[Asterisk-Users] fax and codecs

[Claudio Loletti]

Hello!

I'm try to implement a fax service using spandsp (0.0.2-pre10) and
NVFaxDetect (since I'm using a SIP channel).
I receive the call from pstn on my SIP/PSTN gateway (welltech 3804).
The fax is detected by NVFaxDetect and than a macro is started.
The welltech use Alaw codec.
The problem is the following:

NOTICE[22270]: Dropping incompatible voice frame on
SIP/192.168.103.139-0817a2e0 of format slin since our native format has
changed to alaw

It seems the "slinear" codec is set inside the fax applications but I
don't really understand why, since it should be possible to use G711
codecs for faxes within lightly loaded LAN.

Here is my extension.conf

exten => s,1,Wait(6)
exten => s,2,Answer
exten => s,3,DigitTimeout(10)
exten => s,4,ResponseTimeout(20)
exten => s,5,NVFaxDetect(10)
exten => s,6,Background(vm-extension)

exten => fax,1,Goto(fax,2201,1)

[macro-faxreceive]
exten => s,1,SetVar(FAXFILE=/var/spool/asterisk/fax/${UNIQUEID}.tif)
exten => s,2,DBGet(EMAILADDR=extensionemail/${MACRO_EXTEN})
exten => s,3,rxfax(${FAXFILE})
exten => s,103,SetVar(EMAILADDR=me at mysys.com)
exten => s,104,Goto(3)
[fax]
exten => 2201,1,Macro(faxreceive)
exten => 2202,1,Macro(faxreceive)
exten => 2203,1,Macro(faxreceive)
exten => h,1,system(/usr/local/sbin/mailfax ${FAXFILE} ${EMAILADDR}
"${CALLERIDNUM} ${CALLERIDNAME}")


Here is my relevant sip.conf

[pstn01]
context = pstn-gw
type = friend
host = 192.168.103.139
dtmfmode = inband
qualify = yes
port = 5060
canreinvite = no
disallow = all
allow = alaw


Any help is appreciated.
Thnks