Media access protocols for Gb/s LANs with spatial reuse, fairness, and isochronous service

Abstract

The authors describe the design principles of a ring-based LAN (local area network) with spatial bandwidth reuse and support of isochronous channels. The network uses buffer insertion which, in contrast to token passing principles, allows concurrent media access. Spatial reuse and concurrent access allow simultaneous packet transmissions over disjoint segments of the ring. As a result, the potential aggregate throughput of a dual ring can be 8 times the data rate of a single link. Buffer insertion coupled with spatial bandwidth reuse can cause unfairness. The author describes two algorithms to eliminate this deficiency: (i) a flow-based fairness algorithm and (ii) a reservation-based fairness algorithm. Conventional buffer insertion introduces variable amounts of delay and is therefore not directly suitable for isochronous traffic. A novel method to combine asynchronous (packet-oriented) and isochronous traffic on the same buffer insertion ring is outlined.