TELECOM Digest OnLine - Sorted: Re: Hookflash and Ground Start Analog CO Trunks From PABX

Re: Hookflash and Ground Start Analog CO Trunks From PABX

Ken Abrams (k_abrams@[REMOVETHIS])
Thu, 03 Mar 2005 19:21:15 GMT

John Bartley <> wrote

> It's my recollection that the use of hookflash signalling, opening the
> tip-ring connection on the CO line, even for ground-start lines, is
> decades old , yet the local Toshiba dealer (which shall remain
> nameless) has a repair clerk who's asserting that is was *not* a
> standard in 1994 when the sytem was delivered.

I think your recollection is a little "foggy". ;-)

> I want to build a case for hookflash on ground start lines being a
> normal practice, something any line card sold for ground start use
> should be able to do when sold, even back in '94.

Just because you WANT it to be true doesn't necessarily mean that it IS.

A flash was (and still is, I believe) never intended to be passed from one
switch to another. It is a means for the subscriber (phone) to signal the
nearest switch in the chain.

It appears that your equipment can serve either as a switch (PBX) or
as (dumb) terminal equipment (CENTREX). When a CO termination is
ground start, that makes it a trunk between two switches and by design
will not pass a flash. When it is loop start, it is a line and will
pass the flash.

The difference between a PBX "trunk" and a Centrex "line" is not just
one of terminology. There are technical design differences between
the two. This was true when there was only one supplier for the
network and a lot of these standards carried well beyond the date of
deregulation. The fact that they offered you a solution by changing
cards probably means that this "standard" has been corrupted.

One final thought: At the CO end, a ground start PBX trunk originally
was not capable of recognizing a momentary open as a flash. Thus, any
momentary open exceeding 20 ms (or so) would effect a disconnect.
That might still be true.

Has the LEC really offered to provide you ground start Centrex lines?
At one time those were mutually exclusive.

[TELECOM Digest Editor's Note: Actually, on my PBXtra, which goes
under the brand name 'Total Com' and is manufactured by ACNC at the
phone number 630-241-2800, (but distributed by Mike Sandman through
his online catalog [and he is a good friend of the
Digest and well trusted on the net]) you _can_ pass along a hookflash
to the next switch down the line, i.e. the central office.

It is a three step process: You flash the hook, get back dial tone
from the PBXtra, then dial *6 (or 26 if on a rotary dial phone) then
when dial tone returns, flash the hook again; that time the PBXtra
ignores the flash, the central office sees it instead. It is not a
feature I use very often on my system, but I suppose I would use it
if I got a 'call waiting' signal on my line, or wanted to make a
three-way call. So I guess my answer to the original correspondent
would be 'it can be done through software with some types of systems.'

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