T.38 passthru on 1.8.5

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Hello
We want to implement T.38 passthru with asterisk 1.8.5 [Asterisk 1.8.5.0 built by root @ asterisk1-8.labdomain.com on a x86_64 running Linux on 2011-08-26 21:31:22 UTC]

The call flow is:
quintum gateway –> asterisk –> Dialogic IMG 1010

the call starts as a voice call, the remote fax picks up and we hear the fax tone, the we see the re-invite from the IMG asking for t.38, the RE-Invite is passed back to the user side [quintum gateway] whcih reply with 200 OK with t.38 and the nothing else happens. After 20 secs of “inactivity” the quintum sends another Invite with voice only and then a BYE.

We do see that the quintum sends a lot of messages like this from the quintum’s IP [192.168.1.18] but we do not see that asterisk sends the packages to the destination

UDPTL (SIP/2345850624337933): packet to 192.30.189.146:12020 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)

we have this settings on sip.conf
faxdetect = yes
t38pt_udptl = yes,maxdatagram=400 [I have tested with several combinations t38pt_udptl = yes;t38pt_udptl = yes,fec etc]

When we send the fax from the quintum to the Dialogic IMG the fax works 100% of the times.
I enabled fax set debug on and udptl set debug on but the console does not show almost anything but the udptl packets shown above.
What else should I do?Any ideas/help is greatly appreciated

txs a lot
fborot

4 thoughts on - T.38 passthru on 1.8.5

  • Hi,

    Am Dienstag, den 30.08.2011, 09:44 -0400 schrieb Fabian Borot:

    I assume there is some NAT/firewall on the way? (The 192.30.189.146 is
    public internet and 192.168.1.18 is RFC1918). Be sure to let udptl pass
    through your firewall/NAT. Udptl is using a port range of its own
    (different from the range used for audio).

    Audio is always symmetric. Audio in one directions implies audio in the
    opposite direction. A NAT Gateway open for one direction is normally no
    problem for audio.
    T.38 is not symmetric. One side sends and waits for some kind of ACK.
    The other side waits for data. If the sending side gets through the NAT
    Gateway all is fine. If the sending side is not getting through, the
    transmission is aborted (after timeout).

    HTH,

    Karsten

  • will installing spandsp help with t.38 pass-through?

    both endpoints use public Ips, I just changed the real ones for the privates ones to protect our ips but made a mistake and left the dest as a pub and the orig as private, my bad.
    but for the record, both are public IPs, there is no nat and iptables is off

    also, I see that the quintum sends a lot of these packages but asterisk sends only 1 or 2 to the other side.

    Hello
    We want to implement T.38 passthru with asterisk 1.8.5 [Asterisk 1.8.5.0 built by root @ asterisk1-8.labdomain.com on a x86_64 running Linux on 2011-08-26 21:31:22 UTC]

    The call flow is:
    quintum gateway –> asterisk –> Dialogic IMG 1010

    the call starts as a voice call, the remote fax picks up and we hear the fax tone, the we see the re-invite from the IMG asking for t.38, the RE-Invite is passed back to the user side [quintum gateway] whcih reply with 200 OK with t.38 and the nothing else happens. After 20 secs of “inactivity” the quintum sends another Invite with voice only and then a BYE.

    We do see that the quintum sends a lot of messages like this from the quintum’s IP [192.168.1.18] but we do not see that asterisk sends the packages to the destination

    UDPTL (SIP/2345850624337933): packet to 192.30.189.146:12020 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)

    we have this settings on sip.conf
    faxdetect = yes
    t38pt_udptl = yes,maxdatagram=400 [I have tested with several combinations t38pt_udptl = yes;t38pt_udptl = yes,fec etc]

    When we send the fax from the quintum to the Dialogic IMG the fax works 100% of the times.
    I enabled fax set debug on and udptl set debug on but the console does not show almost anything but the udptl packets shown above.
    What else should I do?Any ideas/help is greatly appreciated

    txs a lot
    fborot

  • Txs a lot Kevin.
    I had just created and account on https://issues.asterisk.org/jira
    Let me know if this is the right place to post both the pcap capture and the sip logs. If not please help me out creating the account in the right place so that I can provide all the information you need.
    The sip debug logs I can post here but I need to change the real IPs, which is easy to do because it will be a text file.
    I appreciate your time and effort in helping us find the roout cause.
    Fborot

    txs a lot for your explanation steve
    so, it should work w/o spandsp fairly fine if we do not have a bad connection. I see that this version has a lot of fixes related to t.38
    but is the implementation already mature enough to guarantee a decent success rate with fax calls?

    will installing spandsp help with t.38 pass-through?

    both endpoints use public Ips, I just changed the real ones for the privates ones to protect our ips but made a mistake and left the dest as a pub and the orig as private, my bad.
    but for the record, both are public IPs, there is no nat and iptables is off

    also, I see that the quintum sends a lot of these packages but asterisk sends only 1 or 2 to the other side.

    Hello
    We want to implement T.38 passthru with asterisk 1.8.5 [Asterisk 1.8.5.0 built by root @ asterisk1-8.labdomain.com on a x86_64 running Linux on 2011-08-26 21:31:22 UTC]

    The call flow is:
    quintum gateway –> asterisk –> Dialogic IMG 1010

    the call starts as a voice call, the remote fax picks up and we hear the fax tone, the we see the re-invite from the IMG asking for t.38, the RE-Invite is passed back to the user side [quintum gateway] whcih reply with 200 OK with t.38 and the nothing else happens. After 20 secs of “inactivity” the quintum sends another Invite with voice only and then a BYE.

    We do see that the quintum sends a lot of messages like this from the quintum’s IP [192.168.1.18] but we do not see that asterisk sends the packages to the destination

    UDPTL (SIP/2345850624337933): packet to 192.30.189.146:12020 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)
    UDPTL (SIP/): packet from 192.168.1.18:10260 (type 0, seq 0, len 6)

    we have this settings on sip.conf
    faxdetect = yes
    t38pt_udptl = yes,maxdatagram=400 [I have tested with several combinations t38pt_udptl = yes;t38pt_udptl = yes,fec etc]

    When we send the fax from the quintum to the Dialogic IMG the fax works 100% of the times.
    I enabled fax set debug on and udptl set debug on but the console does not show almost anything but the udptl packets shown above.
    What else should I do?Any ideas/help is greatly appreciated

    txs a lot
    fborot