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New Member

Videoconferencing over IP Problem

We have a Polycom unit and are trying to videoconference to our HQ office over a T1 frame relay connection. The voice part is bad and some of the video is jerky. We have a Cisco 2500 router at our location, Cisco 3500 XL switches, Cat5e cabling, and still have tried swapping the Polycom equipment with the same results. Any idea what could be the culprit? I am not a Cisco engineer, so layman's terms please. Thanks

  • Video Over IP

Re: Videoconferencing over IP Problem

It sounds like you are dropping packets, which could be caused by many things. Are you sure you have enough bandwidth? The 2500 does not support most current QOS techniques, so you may be dropping packets due to congestion. This would be expected to vary according to network loading. Have you tried it at a time when other activity would be low?

You might also have a basic networking issue that is showing up due to the unforgiving nature of voice and video traffic. A data application using TCP like FTP or HTTP will retransmit lost packets, resulting in slowdowns, but often will not be noticable.

Good Luck


Re: Videoconferencing over IP Problem

Thanks for your reply. I double-checked (I need to make an eye appointment) and we have a Cisco 2600 and according to the network administrator in D.C. it does have QoS configured on the router. I am not sure about the switches, though (all Cisco 3500's).

We only have about 70 users at our location, so I would think a T1 would be enough bandwidth. How would you test it? Thanks for your help!!


Re: Videoconferencing over IP Problem

A good starting point would be ping testing to rule out basic problems. The network admin should be able to log into the routers and ping the video endpoints. Either a sweep ping or continous ping with fairly big packets should be run for a few minutes to each terminal. If the testing shows packet loss, then you would try to pin it down by pinging intermediate points like router interfaces, or switch management addresses.

You can do this yourself from your PC if you know the IP addresses, or the host names if they are resolvable via DNS. Hopefully your PC is on the same LAN as one of the endpoints. From a DOS prompt:

ping -t -l 500

would ping address with 500 byte packets until you do a control C to stop it. Note the times on the responses, they should not vary more than 20 ms if the network is lightly loaded.

If the pings are solid then you are heading into a higher level of complexity with your troubleshooting that would involve router commands and debugging, or the use of a network Sniffer.


New Member

Re: Videoconferencing over IP Problem


Looks like a duplex issue: a 2500 has only 10Mb/s intfs and I think it does not support full duplex on them, so if the 3500xl port connected to 2500 stays in its default config (auto speed/auto duplex), there is a chance it will not negotiate the proper settings. Try to set the port on the switch to 10/half.

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