[asterisk-users] SPA941 -> Asterisk -> Voip provider -> PSTN -> ShoreTel garble

Rich Adamson radamson at routers.com
Fri Sep 22 16:42:13 MST 2006

Cliff Brake wrote:
> I am using the following setup:
> Linksys SPA941 -> Asterisk -> NuFone -> PSTN -> ShoreTel system
> The system works great for the most part.  Most people I call say it
> sounds good.  However, every time I call a certain company that uses a
> ShoreTel system, they claim the sound is garbled (understandable, but
> not pleasant to listen to).  Everything sounds fine at my end.  If I
> make a call w/ the following setup, it sounds fine:
> Analog phone -> Asterisk:TDM400 -> NuFone -> PSTN -> ShoreTel system
> So, it seems there is some type of weird interaction between my system
> and the ShoreTel system if I use the SPA941 IP phone.
> Does anyone have suggestions as to how I can start debugging this?

Check the RTP Packet Size (under the Sip tab). Set it to .020 (20 
milliseconds) and place another test call. For whatever reason, the 
Linksys/Sipura products default to 30 milliseconds and has impacted the 
quality of audio on some systems.

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