Distributed fairness algorithms for local area networks with concurrent transmissions

Abstract

In this work, it is shown how multiple nodes can access a ring network concurrently with spatial reuse and in a fair manner. Traditionally, most ring and bus networks do not allow spatial reuse, e.g., FDDI, DQDB (IEEE 802.6). Concurrent access with spatial reuse enables the simultaneous transmissions over disjoint segments of a bidirectional ring, and therefore, can significantly increase the effective throughput, by a factor of four or more.

Spatial reuse can be easily implemented using a full-duplex buffer insertion or slotted techniques. However, these techniques may also cause starvation and thus have an inherent fairness problem. Two types of fairness algorithms are presented, global and local; both are shown to be stable and fault tolerant. The global fairness mechanism provides a complete fairness and is immune to control messages loss or duplication. This global algorithm views the whole ring as a single resource, while the local fairness algorithm views the ring as multiple disjoint resources. The local fairness mechanism is triggered only if potential starvation exists and is usually restricted only to segments of interfering nodes. If the segment of the interfering nodes covers the whole ring, we show that the local mechanism is equivalent to the global one.

The combination of a full-duplex buffer insertion ring, spatial reuse, reliable fairness mechanism and the exploitation of the recent advent in fiber-optic technology are the basis for the Metaring network architecture. This network is currently being prototyped at the IBM T.J. Watson Research Center.