Re: [hylafax-users] DID/DNIS clarification needed ASAP

["Jay R. Ashworth" <jra@baylink.com>]

On Tue, Jul 09, 2002 at 11:07:38AM -0400, AEleen Frisch wrote:
> I am trying to finalize a SHORT book section on HylaFAX. However, I am 
> having trouble getting definitive/consistent information about DID 
> and/or DNIS support. This is my current understanding:
> 
> * Both of these are ways to map n virtual numbers to one or more
>    actual numbers. DID is analog and DNIS is digital.

Not really.  

(This is my fault, being the telecom geek, so I'll take a swing at it.  :-)

> * HylaFAX supports both via CIDNUMBER.

DID and DNIS are both services provided by phone companies to identify
which phone number was *dialled* when a call is delivered to an end
user with a different number of Directory Numbers than they have lines
(or trunks).

In general, local service uses DID (Direct Inward Dialling), which
*used* to be delivered over a special type of analog circuit called a
'DID trunk', using in-band DTMF (touch tones) to identify the called
number -- usually as the last 4 (or 5, if you were big enough) digits
of the dialled number.

DNIS (Dialled Number Iidentification Service) is a vaguely different
animal.  It was almost always delivered across T-1 service -- but,
being analog, was also in-band DTMF.  The major difference was that in
the case of DNIS, you usually had only a few phone numbers, but scads
of lines (a call center with 600 operators, answering calls for 15
companies, for example). 

The other difference is that, historically, DID came only from Local
Exchange Carriers, DNIS only from Inter-eXchange Carriers (IE, Long
distance companies).

These days, for the purposes of HylaFAX, it's likely that anyone trying
to hang a modem on some line providing DID *or* DNIS is doing it
digitally, using an ISDN connection (even if only for a few feet, to a
smart box like an Adtran Atlas), so the difference (between analog and
digital, or between DID and DNIS) is likely moot.

---

The short version is (correct me, Lee or others, if I'm wrong) that
most of the modems we've heard about to date deliver DID/DNIS
information (if they deliver it at all) in one of two pretty
standardized ways, and HylaFAX supports one (after the RING, on a
separate line, like CNID is usually delivered) natively since 4.1.1. 

The other method (*on* the RING line: "RING DID:7275462359") is
supported by a publicly available patch which is likely to become
standard in a version in the near future.

And, of course, since HylaFAX is an open source package, if someone
comes up with some device that won't report in either of those ways,
they can always modify the package to support that device -- or, if
they're particularly sweet to the mailing list (or wave cash around :-),
get someone else to do it.

> ======================================================================
> In practical terms, the most useful routing items are the originating 
> phone number (which must be obtained via caller ID) and the incoming 
> phone number.  In the latter case, HylaFAX has the ability to route on 
> the direct inward dial (DID) or direct number identification service 
> (DNIS) telephone number. DNIS is a digital service offered by the 
> telephone company in which a block of virtual telephone numbers are all 
> routed to one or more real phone line(s). DID is a similar analog 
> service.* Using either of them, various employees in a company can each 
> be assigned their own, unique fax number, but all incoming faxes 
> actually go to one or more phone line(s) managed by the HylaFAX server. 
>   The DID/DNIS number of the incoming call is passed to HylaFAX which 
> can use it as a key for determining where to route the fax.
> 
> * DNIS is also used in other contexts (e.g., for routing voice calls to 
> the correct person based upon the which of several 800 telephone numbers 
> was dialed). Similarly, DID is also used, for example, to route incoming 
> phone calls to employee extensions without requiring an operator. Both 
> services are expensive. DNIS typically uses a T1 line, and its monthly 
> costs start at around $100-$200 US. In my area (CT, USA), DID currently 
> costs about $100 per month for 20 virtual numbers, and also requires a 
> startup fee of about $750 (as of July 2002).
> ========================================================================

That's much closer than the draft I saw last night, except that, as I
say, these days, they're *both* digital.

The *real* problem, though, isn't the price of the lines, it's the
price of the *terminal gear*.  The common way to do high-density DID
these days is with an ISDN PRI line (similar to a T-1) either directly
into a Digi Datafire or Eicon Diva board, or feeding an Adtran Atlas,
which can translate the DID into CNID for analog modems; both solutions
are up into 4-digits, price wise.

If you can get by with just a few incoming circuits, you can use the
USR Courier I-Modem, or a ZyXel model I forget the name of, both of
which also can capture that information ... if you can get a telco to
*send* it to you on an ISDN BRI (2-channel) line; telcos can be
problematic.

My personal outlook on it is that while DID is neither cheap nor easy,
if you really need it, you need it bad, and HylaFAX can now do it, with
more or less work depending on how carefully you choose.

I know that's more information than you can print; hopefully, though,
it's enough information to let you condense into what you *can* print.

And thanks for thinkin' bout us; we're alive, and doin' fine.  :-)

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra@baylink.com
Member of the Technical Staff     Baylink                             RFC 2100
The Suncoast Freenet         The Things I Think
Tampa Bay, Florida        http://baylink.pitas.com             +1 727 647 1274

   "If you don't have a dream; how're you gonna have a dream come true?"
     -- Captain Sensible, The Damned (from South Pacific's "Happy Talk")

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