Am having a heap trouble faxing on SIP trunks, i have setup for g711 and is using T38. It seems to recieve 3/4 of the page and then gets Comm Error.
It does work set as 'pass through' but i cant make the fax not use T38.
Systrem is a 7030 4.7 software.

Faxing on sip is hit and miss at best.

T.38 is controlled by the system, if you have the codec set to g.711 and passthrough it shouldn't be using t.38.

T.38 isn't needed when using g.711, only g.729 from memory.

Make sure you are set to g.711a in the sip carrier options for the 1st or 2nd choice (it should re-invite from 1st choice to g.711 as the 2nd choice.

What nameless said and try turning off ECM (error correction Mode) on the machines themselves. Most of the time this will fix the problem.

I forgot about ECM, Also turn off high speed helps