Abstract: A Synchronous Multiport Digital Communications Network (SMDCN) including a HEAD end Unit (HEADU) and SUBscriber Units (SUBU) providing a large number of simultaneous isolated two-way dial-up digital communications channels between a common head end facility and a large number of subscriber facilities over a broadband transmission medium such as coaxial cable or optical fiber arranged in a bus or tree topology, such as a local area network (LAN) or a cable television (CATV) network. The basic digital channel provided is a 64,000 bit per second data stream, the current standard of the digital telephone industry's T1 technology, and therefore readily accommodates voice telephone services. However, the network expressly accommodates higher bit rates up to 1.544 MB/s by combining basic channels.