Packet Loss - help?

[Seagull]

Hi,

We have got two VSX7000 devices talking across a 6Mb link. I have setup QoS on all routers allowing 768Kbps and a burst of 72Kbps - we are trying to connect at 384Kbps.

The connection is fine however there is quite a bit of packet loss - about 1%-7%, and at times or movement the quality isn`t great. The units are both hard-coded as 100Mb FDX. There is one router in the middle of the 6Mb which is running at 10Mb Hdx on each interface - i was wondering if collisions here would be causing the problem, or would the QoS over-write this?

Any ideas?

Thanks

[CallOne]

QOS will not fix this problem. All of your routers and switches between the two connections must be hardcoded 100Mbps Full Duplex, or change the settings on your equipment to be 10Mbps Half. Anytime you have different settings on your switches, routers, and systems, you will have collissions causing packet loss.

[Seagull]

Thanks,

I will get the middle router changed to 10Mb Full duplex, so that all switches and router ports are running full duplex.

Cheerss

[Seagull]

I presume that the video conferencing uses UDP ports for its transmission, and if these are lost then the system will not resend them? Collisions on the other hand would slow down the picture and voice quality momentarily which is what i seem to be experiencing.

Cheers

[Glen Sykes]

You're correct it's UDP.

Collisions will manifest themselves as packet loss and distortions of picture and / or sound.

Full Duplex would be my first suggestion, also be aware that over a half duplex link, the calculation for bandwidth utilisation is double the rate selected on the endpoint. So for a 384Kbps call over a half duplex link, you will actually be placing 768k (+ packet overhead of between 10 and 15%) of data.

[hhmmb]

Checking speed/duplex mismatch over the network link is ofcause important, but I would start with the Polycom endpoints. Are there any errors on the switch interfaces they are connected to ?
Are you running latest 7.5x software ? There was a bug in 7.0x software! If you forced 100 FD on the VSX the real settings was in fact Auto anyway causing massive packet-loss since auto vs forced 100 FD on switch means no luck with videoconference.

[Seagull]

Thanks

Both Units are hard-coded as 100Mb FDX on the switches. However both are using:

Release 7.0.1 - 27 Jul 2004

Should i upgrade this at both sides as well? I`ll also change the duplex settings on the intervening router.

Cheers

[CallOne]

I would upgrade the systems first. Then do some testing between the two. If this doesn't solve the problem, and it might, I would make the appropriate changes on the router.

[Skylark]

My money is on the duplex mismatch since its a known network problem.

[Seagull]

Updated both sides to latest software revision and users report that the quality is excellent.

Also updated older Mp512 units and they work well too.

Thanks to all

[glennder]

Just an FYI. Polycom "recommends" setting the ports on their EndPoints to Auto. Not 10full/half, 100full/half. I have seen it multiple times where a system is getting flaky video with ALL hardcoded ports throughout the connection but once just the endpoints are set to AUTO it works great.

I am glad your systems are working great. I just wanted to give you something for the back of you mind.