Getting started with Polycom Video over IP and QoS

loughlind · ‎11-02-2006

Hello,

I manage a medium sized university departmental network with 35 cisco catalyst 3500xl (latest IOS for 3500xl) at the access layer and a collapsed core-distribution Cat6509 aggregating the uplinks running 12.2(18)SXF4. I have a GigE uplink out to main campus.

We do video conferencing with other universities using polycom viewstations. Our model is the polycom viewstation SP 128. It can do 768k for video over IP.

I'm seeing performance problems periodically when we have a video conference with a remote university. It will negotiate for the full 768k for video and 64k for voice and then over time it steps down the available bandwidth until it is unusable.

I'm wondering how I should go about troubleshooting this. I look at the LAN interfaces within my network between the viewstation and my link to main campus, and I'm not even close at saturating them at all.

So I'm wondering how I should go about troubleshooting this. What do I need to look at? One item that I know I need to address, I do not have QoS. So my first thought was to come up with a QoS solution and get rid of the default FIFO behavior.

So to address the lack of QoS, I'm looking at DiffServ. With the 3524XLs I know I can set CoS values, I can't trust incoming CoS values.

So I believe I need to set the access port for the viewstation as follows:

interface FastEthernet0/2

description a226 classroom

switchport access vlan 30

switchport priority default 5

spanning-tree portfast

The 3524XL does not support the switchport priority override command. The 3548xl does... :(.

My thinking is that I need to mark the frames coming in from the viewstation with CoS value beyond the default of 0. I know that the 3524xl supports 2 queues. CoS values above 4 automatically go to the higher priority queue.

So after that, I'm stumped. Do I need to configure anything else on the switch? On the Trunk out of the switch?

The 3524xl connects via GigE to my Cat 6509. What do I need to configure there? What queueing strategy should I look at to prioritize this video traffic?

Thanks!

mheusinger · ‎11-02-2006

Hi,

QoS is an end-to-end problem. Usually QoS is most critical, where the least resources are: the WAN. So I would assume your campus and the switches are not likely the issue- especially as your interfaces are from being overloaded. Which WAN connectivity is given to other universities? Which QoS measures are in place there? Also be aware that QoS should be applied in both directions. It could be a problem at the remote end.

First I would try to locate the problem (campus - WAN - remote campus) before trying to fix a maybe perfectly working network.

Regards, Martin

loughlind · ‎11-02-2006

Yes, I should definitely look at the bottleneck before I dive into this. I'm going to have the admin responsible for the remote network involved in troubleshooting from his end. Thanks for your advice.