Re: [hylafax-users] Question about Multitech DID modem? Type of analog trunk?

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

On 2004.11.17 14:11 Ben Chapman wrote:

> I've talked briefly with one of our telecomm engineers and he's 
> asking about the provisioning required for the Multitech; I believe 
> that he is thinking in terms of a PRI circuit.

A PRI (or any other kind of T1 circuit) is not what you're looking for.

I've set these DID modems up with a few different telcos (Sprint, 
Qwest, and Verizon).  Sometimes I had to talk with them for long 
lengths of time about it, but all of them ended up using the 
terminology of "analog DID trunk".

> I located and downloaded the quick start manual for the Multitech DID 
> modem. According to the Multitech manual, it requires "a nearby 
> analog DID trunk line with a block of associated DID telephone 
> numbers", but it wasn't any more specific than that. That didn't seem 
> to satisfy the engineer. Does anyone have any guidance for what I 
> should tell him as far as the requirements?

From the manual:

"On a DID line the roles of the central office and the DID modem are 
somewhat reversed.  The DID modem must provide a DC voltage, around 
48V, to the line.  When there is an incoming call, the central office 
will complete a loop and draw current from the DID modem.

"On a standard POTS line, the central office provides the DC voltage 
and the user will close the loop by lifting the handset of a phone or 
making a call with a standard modem.

"There are two critical points about the DC voltage:

"1. The central office is sensitive to the DC polarity.  TiP (positive) 
and riNg (Negative) must be connected to the line from the central 
office with the proper polarity.  If not, callers will receive an 
immediate busy signal or may be allowed to make a short connection but 
become unexpectedly disconnected after a short time.

"2. The DC voltage should be applied by the modem at all times, even 
when not in use.  Occasionally, the central office will check the line; 
and, if a voltage is not sensed, the line will be put out of service.  
A call to the phone company will be required to get the line back in 
service.

"A DID modem may use line reversals to signal the central office to 
send digit information or open the channel to the calling party 
depending on the start protocol of the DID line.  The central office 
will forward several of the last digits of the incoming call to the DID 
modem through one of three formats, DTMF, MF, or pulse signalling."

In all of my installations the configuration was *always* wink start 
signalling with DTMF digit formatting.  Again, ultimately all of the 
telcos ended up calling this an "analog DID trunk line".  The monthly 
price has varied between $40 and $50 per line (one line per 
modem/simultaneous inbound call).  You'll probably be the only one at 
the local telco to have such a service as it is rather uncommon.

Lee.

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