ITU-T H.239 PDF

This Recommendation defines the procedures for use of more than one video channel in ITU-T H.320-based systems, and for labelling individual channels with a "role", which indicates requirements for processing the channel and the role of the channel content in the call. Role labels are applicable to both ITU-T H.320 and ITU-T H.245 signalling-based systems.

The defined procedures include control, indication, and capability exchange mechanisms.