What Is H.239?
ITU-T Recommendation H.239 is the international standard for the use, control and labeling of two simultaneous channels of video in a single videoconference. It is an addition to the umbrella of protocols in the H.323 videoconferencing suite.
- Approved by ITU-T in July 2003
- Offered by MOREnet as a service enhancement in December 2006
How It Works
During the H.323 calling process, the H.245 protocol performs the capabilities exchange and establishes several transport channels for audio and video. In the past, these channels were never labeled or assigned a specific duty. With the advent of H.239 these channels are treated as logical channels that can be claimed and assigned labels such as audio, video and content.
The audio stream uses 64 Kbps of a 384 Kbps call, leaving 320 Kbps to divide between video and content. (Audio bandwidth is never used for content.) The video stream is then subdivided to provide the bandwidth for video and content.
Receive Site Views
Before H.239, presenters had to switch between video and content on the video unit. Receive sites could only get audio and video or audio and content. With H.239, receive sites see both video and content streams simultaneously.
Single Monitor Configuration
Content displays in the full-screen view, while the speaker displays in the “picture-in-picture” view.
Dual Monitor Configuration
Content will display in full-screen view on the remote site monitor and the instructor will display in full-screen view on the local site monitor. The local-view image will display in the “picture-in-picture” view.
Remote Site Monitor
Local Site Monitor
|Polycom||VSX 7000s||Yes||Yes - Requires the Visual Concert VSX appliance||Visual Concert VSX appliance|
|Polycom||VSX 7000e||Yes||Yes - Requires the H.239 license key to enable this feature||Ports for audio and video are built into the appliance. A license key must be purchased to enable the broadcasting of H.239 content.|
|Polycom||VSX 8000||Yes||Yes||Ports for audio and video are built into the appliance. A license key is included.|
|Polycom||PVX||Yes||Yes||License key and desktop sharing are included with the software.|
|Yes - Requires a license key.||Yes - Requires a DVI to VGA cable and a license key for NPP.||Ports for audio and video are built into the appliance. Requires DVI to VGA cable and a license key for the Natural Presenter Package.|