fibre channel arbitrated loop (FC-AL)
Fibre Channel Arbitrated Loop(FC- AL) is the most commonly used Fibre Channel (FC) topology. With this FC topology, the L_Ports of servers and storage are interconnected via hubs to form a redundant double ring. With this topology, up to 126 devices can be connected at 100 MB/sstorage band width, but they must share the bandwidth among themselves.
The number of devices connected to an arbitrated loop is related to the limited addressing option of 8 bits in the FC-AL protocol. FC-AL does not use a token in the ring topology and does not impose a time limit on the devices for loop control.
Here, the access algorithm controls multiple switching of a device according to an optimal fairness principle before all other devices have been given the opportunity to transmit. To prevent defective nodes from causing the failure of the entire arbitrated loop, bypass functions(portbypass circuits, PBC) can be activated in the devices. The arbitrated loop has limitations in terms of addressing, data security and availability.