[cisco-voip] Jitter buffering on NEC phones

[Dennis Heim]

I suspect that adjusting these settings is just masking an underlying network issue. What is your latency and jitter like on your network? I am not a NEC guy, but this sounds like this could be trying to mask the problem instead of fixing the problem. 

Dennis Heim
Senior Engineer (Unified Communications)
CDW  Advanced Technology Services
10610 9th Place
Bellevue, WA 98004

425.310.5299 Single Number Reach (WA)
317.569.4255 Single Number Reach (IN)
317.569.4201 Fax 
dennis.heim at cdw.com
cdw.com/content/solutions/unified-communications/

-----Original Message-----
From: cisco-voip-bounces at puck.nether.net [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Andreas Sikkema
Sent: Tuesday, February 21, 2012 5:22 AM
To: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] Jitter buffering on NEC phones

> phone.audio.rfc2833.dtmf.relay="0" phone.audio.onhook.dtmf.mode="1"
> phone.audio.pcmu.pref="4" phone.audio.pcma.pref="5"
> phone.audio.g722.pref="3" phone.audio.g729.pref="6"
> phone.audio.g7221.24kbps.pref="1" phone.audio.g7221.32kbps.pref="2"
> phone.audio.g729.vad="1" phone.audio.pcmu.ptime="80"
> phone.audio.pcma.ptime="80" phone.audio.g722.ptime="80"
> phone.audio.g729.ptime="80" phone.audio.g7221.24kbps.ptime="80"
> phone.audio.g7221.32kbps.ptime="80"
>
> The codec we are using is G711, so it's probably among the default 
> values, rather than the values aimed specifically at g722 or others.

And

> Almost all of the issues identified by wireshark at 50ms jitterbuffer 
> are packets dropped for exceeding the jitter buffer.

That's because you have the packetization time set to 80ms, even for
G.711 (pcma or pcmu depending on which G.711 you're using). Those values are not settings I see very often, so it's probably no wonder that endusers are complaining. Since 80 msec between each packet is larger than the wireshark jitterbuffer so every other packet is being dropped especially since the wireshark jitterbuffer is not adaptive as far as I'm aware.

Is 80ms a value you've chosen yourself? Usually these are 20 or 30ms...

--
Andreas Sikkema
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