Ubiquitous Issue 1 File 8: In Introduction to Australian Telephone Exchanges
In Introduction to Australian Telephone Exchanges - By mE!
If you don't know what a telephone exchange is, then you really shouldn't be reading this magazine! But in any case, I will give a brief history of the exchange as well as the different exchange types.
The first exchanges started springing up before the end of the 19th century. Melbourne was to boast the first telephone exchange in Australia, run by the Melbourne Telephone Exchange Company - managed by a man called H. Byron Moore. This was merely two years after the first American exchange and only four years since Bell had first talked on the telephone.
(C'mon you must know who Alexander Graham Bell is!!)
The first sort of exchange was completely manually operated. Ie you picked up the handset, turned the lever to Generate an electrical current, and a light would light up on an Operator's console at the exchange. You then asked to be connected to your desired number. Now this was all fine and dandy. But as more and more subscribers began to use the fone system, more and more people had to be employed. This would have proved to be a real fucking headache, had the new automatic exchange not come into being.
The Step by Step (SxS) Exchange:
The real trip out was that the automatic exchange was invented by an American funeral director! His name was Almon B. Strowger. It is said that he was getting just a tad pissed off about his business rival's wife, who worked at the local telephone exchange, switching his customers to his competition, so he said "fuck it! I'm gonna get rid of those stupid tart operator bitches!!" He did this by inventing a device similar to the Step-by-Step exchange.
The SxS exchange simply handles each number one step at a time. When the receiver is picked up, it is connected to a device called a UNISELECTOR which is just a moving arm making contact with a selected point. The purpose of a uniselector is to find a free BIMOTIONAL Selector. A Bimotional selector is simply a two dimensional version of the uni-selector. You are ofcourse given a dialtone when the uniselector connects to the first BMS. When the first number is dialed, you are connected to another bi-motional selector. The selector connected to is dependent on the number dialed. Each number dialed connects you to the relevant selector until the telephone number you are calling is reached.
|
o | o o o o o
--------o o | o / o o o --------------------->
\ o | o/o o o o To BMS #2 which is
\ o | / o o o o dependent on the
\ o |/ number dialed.
\o----------// ---------|
|
Uniselector Bi-Motional Selector 1
(1 Dimensional) (2 Dimensional)
For more details and better pictures than bloody ASCII drawings, read a telephony History book, or Check out the Telstra Internet home page. Or get the Information kit #3 from Telstra, which is on the internet and from Telstra's Public Relations service. (It's FREE - For a change!!)
The last SxS exchange in Australia was predicted to be replaced as late as 1995. Whether that has happened or not, I wouldn't have a clue! (An interesting point to note is that the last MANUAL exchange was at Wanaaring is New South Wales. This was decommissioned in December 1991!!!)
The Crossbar Exchange:
Although better than employing ten million bloody operators, the SxS exchange was a pain in the arse to maintain. Numbers were hardcoded into the system which made things a pain in the arse if you wanted your number changed!! The Crossbar (or XBar) exchange was to come to the rescue. The XBar had the advantage of having the control system separate from the switching system. This made the exchange a hell of a lot more versatile.
--------------------
----------- | Switching | ----------
| Fone 1 |--------------| System |---------------| Fone 2 |
----------- | | | | ----------
| -------------------- |
| |
| |
| ---------------- |
| | Control | |
----------| System |----------
| |
----------------
The XBar exchange brought back the common control system which was absent in SxS exchanges. The Control system can be Relays, microprocessors, or people. (Ie in old manual exchanges.)
The Crossbar works in a similar way to the old Manual switch boards but are controlled by relays rather than people. The switchboards are of course part of the switching system while the relays are part of the control system. It was during the XBar era, that many services like STD came about.
Computerized Exchanges:
A modern Crossbar exchange works on the same principle as any XBar exchange. However the relays are gone and the Common Control System is controlled by microprocessors. This gives the exchange some of the features that a fully computerized exchange offers.
The next step was the fully computerized exchange. Unlike the computer controlled XBar, which has a computerized control system and the XBar style switching equipment, the modern computerized exchange digitizes the signals rather than switching the analogue signal. The digitized information is then switched using logic circuits (AND gates, OR gates etc.) to a multiplexer where it is either converted back to an analogue signal and sent to the other fone (if both fones are on the same exchange) or sent digitally (along copper, microwave, fibre optic etc.) to a remote exchange where is converted back to an analogue signal and sent to the other fone. With modern computerized exchanges, features like tone dialing, easycall and a whole heap of other shit are available. Modern exchanges also handle stuff like ISDN. Integrated Services Digital Network - In which the signal is digital right up to your door. This would render modems useless. But Telescum prices it so fucking high that it is out of reach to 99% of the population!
What do those acronyms mean?
The following is a description of exchange acronyms and what they mean:
SxS: Step by Step exchange. In Australia this includes:
SE-50,SR-B
XBar: Crossbar exchanges. In Australia, this includes:
ARF, ARK
ARE: Computerized Xbar. These include ARE-11, ARE-113, ARE-114 Most ARE-11 Exchanges have been converted from old ARF XBar exchanges.
AXE/S12: AXE and System 12 exchanges are fully computerized. System 12 is a little smaller than AXE but they are pretty much the same. AXE (And I think ARF and ARK) are made by Erricson. A scary thought for you. ALL calls made on AXE and S12 and probably recent ARE exchanges have the numbers logged and stored for later reference if needed!!! (Figure that out!!)
PABX/PBX: Private (automatic) branch exchange. A small exchange that is run by a business. Will cover these in detail in the future.
This was meant to be an INTRODUCTION to telephone exchanges and by no means a comprehensive guide. The best places to find more info is from the following places: (There are probably other places to go as well!!)
The Internet (FTP, USENET, WWW etc.)
The Fidonet echo: Aust. Telecommunications
Telescum (Social Engineering, Public relations etc.)
Text files & zines and like this one.
Library, Bookstores etc.
Go trashing!!
I hope this file has taught you a thing of two. Look out for more advanced and more comprehensive articles in future.
mE!
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