In this article, SIP would be a simple protocol. But SIP can be a base protocol for IMS. It is very complex.
The Session Initiation Protocol (SIP) is a communications protocol for signaling and controlling multimedia communication sessions.
In this article, SIP would be a simple protocol. But SIP can be a base protocol for IMS. It is very complex. Normally IP-PBX can be a SIP server. Sometimes service server also can support server mode. If you want to integrate with other equipment, you need to consider supporting SIP. In the world, there are number of SIP devices.
< As a SIP server >
< As a SIP client >
|SIP||Session Initiation Protocol||RFC 3261|
|SDP||Session Description Protocol||RFC 4566|
|RTP||Real-time Transport Protocol||RFC 1889, 3550|
|RTCP||RTP Control Protocol||RFC 3550|
|ICE||Interactive Connectivity Establishment||RFC 5245|
|STUN||Session Traversal Utilities for NAT||RFC 5389|
|TURN||Traversal Using Relay NAT||RFC 5776|
Client call to peer.
Client can have a call from peer.