Opening Channel for One-Way Video (Q38)

The information in this article applies to:

For one-way-video calls, H.245 says that the bi-directional channel must be opened with the nullData type for the direction without video. Section 7.3.1/H.245v2: "Terminals capable only of uni-directional (transmit or receive) operation on media types which make use of bi-directional channels shall send capabilities only for the supported direction of operation. The reverse direction shall use the nullData type, for which no capability is necessary." However, in practice, vendors open the channel for video in both directions and assume that the remote terminal will accept the open request. This is because, early on, some incorrect implementations led to problems establishing the call when the nullData type was used.