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The article focuses on developments related to data transmission systems in Great Britain. British communications services are intended to remain under the firm control of GPO, the Great Britain Post Office. GPO control of data transmission has raised the fear that a nationwide network will not materialize if data transmission services continue to be provided at the present slow rate. Underlying much of the GPO's need for gradualism is the limited capacity of the national telephone network. This network, which is used by at least two thirds of installed terminals, was originally designed to accommodate vocal messages averaging three minutes in length. This time period has served as a standard in determining future investments in equipment. However, the average duration of a single computer/teletype interexchange is 25 minutes. Thus, the operation of a single computer linked to 80 terminals going through the same switchboard would be the equivalent of 600 to 700 voice communications. The British telephone network's capabilities are being increased to serve the expansion of data traffic.