asterisk users - Oct 2007 - channel.c switches to gsm even when sip.conf only allows ulaw

Hi Guys,

I have noticed a weird behavior in 1.4.12. When using Authenticate or
DISA in the dial plan the channel immediately switches to gsm format (if
you request a password) or slim (if you run DISA without password). The
debug log says...

==============================[Oct 14 21:23:00] DEBUG[9013] channel.c: Set
channel
SIP/1970xxxxxx-0821aad0 to write format gsm
[Oct 14 21:23:00] DEBUG[9013] rtp.c: Difference is 82008, ms is 10271

==============================
It does this without caring about the fact that you are ONLY allowing
ulaw in the channel configuration. I have so far played with SIP but it
seems the behavior is there for other channels as well (briefly tried it
on IAX as well)

The problem with this is that some SIP providers (ViaTalk) only allows
DTMF of the type inband, which only works on ulaw. Therefore this switch
to GSM makes it impossible to enter the DISA or Authenticate password.

This behavior seems to have been introduced with 1.4.12 as I didn't have
any problem in 1.4.11. Has somebody else seen this.

Cheers,

// Jonas

Jonas Arndt wrote:
> It does this without caring about the fact that you are ONLY allowing
> ulaw in the channel configuration. I have so far played with SIP but it
> seems the behavior is there for other channels as well (briefly tried it
> on IAX as well)
> 
> The problem with this is that some SIP providers (ViaTalk) only allows
> DTMF of the type inband, which only works on ulaw. Therefore this switch
> to GSM makes it impossible to enter the DISA or Authenticate password.
You are misunderstanding the message, and this why in general we ask
users who are not well versed in how Asterisk works to *not* enable the
DEBUG messages on the console.

What you are seeing is *not* Asterisk changing the format of the audio
stream between it and the provider, but instead it is changing the
internal 'write format' of the channel to GSM (by putting a GSM to ULAW
transcoder in the path). It is doing this because you are running an
application that wants to play sound files, and you don't have ULAW
sound files installed. Since the only sound files you have are GSM, it
has to transcode that to ULAW before sending it out the channel.

-- 
Kevin P. Fleming
Director of Software Technologies
Digium, Inc. - "The Genuine Asterisk Experience" (TM)