TABLE OF CONTENTS The original Fibre Channel architecture had only the Point-to-Point and switched network (i.e., Fabric) topologies defined. However, both of these topologies have significant disadvantages for a number of communications applications. The Point-to-point topology guarantees maximum bandwidth availability and freedom from collision or congestion, but it is usually a relatively inefficient usage of hardware, since very few systems or applications can effectively use a 100 MBps link for any reasonable fraction of the time, and because the number of required links grows very quickly (N**2) versus the number of attached ports. The Fabric topology provides the connectivity and link bandwidth utilization flexibility, but can be a quite expensive topology, since the switches are complex components that will be sold in relatively low volumes. The Arbitrated Loop provides a compromise between these two architectures, with many advantages of both.
In the Arbitrated Loop topology, the outgoing and incoming fibers to a Port are split off to attach to different remote Ports, such that the aggregation of fibers forms a unidirectional Loop which passes through every Port exactly once. The general picture of traffic generation on this topology is that (1) a single Port arbitrates for usage of the entire Loop, (2) once it obtains Loop access, it opens up communications with another Port on the Loop, and then (3) transmits normal Fibre Channel traffic at the full guaranteed link bandwidth as if they were attached point-to-point until it is done, when it (4) releases the Loop for usage by another...
