Fibre Channel Primer

Chapter 6: Topologies

Fibre Channel storage enclosures have a loop built into the

backplane. Each backplane node also has a PBC just like those used

in hubs. Disks can be hot swapped in and out of the loop. This hot-

swap feature is the foundation for Fibre Channel’s 7 x 24 on-line

storage management capabilities.

SWITCHED SCALED-BANDWIDTH TOPOLOGY

Fibre Channel switches are extremely easy to install and use because

the Fibre Channel protocol provides self-configuration and self-

management. When a Fibre Channel switch or node powers on, it

determines what is on the other end of the cable and figures out how

to work with it. If it is node-to-node, they automatically operate point-

to-point. If it is switch-to-node, the node logs in with the switch and

exchanges interoperability parameters. If it is switch-to-switch, the

automatic, without operator intervention.

F_Port

FL_Port

N_Port

NL_Port

E_Ports

Figure 6.10 Switch ports are automatically configured

As shown in Figure 6.10, ports on a switch are either F_Ports /

FL_Ports or E_Ports (expansion ports used to interconnect switch

chassis). Switch ports connect to N_Ports, NL_Ports, or other

switches. If a port is both an F_Port and an E_Port, it is called a

G_Port (generic). Most switches come with G_Ports that

automatically determine the correct use of either F_Port or an E_Port

functionality during initialization and operate accordingly.

Fibre Channel switches that offer connection and connectionless

switching actually are two separate switches in one. As shown in

Figure 6.11, Class 1 and 6 services are provided with the circuit switch

and Class 2, 3, and 4 services are provided using the frame switch.

This unique Fibre Channel feature lets applications take advantage

of the best features of both switching technologies. Using both a circuit