How to configure t38 between AS5350 and Asterisk ?

[jouk]

I have IP-PBX Asterisk connected to Cisco AS5350 using SIP protocol. Users of Asterisk may call through the AS5350 but they can not send fax using t38 in conjunction with G729 but fax can pass when i change codec to the g711.

I have noticed that when i use g711 and try to send fax the  codec of session is changing to the t38 and fax is passing. But when i use g729 and try to send fax the changing of session codec to t38 not occur, fax does not pass and session terminating occur.

At the Asterisk side i use DigiumFax application.

Here is configs of cisco and asterisk:

voice class codec 701

codec preference 1 g711alaw

codec preference 2 g729r8

codec preference 3 g723r63

codec preference 4 g723r53

codec preference 5 g726r16

codec preference 6 g726r24

codec preference 7 g723ar63

codec preference 8 g723ar53

codec preference 9 g711ulaw

codec preference 10 g729br8

codec preference 11 clear-channel

!

dial-peer voice 59536311 pots

destination-pattern 050564....

direct-inward-dial

port 1/0:D

forward-digits 7

!

dial-peer voice 595363111 voip

incoming called-number 050564....

voice-class codec 701

session protocol sipv2

dtmf-relay rtp-nte

fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback none

no vad

[general]

context=default

bindport=5060

bindaddr=0.0.0.0

t38pt_udptl=yes

allow=alaw

allow=g729

dtmfmode=rfc2833

language=en

canreinvite=yes

t1min=1000

rtcashefriends=yes

defaultexpiry=60

[TO-5350]

type=friend

host=192.168.11.2

fromdomain=192.168.11.2

context=default

canreinvite=yes

t38pt_udptl=yes

disallow=all

allow=g729

allow=alaw

dtmfmode=rfc2833

nat=no

Help me to fix this problem.

[Carlo Poggiarelli]

Hi.

g729 is not a suitable codec for t38 with modern fax machines. This because g729 can scale up to 7200 bps and higher fax speed requires an higher bandwidth then g729 can offer.

That's probably why your faxes ar passing while using g711.

HTH

Regards

Carlo

[wesphillips]

Try adding this to the voip dial peers at both ends of the IP link:

fax-relay ecm disable

fax rate 7200

fax nsf 000000

This will tell the 5350 to limit the fax rate to 7200 baud, and also overwrite any NSF codes that are not supported. Where I work, the ECM tends to mess things up for us at this data rate, so we also disable it as well.

This will force the fax machines to train at the slower rate, and they will take longer to complete, but this will use less bandwidth to do it.

Wes

[wesphillips]

Try adding this to your voip dial peer:

fax-relay ecm disable

fax rate 7200

fax nsf 000000

This will tell the 5350 to limit the fax rate to 7200 baud, and also  overwrite any NSF codes that are not supported. Where I work, the ECM tends to  mess things up for us at this data rate, so we also disable it as well.

Wes