[Asterisk-Users] ISDN BRI one way voice quality problem

[Christiaan Brink]

Hi

 

I have a particularly painstaking problem with ISDN BRI.  Currently I'm
running Fedora Core 2.  I was running Red Hat 9 (2.4.20-8 kernel) but the
problem remains the same.  My problem is as follows:

 

I have a BRI ISDN card installed which is based on the HFC chipset.  I have
had no problem loading the card into the kernel with the Hisax drivers
(modprobe hisax type=35 protocol=2).  Running dmesg shows that the card was
picked up fine.  Also, I've had no problem configuring the card within
Asterisk.  However, if I make a call from the public operator to the ISDN
card of the Asterisk box, it rings fine but when the person on the Asterisk
side picks up, they can perfectly hear the caller from the outside, but the
outside caller only hears a very scrambled or very low quality voice.

 

Our public operator uses ALaw.  My guess is that Asterisk has no problem in
detecting the alaw encoded voice and decoding it properly.  Therefore the
Asterisk caller can hear a perfect audio quality.  However, I believe that
Asterisk does not encode the audio back into alaw and therefore the outside
caller hears a bad quality audio.  There is not problem with the call
progress analysis which leads me to believe that EuroISDN protocol is
running fine.  The problem probably lies within the voice codecs used.

 

Does anybody know how to fix this?  Is the problem with hisax?  Is the
problem with Asterisk?  Should one use a different driver like zaphfc or
capi?

 

I've played a bit with zaphfc but have not been very successful.

 

Kind regards

Christiaan Brink

 

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