[GreenKeys] TWX Services

[Jim Haynes]

TWX used manual switchboards until about 1959 when Dial TWX went into
operation.  Telex in Europe (and introduced into the U.S. by Western
Union) was dial up.  My belief is that this had to do with customer
expectations for billing.  In the U.S. long distance phone calls and
TWX calls generated bills showing the date and time of day, the number
called, the location of that number, and the duration of the call and
how much was charged for it.  Switchboard operators used the Calculagraph
clock to measure the time duration of calls.  This was printed on toll
tickets, which then were manually processed by the people who handled
billing.

Telex in Europe and perhaps long distance telephony there too used a
simpler method.  When a call was connected a counter associated with the
caller's line was connected to a pulse generator.  The pulse rate
depended somewhat on the distance called.  The customer bill showed
just the number of pulses that had been accumulated during the billing
period.  This was all easily done by standard telephone switching
equipment.

The Bell System started what was once called fully automatic customer
dialing about 1949.  Where it was available the caller could dial his
own long distance calls.  Equipment would record the calling and called
numbers and the starting and stopping time of the calls on punched paper
tape.  Then a data processing machine built of relays could read the
tapes and sort the data into individual call records that could be handled
just like switchboard operators' toll tickets.  It took until about 1959
for the entire Bell System and the independent companies to get 
substantially all customer telephones' toll charging working this way.

Now manual TWX had used a variety of transmission mechanisms.  Narrow
bandwidth telegraph circuits in places, voice frequecy carrier channels
over voice-grade circuits, concentrators that shared a number of
circuits among a larger number of customers.  With customer dialing
of toll calls in place the company decided the voice switched network
could also be used for TWX and other switched data services.  And
customers were also doing it themselves by using acoustic-coupler
modems with voice telephones.

TWX remained a data-only service, but TWX machines had to have an earphone
or a speaker so the callers could hear dial tone and other tones and voice
announcements.  DataPhone had the assumption that callers and callees
would converse by voice before switching to data transmission, so its
terminals included telephones.  Other services were proposed but not
implemented.

In that connection, the low-speed TWX and DataPhone modems were full
duplex and FSK. So there were two different frequency pairs that could
be chosen for the calling station to transmit on.  And for each of those
there was an option whether the higher or lower tone would be mark or
space.  Thus by strapping options in the modem there were eight different
mutually incompatible combinations that could be used for different 
services and charged for at different rates, should the company and the
FCC agree that they were needed..

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 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man