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The physical connection between devices varies from one topology to another.
In all of these topologies, a transmitter node in one device sends information to
a receiver node in another device.
Fibre Channel networks can use any combi-
nation of point-to-point, arbitrated loop(FC_AL), and switched fabric topologies
to provide a variety of device sharing options.
Point-to-point
A point-to-point topology consists of two and only two devices connected by N-
ports of which are connected directly. In this topology, the transmit Fibre of
one device connects to the receiver Fibre of the other device and vice versa.
The connection is not shared with any other devices. Simplicity and use of
the full data transfer rate make this Point-to-point topology an ideal extension
to the standard SCSI bus interface.
The point-to-point topology extends SCSI
connectivity from a server to a peripheral device over longer
distances.
Arbitrated Loop
The arbitrated loop (FC-AL) topology provides a relatively simple method of
connecting and sharing resources. This topology allows up to 126 devices or
nodes in a single, continuous loop or ring. The loop is constructed by daisy-
chaining the transmit and receive cables from one device to the next or by
using a hub or switch to create a virtual loop. The loop can be self-contained
or incorporated as an element in a larger network. Increasing the number of
devices on the loop can reduce the overall performance of the loop because
the amount of time each device can use the loop is reduced. The ports in an
arbitrated loop are referred as L-Ports.
Switched Fabric
A switched fabric a term is used in a Fibre channel to describe the generic
switching or routing structure that delivers a frame to a destination based on
the destination address in the frame header. It can be used to connect up to
16 million nodes, each of which is identified by a unique, world-wide name.
In a switched fabric, each data frame is transferred over a virtual point-to-
point connection. There can be any number of full-bandwidth transfers occur-
ring through the switch. Devices do not have to arbitrate for control of the
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Introduction
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