Strange quality issues

[sligbot]

Hi all,
We use v.5.5.3 with Polycom IP550s and have experienced some strange quality issues lately. Calls between extensions randomly become garbled and unusable. However, incoming and outgoing calls remain fine. If I restart the Switchvox software the issue is fixed. Several hours later the issue returns. I first thought it might be a QOS issue since we don't have much in terms of QOS on our network but the issue persists when there is no traffic at all on the network as well and it also persists on incoming and outgoing calls (we tested this).
Any thoughts or suggestions?

Thanks,
Rich

[brucexx]

What codecs are you using ? Try changing your extensions to use g711 only as this codec does not require transcoding and does not use system resources. Check system resources when this is happening. The "Server Information" stats are collected every few minutes but if you are using a lot of resources you should see it there if not contact support and have them look at the ssh top output.

How many users you have, are they using swtichboard ?

The other thing I can think of would be to setup a trace on a dedicated workstation and mirror the Swtichvox port. We had a problem with traces being perfect when taken on the Switchvox and the same call was problematic when looking at the trace taken from a mirrored port.

[sligbot]

Thanks for the feedback. Changed codecs to use exclusively ulaw and the issue disappeared -- at least for now. Quick follow-up question concerning CPU usage: the manual describes no CPU usage for this codec -- is this CPU usage of the Polycom phones or of the Switchvox?
Thanks again!

[brucexx]

Well there is no transcoding when you use ulaw. The ulaw is the native codec that does not require transcoding, majority of carriers and SIP providers use ulaw as well. If you are suing g729 or g722 there will be transcoding while the system (CPU) processes the information changing the codec from for example g722 to g711 to mach what your carrier has.

I do not really know if the g722 to g722 call would be transcoded to g711 inside Swtichvox and then back to g722 when being sent to the other phone - I doubt it, it would be stupid. However there might be additional load when processing the g722 codes vs. native g711 - but this would be rather question to Digium.

This might be also problem with Phones itself having problem processing g722 coded and might not have anything to do with the system - keep us posted what happens with the g711 codec.

[sligbot]

So far, so good. It's been a couple of days and the issue hasn't popped back up again. We also made a small change in the call queue routing at the same time but I doubt that would have any effect -- although you never know as I've changed some settings which really should not affect another variable and for some reason it does.
Thanks again for the advice.