The fair distributed queue (FDQ) protocol for high-speed metropolitan-area networks

Abstract

A new protocol, fair distributed queue (FDQ), suitable for very high-speed metropolitan-area networks (MANs), is presented. FDQ is a slotted system implemented on a unidirectional fiber bus. It has similarities to distributed queue dual bus (DQDB), the IEEE 802.6 Standard for MANs, including the bus topology and same nodal hardware. Like DQDB, FDQ achieves full throughput efficiency independent of the bus length, the transmission speed, and the number of nodes. Unlike DQDB, FDQ allocates equal bandwidth under heavy load to all active users in a time period less than or equal to the round-trip propagation delay without wasting bandwidth. Its delay characteristics are studied via simulation and compared to DQDB. FDQ has lower average delays under Poisson load than DQDB with or without the bandwidth balancing (BWB) mechanism. Two distinct implementations of priority levels are given and their characteristics are discussed. It is shown that FDQ's delay and throughput characteristics are little affected with increasing distances or transmission rates. Thus, FDQ possesses excellent scalability properties which allow its total length to extend over 100 km and transmission rate well above 1 Gb/s.