Distributed-queue dual-bus
In
IEEE 802.6 is an example of a network providing DQDB access methods.
Concept of operation
The DQDB medium access control (MAC) algorithm is generally credited to Robert Newman who developed this algorithm in his PhD thesis in the 1980s at the University of Western Australia. To appreciate the innovative value of the DQDB MAC algorithm, it must be seen against the background of LAN protocols at that time, which were based on broadcast (such as IEEE 802.3 Ethernet) or a ring (like IEEE 802.5 Token Ring and FDDI). The DQDB may be thought of as two token rings, one carrying data in each direction around the ring. This improves reliability which is important in Metropolitan Area Networks (MAN), where repairs may take longer than in a LAN and Wi-Fi because the damage may be inaccessible.
The DQDB standard IEEE 802.6 was developed while
Currently DQDB systems are being installed by many carriers [who?] in entire cities, with lengths that reach up to 160 km (99 mi) with speeds of a DS3 line (44.736 Mbit/s). Other implementations use optical fiber for a length of up to 100 km and speeds around 150 Mbit/s.
References
This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22.