atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers Telco switching

Guys, I am trying to wrap my mind around the older systems the telcos used to use for switching before ESS. What I am looking for is the order in which these systems were used. For example, what came first, panel or step-by-step?

Thanks,
Jeff

I suppose you mean the PLUNGER LINE SWITCH.

It's not just which came first in simple chronological terms, but also which was considered suitable for service in a particular area at that particular time.

As I understand it, panel was only a viable option in larger offices, hence its widespread adoption in places like New York City (although if I recall correctly, the very first panel switch to go into service in the U.S. was in Omaha, NE).

Before crossbar switches appeared in the 1930s, Strowger SxS was very much the system of choice in places too small to make panel suitable, so it got adopted everywhere from tiny rural areas right up to places like Los Angeles and Atlanta.
There was also an "XY" switch made by Stomberg-Carlson which was functionally and trunking-wise practically identical to Strowger, but the physical design of the switches was different (horizontal movement in two planes rather than step vertically then rotate).

Jeff,

There were also hybrid systems - the industry was in flux then.

Norelco made a motor drive system (kind of a cross between a stepper and a xbar). I think it was called the U55H, but don't hold me to it.

NEC made the NEAX 11, 21 & 31 switches that were all hybrid Xbar and electronic.

Here's one of the big differences as I remember:

Early switches (like Steppers) had no intelligence - they just DID.

Later switches had Wired Logic in the form of Markers in a Xbar (and other similar types).

Electronic Switches offered Stored Program in Ram and/or Rom.

Then there was the question of Space Division (Analog) or Time Division (Digital)for the internal Networking.

So the WE 701 SxS was Space Division, no common control.

The OKI 120 Xbar was Space Division, Wired Logic.

The NEC Neax 31 was Space Division, Stored Program

The ITT TD-100 was Time Division, Stored Program

That brings us up to about 1976.


Sam

That's a great site, thanks Bill!

This killer link has two parts: Telephone Tribute and Bell System Memorial.

I think it was posted elsewhere on the board, but the Bell System Memorial piece is now hosted at https://www.porticus.org/bell/bell.htm The link to it from Telephone Tribute is broken.

Was that a two-motion motor drive?

Single-motion rotary systems (either motor driven or stepping, uniselector style) were quite common in some European countries, and although rare it seems that a few were used in the U.S., Las Vegas being an example.

The main advantage over straight SxS was in the more flexible trunking arrangements. With Strowger you have a fixed 10 outlets (20 with bank wiper switching) on each level, whereas with rotary you could assign as many or as few positions for each dialed digit as you required, e.g. if the 3 "level" was heavily used for local numbers but 7 only served a tiny remote office you could wire the switch to give you 30 trunks for the former and only 2 or 3 for the latter.

Paul -

I think it was a two motion but I won't swear to it. I saw a couple of them, but they were a rarity here. I only worked the key equipment on those jobs, not the switch. Also, it was close to 30 years ago.

I could try to ask around. There still might be a few of the guys that worked on them alive yet.

Sam

That would be interesting to know Sam, but don't go to too much trouble. It's just a passing curiosity as I don't think I've ever seen a two-motion motor-driven system before.

Jeff, I don't know if you're interested in the international aspect, but over here in Britain Strowger SxS was used almost exclusively at one time, since it was adopted as the system of choice by the Post Office, which had a monopoly on telephone service from 1914 onward (with the exception of just one city).

I understand that our older SxS switches were very similar to American Strowger equipment of the era, which isn't too surprising. One of our early producers of SxS was the Automatic Telephone Manufacturing Co., which was formed to make equipment under license from Automatic Electric of Chicago.

Later in the 1930s the Post Office came up with its own revised design of switches, resulting in British SxS acquiring its own little twists. The most obvious difference you'd notice in observing the selectors in operation is the method of release. Instead of having a separate release magnet they were released by driving the wipers horizontally to a 12th position outside the far end of the bank contacts. The wipers would drop vertically to the bottom, then rotate back to the released position. It was reckoned that this release arrangement resulted in more even wear on the bank contacts than the "back out the way you came in" system of the older switches. There were other variations in the newer designs too, such as extending the frame across the bottom of the banks and providing the lower end of the shaft with a bearing.

Those differences aside though, SxS was adopted right across the country from tiny rural offices serving less than 100 lines right up to large cities. Standard types were installed in small villages and towns, designated by UAX7, UAX13, UAX14 etc. where UAX = Unit Automatic eXchange. Larger cities had exchanges which were custom-built from racks as needed and all went under the general description of "non-director" exchanges.

London and five other major cities were "director" areas, still with everything running on SxS but using directors (register-translators) on the first three digits, just as in some parts of the U.S.

Crossbar switching was rather a late-comer here. I believe our first X-bar exchange opened in 1964, a good 25 years or so later than America. X-bar exchanges served quite a number of towns or parts of cities by the 1970s, but never (proportionally) in anything like the numbers in the U.S.A. (I did just find out recently that my local C.O. was X-bar in the 1970s -- having moved here about 12 years ago I didn't know the full history of the area before).

Electronic exchanges started to go into full service here from 1966 onward, following experimental systems in the early 1960s. The TXE2 (TXE = Telephone eXchange Electronic) had stored program control with reed relay switching, very much akin to the American 1ESS as I understand it. The TXE2 was quite a common replacement for the old UAX13 SxS switches in the 1970s for villages and surrounding areas which were growing in size quite rapidly at that time. The larger TXE4 for bigger towns appeared in the mid 1970s.

Digital exchanges went into service from about 1980 with "System X," jointly designed by the Post Office (at that point soon to become BT), Plessey, GEC, and STC. Although originally intended to be the sole replacement for the entire network, by the mid-1980s BT decided to also start using the Ericsson AXE10 (which is dubbed "System Y") so as not to be completely reliant upon GEC.

System X and system Y/AXE10 gradually replaced everything else through the 1980s/90s. All the old electromechanical and TXE exchanges were gone from the PSTN by 1998.