3G video telephony is usually implemented over the 3G-324M protocol. Today, handset manufacturers who wish to roll out a 3G UMTS or TD-SCDMA handsets are well aware that 3G-324M support is a mandatory requirement for success. As Windows Mobile gains popularity and becomes more widely deployed in Smartphones and PDAs, the smooth integration of 3G-324M in Windows Mobile is becoming more and more important. How can this be accomplished?
Mobile video telephony
Today, the UMTS (WCDMA), and its Chinese equivalent, TD-SCDMA, enable a circuit-switched data connection of 64 kilobits per second. This connection is used for real-time video telephony over mobile networks, and is a popular service on UMTS networks in Japan, Korea, Taiwan, Europe, and many other countries and regions around the world. As operators are looking for additional services to leverage their networks and increase their income per subscriber, the addition of real-time video has become a real opportunity for growth. 3G handset manufacturers must include video telephony in their products. To do this they use the 3G-324M standard.
3G-324M overview
3G-324M is based on the ITU H.324 standard and is designed to send several different channels over low bit-rate networks. In 3G, this rate is 64 kilobits per second over a circuit-switched UMTS or TD-SCDMA connection.
The 3G-324M standard design
This technique for mobile video telephony is currently the best solution available for handling latency and roundtrip delay issues, implementing authentication and billing mechanisms, and minimizing equipment upgrade costs for operators.
Since we have very limited bandwidth for the large amount of data required (audio, video, and some control), the 3G-324M standard employs a multiplexer (H.223), which takes different channels and multiplexes them together into a single bitstream—while adding as little overhead as possible. This lets the actual audio and video exploit as many bits as possible.
The actual implementation of the 3G-324M standard is usually not done by the application developers, but is outsourced to other companies whose core competency is developing toolkits for communication standards and that offer a 3G-324M toolkit.
As a standard, the 3G-324M protocol does not need to know who is actually dialing and connecting the bitstream, or how the data is being sent and received. This makes it a superior solution for other scenarios as well, but for application developers, it introduces an additional complexity because they have more to implement.
There are three different issues application developers must deal with once a 3G-324M stack implementation is available:
- Integration with the network through the baseband. This includes dialing and tearing down calls as well as sending and receiving 3G-324M related bitstreams using the H.223 component.
- Integration with the media codecs. This includes audio and video codecs, including optimization when required. In order to achieve the best quality, auxiliary algorithms such as AEC (Acoustic Echo Canceller) and NR (Noise Reduction) are also required.
- Building the application itself.
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