TIPS FAXing in the Land of VoIP

rdoac

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Just ported my fax number from Comcast to Voip.ms. I had it previously on a obihai 110, however, I can't get it working with the Voip line. Debugging gets me here:

[2014-07-22 21:44:09] VERBOSE[2952][C-0000000c] pbx.c: -- Executing [8156333951@from-trunk:13] Goto("IAX2/voipms-3423", "custom-fax-iaxmodem,s,1") in new stack
[2014-07-22 21:44:09] VERBOSE[2952][C-0000000c] pbx.c: -- Goto (custom-fax-iaxmodem,s,1)
[2014-07-22 21:44:09] VERBOSE[2952][C-0000000c] pbx.c: -- Executing [s@custom-fax-iaxmodem:1] Answer("IAX2/voipms-3423", "") in new stack
[2014-07-22 21:44:09] VERBOSE[2952][C-0000000c] pbx.c: -- Executing [s@custom-fax-iaxmodem:2] Wait("IAX2/voipms-3423", "1") in new stack
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] pbx.c: -- Executing [s@custom-fax-iaxmodem:3] SendDTMF("IAX2/voipms-3423", "1") in new stack
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] pbx.c: -- Executing [s@custom-fax-iaxmodem:4] Dial("IAX2/voipms-3423", "IAX2/iax-fax0/s") in new stack
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- Called IAX2/iax-fax0/s
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/voipms-3423 requested media update control 20, passing it to IAX2/iax-fax0-282
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/voipms-3423 requested media update control 20, passing it to IAX2/iax-fax0-282
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/voipms-3423 requested media update control 20, passing it to IAX2/iax-fax0-282
[2014-07-22 21:44:10] VERBOSE[1926][C-0000000c] chan_iax2.c: -- Call accepted by 127.0.0.1 (format ulaw)
[2014-07-22 21:44:10] VERBOSE[1926][C-0000000c] chan_iax2.c: -- Format for call is (ulaw)
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/iax-fax0-282 is ringing
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/voipms-3423 requested media update control 20, passing it to IAX2/iax-fax0-282
[2014-07-22 21:44:10] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/voipms-3423 requested media update control 20, passing it to IAX2/iax-fax0-282
[2014-07-22 21:44:11] VERBOSE[2952][C-0000000c] app_dial.c: -- IAX2/iax-fax0-282 answered IAX2/voipms-3423
[2014-07-22 21:44:16] VERBOSE[1922] chan_iax2.c: -- Channel 'IAX2/voipms-3423' unable to transfer
[2014-07-22 21:44:48] VERBOSE[2952][C-0000000c] chan_iax2.c: -- Hungup 'IAX2/iax-fax0-282'
[2014-07-22 21:44:48] VERBOSE[2952][C-0000000c] pbx.c: == Spawn extension (custom-fax-iaxmodem, s, 4) exited non-zero on 'IAX2/voipms-3423'
[2014-07-22 21:44:48] VERBOSE[2952][C-0000000c] chan_iax2.c: -- Hungup 'IAX2/voipms-3423'
Why can't it transfer.. (The stuff above this is caller id working itself out).
 

phoneguy

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Welcome to faxing over SIP. You should of kept that on a analog line.
 

rdoac

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Ha.. Although the alternative was Comcast, which is also SIP, just within their private network. I did run some tests before I ported, and had success.

Testing this morning, it seems that if I try to fax from another system, it fails, however, if I send a fax from a machine, it's fine.

Still wondering what that transfer failed means though? Is it just that the call dropped?
 

rossiv

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I've seen that message on my system and the call went through fine, so I don't think that's the issue. What exactly doesn't work? I'm confused since there were not too many details in the first post.
 

rdoac

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I setup the inbound route on the new (ported) number, and rewired the obi110 yesterday from the old, ported line, to the only remaining comcast line we have.

While at home I wanted to test the fax still worked (on the voip.ms iax2 trunk), so used a free internet to fax service, (faxzero.com), which tried a few times to deliver the fax, hanging up just after saying "can't transfer" - I then got an email from them saying they were giving up. After about five tries I gave up and pointed it at the fax machine's extension and posted the above.

This morning, from work, I repointed the incoming route to hylafax again and sent a sheet of paper from our office fax machine - which worked, and noted that it still says can't transfer in the logs, so I realize now that's not the issue.

I guess that two IP systems just can't communicate with each other. We successfully received a few pages of junk unsolicited fax publicity today (which my receptionists are thrilled about), so I guess it works good enough.
 

billsimon

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Analog faxing over VoIP really stinks. But during a time that I was really interested in this idea, I found that I got really good results by forcing the modem protocol to V.29 (max speed 9600bps) rather than allowing V.17 (14.4k) or V.34. This was with the spandsp software and not with Asterisk.

Downsides to this are that some remote fax terminals were forced to use V.17 and so would not negotiate. Also, because the bit rate is lower, faxes took longer to send. But who cares--you're doing a conversion from image to digital (fax) to analog (modem) to digital (VoIP) to different digital (PSTN) to analog (modem) to a TIFF that gets printed on a sheet of paper. It needs time.

When I think about it in that way, I'm surprised it works at all.
 

MGD4me

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Just a couple of suggestions:

As Bill pointed out above, force the maximum speed to 9600 bps. Remember that Voip has set up a virtual circuit between the two end points, not an actual switched circuit like you would get with a dial-up POTS line. The actual routing the packets are taking will depend on the traffic and availability at that instant, and changes moment to moment.

A FAX machine takes a digitally scanned image, and converts the digital signal into audible "tones" (FSK, etc). To transport these tones requires the highest fidelity codec, so it is equally important that you only use the ulaw (or alaw) codec, if expect these tones to be reproduced.

Finally, you are probably still using an ATA to connect the FAX to the PBX (you mentioned that you did have an obihai 110 at one time), so ensure that Echo Cancellation is turned off, so that the "voice" transmission operates in Full Duplex.

Jitter and Delay can also cause problems, but these are just general rules. If you only need to send or receives faxes rarely, this solution might be good enough.
 

rdoac

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Using the fax setup in incrediblefax11.sh, how would I set the max speed for receive to be 9600bps? (No problems have been reported sending faxes from the faxmachine yet).
 

MGD4me

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Speed settings would be found on the fax machine itself. Look for something like "Fax Settings" in the various menus of the fax machine, along with other settings like Date and Time, etc.
 

atsak

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While we're talking about faxes, I've done some more deployments using the following specs:

Cisco SPA112 or Obihai 200 / 202
Echo Cancellation off (SPA112)
RTP packet size changed to .020 (SPA 112)
Reverse DSL filter on the line between the SPA or Obihai and fax machine
9600 baud with error correction off on the fax machine (if possible)

I have also used this for two alarm systems so far on varying connections (ie some higher latency ones) carrying the voice on voip.ms and anveo direct.

It has been working actually 100% for a while now. On one alarm system I had to use an OBI 200 with wifi adapter on it and it still worked.

I think the reverse DSL filter seems to actually be making a difference . . . prior to this I always had a lot of issues. I'm going to continue to monitor this of course, but thought I would share in the YAFT (yet another fax thread).
 

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