Cisco TelePresence MCU 4500 Series

Bandwidth sent from an MCU to an endpoint drops

Why does the bandwidth sent from my endpoint to my Cisco TelePresence MCU drop?

This article applies to the following products:

  • Cisco TelePresence MCU 4200 Series
  • Cisco TelePresence MCU 4500 Series
  • Cisco TelePresence MCU 5300 Series
  • Cisco TelePresence MCU MSE Series

In H.323 calls each end controls the bandwidth sent to it. So when the bandwidth to the Cisco TelePresence MCU drops, it is because the MCU has requested it.

There are two main reasons the MCU reduces the bandwidth being sent to it:

  • If a participant is only being shown in a small screen, or is not being shown at all in the conference, then there is no need for a high bandwidth link. The MCU will reduce the bandwidth from that endpoint in order to stop the bandwidth being wasted. That behavior can be turned off on the Settings > Conferences page using the Video receive bit rate optimization check box.*
  • The MCU will reduce the bandwidth if it detects packet loss from an endpoint. If there is packet loss it is possible the link cannot support such a high bandwidth, and reducing it could reach a bandwidth which is supported. Receiving all the data from a lower bandwidth link gives a much better picture than receiving some of the data from a high bandwidth link, so this can improve the picture quality. This behavior can be turned off on the Settings > Conferences page using the Flow control on video errors check box.*

*Note that in HD, HD+ and Full HD modes (4500 Series and MSE Series only), Video receive bit rate optimisation and Flow control on video error settings are forced to On and are not changeable.

The MCU can tell you why the bandwidth is reduced. Click on a participant in a conference, then on the Statistics tab. There is a small question mark icon next to Received bit rate - hover over this to show the reason for the reduced bandwidth.

April 22nd, 2013 TAA_KB_198