Design and Use of an Integrated Cambridge Ring

The Cambridge ring is a local area network used both in universities and industry. It is based on the empty slot principle and data are transmitted using minipackets containing two bytes of data. This paper describes the design process, decisions, and tradeoffs in implementing an integrated system which incorporates both analog and digital components. The technology chosen is a bipolar gate array. A number of options are provided for the implementor who can optimize network parameters such as minipacket size and transmission speed to his needs. He can also choose the style of interface between the communicating device and the network. An important option provided by the integrated Cambridge ring is the ability to simultaneously transmit short control minipackets and long data packets. A system exploiting this feature has been built and is described. Its proposed uses are to interconnect telephones and other real-time systems as well as computers where the partitioning of bandwidth and precise performance specification are important.