THE FAIR DISTRIBUTED QUEUE (FDQ) PROTOCOL FOR HIGH-SPEED METROPOLITAN-AREA NETWORKS

A new protocol, fair distributed queue (FDQ), suitable for very high-s peed metropolitan-area networks (MAN's), is presented, FDQ is a slotte d system implemented on a unidirectional fiber bus. It has similaritie s to distributed queue dual bus (DQDB), the IEEE 802.6 Standard for MA N's, including the bus topology and same nodal hardware. Like DQDB, FD Q achieves full throughput efficiency independent of the bus length, t he transmission speed, and the number of nodes. Unlike DQDB, FDQ alloc ates equal bandwidth under heavy load to all active users in a time pe riod less than or equal to the round-trip propagation delay without wa sting 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 chara cteristics are discussed. It is shown that FDQ's delay and throughput characteristics are little affected with increasing distances or trans mission rates. Thus, FDQ possesses excellent scalability properties wh ich allow its total length to extend over 100 km and transmission rate well above 1 Gb/s.