ABSTRACT
The Request-Uniform Resource Identifier (Request-URI) of the Session Initiation Protocol (SIP) carries the logical public address for reach-ability in establishing the session between the communicating parties. The different kinds of URIs, such as SIP, SIP Security, and telephone (tel) URI, that the SIP messages can use are described here. The rules for the formation of SIP Request-URI with different kinds of URIs, the relationship between these different URI types, and their mapping among themselves are explained. The creation and registration of the unique globally routable user agent (UA) URI out of multiple URIs for the same SIP address-of-record for reaching the SIP UA is also described in detail. Finally, some service URIs that are created using informational Requests for Comment (RFC) and may be useful for using or offering SIP-related specific services are discussed. In addition to RFC 3261, the material from many other RFCs that have enhanced SIP is included here.
