IMS based client aplications

IMS stands for Internet Multimedia Subsystems or IP Multimedia Systems

Many of us heard about VoIP calls or Video Telephony calls….how these works??

I will give alittle idea about this…

 Voice over IP calls are made from 1 phone client to other by means of establishing SIP session. (Session initiation protocol). Suppose A wants to call B, then A will send a request to its local SIP proxy server which in turn forwards the request to B local proxy over internet.

Various routing algorithms are there for proper mapping. All set of rules for establishing SIP session is there at RFC 3261.
Once SIP session is established, a separate media session will be created called RTP session on separate ports, infact two session gets created RTP and RTCP session. Media flow happens over these sockets directly from client A and B. RTP (Real time transport protocol) uses various  media codec for encoding and decoding mechanism.

Few example may be MPEG, H263, H264 (video codec) or AMR, EVRC audio codec.Codec helps in compressing the raw data and encapsulates it in RTP packets. With proper headers these RTP packets are again written over socket, and other client simply keeps on polling the socket and receives it.

Codec area gain classified as hardware and software codec, hardware codec are those which is dependent on chipset special capabilities. Qualcomm manufactures specifies various capabilities of chip set. Samsung is also into the same business. Software codec are simply written codes for encoding decoding raw data. Once the communication is done again SIP signalling comes in place. First RTP sockets are closed and then SIP.

This is abrief idea. if you want you can explore these

RTP: RFC 3550

SIP : RFC 3261

All codec RFC are there..just google it 😛

Image Source: Wikipedia

IMS OverviewIMS Architecture

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