[asterisk-users] Outbound fax issues

[Mikel Lindsaar]

Hello all.

I have the following setup:

Fax machine
    |
Sipura SPA-3120
    |
SIP 100BaseT
    |
Asterisk 1.4
    |
IAX2 100BaseT
    |
Asterisk 1.6
    |
ISDN PRI TE210P
    |
Traditional Telco



The fax lands on the Internal Asterisk 1.4 box, the sip config for this
extension looks like:

[35081]
type=friend
secret=************
qualify=yes
port=5060
nat=no
host=dynamic
dtmfmode=rfc2833
dial=SIP/35081
context=fax-line
canreinvite=no
callerid=device <35081>
disallow=all
allow=ulaw
allow=alaw


Now, inbound faxing (from the other side of the Telco to me) is working and
from what I can tell, never fails to receive.

Sending though is a bit touch and go.  Sometimes works, sometimes doesn't.
 It's about a 40% success rate, and does not seem to depend on what number
dialed (ie, the problem has been basically isolated to my internal network).

The symptoms are long handshake times with the fax trying to get carrier,
then failing.  Redialing 2-6 times eventually gets the fax through.

The extensions.conf simply answers and dials out through the ISDN line.  No
special config here.

I believe from what I have read via our friends at Google and voip forums
around the place, that it is probably an echo or jitter problem, but what I
have found so far has been a bit vague.

Does anyone have any pointers on what I should be looking for to improve the
outbound call?

Thanks!

Mikel
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