2

My provider switched me to an IP-based line. Now my analog ISDN (G3) Fax does not work anymore.

Is there any way I can use the conventional Fax with a SIP connection? My Router supports T.38 Fax protocol as well as many codecs.

NoMad
  • 302
  • 1
  • 4
  • 14

3 Answers3

2

Short answer: Use G.711 Codec and turn off T.38 support in your Router. If that still fails, try lower baud rates in your Fax machine.

In the case of German Telekom, T.38 isn't supported. Your router might only try T.38 if that option is on. G.711 has (one of) the best quality when it comes to the ISDN frequency spectrum.

Long answer:

You can still send faxes, even over IP-Based lines. As these may be lossy (drop packets, async packet receiving), transmitting faxes may actually fail if your connection is bad.

Using the proper Codec to encode the analog tones digitally, analog fax signals can still be sent to and received from true analog telefax machines and lines.

Also, some routers only try to transmit a fax via T.38 if that option is available. Try disabling T.38 support as well.

NoMad
  • 302
  • 1
  • 4
  • 14
1

If the carrier won't support t.38 you'll have issues, most don't and act like you are crazy for asking. g.711 can work but will probably give you headaches.

Best solution is get an analog line for fax only or look into a carrier that offers t.38 (https://us.babytel.net/en/fax/t38fax/). If fax is important just get a POTS line for each fax machine and be done with it.

jhayes
  • 476
  • 2
  • 6
  • 12
  • Unfortunately, additional analog lines often aren't available here in Germany, as the quasi-single provider Deutsche Telekom transitions most (business) customers to IP-Based / VoIP lines. If that's the case + G.711 doesn't work, I guess redirecting the original phone number to a SIP provider w/ T.38 support is one of very few options left. – NoMad Jun 13 '16 at 14:37
  • Yep, fax is really, really old and it seems most carriers would like to forget about it, not many options – jhayes Jun 14 '16 at 05:17
  • If it wasn't earning me a living, personally, I'd certainly like to see this legacy technology die. But some organisations still swear by FAX, be it for legal reasons, or just for having a dedicated machine for written correspondence. We need a fax-like machine that can scan and send documents via encrypted mail. Sorry for OT... – NoMad Jun 15 '16 at 08:52
  • I'm with you, fax is still heavily used by many so it should be supported, but I see lots of customers who go to SIP and the carrier says 'oh yeah, no problem' then when it doesn't work they say 'not my problem'. right, now it's MY problem (voip implementation) :-\ – jhayes Jun 16 '16 at 18:47
0

It's a fact that Fax machines don't and won't work over VoIP Phone system. The only challenge that exists is that While VoIP converts the audio signal into computer language(0s and 1s), it distorts the signals received from fax machine and it can't be understood on the other hand.

There's no way of fixing this issue, however you may follow tips to resolve the same:

  1. By reducing the transmission rate i.e baud rate.
  2. Enable "QoS" via router. Doing so, this will make the transmission understood on other hand.
  3. Get an online fax number.

Hope these tips helps you!!

Sushant Parasher
  • 1
  • 1
  • Reduced baud rate makes it easier to sample and conserve the data of the analog signal. So yes, as you described, it IS possible for fax machines to work over VoIP. QoS might help too, but only if Faxes aren't transmitted correctly within your network. For me, using the right codec/sampling and disabling T.38 enabled me to reliably send and receive faxes to and from ISDN endpoints using an all digital SIP line. – NoMad Jul 07 '16 at 14:47