# Defining a media bridging configuration

A media bridging configuration allows video server applications to forward video and audio streams:

- From external IP sources to 3G-324M terminals.

- From 3G-324M terminals to external IP devices.

- In both directions at once.

This configuration is typically a temporary modification of one of the previous configurations. For example, after having played an audio/video file, an application can switch to an external incoming RTP stream for a while, and later on, switch back to the host to play another file.

The following illustration shows a media bridging configuration derived from a playback configuration:

To bridge an external RTP source through the Video Messaging Server Interface, the application creates and connects a server pass-through channel, similar to a standard Fusion RTP switching channel. No DSP resources are consumed by the forward operation. For information about a Fusion RTP switching channel, see the Fusion Developer's Manual. For information on video specific endpoints and server pass-through channels, see Creating server pass-through channels.

Audio/video bridging is a temporary re-configuration of one of the previous configurations. In the media bridging configuration, play and record from or to the host is not supported.

## Initialization function sequence

The following table presents a typical function sequence to initialize in a bridging configuration. This sequence contains both video-specific calls and non-video-specific calls.

Note: The bridging configuration is typically initialized in one of the other configurations (for example, pass-through with silence detection).

Step | Call | Description
Forwarding the RTP packets from an external source.
1 | mspCreateEndpoint ( video_ctahd, &extvideo_ephd) | Creates a video RTP endpoint to receive packets from the external video source.
2 | mspCreateEndpoint ( audio_ctahd, &extaudio_ephd) | Creates an audio RTP endpoint to receive packets from the external audio source.
3 | mspCreateChannel ( video_ctahd, &extvideo_chhd) | Creates a video server pass-through channel (type RTPPassthruSimplex). See Creating server pass-through channels for more information.
4 | mspCreateChannel ( audio_ctahd, &extaudio_chhd) | Creates an audio server pass-through channel (type RTPPassthruSimplex). See Creating server pass-through channels for more information.
5 | mspConnect ( video_ephd, extvideo_chhd, extvideo_ephd) | Connects the regular video RTP endpoint, the server pass-through channel, and the external-source-RTP-endpoint together.
6 | mspConnect ( audio_ephd, extaudio_chhd, extaudio_ephd) | Connects the regular audioRTP endpoint, the server pass-through channel, and the external-source-RTP-endpoint together.