A new topology for MANs: the pretzel ring

The authors propose an efficient, fair, and simple capacity-1 protocol that outperforms both fiber distributed data interface (FDDI) and distributed queue dual bus (DQDB). In the recent years, two network protocols gained predominance in very fast local and in metropolitan area networks: FDDI (using a single or dual ring) and DQDB (using a dual bus). The authors propose a network topology that is very similar to the dual ring of FDDI and a token-passing protocol suitable for this topology. Their solution yields a true capacity-1 network with zero access delay under light load. Moreover, it naturally accommodates synchronous traffic and is absolutely fair. The proposed protocol has a much better performance than FDDI; it also outperforms DQDB for sufficiently fast (or long) networks.