In November 2000, the Session Initiation Protocol (SIP) was accepted by 3GPP as a signaling protocol of the IP Multimedia Subsystem (IMS) network for IP-based streaming multimedia services. Later it was extended for video conferencing, streaming multimedia distribution, instant messaging, presence information, file transfer, etc.
The SIP protocol is easy to understand as it is text-based and practically derived from the Hypertext Transfer Protocol (HTTP) and the Simple Mail Transfer Protocol (SMTP). SIP is very flexible and well designed for Internet telephony, on the other hand it has also some disadvantages and limitations. If you’re new to IMS signalling or you just need some brief introduction into SIP, I hope you’ll find this post useful.