• In FC-AL devices must arbitrate to gain control and connected via hubs. Using a hub, multiple servers can access multiple storage devices.

• When a node in the FC-AL topology attempts to transmit data, the node sends an arbitration (ARB) frame to each node on the loop. If two nodes simultaneously attempt to gain control of the loop, the node with the highest priority is allowed to Communicate with another node. This priority is determined on the basis of Arbitrated Loop Physical Address (AL-PA) and Loop ID.

• When the initiator node receives the ARB request it sent, it gains control of the loop. The initiator then transmits data to the node with which it has established a virtual connection. See the figure below.

Node A want to communicate with Node B

1. High priority initiator, Node A inserts the ARB frame in the loop.
2. ARB frame is passed to the next node (Node D) in the loop.
3. Node D receives high priority ARB, therefore remains idle.
4. ARB is forwarded to next node (Node C) in the loop.
5. Node C receives high priority ARB, therefore remains idle.
6. ARB is forwarded to next node (Node B) in the loop.
7. Node B receives high priority ARB, therefore remains idle and
8. ARB is forwarded to next node (Node A) in the loop.

9. Node A receives ARB back; now it gains control of the loop &can start communicating with target Node B.

   

FC-SW Communication

• FC-SW has dedicated bandwidth between devices, support up to 15 million devices and higher availability than hubs.

• FC-SW uses switches that are intelligent devices.

• It involves a switching device (fabric) which interconnect two or more nodes. Frames are routed between the source and destination node by the switching device.

• They can switch data trafficfrom an initiator node to a target node directly through switch ports. Framesare routed between source and destination by the fabric.

• As shown in Figure below, if node B wants to communicate with node D, Nodes should individually login first and then transmit data via the FC-SW. This link is considered a dedicated connection between the initiator and the target.