Video Call is quite an exciting and new term in the telecommunication industry for last few years. Since the time telecommunication network started to adapt IP networks as one of their dependable network protocol and started to move the functions and functional components to IP network, a lot of basics has changed and a huge window of opportunity has opened up to the world. Video Call is one such enablement that came as part of IP Based calling facility in the telecommunication world.
Before going to the Video Call I would like to go through the basic call setup process in IP based protocol. There are two main set of protocol that can help setting up a call in IP – SIP and BICC. SIP is transported over UDP and BICC is transported over SIGTRAN stack. There are many possibilities for transporting BICC – I am not going into those details. For simplicity let us assume that BICC is being transported over M3UA or MTP3 over M2UA (protocols that are transported over a layer 4 protocol call SCTP – parallel to TCP and UDP).
Whatever may the protocol be – a call has two process – call setup and media transport/communication. Call setup is done using signaling protocols e.g. SIP or BICC (as discussed earlier). Media is transported over RTP protocol (on a high level). Since call setup and media transport are being done separately and in modern telecom network these are responsibility of two separate nodes, there should be some protocol to connect/interrelate these two functions. There is a protocol named SDP (Session Description Protocol) for this purpose.
As a whole the process of Call Setup is done following the process described below
Main advantage of this process is – theoretically if both party (Caller and Receiver) supports a specific media type they should be able to establish call using that media type. So theoretically the above process should remain same for setting up audio and video call both. And in practice this is the case. Only difference is that the granular details vary from protocol to protocol.
If call is being setup using SIP – in many cases – two separate media communication is established for transporting audio and video media stream. But often both audio and video data is transported in same media communication channel. This depends on the protocol or codec used to transport the media.
If call is being setup using BICC – For Video Call i.e. 3G Video Call, there is a single media communication established and media is multiplexed over H.324/H.223 protocol. Audio is mostly transported over AMR and Video is transported over H.263 or other supported protocols by the negotiating devices.
If you want to go further details please go through the following topics and associated protocol specifications for better understanding