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Choppy voice on IP Phone with external calls


Having a issue where the IP Phone side of the call hears choppy voice (jitter) on some external calls coming in/out a MGCP PRI Gateway across WAN from the users. The PSTN (outside party) is fine and doesn't hear a problem.

The users can call other IP Phones at the main location fine and don't have this problem, problem is only with calls going out the PRI on the gateway now and then.

QoS is in place and no drops on the policies.

The WAN connection is a Multilink frame relay connection with 2 T1s. FRTS is configured and set to shape to 10ms with a fragment size of 1600 bytes.

The 'mgcp playout adaptive' command was added and set to 250 which improved things a little and it happens less often then before but still there.

The gateway is IOS 12.4(3b) and CCM is 4.1(3)Sr1 with 7.2(2) phone load on the 7940/7960 phones. Using G729 codec across WAN.

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Re: Choppy voice on IP Phone with external calls

Fragment size 1600 ? It should be quite smaller to be effective.

Also, how big the the queues ? If too large, you can experience delay without drops.

Finally, check your FRTS values and perhaps bumping up a little. More often than not WAN networks are a little more tolerant of what the contract guarantees.

Re: Choppy voice on IP Phone with external calls

Yea.. I'm coming in this as third person so it was already that way for other reasons I am being told. I discovered the g729 was set to g729b (silence suppression/VAD) so going to set it to true so g729 doesn't do VAD as part of codec.

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