[Freeswitch-users] Major deployment of outbound FAX on latest version of Freeswitch question

[Steve Underwood]

On 05/09/2011 01:16 AM, Juan Antonio Ibañez Santorum wrote:
> How much reliable FS + mod_spandsp is compared to other solutions 
> (open source or not)?
The open source options are:

     Asterisk + spandsp
     Asterisk + Hylafax + iaxmodem + spandsp
     Freeswitch

These are all tested and proven to give well below 1% failures, even 
with quite a lot of concurrent FAX channels in use, if things are set up 
well. They can give you bad failure rates if things are not set up well. 
I believe that right now you will have less trouble achieving a reliable 
setup with Freeswitch. Going forward, most of my effort goes into making 
the Freeswitch option the most thoroughly implemented one.

The main commercial option is:

     Asterisk + Digium's commercial FAX

Of course, there are numerous other fully commercial FAXing options 
which could be used in conjunction with things like Asterisk or Freeswitch

The Digium FAX module is based on the well known Commetrex FAX engine, 
which is widely deployed, and should be capable of solid results. 
However, the module is more than just the core FAX engine, and some 
people do have serious trouble with the module. I have helped moved 
people off this, and onto Asterisk + spandsp, to improve their 
reliability. In a couple of those cases people were getting quite a lot 
of pages cut short when receiving FAXes with T.38, even though a 
wireshark log showed a perfect exchange, from which I could correctly 
decode these FAXes. The module was not reporting any errors. In a couple 
of cases strange machines were sending weird things the Digium FAX 
didn't cope with very well. I worked with these people to make sure 
spandsp did handle the weird stuff well, and we ended up with a more 
usable solution. These people told me that when they complained to 
Digium they got little help. The best was an offer of a refund. Paying 
to get some support didn't seem to work out too well for these people, 
but I guess if the support you are looking for is mostly in getting 
things configured and working on day one you might get value for money.

All these solutions require reliable signaling and reliable media 
timing, and many people have setups which cannot achieve that. Most 
people don't understand how things work, and will claim a solution 
doesn't function for spurious reasons. For example, a number of people 
say the spandsp module for Asterisk doesn't work, because they keep 
getting a 488 response. That response has nothing to do with the FAX 
engine. It is a negotiation error that occurs outside the FAX engine. If 
they fixed their configuration the error would go away. However, many 
just move on, having "proven" to themselves the solution doesn't work.


> 2011/5/8 Steve Underwood <steveu at coppice.org <mailto:steveu at coppice.org>>
>
>     On 05/07/2011 04:02 AM, Andrew Keil wrote:
>     > Steve,
>     >
>     > Thanks for your response.
>     >
>     > Further clarification on my part:
>     >
>     > 1) 20,000 to 30,000 pages per day to be sent out.
>     So, this is fairly small scale. A single E1 will do fine.
>     > 2) It will be an e-mail to fax style gateway (not fax to e-mail
>     since that would involve inbound faxes)
>     That covers a few requirements, depending what you expect to be in the
>     e-mails - send the whole e-mail as a FAX; extract a PDF, Word
>     document,
>     etc. from an e-mail, and turn that into a FAX; and so on.
>     > 3) The reason I asked about e-mail to PDF is the initial
>     comments from my client requested the ability to send PDFs and
>     WORD documents (I guess from attachments to the original e-mail),
>     I understand the format that gets faxed should be TIFF so I saw on
>     the freeswitch wiki email2pdf mentioned.  Then ImageMagick can
>     help get a PDF to TIFF.
>     If the incoming e-mails are limited to ones containing PDFs and doc
>     files to be extracted and turned into FAXes things you seem to have a
>     fairly well defined requirement. OpenOffice can be used to turn
>     the doc
>     files into FAXable images, but I am not clear how well the newer docx
>     files are handled. Ghostscript can be used to turn PDFs into TIFF
>     files.
>
>     Avoid ImageMagick for this kind of work. It uses Ghostscript to do the
>     hard work, but it doesn't get the best from it. If you use Ghostscript
>     directly you get better control, and you can achieve good results.
>     > Can I ask some more questions:
>     >
>     > Q1) Based on your experience what would be the average time (in
>     seconds) to send a single fax page (TIFF file) via Freeswitch&
>      Sangoma TDM?  You can quote a TIFF file size to make it more
>     accurate.  From there I should be able to do the math to calculate
>     my Client's requirements better.
>     The time per page depends a lot on its complexity. I use a torture
>     test
>     file with images that take half an hour to send. Typical office
>     work is
>     probably 20s per page at 14400bps.
>     > Q2) Running on CentOS and using mod_spandsp/Freeswitch&  Sangoma
>     TDM what percentage CPU usage would I expect to see if 30
>     concurrent faxes are being sent at the same time (ie. All channels
>     of my E1 are faxing)?  (The hardware would be a new 1U rack server
>     from a major hardware vendor)
>     The greater part of the CPU load is likely to be what you didn't list
>     there - the processing from e-mail to FAXable TIFF files. A single
>     E1 of
>     FAXing is a really low load these days, though.
>     > Q3) What version of CentOS 5.x would you recommend?  Would the
>     latest version 5.6 be fine?
>     5.6 is fine.
>     > Q4) From memory there used to be different fax quality modes on
>     fax machines (STANDARD, FINE&  SUPER FINE or something like that).
>      Is it possible to set the fax send quality from mod_spandsp (also
>     can you provide an example)?  If this is the case could you also
>     answer question (Q1) based on the different fax send quality modes.
>     You can't really set the quality in mod_spandsp. The quality
>     follows the
>     TIFF files to be sent. You can, however, select the image quality
>     as you
>     generate the TIFF files in Ghostscript. STANDARD, FINE and
>     SUPERFINE are
>     the right names, although many machines refuse to use SUPERFINE.
>     > Q5) From exisiting deployments of Freeswitch using mod_spandsp
>     (&  Sagoma TDM cards (although this is not critical)) what is the
>     largest number of concurrent outbound faxes done on a single box
>     that you know of?
>     I'm not sure of the biggest, but an E1 of FAXing is pretty small
>     volume
>     these days. The biggest number of channels should be in the hundreds.
>     > I appreciate your feedback and experience.  It sounds like this
>     will work fine with the mod_spandsp/Freeswitch&  Sangoma TDM
>     combination on CentOS.
>     >
>     > I will most likely go for two servers with at least 2 x E1s in
>     each, that way I future proof it a little and add redundancy.
>      Plus my Client can start using Freeswitch for Voice related
>     services also.  On my side I can also test faxes going out on the
>     first server and via a cross-over cable I can terminate them on
>     the second server (for testing) - much nicer.
>     >
>     > Thanks again,
>     >
>     > Andrew
>     Two servers with one E1 in each sounds like more than enough to meet
>     your needs, unless your 30k pages per day occur over a fairly short
>     working hours, and the customer demands rapid delivery. Then you might
>     need more channels to deal with rush hour.
>
>     Steve
>
Steve