[asterisk-users] Asterisk T.38 Pass-Through doesn't work

[Larry Moore]

On 2/06/2013 9:34 PM, Андрей Половов wrote:
> What I have is:
> * Asterisk 1.8.10.1~dfsg-1ubuntu1,
> * SPA112 ATA with analog fax in 1-st FXS port connected,
> * SIP trunk with provider supporting T.38.
>
> My network looks like this:
> * spa112 (192.168.33.200/24) and Asterisk (192.168.5.253/24) in
> neighbouring LANs,
> * Asterisk connects to the provider (80.75.130.136) via router
> (82.200.7.184). Router has full DNAT to Asterisk server.
>
> What happens?
> * The fax from SPA112 to Asterisk cmd ReceiveFax works well,
> * The fax from Asterisk cmd SendFax to PSTN fax works well,
> * However, the fax from SPA112 to PSTN fax doesn't work. Using udptl
> debug, I can see packets between Asterisk and both sides (SPA112 and
> PSTN fax) but it seems that faxes can't agree how to send image.
>
> == sip.conf:
> [general]
> tcpenable=yes
> videosupport=yes
> transport=udp,tcp
> dtmfmode=rfc2833
> qualify=yes
> directmedia=no
> allowguest=no
> alwaysauthreject=yes
> rtcachefriends=yes
> rtupdate=no
> callcounter=yes
> t38pt_udptl=yes,redundancy,maxdatagram=200
> t38pt_rtp=no
> t38pt_tcp=no
> ignoresdpversion=yes
> disallow=all
> allow=alaw
> allow=ulaw
> externip=82.200.7.184
> localnet=192.168.0.0/255.255.0.0
>
> [mtt]
> type=peer
> host=80.75.130.136
> fromuser=74957777777
> disallow=all
> allow=alaw,ulaw
> directmedia=no
> canreinvite=no
> nat=yes
>
> == udptl.conf:
> [general]
> udptlstart=4000
> udptlend=4999
> T38FaxUdpEC=t38UDPRedundancy
> T38FaxMaxDatagram=200
> udptlfecentries = 3
> udptlfecspan = 3
> use_even_ports = no
>


I don't have access to one of these devices though some suggestions you 
could try;

1) On SPA112 set "FAX T38 Redundancy" = 3
2) Add t38pt_usertpsource=yes in [mtt] section
3) Change maxdatagram=200 to maxdatagram=1400
4) In udptl.conf change T38FaxMaxDatagram to a value of 1400
5) In udptl.conf change use_even_ports to yes


You don't appear to list the sip.conf entry for the SPA112.

Where did t38pt_rtp & t38_tcp come from?

You may also want to experiment with the SPA112 setting "FAX T38 ECM Enable"

Cheers,

Larry.