T-38 Re-invite Issue

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Asterisk Users 8 Comments

I have an error sending to a specific fax number. It may be more than one but this is the one I investigated. It seems the delay for the SIP
negotiation in T.38 was initiated after 6 seconds, however, our system sent the BYE after only 4 seconds, possibly cutting the call before all the communication necessary for the negotiation was completed. Here is the trace from our provider showing their successful call to the number and our failure.

FAIL:
2018-06-01 08:34:16.475 – Detected CED modem tone ***********
Universal Media Gateway MGW02-EDTMTDS
2018-06-01 08:34:16.911 – Detected CEDPR modem tone Universal Media Gateway MGW02-EDTMTDS
2018-06-01 08:34:20.692 – Incoming SIP message received : BYE From:
5555551111@tor.trk.tprm.ca To: 5555552222@206.80.250.100
5555552222@209.197.130.80:5060 **********
MetaSphere CFS Distributel-Western-CFS
555-555-1111: Vybe Networks Inc. 98.158.139.74

SUCCESS:
2018-06-01 08:30:56.959 – Detected CED modem tone ***********
Universal Media Gateway MGW02-EDTMTDS
2018-06-01 08:30:57.388 – Detected CEDPR modem tone Universal Media Gateway MGW02-EDTMTDS
2018-06-01 08:31:03.187 – Detected V.21 flag fax tone *********
Universal Media Gateway MGW02-EDTMTDS
2018-06-01 08:31:03.188 – SIP media renegotiation has commenced. MetaSphere CFS Distributel-Western-CFS
555-555-3333 NxGen Networks Inc. 192.243.214.73
2018-06-01 08:31:03.188 – Outgoing SIP message sent : INVITE (SDP) From:
5555552222@208.68.17.52 To: 5555553333@10.0.5.61 192.243.214.73:5060
*********
MetaSphere CFS Distributel-Western-CFS
555-555-3333 NxGen Networks Inc. 192.243.214.73

I tried increasing the t38timeout but it did not seem to have any effect. Is there another variable to adjust somewhere?

—
D’Arcy J.M. Cain Vybe Networks Inc. http://www.VybeNetworks.com/
IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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8 thoughts on - T-38 Re-invite Issue

  • Pinging the list to see if anyone has any thoughts. Perhaps someone can explain what t38timeout is supposed to do as it seems to have no effect at all. It certainly doesn’t seem to increase the time that it waits for a T38 re-invite.

    —
    D’Arcy J.M. Cain Vybe Networks Inc. http://www.VybeNetworks.com/
    IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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  • Pinging the list to see if anyone has any thoughts. Perhaps someone can explain what t38timeout is supposed to do as it seems to have no effect at all. It certainly doesn’t seem to increase the time that it waits for a T38 re-invite.

    —
    D’Arcy J.M. Cain Vybe Networks Inc. http://www.VybeNetworks.com/
    IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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  • DC> Perhaps someone can explain what t38timeout is supposed to do

    A ‘git grep t38timeout’ on the src leads one to res/res_fax.c, where one case see that it is the number of miliseconds to permit for t38 negotiation to complete once it starts.

    Ie after both sides select t38, until they agree on the t38 terms.

    -JimC
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    James Cloos OpenPGP: 0x997A9F17ED7DAEA6

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  • OK, so does that mean that setting it to 25000 should leave time for the re-invite or does the timeout start after that. If so is there another control for waiting for the re-invite?

    Note, a test by my provider shows that this particular number gives the re-invite after 6 seconds. I hang up at 4.

    —
    D’Arcy J.M. Cain Vybe Networks Inc. http://www.VybeNetworks.com/
    IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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  • As I wrote above, after that. After the sip/sdp.

    -JimC
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    James Cloos OpenPGP: 0x997A9F17ED7DAEA6

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  • Does anyone have any ideas on this? We now have another number that is failing the same way. If someone can point me to the area in the source where this other timeout is I will try to make the change there. Perhaps I can even send a patch to control it.

    —
    D’Arcy J.M. Cain Vybe Networks Inc. http://www.VybeNetworks.com/
    IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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  • I don’t want to be a total pest but I can’t be the only one who has been tripped up by this. Please, does anyone have any clue about this?

    —
    D’Arcy J.M. Cain Vybe Networks Inc. http://www.VybeNetworks.com/
    IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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