What Is Meant By SIP (Session Initiation Protocol) In Telecom?

Session initiation Protocol (SIP) is one of the signalling protocols which are used for communication between two bodies. Msn messenger, Skype and other telephone card companies use this protocol for providing communication facilities to the users .There are different entities are used in SIP network. Each entity has its own role in SIP communication. The logical SIP entities are:

• User Agent
• Proxy server
• Redirect server
• Registrar server
• Back-to-Back User Agent (B2BUA)
In SIP, end users are known as user agent or you can say the communicating bodies are known as end users. User agent can initiate a request if he/she want to talk with other user and also can terminate the request. Proxy server is used for authenticating a proxy. When a redirect server receives a request, then it maps the request to the required address and then returns the address to the clients. Purpose of registrar server in this network is to register requests. The purpose of these requests is to update the database location. A B2BUA, can process a request in two different ways as user agent server and user agent client depending on the situation. Above five entities make it possible for SIP to provide its services.