# 3G-324M Interface data flow

The 3G-324M Interface works as follows for data flowing from a 3G terminal:

- The host application configures the Interface by creating endpoints and channels with the video-enhanced MSPP functions. The host application then manages calls by using the H.324M Middleware.

- On the PSTN side of the Interface, audio and video media streams, as well as H.245 control information, are multiplexed and demultiplexed using H.223 MUX/DEMUX on PSTN channels.

- For incoming calls, the DEMUX in the 3G-324M Interface splits up the incoming data into three streams: control, audio data, and video data.

- The host application receives control messages through H.324M events and sends control messages through H.324M functions.

- On the IP side of the Interface, the audio and video streams are output as two separate RTP streams.

The 3G-324M Interface works in a similar fashion for data flowing from the IP side. The data on the IP side enters the Interface as two separate RTP streams and is output on the PSTN side as a single multiplexed 3G-324M stream.

The video data stream is not transcoded in the 3G-324M Interface, but audio data can be transcoded, if required.

The following illustration shows how data flows through the 3G-324M Interface: