This article introduces the Session Initiation Protocol (SIP), which is an application layer protocol for creating, modifying and terminating interactive communication sessions among multiple users on an IP telephony network. It is the IETF protocol for VOIP and other text and multimedia sessions, like instant messaging, video, online games and other services. It easily integrates and reuses several other existing and mature Internet services and protocols such as DNS, LDP, UDP, TCP, RTP and RSTP etc. No new services have to be introduced to support the SIP infrastructure. It runs on the top of several different transport protocols. As the name implies it is used for establishing a session and the latter part is handled by the other layer protocols, in which Session Description Protocol (SDP) is the one used to hold the whole description of the session. It uses messages to initiate a session, which can be either a request from a client to a server, or a response from a server to a client. Thus, it works on request-response paradigm.
The Session Initiation Protocol (SIP) is a unifying protocol for providing integrated telephony and Internet types of services, such as Web, presence, instant messaging and chat. The growing thirst among communications providers, their partners and subscribers for a new generation of IP- based services is now being quenched by SIP. An idea born in a computer science laboratory less than a decade ago, SIP is the first protocol to enable multi-user sessions regardless of media content and is now a specification of the Internet Engineering Task Force (IETF).
Let us consider, people will have several telephone numbers, have at least two e-mail addresses, carry cell phones, pocket PC, laptop and lease IP addresses wherever they log in. Sitting in an ideal place it is not unusual to see road warriors with laptops open, cell phones pressed to their ears, and palm devices on to check calendars or look up names. What if it is possible to combine these devices or at least minimize the number? The answer to all these questions and situations is SIP.
SIP (Session Initiation Protocol) is an application layer control (signaling) protocol for creating, modifying and terminating interactive communication sessions among multiple users. It is the IETF protocol for VOIP and other text and multimedia sessions like instant messaging, video, online games and other services. The two SIP User Agent Clients (UAC) communicating directly will be the most fundamental SIP operating model where the users may be computer-based end user applications or LAN telephones or gateways interfacing to the PSTN. SIP can also invite participants to already existing sessions, such as multicast conferences. |
