[GreenKeys] Early Dial TWX Teletype machines and their network...

[Don Robert House]

The 101A,B, and C datasets were full of wire spring relays.
Miles of green wire.  Nothing in them more advanced than simple  
transistors.
These early modems were expected to perform quite a few functions.
Designed over special channels through a complex network,
  they needed to connect with machines running at different speeds  
through
8 level ASCII to 5 level ITA2 and vice versa.

These units were added over a two year period to the previous private  
line
machines and each station was cut over to the dial TWX network on  
8/31/1962

The entire USA and Canada shared two teletypewriter area codes 910 and  
710
respectively... the switches, facilities and convertors were dedicated.

An example is a 33ASR sending to a Model 19ASR over the network.
A restraint signal was sent by the convertor to hold the tape  
transmission
until the 19 could catch up.  The other way around was interesting  
also to
watch the 33 start stop and start again.

You did not want to be on duty at one of the convertor offices during  
the
Christmas and New year holidays as the convertors would load up with
artwork. Another problem was billing as the offices recorded the time of
the call and the location on punched tape with a BRPE punch.

Late in the market came the 105 dataset with a more modern design. Less
wire and less relays.  However by this time a judge decided Bell had  
to give
Western Union the entire network, machines and all.  By the time WUTCo
had everything worked out the market started to disappear.

Memories,
Don
K9TTY