[Asterisk-Users] Asterisk and unknown codecs and GSM

[Michael Graff]

I have a Cisco 2600 which understands the "gsmfr" codec, which appears to
be what Asterisk calls "gsm" -- at least it ends up using it.

I also have a PSTN gateway which is speaking ulaw.

When the 2600 calls through Asterisk to the PSTN, it negotiates the
g711ulaw codec, but when the PSTN calls through Asterisk to the 2600,
it seems that Asterisk is doing translation, and it is doing it very
badly.  I get stuttered, choppy speech which sounds like it's being
played back at half speed.

My first question is why is Asterisk attempting to do codec
translation on this call, and how can I make it stop but still
support gsm <-> gsm calls?

My second question is, can Asterisk pass unknown codecs along without
modification, or is the codec negotiation set up before that happens?
It seems that it wouldbe handy to have SIP to SIP calls use G729
even if Asterisk can't speak it itself.

--Michael