Fibre Channel SAN Topologies
Arbitrated Loop
The Arbitrated Loop Topology
•FC_AL
– Fibre Channel Arbitrated Loop protocol
• Shared bandwidth:
– Only one pair of devices
can talk at a time
• Limit of 127 addresses:
– 126 NL_Ports
– One address reserved
for fabric attachment
(FL_Port)
Fibre Channel Arbitrated Loop (FC-AL) topology:
Physical devices are connected to the hub in a star topology
Data moves in a loop
Limits throughput and limits the scalability of the SAN:
Adding more devices increases the physical length of the loop
FC-AL protocol supports limited management features
Fibre Channel hubs are less expensive than switches (just like Ethernet)
Hub topologies are most appropriate for:
The “edges” of a larger distributed network
Fibre Channel Arbitrated Loop (FC_AL) was introduced as a
replacement for parallel SCSI.
FC_AL supports more devices (126) than wide SCSI (16)
FC_AL supports full duplex operation, SCSI is half duplex
FC_AL supports greater shared bandwidth between devices
- 2 x 400MB/s (4 Gb/s Full Duplex)