Re: True DID on channelized T-1 compatibility with PM-3

Charles Scott (cscott@freeway.net)
Sun, 11 May 1997 00:50:17 -0400 (EDT)

Jay:
Our channelized T-1's came in bahaving as you describe below. We
didn't know that initially and what was happening was that the PM3 would
answer the line and attach a modem, they it would never handshake with
the other end. We saw what was happening when we put a test set on the
T-1 and broke out a channel to listen to it. The dialed number came in
as DTMF after the PM3 accepted the call, but then nothing--you could
hear the carrier from the PM3 modem but not the other end even though we
knew the other modem was sending. At that point I knew that the switch
(5ESS) wasn't completing the call.
I ran into an amazing amount aggrivation when I tried to describe this
to the Ameritech switch people until I got some guy on the line who asked
if I wanted to "delete all digits" (huh?). I said "sure, do it" and it
all started working. The switch was apparently waiting for us to signal
that the call had been setup on the desired extention but when they
deleted all the digits so that it didn't send us any of the called number
it just went ahead and completed the calls to the PM3.
I'm sure that someone has a much more elegant explanation of all this
and how we probably asked for the wrong type of service. In any case it's
working!

Chuck

On Sat, 10 May 1997, Jay Hennigan wrote:

> True DID trunks use a signalling arrangement whereby a block of telephone
> numbers, such as from 555-1000 through 555-1999 are delivered and uniquely
> identified over a fewer number of actual trunks. The signalling is as
> follows:
>
> When a call arrives for any number in my DID block, telco seizes one of
> the DID trunks assigned to me. I acknowledge the seizure and my readiness
> to accept digits by sending a wink. Telco then outpulses the final dialed
> digits to me via DTMF. For example, if the caller dialed 555-1147, telco
> would outpulse "147" in DTMF. This way, if the DID trunks terminated on a
> PBX, the PBX could route the call to the appropriate extension based on
> the number that the caller dialed (in the above example, extension 147).
> When the call is answered, my equipment seizes the trunk, and releases it
> when the call is disconnected. The original intent of DID was to allow a
> large number of dialable numbers to be uniquely identified and routed over
> a small number of trunks. DID is also popular with paging and voicemail
> companies, answering bureaus, etc.
>
> I am familiar with this signaling and have used it in the PBX environment.
> It is *NOT* the same as regular "inbound-only" trunks, although telco
> marketing droids continue to confuse the two.
>
> Telco here is proposing DID trunk signaling for use with PM-3 for inbound
> modem usage.
>
> My questions are as follows:
>
> Will the PM-3 work at all with true DID trunks configured as described
> above?
>
> If so, is there a means of passing the actual dialed digits that the
> telco sends as part of the setup to RADIUS or otherwise handling the
> incoming call differently based on the DTMF digits passed by the telco?
>
> Anyone actually doing this?
>
> -- Jay Hennigan jay@west.net --
> WestNet: Internet service to Santa Barbara, Ventura and the world.
> 805-892-2133 805-289-1000 805-578-2121
>
>
>