Index Thing

Index

Telephony Stuff



Telephony was my world

How the world changes -


When I started in a job as a trainee telephony technician in 1973 little did I know the sweeping changes of technology that awaited.


The stuff ::::::


Plessey/GTE Step x Step MAX (Main Automatic eXchange)

- along with travelling run of UAX's (Unit Automatic eXchange) and PMBX's (Private Manual Board Exchange)


NEC Crossbar ZCX and HTX (Zone Centre and Hybrid Tandem eXchanges)


Western Electric Rotary 7A and 7A1 Exchange (with 7A2 registers)


Varying types of Transmission gear (PCM, etc)


PABX (Private Automatic Branch Exchange)

- Electromechanical

Pentomat Crossbar

SxS 100 type

SxS 300 type


- Electronic

Mitel SX/Super10, SX20

Mitel SX2000

GEC Maxinet/Monarch

STC 4022/4022X


- IP based

Cisco CallManager and data stuff


Nortel SWRS/SWCP product (Symposium Web Response Server/Symposium Web Centre Portal)


All in all the technology spread across three centuries - I actually saw patent marks on relays in the 7A Rotary exchange dated as 1898 although the exchange was installed in 1925. I started replacing ribbons in calculagraphs on manual boards (used for timestamping call durations) and ended up ploughing through Cisco IOS and Windows apps.


I was most impressed with the 7A rotary equipment which I found to be of good quality design compared to say the Step x Step stuff which was made for a price.

The big weakness of 2000 type SxS was that the selectors would pick to a dis(connect) as it was known in the trade whereas the rotary picked to a battery. Needless to say picking to a dis is not good on dirty contacts or dry joint circuits.


7A rotary was easily worked on compared with the 7A1 because the driving gears were easily disengaged and brush carriages were easily dismantled. Having said that it was easy to "get into the job" - just before finishing one night the pocket of my dustcoat was grabbed by a gear and I was being sucked into the machinery until I managed to disengage the shaft (Occupational Safety and Health is a relatively modern idea I think).


For me a major change in the industry was the fact that the older equipment was maintained by generations of technicians/engineers whereas the newer equipment changes regularly during one generation so whilst interesting the pace is definitely a lot hotter these days.



Rough Glossary of Terms :::::

What is a "boomatang"?

You may well ask but for us in the trade it was the term for a dental probe used for all sorts of occasions in telephony (these were obtained from dentists stockpiles of broken tools and could be all sorts of shapes).


What is a "pick and drop"?

Generally used in SxS when wiper cords were broken and the selector would pick to the bank then immediately drop off the bank - these faulty switches could be heard by trained ears in the switchroom.


What is a "dry joint"?

Cannabis not soaked in water - no not really - it is a wired joint where there is insufficient or no solder to hold the wire so the electrical circuit can be intermittently or permanently incomplete.


What is a "butt test"?

Well, first you get a rubber glove .....  Actually it refers to the routine test that used to be done by technicians on 2000 type selectors to find pick and drops. A butt refers to the Buttinski Test Handset used by techs for making/monitoring calls across the exchange equipment.


What is a "crash in"?

Happened a bit on 2000 type SxS systems with dirty selector wipers and out of adjustment relay timing causing two calls to be connected together.


What is a "punchdown tool"?

Used to connect wires to solderless contacts.


What is a "routiner"?

A test rack that does routine tests on 2000 type SxS exchange equipment to check relay timing functions, etc are within spec - a pig to fix if it ever broke down.


What is "dope"?

Given some of the terms for things a person could be forgiven the thought that telephone exchanges were staffed by a bunch of drug addicts ....   In this case dope was a special liquid used on the driving surfaces of the 7A selectors. It should be understood that the rows/bays of switching components (Linefinders, Group/Final selectors) were all gear shaft driven and in the case of 7A the individual switch carriage assemblies were friction driven. When new the friction driving wheels had rough surfaces but with age they became smooth and the carriages would slip rather than drive. Dope was used to provide a rough sticky surface on the wheels to provide sufficient friction but this needed to be replenished on a regular basis. New parts if available could be fitted but this was far more expensive than bottles of dope.


What are the EI's?

These were the Engineering Instructions which were living documents that contained all the procedures/processes for installing/maintaining telephone equipment. The most useful section I ever encountered was one on Nickel-Cadmium cells and the memory effect when charging which was info that was popularly recognised in the wider world only years later.


What is a "Kamakuza"?

In our world this became the nickname for the STC 4022/X electronic PBX. When introduced this unit was a lemon with a huge number of defects and operational problems. Although it took a bit of time all credit to STC/Alcatel who spent a lot of effort on debugging/re-engineering the PBX's and they eventually became the most reliable units around.


What is "Carrier Experience"?

Usually referred to experience with transmission/carrier equipment used between exchanges but often taken to be the carrying of boxes/loads around and about the place.


What is a "long weight"?

The old toll boards used weights to retract the cords after use however this particular term was used when sending a trainee to the store for a .... long wait!!!

The storeman having heard the request for a long wait would immediately proceed to get the required article off the shelf and return at some stage convenient to himself ... (if there was a back door he would go and grab a cuppa)


Ah yes the poor trainees, sent off also for a tin of magnetic flux. Particularly tricky since flux was actually used in association with soldering but of course wasn't the magnetic variety.


What is a "bongo"?

Apart from a type of drum this term came to be associated with a particular type of Mazda van (F1000) that we used on the PABX rounds. The name I believe came from the manufacturer of the heater in the vehicle and later models of Mazda vans were actually badged with the Bongo name. Many laughs were had with the front air vent that could be slammed loudly shut with the foot - particularly effective when pulling up behind another car at the lights!


Scariest moment?

Probably trying to synchronise two diesel generator sets when one of them starts drifting out of synch (the said diesel moved considerably on the mounting cradle when this happened - this was pants filling stuff when the result could have been a flywheel sent careening through the wall and through a couple of restaurants as well...  The power of electromagnetism and back EMF is indelibly etched on the mind!


Most pleasing moment?

Being able to point to a computer chip or router box and say to somebody - "I used to work in one of those!"


Biggest regret?

Probably not keeping some circuit drawings of the gear (especially the rotary) - they were really quite neat.


Most tedious task?

The battery room of an exchange was usually fairly high on the list especially when the spray plates on the top of the secondary cells needed washing.


This could be matched by drive doping duties in the 7A rotary exchange.

 

What is "ESD?"

It means Electro Static Discharge and can affect electronic devices in various ways. Earlier electronic PBX's used components that were highly susceptible to static discharges and required arcane earthing arrangements for self-protection. Just walking across a carpet (usually a synthetic type) and then touching the phone system was enough to "blow" it up.

This was a particular problem with a type of console that used touch sensitive keys (using capacitive technology) and required more than a few discussions with management about secretaries wearing nylon knickers!

 

 

 

Types :::::

 

Switchboard (Manual):

The original type of system using common control switching intelligence - in this case a human being. The switch fabric used cords under control of the human.

 

 

Step x Step (electro-mechanical):

Otherwise known as Strowger, pre-2000, 2000 type.

A simple step x step intelligence control system.

 

The originating phone would go off hook and the switching train would be set up in a step x step fashion to the destination using the number for routing.

 

Origin Phone

Uniselector (one to many switch - finds free 1st G/S)

1st Group selector (1st local digit)

2nd Group selector (2nd local digit)

3rd Group selector (also penultimate - 3rd local digit)

Final selector (last 2 local digits)

Dest phone

 

 

Rotary (electro-mechanical):

Used a common control system for call control. The switch train was similar to step x step in using group/final selectors but the number was sent to a Register which then controlled the setting up of the switch train. The Uniselector replaced by a Linefinder (many to one switch). The Register would be released once the call had been setup.

 

Crossbar (electro-mechanical):

Used a common control system for call control and the switch train was replaced by a switch matrix with vertical and horizontal bars. The horizontal bar held the flexible fingers that were moved into position for the contacts and the vertical bar would cause the finger to operate the contact.

The number was sent to a Register and the call control was handled by a Marker/Translator unit.

 

Electronic PBX (analog electronic):

Similar to Crossbar but the control done by microprocessors and the switch fabric used analog crosspoint chips.

 

Electronic PBX (digital electronic):

The switch fabric changed to using digital crosspoint chips switching PCM (Pulse Code Modulation) streams.

 

Up to this point with all these systems there were two distinct parts of the whole network. Part one was the exchange/central office which handled the routing/setup of the calls and part two was the carrier/transmission network between the exchanges. Originally part two was all copper cable using analog transmission gear then PCM based gear. The distinction between Transmission and exchange faded with the electronic units but the overall network was largely a voice orientated one (Data was switched but on separate exchanges and was changing to the TCP/IP methodology).

 

The big change in the voice world arrived with the use of VOIP (Voice Over IP) gear. The switch fabric used Routers/Switches, etc. The number is received by the originating interface/controller and then transported over the routed network.