Session groups are container objects that hold one or more sessions. A session group is local to an application and does not imply symmetrical association or "view" for other participants in individual channels.If a client application needs to provide the ability for users to listen to multiple channels at the same time, then you can use a session group to add or remove channels (sessions).
Note
When you use the session create command, a session group is automatically created.
A session group enforces a common codec for all participants. There is only a single negotiated audio codec for a session group because it is a property of a SIP session.Use session groups to support multi-channel mode. One example of multi-channel use is in a MMOG with a hierarchical organizational structure such as fleets, nested groups, or gangs. Another multi-channel example is using one channel to talk to others located "near" you in a virtual world, and using a second channel to bridge non-proximate participants from the different regions in that world.You can also use a session group to manage the channels in a session group. For example, consider an example scenario where one channel might need to be the "focus" channel, and all other channels are in the background (which makes the focus channel louder and the other channels quieter). In this example, you would use a session group handle to change these aspects within the session group.