Z-NET: a dual bus fiber-optic LAN using active and passive switchers

Z-NET, a high-speed local area network scheme using a dual unidirectional bus architecture and an optical-fiber transmission medium, is introduced. At very light loads, the protocol behavior is similar to a random-access scheme with zero packet delay. As load increases, the operation is similar to an implicit token-passing scheme and ensures fair round-robin scheduling among stations. The protocol is completely distributed, with no station performing any special function. When collisions occur, one station always continues its transmission to completion. Thus, the wastage of bandwidth caused by collisions is minimized. This is achieved using active and passive switches on the buses. Delay performance of Z-NET is superior to Expressnet. Fasnet and tokenless protocols at very light loads. At heavy load, performance is similar to that of Expressnet, with bounded packet delay. No special mechanisms are used to start new rounds or for transition between random and controlled access modes of transmission. Thus, the proposed scheme has the added advantage of simplicity