Message Switching Centres
Torn Tape Message Centre
This describes the functioning of a torn tape teleprinter message switching centre like those used by the ROC prior to their communications upgrade in the mid 1980's. Their use was widespread beyond the ROC, as a child I recall a conducted tour at the USAF base at Croughton, Oxon. (possibly 1967) Being shown the tape centre and the new 80-hole punch card system that had just been installed. They gave us a punched card that I kept for many years saying something like 'Welcome to RAF Croughton from the officers and servicemen of Autodin.'
In the case of the ROC each group HQ had its own message centre. Each was connected to a small number of adjacent centres. The links normally worked over the landline but could be switched to an alternative radio link and would send messages in either direction. Each link had a paper tape reader connected to the 'send' and a paper tape perforator connected to the 'receive'. There were local teleprinters connected to tape reader and perforator.
Sending a Message
A typist would prepare a message by typing on a teleprinter and producing a paper tape as well a a local printed copy. The message would start with a header indicating the destination(s) of the message, the message itself and a run out of blank tape. This was torn from the perforator and carried to the tape reader on the link to the desired recipient.
The tape was placed in the reader and the start button pressed. The teleprinter signals would be sent to the distant end, if that were a teleprinter the message would be printed on the paper roll. If it were another message centre, the signals would cause the associated tape perforator to reproduce the sent message tape. If the message was a broadcast it would be transferred to the next reader and sent again to that destination.
Receiving a message
An incoming message would be perforated onto paper tape and a lamp illuminated to indicate the arrival of the message. The operator would tear the tape from the punch and visually inspect the header. The tape would be transferred to a reader associated with a local teleprinter. This would print the message on a paper roll. The paper was torn from the machine and placed in the out-tray to be taken to the recipient.
Indirect and through messages
If the originating message was destined for recipient at a location without a direct link, or the direct link was faulty or destroyed by enemy action the tape would be sent to another message centre. On receipt the operator would inspect the header and see that it was not for their centre. If the message was for a destination which centre had a working direct link. The tape would be placed on the reader of that link and sent. Otherwise it would be sent to another centre with a possible link. The choice of alternative centres is known as the 'routing'.
Perforated Teleprinter Paper Tape
Flexibility and Economy
A torn tape message centre was a way to achieve full message interconnection throughout the ROC without having to connect every group to one another. With 25 group HQ's in the UK, a fully interconnected system would have needed 293 links. Many of these may never have carried a message. The system is very flexible as the operators can use their intelligence to work around a fault.
Communications Modernisation in the mid 1980's
Within the ROC the old torn tape centres were replaced with data switches. These were computer controlled but still had to have 'Routing' tables set up to configure the system to route messages around available links. I have seen link maps of the Regional Government HQ's network from this era on display at Hack Green and Kelvedon Museums.