Re: [hylafax-users] Digital vs Analog

["Darren Nickerson" <darren.nickerson@xxxxxxxx>]

"precioso arabche" <precioso77@xxxxxxxxxxx> wrote:


> im trying to decide on a new modem for hylafax and wanted to know if 
> "theoretically" digital should have less problems than analogue..
>
> the main "unsolvable/firmware" problems ive seen on this forum would be 
> "Ring detected without successful handshake" etc.. etc.. etc..
>
> if i go ahead and purchase one of the digital boards listed on ifax 
> http://shop.ifax.com/index.php?cPath=31_1_24
>
> can i expect a similar/slightly higher/higher/much higer success rate.. or 
> is there a different set of problems??

Precioso,

Unfortunately, there is no simple answer to this question. When someone 
calls us looking to build a fax solution we usually need to ask a great 
number of questions before we know whether to encourage them to consider 
analog or digital fax board/modem technology. A lot of it depends on 
existing infrastructure, the interconnect requirements, and what they're 
trying to do with the technology - for instance do they need to do inbound 
fax routing using DID/DNIS?

Because you asked if there are any advantages to digital, I will answer that 
specific question. Here's a few:

1. Virtually error-free 'last-mile' from telephone company's interconnect to 
your fax equipment.

You can't control most of the phone circuit between the sender and receiver, 
but you CAN control (and optimise) the last mile, which is in most cases the 
circuit between the demark (the interface between telco and customer prem 
equipment) . If the telephone company is doing their job, their circuit path 
is very high quality audio. All bets are off on the remote side of the call 
... you can't control that and it's best not to try. What you _can_ do 
though, as a responsible faxer,  is make certain your own audio path is as 
clean and free from artifacts as possible. While troubleshooting support 
cases for our customers we have seen several instances of 'line noise' being 
introduced into analog wiring which can manifest as crackles, pops or hiss. 
These can make for challenging fax conditions that threaten to introduce fax 
errors (there are ways to minimise the impact of these artifacts but that's 
a little too off-topic). I'm not an electrical engineer so I can't explain 
what causes these problems, but imagine how many sources of electrical 
'noise' exist in most industrial settings and I g uess it's not too 
surprising.

By contrast, a digital (T1/E1/J1) last-mile should be free from audio 
artifacts, unless you're seeing framing or CRC errors on the circuit in 
which case you have a physical/electrical problem that needs fixing. Once 
again, this is only the last part of the circuit, but we _have_ seen cases 
where poor fax performance could be tied to problems with that last mile.

2. Detailed call progress information

If you run the boards in ISDN PRI mode (which we recommend over channelised 
mode) both the Eicon and Brooktrout products offer valuable insight into the 
actual ISDN call setup and call progress messages. This allows us to 
unambiguously determine what happened to the call in the large majority of 
cases. This is invaluable when troubleshooting fax problems for our 
customers. To explain this a bit more, analog fax modems 'listen' to the 
audio, meaning they sample/monitor it in-band to try to determine if there's 
a busy signal, if there's no dialtone, if there's a human on the other side, 
no answer, etc. Some products are better at this than others, but in the end 
it's a guessing game that's prone to misdiagnosis.

In an ISDN call, the call setup happens out-of-band on a special channel we 
can monitor called the D-channel. This allows us to know for certain if the 
call was correctly switched through the PSTN and answered.  If it wasn't, 
for instance if the number was invalid, we can learn a great deal about why. 
To get a feel for how powerful this can be, have a look at:

         http://www.eicon.com/support/helpweb/diva/getcode2.htm

Note that this does not answer _all_ questions you might have about a failed 
fax. It doesn't help explain fax protocol errors, and once the call is 
answered both these products also have to play the guessing game by 
listening to the audio to see if there's a fax there or not. Both digital 
boards we sell are pretty good at it ... they listen for audio energy levels 
that sound like human voice, they check for SIT tones, and report that back 
to the application. The icing on the cake though, is that in digital land we 
can also determine who initiated the call hangup, and again that information 
can be very helpful when troubleshooting.

3. Painless inbound fax routing

Digital circuits pass "called number" and "calling number" information (DNIS 
and ANI in the digital world) transparently, so you can assign as many 
virtual fax numbers as you like, and route them all into the same T1/E1/J1 
circuit, and have HylaFAX send them to the right place by looking at the 
called number. This is possible with analog circuits (on loop-start use DTMF 
routing and on analog DID trunks use wink, ground start or delay dial 
signaling) but it's a _lot_ messier and requires a _lot_ of PBX and/or telco 
tweaking.

4. High density

Digital boards allow you to add channels in increments of 23 or 24 (and 30 
in the case of E1) per PCI slot. Dual-PRI boards exist (although we do not 
presently support them ourselves) that would allow double that.

I could go on here, but those are the first advantages that come to mind and 
my fingers are growing as tired as I'm sure your eyes are at this point. 
Please don't take this as a crusade for digital fax board technology - I'm 
sure I could write a lot about the advantages of analog boards also and we 
would never list a product on our store that we didn't recommend for use 
with HylaFAX. One of the most significant advantages of course is lower 
cost!! As I alluded to earlier, it kind of depends on your existing telco 
setup, and what you're trying to do with fax. It's also not as simple as 
just judging analog versus digital - it depends on the particular 
manufacturer, and it also depends a massive amount on the fax software 
product you're using, and _EXACTLY_ how it uses the modem/board. I'd be 
happy to discuss this with you in more detail in person if you'd like to 
give me a call - you can reach the sales team here at 800-260-8498 (Option 
1), and myself at the number below.

Sincerely,

--
Darren Nickerson
Senior Sales & Support Engineer
iFAX Solutions, Inc. www.ifax.com
darren.nickerson@xxxxxxxx
+1.215.438.4638 x8106
+1.215.243.8335 (fax) 


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