Fibre Channel Primer

Chapter 6: Topologies

Figure 6.8 Powerful, redundant 100 MBps loops connect multiple servers

with Fibre Channel storage

the two N_Ports have 100% utilization of the bandwidth. The

communication is full-duplex; therefore, a one-gigabit transmit and

receive link is delivering two Gbps of dedicated bandwidth.

LOOP SHARED-BANDWIDTH TOPOLOGY

Fibre Channel loop provides a low-cost solution for allowing multiple

devices to share gigabit bandwidth. Nodes share access to the loop

but have full use of the gigabit bandwidth when making logical point-

to-point connections. Up to 127 nodes may be in a loop. Only one of

these nodes may be a switch port. Loops are used for networks and

are the replacement for SCSI as the next standard disk interface.

Nodes request control of the loop by sending a Fibre Channel

signal called a primitive. If the signal is returned with the sending

node’s address, that node or switch port has control of the loop. If

two or more nodes or the switch port are contending for control at the

same time, loop control is given to the lowest address. After a node

or switch port has control, it opens a full-duplex, point-to-point circuit

Fibre Channel disk system

Hub

Port Bypass

Circuit

Hub

Servers