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Sporadic Audio Jitter in RTP stream

asked 2022-09-22 07:20:55 +0000

aidybarker gravatar image


I'm caught between suppliers and hoping someone can point me in the direction of what's wrong. We have a number of ShoreTel (Mitel) softphones which experience occasional jitter or at least what I would best describe as that. The issue happens on some calls but not all. When it happens, it is for the entire duration of the call. It is always in one direction. A subsequent call within a few minutes will be 100% OK.

There are no dropped packets on either switches or routers at either site. The connections are 100Mb MPLS 1:1 over fibre. QoS is configured. There are no sleep policies applied to the clients. Wireshark shows packets are tagged as they should be. The issue happens even when there is very little other network traffic, which is very light anyway, usually under 5Mb.

The biggest difference I can see with Wireshark of a bad call looking at the RTP stream is that the Skew between packets just accumulates. Jitter goes from 2ms on a good call to 8ms which still seems OK.

The RTP Analysis shows no gaps or highlights anything 'wrong' I can see.

Pictures of the RTP Analysis and player graph are here

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answered 2022-09-22 09:32:53 +0000

hugo.vanderkooij gravatar image

It seems your RTP connection is using 30 ms packet intervals. I recall having an issue like this and the result was no audio at all in 1 direction.

This was an issue in our SIP solution but it did impact only on 1 ISP. So we had to fix the settng in our ATA's from 30ms to 20ms and all was well again. Most carries corrected the issue themselves and used 20ms even when we asked for 30ms but 1the biggest carrier did not and those connections were only one way.

I guess you have something similar.

Regards, Hugo.

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Thank you. This seems to have pointed me in the right direction as the client softphone being the issue. Once pressed and pointing to the Jitter Drops identified in Wireshark - regular and in line with a ptime mismatch, Mitel have an update that addresses 'MIVC-1144 - Poor Audio - Intermittent Jitter from Softphones'. Depends what they mean by sporadic and didn't specifically mention ptime. Following that update we've so far not had a problem call which is after testing all morning and I would previously have been able to replicate this in minutes.

aidybarker gravatar imageaidybarker ( 2022-09-23 11:41:12 +0000 )edit

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Asked: 2022-09-22 07:20:55 +0000

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Last updated: Sep 22