Fax transmission


I have a question about fax transmission ability on Asterisk. We know that Asterisk supports T.38 gateway from version 10. we know spandsp project and res_spandsp too.
Beside these, We can send and receive faxes with Asterisk to/from PSTN and VoIP network?

I see many people offer HylaFax (+) /AvantFax for fax transmission, so Asterisk can’t do this work with us?

In addition, Fax for Asterisk that is a commercial solution, what does do ?

thanks for helps.

Fax for Asterisk is a commercial fax stack which handles the fax itself, it’s a drop-in for Spandsp in some circumstances. As for the usage of fax directly in Asterisk or HylaFax/etc - it really depends. Some work better for people depending on the environment.

What do you mean depends?
I want enable send and receive fax for my Asterisk users. So which solution is stable?
It clear that Hylafax or others makes complexity .
Asterisk can handle full fax functionality?

Fax has a lot of factors. The VoIP provider’s T.38 implementation, the source TIFF files if sending, quality of the underlying PSTN connection if using the PSTN. It depends and you have to try things out, determine success/fail rates, tweak, continue. Fax isn’t something that generally “just works”.

These are right. But is not the answer.

If the response isn’t the answer you seek, perhaps you’ve not asked the proper question.

This is simple question, Asterisk in latest versions, can handle fax transmissions without an third party software/server ?

Asterisk + Analog/Digital card or gateway

What do you mean by “handle?”

What do you mean by “third-party?”

What are your scenarios involving Asterisk and an analog or digital card or gateway?

handle : send/receive (T.30 ----T.38)
third-party: Hylafax (+)
Scenario: system telephony for a mid size office. (24 FXO lines)

Handle - Asterisk can send/receive T.30 or T.38 using the sendfax/receive fax dial plan applications that depend on the external spanDSP library (available for newer versions of Asterisk) or the Fax for Asterisk resource module (not available for newer versions of Asterisk).

Third-party - Asterisk does not depend on Hylafax in order to be able to turn a received fax into a TIFF nor to take a TIFF and fax it out. That’s where the receivefax / sendfax applications and the spanDSP library come in.

1 Like

Just a tip, if you are going to use hylafax you will need also iaxmodem to connect to asterisk and receive/send.

Yes, I mentioned that it will be complicated solution.

HylaFax does indeed add a lot of complexity and it’s a non trivial tool. I built fax TX/RX for my system and started with HylaFax…and quickly abandoned it. That said I ended up using FFA (Fax For Asterisk) because while it is commercial, it comes with one channel for free, which works fine for me and I send/receive tens of thousands of faxes every month.

The dialplan apps that FFA exposes are very simple and both TX and RX can be built in a few dozen lines of config as well as some supporting DB tables and func_odbc calls.

Also like jcolp mentioned fax is very much hit or miss even when very highly tuned. You must understand that a non negligible amount of the time you’re going to be interfacing with a peer that straight up fails to properly negotiate T.38, which means you’re always going to have a somewhat unpleasant failure rate.