avoid replaying event notifications that have already been received by
a user agent. This specification 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. This "conditioning" of the subscription requests uses the
well-known concept of entity tags (eTags).
Working Group Summary
This document received extended working group review during a SIP WGLC
period that exceeded one year in duration. One critical clarification
came up in this review period: this specification does not provide
"versioning history" for events; rather it lets a subscriber know
whether the current event state is consistent with the event state as
currently known by that subscriber. The distinction is subtle. For
example, if the subscriber knows of event state "A", but the actual
state has changed to "B" and then back to "A" before a NOTIFY would
be sent (if the subscriber were offline for example), the subscriber
will not be informed about the B state through this specification.
Following WGLC, the proto review process detected and corrected a
minor error in the ABNF, and further review by Adam Roach detected and
corrected problem related to suppressed NOTIFYs on initial dialogs.
Document Quality
The Open Mobile Alliance SIMPLE Presence specification references this
document, and has done so for several years.
Personnel
Dean Willis is this document's shepherd.
Robert Sparks is the responsible AD.