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Abstract

A learning half bridge and bridge for a Fibre Channel Arbitrated Loop and switching protocol. A half bridge can be coupled to a local loop segment and a remote loop segment. The half bridge includes transmit and receive ports implementing predetermined switching and conflict resolution rules and a memory storing a forwarding table. Typically the switching rules are implemented using state machines. The state machines implement a switching protocol that controls transitions between states which control switching connections, writing of data to memory and reading of data from memory and preemption of conflicting OPN primitives. Each half bridge includes a local return segment that can be switched by the state machines to bypass the remote loop segment if both the source node and destination node are on the local loop segment so as to make the local loop segment a complete Fibre Channel Arbitrated Loop. Each half bridge learns the locations of nodes by watching the direction of flow, the loop segment from which certain primitives arrived and sequence of OPN, RRDY and CLS primitives propagating on the loop segments and records data in the forwarding table in memory reflecting the locations of nodes about which conclusions have been drawn in accordance with learning rules. A learning bridge is comprised of two half bridges having their remote loop segments cross coupled. Full bridges can be combined with accelerated or nonaccelerated hubs. Conflicting OPNs are preempted using a highest priority address rule.

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