How To Diable Fax Header (OR: What Module Could Add That Header?)

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Asterisk Users 2 Comments

Dear colleagues,

after hundreds of hours I finally managed to figure out how to send faxes from a T.38 capable endpoint reliably via Asterisk / PJSIP. My setup is as follows:

A T.38 capable endpoint sends the fax to Asterisk which passes the fax to a T.38 capable trunk which then sends the fax to its final destination. This works great, but I have left a little problem which I couldn’t solve yet (despite of googling nearly a whole day now …):

Some of the software components involved is inserting an unwanted header line into the fax. The header is always formatted the same way; an example (using a two page fax which I have just sent): “13.10.2015 18:22:05” (at the left border of the page) and “001/002” (at the right border of the page).

My question is if Asterisk’s or PJSIP’s software components possibly add such headers and how to remove these.

What I have researched so far:

– The endpoint which initially produces the fax does not insert that header.

– res_fax does not insert that header (res_fax is not even loaded in my configuration).

– Set(FAXOPT(headerinfo)=TEST) in the dialplan didn’t alter the header in any way. I expected that because the fax probably somehow is passed through Asterisk more or less directly from the sending device to the trunk, so probably none of the FAXOPTs are applied.

– I am wondering why the format of the date in the header line is the German format. I’m located in Germany, and there are German locales installed on the Linux system where Asterisk runs on, but the system-wide default locale on that system is en_US.UTF-8 (i.e. LANG=en_US.UTF-8).

This is on Debian Wheezy, Asterisk 13.5.0 and PJSIP 2.4.5.

What do you think about that situation?

Thank you very much,


P.S. The hundreds of hours were not due to flaws in Asterisk or PJSIP (although for a long time I was convinced that this was the case) 🙂

2 thoughts on - How To Diable Fax Header (OR: What Module Could Add That Header?)

  • Are you using ReceiveFax()? If so, are you sure the unwanted information is already in the TIFF file? Or could it be produced by whatever program is being used to convert and/or view the TIFF file?

  • We have tested sending to third party endpoints as well as using ReceiveFAX(). In every case, the header is there, meaning it’s in the TIFF file which ReceiveFAX produces.

    But in the meantime, I have found out where it comes from. We don’t use hardware faxes, but a network fax software which is based on CAPI on the server side. So we are using a T38 CAPI emulator on the server, and it has turned that this piece of software is inserting the unwanted header. Nor Asterisk nor our fax software are responsible, but the T38 “driver” – the last place where I had thought of.

    I had a conversation with the developer of the emulator; he promised that he would change the software and the configuration dialog in a way that users could disable the unwanted header.