What is the minimum bandwidth required for H.239 for Cisco TelePresence MCU, IP VCR and ISDN GW units/blades and the Serial Gateway Series units/blades?
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, Cisco TelePresence ISDN GW units, MSE 8000 ISDN GW blades, and the Serial Gateway Series unit/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.
This article applies to the following products:
- Cisco TelePresence IP VCR 2200 / MSE VCR blade
- Cisco TelePresence ISDN GW 3200 and 3241 / MSE 8310 and 8321 ISDN blades
- Cisco TelePresence MCU 4200 / MSE 8420
- Cisco TelePresence MCU 4500
- Cisco TelePresence MSE 8510 blade
- Cisco TelePresence Serial GW 3340 / MSE 8330
|May 10th, 2012