I've also had mixed luck with t.38, but the t.30 fax standard allows only 3 errors; after the third error is detected, the fax is to be cancelled. But working to make t.38 work is worth the effort. The networks have to be phenomenally clean to have a reliable faxing service that works all the time: If you're doing 10 pages at 28800 bps, that'll take 350 seconds, and tolerate no more than 0.017% packet loss. That's an unusually clean network. If the fax is slower, e.g. 9600 bps, the fax is longer (600 seconds at 9600 bps), so the exposure to errors is greater and the network reliability requirement is higher -- <=0.01% loss allowed. This assumes errors are randomly distributed; if they come in clusters the requirements are much stricter. --- Mark R Lindsey mark at ecg.co +1-229-316-0013 http://ecg.co/lindsey On Sep 30, 2016 at 18:18, Greg Lipschitz <Greg at thesummitgroup.com.au> wrote: Have you tried the opposite, disable T.38 and use G711a/u for the payload. We have had far greater success with the G711a/u RTP. T.38 still seems to be very hit and miss cross devices be it ATA or even a real fax machine. Cheers Greg Greg Lipschitz | Founder & CEO | The Summit Group *Greg at thesummitgroup.com.au* <Greg at thesummitgroup.com.au> *thesummitgroup.com.au* <http://thesummitgroup.com.au> *1300 049 749* <1300%20049%20749> *Level 1, 39 Railway Road, Blackburn VIC 3130* <https://www.google.com.au/maps/place/The+Summit+Group+(Australia)+Pty+Ltd/@-...> [image: The Summit Group] <http://thesummitgroup.com.au> ------------------------------ *From:* VoiceOps <voiceops-bounces at voiceops.org> on behalf of Nelson Hicks < nelsonh at socket.net> *Sent:* Saturday, October 1, 2016 4:47:30 AM *To:* voiceops at voiceops.org *Subject:* [VoiceOps] Problems with T.38 fax with Grandstream GXW-4248 We have a customer with multiple Grandstream GXW-4248 voice gateways that wants to use T.38 for sending and receiving faxes. They are running the most recent release (1.0.5.16). We have tested this successfully with other devices, including a Grandstream HT-702 and a Grandstream GXW-4004, but when configuring the Grandstream GXW-4248 the same way, the audio from the Grandstream to the fax machine cuts out at the renegotiation to T.38 and does not resume. When looking at a packet capture of the fax call, the Re-INVITE appears successful, but the first and only UDPTL packet sent by the Grandstream is reported as malformed by Wireshark: ITU-T Recommendation T.38 [Stream setup by SDP (frame 510)] [Stream frame: 510] [Stream Method: SDP] UDPTLPacket seq-number: 32768 primary-ifp-packet type-of-msg: t30-indicator (0) something unknown here [too long integer(per_normally_small_nonnegative_whole_number)] [Expert Info (Warn/Undecoded): something unknown here [too long integer(per_normally_small_nonnegative_whole_number)]] [something unknown here [too long integer(per_normally_small_nonnegative_whole_number)]] [Severity level: Warn] [Group: Undecoded] [Malformed Packet: T.38] [Expert Info (Error/Malformed): Malformed Packet (Exception occurred)] [Malformed Packet (Exception occurred)] [Severity level: Error] [Group: Malformed] Does anyone have any experience with trying to use T.38 with a Grandstream GXW-4248? Thanks, -- Nelson Hicks Network Operations SOCKET (573) 817-0000 ext. 210 nelsonh at socket.net _______________________________________________ VoiceOps mailing list VoiceOps at voiceops.org https://puck.nether.net/mailman/listinfo/voiceops