Cisco TelePresence Video Communication Server (VCS)

Packet loss and poor audio/visual quality in one direction

Why am I seeing a lot of packet loss in one direction with my Cisco TelePresence network product and why is the audio/video quality poor in that direction?

If you are seeing a lot of packet loss in one direction, this could be caused by a duplex mismatch somewhere in your network.

  • A duplex mismatch occurs when a piece of equipment at one end of an ethernet cable has a different duplex setting from the equipment at the other end.
    Note: Often the duplex mode is auto-negotiated between the two pieces of equipment; however, auto-negotiation will only work if both devices are set to 'auto'. If one device is set to 'auto' and the other has any other setting, the 'auto' device will configure itself as 100/Half. The most common cause of mismatch issues is having one device set to 100/Full and the other to Auto.
  • If you are new to video conferencing over IP, you may have had a duplex mismatch in your network for some time: TCP traffic will be slowed down by it - and this may pass unnoticed - but UDP traffic will be lost.
  • There are a number of tools that can detect packet loss over a route by using a large number of pings to every device on the route. This information will help you locate the devices that have a duplex mismatch. Change the device settings so that the devices at each end of a cable have either the same speed/duplex settings or are both set to Auto.
    • On Cisco acquired Codian devices this is set on the Network > Port A and Network > Port B pages. For more information, see the online help.
    • On the Cisco VCS this is set on the Ethernet page (System > Ethernet). We recommend that both the Cisco VCS and the ethernet switch are set to Auto, unless the switch is unable to auto-negotiate, in which case both should be set to 1000/Full.

This article applies to the following products:

  • Cisco TelePresence IP GW 3500 / MSE IPGW blade
  • 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 Servers
  • Cisco TelePresence Video Communication Server
  • Cisco TelePresence Serial GW 3340 / MSE 8330 blade

May 11th, 2012 TAA_KB_82