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I’m not used to post articles which could be too technical, but in this guest post Tsahi Levent-Levi, Product Manager and System Architect at Radvision, explains in a very easy to understand way how mobile video calls work and how VoIP is a fundamental underlaying technology. Thanks Tsahi for the contribution.

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3G-324M Success is Dependent on VoIP
Today’s mobile video telephony is done using a circuit switched protocol called 3G-324M. It exists in almost every 3G handset in Europe and Asia Pacific. For 3G-324M to be successful, it needs VoIP.

3G-324M is a standard that is used for mobile video telephony. As a standard, 3G-324M is a point-to-point standard, where the actual protocol kicks in once an end-to-end “pipe” has been opened between the two handsets doing the call. The protocol itself doesn’t take care of any of the nitty-gritty stuff of routing, billing, dialing, etc – anything more complex than a simple point-to-point call is done out of the scope of the protocol and in the application’s logic.

That being said, a large number of services have been deployed in the past years for mobile video telephony, which can usually be split into two types of services:

• Bidirectional video
• Streaming video

3G Gateway – the missing link
To enable such services, a 3G gateway is required. The main reasons being:

• VoIP market is larger in terms of companies developing server side solutions, making it easier to use for deploying services
• 3G-324M couples signaling and media streams together, making them harder to split and process separately – a common process in VoIP (think media servers and softswitches).

They way a deployment would look like depends on the type of services required.
1. Bidirectional video

Bidirectional video is what 3G-324M comes to solve. It enables people to connect to each other in a video conversation. These services include video mail, announcement servers (video ring back tones), conferencing, etc.

Today, there is no other way to run such services on mobile handsets – at least not “out of the box”.

For bidirectional video, the 3G gateway is connected on the operator’s IP network to a softswitch, which in turn provides services through media servers and other resources within its own network or through SBCs connected to the internet or other intranets.
2. Streaming video
Streaming video includes a single direction video session, almost always from a server somewhere to the mobile handset. It includes Video IVR systems and other media streaming applications, such as tapping into cameras on the Big Brother reality shows.

There’s a competitive technology to 3G-324M in streaming, which is RTSP. It is also available on most 3G handsets today, but there is a difference: where 3G-324M is activated simply by dialing a number and calling, using RTSP requires entering WAP services or browsing around, making it a bit more clunky to use.

The use of these two technologies, brought some of the operators to deploy such services through both mechanisms simultaneously. This means that you can provide such services through either a 3G gateway or using a streaming server.

Article written by Tsahi Levent-Levi, Product Manager & System Architect at Radvision

Blog: http://blog.radvision.com/voipsurvivor

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