Happy Halloween!

A useful tip for troubleshooting VOIP quality issues in Communication Manager.

Doing a “list trace station xxxx” when an IP station is on a call will result in the following output every 10 seconds during the call:

15:33:46 Jitter:4 3 3 2 3 3 1 3 3 3: Buff:9 WC:26 Avg:2

15:33:46 Pkloss:1 0 1 1 0 1 0 0 0 1: Oofo:0 WC:1 Avg:0

These two lines will tell you a lot about what is going on during a call.
The first line indicates jitter (variations in latency). Each number is 1 seconds intervals. In this case the first second of the call had 4 milliseconds of jitter. Followed by the jitter buffer size (which is dynamic), worst case jitter during this call (26 milliseconds), then the average jitter for this call. In general, 20 milliseconds of jitter or less is desired.

The second line indicates packet loss in percent. In this case the first second had 1 percent packet loss. Oofo is the number of out of order packets, followed by worst case packet loss for this call. Then the average packet loss for the call (in this case 0)
Packet loss at or above 2 percent will be noticed. Above 3 percent will usually result in call quality complaints.

High numbers from this output can tell you that there is something wrong on the network somewhere. It usually take a deeper dive to find out just where the trouble is occurring but this is the place to start.