ABSTRACT: This Special Report, which is part of the Telcordia Notes on... series of documents, describes the Session Initiation Protocol (SIP),
a signaling protocol from the Internet Engineering Task Force [IETF] that supports establishment of voice and multimedia calls (or
"sessions") over the Internet. End systems such as Personal Computers, wireline Internet Protocol (IP) Phones, and wireless IP devices
can use SIP to establish voice or multimedia sessions with other devices that support SIP. SIP can be used to support Internet
telephony, multimedia communication over the Internet (e.g., an integrated voice/data/video conference between multiple end users), and
newer Internet-based applications such as instant messaging and presence management. SIP is also consistent in philosophy and approach
with existing Internet-standard protocols such as the Simple Mail Transfer Protocol (SMTP) for electronic mail, and HyperText Transfer
Protocol (HTTP) for World Wide Web browsing.
This SR reviews the fundamentals of SIP as a protocol, and describes how SIP can be used to support voice and multimedia
communication in IP-based packet networks. The SR also discusses the current status of SIP in the data and telecommunications
industries, and gives an overview of the packet network architecture that is needed to support SIP (such as the use of location
servers, proxy servers, and redirect servers to route session requests between calling and called parties). The document also provides
information on currently available hardware and software products that support SIP, including SIP Phones, SIP Client software for end
user equipment, SIP Server software for network equipment, and SIP software development tools that help software developers add SIP
capabilities to their products.