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SIP and the Internet

The Session Initiation Protocol (SIP) is a signaling, presence, and instant messaging protocol developed to set up, modify, and tear down multimedia sessions; request and deliver presence; and send and receive instant messages [1]. When teaching or lecturing about SIP, I begin by explaining that SIP is an Internet protocol. This actually means much more than just that SIP runs over the Internet. This means that SIP uses and takes advantage of the Internet architecture and protocol suite. This chapter will introduce the TCP/IP protocol suite that is the foundation for the Internet and SIP. First, some of the basic concepts of Internet protocols such as Transmission Control Protocol (TCP), Internet Protocol (IP), User Datagram Protocol (UDP), and the Domain Name System (DNS) will be covered. SIP, along with many other Internet protocols, has been developed by the Internet Engineering Task Force (IETF). The processes, steps, and life cycle involved in the development of Internet standards will also be covered. This chapter ends with a brief history of SIP.

1.1 Signaling Protocols

This book is about the Session Initiation Protocol (SIP). As the name implies, the protocol allows two end points to establish media sessions with each other. The main signaling functions of the protocol are as follows:

•Location of an end point;

•Contacting an end point to determine willingness to establish a session;

•Exchange of media information to allow a session to be established;

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