Re: Hookflash and Ground Start Analog CO Trunks From PABX

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

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[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.' PAT]