7935 conference phone issues

[t.guerriero]

I have a customer with 7935 conference phones. They are having an issue where after 6-8 minutes the voices start to sound very robotic. This happens whether it is a conference or phone to phone. We have tested two locations 7935 to 7935 and get the exact same results. We have upgraded the default load and still no change. Anybody seen anything similar. This is making me nuts. (CM 3.2.2spH, 4k AGM module with dsp farm running 12.2.(13) T3. Any input would be great.

[jasyoung]

Typically, "robotic" voice is a jitter or loss problem. It is sometimes a problem with some gateways having jitter buffers that are set too small by default. You can confirm this finding here:

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_white_paper09186a00801545e4.shtml

That URL has WAV samples of various voice quality problems and distortions, and will generally tell you what's wrong when you hear a particular kind of distortion. Listen to the samples and confirm which problem you're having.

If you confirm you have "robotic" or "synthetic" voice, check for packet loss and jitter. It is possible to adjust jitter buffers on most gateways, however if you have the problem 7935 to 7935 IP to IP, you likely have network/QoS problems to resolve first. If you want to try adjusting the gateway, with recent IOS versions and MGCP, you can adjust the default jitter buffer parameters with something like "mgcp playout adaptive 60 40 200". If you are using H.323, the configuration is on the dial-peers, but the principle is the same.

[t.guerriero]

Thanks for the input. I will try it...........

But, my next question would be why only the 7935's. All other IP phones, mostly 7960's and 40's ,work perfectly fine.

[jasyoung]

It's hard for me to say. They run completely different code, for one - the 7960s and 7940s run identical software. Their jitter buffer management strategy may be different. It's conceivable you have an issue of some sort with the 7935 load you're running - there are upgrades available for download from CCO that you can try:

http://www.cisco.com/cgi-bin/tablebuild.pl/ip-7900ser

You'll need to verify your degredation "signature" against that URL I posted earlier before definitively saying "network issue", but network issues are by far the most common cause. If your network checks out and it's still only the 7935s causing a problem, you probably want to involve TAC.

The Bug Tool shows several bugs possibly relevant to your voice quality problem(CSCdz76035, CSCdz86933, CSCdz36664). If you're not running at least P00503010200 it's probably worth a try to upgrade. Check Device Defaults under the System menu to see what they're running by default.