CvcCallReferenceIdOrZero
A call reference ID correlates the video and audio call entries that belong to the same endpoint. In other words, if an audio call entry and a video call entry have the same call reference ID, these entries belong to the same endpoint. Because an audio-only endpoint creates only one call entry, call reference ID is not necessary and is set to zero. A call reference ID with value greater than zero signifies a video call, the value zero is object-specific and must therefore be defined as part of the description of any object which uses this syntax. Examples of the usage of zero include audio calls.