H.239
H.239 is an ITU-T recommendation from the H.32x Multimedia Communications' macrofamily of standards for multimedia communications over various networks. The H.239 recommendation is titled "Role management and additional media channels for H.3xx-series terminals". Practical importance of this recommendation is its setting forth a way to have multiple video channels (e.g., one for conferencing, another for presentation) within a single session (call). History H.239 builds on the ITU-T's H.32x (which includes H.323) and H.245 series of standards, called "recommendations" by the ITU. Tandberg introduced the ability to send a computer or video presentation along with a video teleconference session in 2000 with their "DuoVideo" feature in February 2000. PictureTel introduced People+Content in July 2000. Polycom then acquired PictureTel in May 2001 and began offering their proprietary, patented method to other vendors on a royalty-free basis in 2002. In Feb. 2003 the ITU-T took up a proposal by vendors to create a standard based on Tandberg and Polycom technology. The ITU-T published this technology as Recommendation H.239 in July 2003. Overview A traditional videoconference has an audio channel, a video channel and an optional data channel. The video channel typically carries the camera image of the participants. H.239 defines rules and messages