This article relates to the Cisco TelePresence MCU 4203, Cisco TelePresence MCU MSE 8420, Cisco TelePresence IP VCR 2210, Cisco TelePresence VCR MSE 8220, Cisco TelePresence ISDN GW 3241, Cisco TelePresence ISDN GW MSE 8321, Cisco TelePresence MCU 4505 and Cisco TelePresence MCU MSE 8510 products.
Q. What is the minimum bandwidth required for H.239 for Codian MCU, IP VCR and ISDN GW units and blades?
A. When H.239 is used in a point-to-point call or in a conference, a second video channel must be opened. Theoretically, the minimum bandwidth for this channel is 4kbps; however, in practise a higher bandwidth is usually required. Even if H.239 can be sent at this bandwidth with your equipment, the quality will be very poor because most endpoints are unable to support two streams of coherent video at very low bandwidths.
For example, it is theoretically possible to fit audio, the main video stream and extended video for H.239 at a call bandwidth of 128kbps; however, it is not recommended because you will experience exceptionally poor quality in all aspects of the call. For this reason, Codian ISDN GW units and MSE 8000 ISDN GW blades do not advertise H.239 for calls with bandwidths lower than 256kbps.
Although MCU and MSE 8000 Media blades and IP VCR units and IP VCR blades do advertise H.239 at 128kbps bandwidth, the quality issue is always present and therefore we do not recommend using H.239 at this bandwidth. If you do open an H.239 channel at this bandwidth, the quality of the stream will depend on the bandwidth used for the main video and audio stream and on the content channel frame rate - you should expect to get very poor quality or no H.239 stream, depending on the endpoint.
We therefore recommend a total call bandwidth of at least 384kbps for a video call with H.239 for both IP and ISDN calls.