Marketing surveys on data communication have indicated the possible need for a new data service. Technical studies have resulted in a number of detailed proposals for providing a service which, although functionally distinct, is physically integrated with other telecommunications services. The proposed network utilizes synchronous digital transmission with a processor-controlled TDM switching structure. A range of speeds is available. Users' data bytes are structured in "envelopes" to provide an inband control signaling facility. The use of a processor for switch control gives greater flexibility, allows the implementation of sophisticated diagnostics, and, with high-speed interswitch signaling, reduces overall call set-up times. The proposed network is hybrid in that it can operate in a conventional circuit switched mode, or operate in a "packet" switched mode. Extensive multiplexing is used to increase transmission utilization and reduce local area transmission costs.