Phone conversations delayed

[ben]

Hello,

We are having an issues with some IP Phone to IP phones calls across our WAN where the conversation will become delayed. It is best described where the 2 parties will become out of sync from each other each other by about a second or 2. This doesn't appear to be every call just some calls.

There are no visable issues on the WAN interfaces involved and ping times are pretty good between the sites.

Does anyone have and idea on good ways to troubleshoot this and resolve it?

[ptredway]

Ben,

You're describing good old fashion latency. The recommendation is no more than 150ms one-way delay.

The best way to test for this is to setup an IP SLA session between two routers traversing the same WAN segment. You can enable the routers (via IP SLA) to place synthetic voice calls (G.729 recommended) ever 20 seconds or so and then collect statistics on the call. Based on your code versions, you'll get quite a bit of information back, max delay, average delay, max jitter, avg jitter. You can even pull one way values so you can see in which direction you're experiencing the problem.

Two things to note before you enable IP SLA. Make sure you've accounted for an additional call in your priority queue. This will take up a calls worth of bandwidth (depends on codec) that CallManager doesn't know about.

Second, make sure you set the TOS value of the ip sla session to be 184 (DSCP EF) so that it gets treated as voice.

Hope this helps!