Re: [hylafax-users] Hylafax+ With E1 card possible ?

[A J Stiles <hylafax_resp@xxxxxxxxxxxxxxx>]

On Friday 14 Dec 2007, George H wrote:
> Hi,
>
> Want to say that hylafax+ is really great and because of it my
> faxserver with 5 external modems is taking on HUGE load (5,000 pages a
> day) and it's going to get larger.
>
> While thinking of solutions I came up with the idea of using an E1 fax
> card that can take 30 lines. I've never tried this before on hylafax+
> but we are using E1s internally for other things.
>
> So wondering if anyone has ever used HylaFAX+ with an E1 card and if
> so does HylaFAX+ see ttyS0 to ttyS30 ?

I don't know about Hylafax+, but the "ordinary" Hylafax certainly has no 
problem with this.  We're using an Eicon Diva server card on our Hylafax 
server, plugged into a Digium 4-port card on a box running Asterisk  (which 
is then plugged into two E1 lines).  The Diva card's devices are enumerated 
as /dev/ttyds01 to /dev/ttyds30.  The most you're likely to need to do is 
edit a configuration file.

> Another thing, E1s are digital and they send like 30 signals within 1
> cable... does this have any impact on fax transmissions ?

Not at all!  All telephone calls are digital anyway nowadays.  With 
an "analogue" line, your phone is actually connected to a line card  (an 
interface with an A-to-D and D-to-A converter, i.e. something like a 
computer's sound card),  which is then connected to a basic rate ISDN line  
(64 000 bits/sec:  enough for 8 000 * 8-bit samples every second, giving 4kHz 
of bandwidth).  30 of these, plus their associated D-channels  (additional 
low-bandwidth channels, used for out-of-band signalling, call setup &c.)  are 
time-domain multiplexed  (i.e. each signal is switched onto the line for a 
brief period of time, and is only allowed to change while it is *not* 
connected to the line)  onto a primary rate line  (AKA "E1", 2 048 000 
bits/sec).

If you have some means of generating the digital data yourself, you can have a 
basic or primary rate ISDN line installed.  This works out less expensive in 
terms of line rental, because you are not paying to rent line cards in the 
local telephone exchange.

And that's exactly what the Eicon Diva card does:  it provides a virtual 
device under /dev/ that looks like a UART, and translates the data sent to 
the fake UART into the same stream of zeros and ones that would have been 
produced by a line card driven by a modem connected to a real UART fed the 
same data.  It also has to do the same thing in reverse, and do it all 30 
times over.  It also intercepts "dial" commands  (such as ATD018118055)  and 
instead of generating DTMF tones, converts them to the appropriate D-channel 
commands.

It all works fine, and the only problems we have ever had have been due to 
customers with clunky old fax machines.

-- 
AJS
(insert figure one before at sign if replying off-list)


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