SIP- The key to Convergence

SIP- The key to Convergence

With the advent of IMS (IP Multimedia Subsystem) Architecture, SIP is largely going to change the way the world will communicate. Inspite of the emerging RFC’s day-in day-out SIP will eventually be throned as the most versatile End to End VOIP protocol.

Although SIP only does call setup and signaling it establishes good connectivity with PSTN through gateways and going forward RTP(Real time protocol) and RTCP(Real time control protocol are going to make streaming data a easy reality. RTCP will also manage QOS and enable the user to receive some very high quality data transmission. One more favourable feature of SIP is ,it can act as a carrier for many protocols. For example in media sessions, SIP acts as a carrier for SDP(Session Description protocol) and RTP.

SIP Messages are very easily decodable. Following are examples of few message responses in a SIP call flow. Any user can understand the call flow in the network.

1xx—Informational Responses (100 Trying , 180 Ringing ,181 Call Is Being Forwarded ,182 Queued ,183 Session Progress)

2xx—Successful Responses (200 OK ,202 accepted: Used for referrals)

3xx—Redirection Responses (300 Multiple Choices,301 Moved Permanently,302 Moved Temporarily,305 Use Proxy,380 Alternative Service)

4xx—Client Failure Responses (400 Bad Request,401 Unauthorized: Used only by registrars. Proxys should use proxy authorization 407,402 Payment Required (Reserved for future use) ,403 Forbidden ,404 Not Found: User not found)

And now some gyan on what are the typical request messages in SIP,

INIVITE,ACK,BYE,CANCEL,SUBSCRIBE,NOTIFY.

(Source :Wiki)

To sum up this beginner level article,

SIP is similar to SS7(Signaling system 7). But SS7 is a much versatile protocol as it interacts with the entire system. SIP can be classified as a peer to peer Protocol and this makes it scalable and adaptive. The key to success these days is De-centralisation :) (The seed for my blog is already here). This also ensures this protocol is here to stay!

Much detailed architecture explanations will continue some time later!