TELECOM Digest OnLine - Sorted: Re: Foreign Exchange (FX) Lines Still in Use?

Re: Foreign Exchange (FX) Lines Still in Use?
19 May 2005 12:28:37 -0700

Isaiah Beard wrote:

> There is something else too that is going the way of the dodo: tie
> lines. These were useful for large universities with multiple campuses,
> as well as businesses with more than one hub operation in distant cities.

They were fairly common in organizations with more than one location.
As mentioned, years ago 7c message units could add up to some serious
money so even a local tie line between plants within a city was cost
justified. (Our hospital had five tie-line trunks to the independent
rehab center next door.)

Also, many PBXs of the old day limited extensions to in-house dialing
only, no outside calls to save money. But tie-lines weren't charge so
they were allowable and allowed employees to conduct business.

Tie lines usually allowed direct dialing in a PBX at another location.
You dialed a special code (often 8 or 8+) and either merely
immediately dialed the distant extension or waited for a second
dial-tone, then dialed the extension. For larger organizations, the
tie-line access codes could be quite large. For Centrex users, tie
lines had their own 3 digit code different than the outside code to
allow direct inward dialing.

Some tie-lines were relayed from PBX to PBX, you kept dialing the
access code and tied together a bunch of systems. I don't think that
was the preferred way, however.

Tie-lines usually allowed dialing in both directions between the two
PBXs. I know one switchboard could connect an outside caller through
the tie-line to the remote location, but they didn't like to do so as
a matter of policy. The tie-line jacks on the switchboard were a
little more complicated -- there was a pair for each line, one jack
used for answering, one used for calling.

Other remote locations may have been served by a simpler extension
basis. That is, the home PBX could only reach the remote PBX operator
who would have to complete the call to the desired remote extension.
I presume this wiring was far simpler than tie-lines due to one-way
instead of two-way signalling.

> Nowadays, cheaper LD and Voice over IP is making tie lines quite
> obsolete.

Yes. My employer once had a network of tie lines to our various
locations and associated codes for them -- each location having its
own code. Our centrex phone numbercards had two lines -- one our
regular number, one our tie-line number. Some years ago all that was
eliminated. To reach a distant location outside our local PBX or
Centrex, we just dial 9+ the external number. The equipment switches
it the most economical way available when the call is made. (My
employer has a series of LD methods from outward WATS lines down to
regular toll network, maybe some tie-lines or FX lines remain but they
are hidden to us.)

Probably the biggest network is the Federal Govt's "FTS" network and
the military's Autovon network. I don't know how they work today. I
always thought "Autovon" used special TouchTone phones, but at my
father's installation, the Autovon lines came in the PBX just like any
other trunk and the phones in his place were plain rotary. They used
Autovon for plain business, not "combat" situations as the literature
suggests. FWIW, they converted to Centrex from PBX, then closed the
whole place down about six months later. It appeared the govt owned,
not leased, the PBX switchboard and switchgear--with govt employees
doing the maintenance on it, not Bell people, even though it was
connected to the Bell System.

Of course on the other hand, Centrex is now available to very small
businesses with wide locations using regular numbers. (Originally you
got a dedicated or near dedicated NNX all to yourself and a huge block
of numbers. For some reason, many, though not all, of the oldest
Centrex's of the 1960s have received new exchanges; I don't know why.)

[TELECOM Digest Editor's Note: And don't forget the other close
relative in that cluster of service types: the OPX or 'off-premise-
extension'. When I worked (back in the late 1950's/early 1960's) at
University of Chicago in the phone room, there were a bunch of these
that were located all over the Hyde Park neighborhood. You'd see
phone booths around the area with both a payphone in them _and_ a
University of Chicago OPX. Almost all the dormitories had their own
switchboards with outside phone numbers, but two or three OPX numbers
terminated on those switchboards as well. Those OPXs were all of the
four digit extension type number, and I guess when the most recent
form of Centrex was installed a few years ago, all those OPXs took
the new number 753-xxxx. PAT]

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