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

Tie Lines (was Re: Foreign Exchange (FX) Lines Still in Use?

Julian Thomas (jt@withheld_on_request)
Thu, 19 May 2005 21:18:20 -0400

(as usual, please obscure my email address - tnx) wrote about Re: Foreign Exchange (FX) Lines
Still in Use? on 19 May 2005 12:28:37 -0700

I'm surprised nobody has yet mentioned the IBM internal telephone

> 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.)

In the early days of the IBM phone network, this was the case between
multiple PBX locations in a large site (I'm familiar with
Poughkeepsie; other sites were probably similar).

There were a multitude of dialling prefixes to go from one local
location to another.


> 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.


Before a unified "dial 8" IBM internal network, there were a multitude
of codes for different locations. Some of them were of the "let your
fingers find the way" where you dialled a code for one location, and
then its code for an associated location.

After the dial 8 network was put in place, you dialed 8 + 3 digits for
location + 4 digits extension.

> 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.

See above - before "dial 8"

> 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.

I had a couple of experiences trying to get from an outside call to a
remote location, it depended on the whim of the operator. On one
occasion, I was able to get a person to agree to call the remote
extension and deliver a message.

<more snippage>

Julian Thomas: jt atsign jt-mj decimalpoint net
In the beautiful Finger Lakes Wine Country of New York State!
Warpstock 2005: Hershey, Pa. October 6-9, 2005 -

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going
to land, and it could be dangerous sitting under them as they fly
overhead. -Request for Comments: 1925 IOOF

[TELECOM Digest Editor's Note: The Stanotel network of Standard Oil
Company was really something in that regard, but the biggest I have
ever seen -- with a seven digit dial in number from the 'outside
world' and absolutely unprotected; no password required -- was the
United Airlines phone system, _Unitel_ based out of the airline's
corporate offices in Elk Grove, Illinois. They had eighty or ninety
tie lines (all dialed into beginning with '1' followed by two more
digits; for example, '147' was the tie line code you would dial to
reach the San Francisco airport. Dial 147 (or 176 for Ohare as
another example), you then heard another dial tone from the centrex
in the distant city. At that point, do what you want, but most of
_those_ centrexes also had tie lines of their own going to still
smaller airports. You got USA WATS lines (band 6 as I recall) by
dialing 181 off of the Elk Grove system. One of the tie lines served
the airport in Seattle, WA, but then from that distant centrex there
was another three digit code which got you the centrex at Boeing
Aircraft, mainly because Boeing was/is a big supplier to United
Airlines. Another three digit tie-line code off of the Seattle
airport centrex (reached from Elk Grove if I recall correctly with
'124') got you _their_ WATS lines from Seattle, still another code
(from the Seattle centrex) got you access to Canadian WATS. If you
let your fingers do the walking, you discovered all sorts of very
interesting three digit (or less) tie-codes and/or outside lines
through those distant centrexes, all directly dialable with their
own tie-codes out of Elk Grove.

This was back in the days when everything in northern Illinois was
312, and subscribers could have an 'unlimited call pak' as they
were known for about $25 per month. All reachable and unpassworded
on 312-954-xxxx (a call-extender for the use of people working from
home rather than the UAL office complex.) The United Airlines 'Unitel'
system was a _m a s s i v e_ thing. One of the tie lines even went
to the United States Department of Aviation Administration, but when
you got to _that_ switchboard you could not get the '9' level or any
of its tie-lines or WATS lines, etc. But you sure could get out to
other points from most of the connecting switchboards/centrexes, etc.

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