SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) is based

off of SIP and is a developing open standard protocol for instant messaging.

Despite its name, SIMPLE is defined by about 30 documents or more than 1000

pages (7 times more than HTTP 1.1, 15 times more than SMTP and IRC). Some of it

has been standardized by the IETF, other parts are still works in progress.

* [IETF Documentation](http://tools.ietf.org/wg/simple/)

* [SIP Protocol](http://www.ietf.org/rfc/rfc3261.txt)

* [Wikipedia](http://en.wikipedia.org/wiki/SIMPLE)

* [SIP Wikipedia](http://en.wikipedia.org/wiki/Session_Initiation_Protocol)