Date Added: Feb 2012
The Session Initiation Protocol (SIP) was developed to control multimedia sessions on the Internet. Shortly after its debut as a standard in 1999, SIP was adopted by the 3rd Generation Partnership Project (3GPP) as the preferred signaling protocol for the Internet Multimedia Subsystem (IMS). This adoption provided a boost to the nascent protocol as traditional telecommunication services were interpreted in the context of the new protocol and as SIP introduced richer services in the form of instant messaging and rich presence to traditional telephony. In this paper, the authors study the evolution of the protocol from its roots to its use in operational networks today and the issues it faces in such networks.