http://www.rfc-editor.org/rfc/rfc5411.txt
RFC 5411: A Hitchhiker's Guide to the Session Initiation Protocol (SIP), J. Rosenberg2009-02-01T23:00:00-00:00The Session Initiation Protocol (SIP) is the subject of numerous specifications that have been produced by the IETF. It can be difficult to locate the right document, or even to determine the set of Request for Comments (RFC) about SIP. This specification serves as a guide to the SIP RFC series. It lists a current snapshot of the specifications under the SIP umbrella, briefly summarizes each, and groups them into categories. This memo provides information for the Internet community.