The design and implementation of a terminal concentrator for the Strathnet local area network is described. Strathnet is an Ethernet-style local network in which all devices are connected to the network coaxial cable by means of microprocessor-based access units. The network protocols (in both hardware and software) are implemented in a layered fashion along the lines of the International Standards Organization open systems interconnection reference model. The terminal concentrator is an access unit with up to seven ports for terminal connection, a Strathnet port implementing carrier sense multiple access with collision detection hardware and all the necessary software layers. Although the lowest layers are dependent upon the Ethernet-style hardware, the intermediate software implements the basic block and byte stream protocols more commonly found in Cambridge ring networks, and the concentrator software at the highest level provides the user with a Unix-like interface. A major aim has been to implement Cambridge ring software protocols over Strathnet hardware.