Q-Logic 59021-05 manual Common Topologies, Cascade Topology, 1. Cascade-with-a-Loop Topology

￿	3 – Planning
	Multiple Chassis Fabrics

3.2.2

Common Topologies

This section describes three commonly used topologies:

■Cascade

■Mesh

■Multistage®

3.2.2.1

Cascade Topology

A cascade topology describes a fabric in which the switches are connected in a linear fashion. If you connect the last switch back to the first switch, you create a cascade-with-a-loop topology as shown in Figure 3-1. The loop reduces latency because any switch can route traffic in the shortest direction to any switch in the loop. The loop also provides failover should a switch fail.

The cascade fabric shown in Figure 3-1has the following characteristics:

■Each chassis link contributes up to 200 MB/s of bandwidth between chassis, 400 MB/s in full duplex. However, because of the sequential structure, that bandwidth will be shared by traffic between devices on other chassis.

■Latency between any two ports is no more than three chassis hops.

■48 Fibre Channel ports are available for devices.

Figure 3-1. Cascade-with-a-Loop Topology

59021-05 A 3-3