Hardware Reference
In-Depth Information
connected to the next and the last workstation is connected to the first again (essentially a bus
topology with the two ends connected). Two major network types use the ring topology:
•
Fiber Distributed Data Interface (FDDI)
—A network topology used for large, high-speed
networks using fiber-optic cables in a physical ring topology
•
Token-Ring
—Uses a logical ring topology
A Token-Ring network resembles a 10BASE-T or 10/100/1000 Ethernet network at first glance
because both networks use a central connecting device and a physical star topology. Where is the
“ring” in Token-Ring?
The ring exists only within the device that connects the computers, which is called a
multistation
access unit (MSAU)
on a Token-Ring network (see
Figure 17.15
)
.
Figure 17.15. A Token-Ring network during the sending of data from one computer to another.
Signals generated from one computer travel to the MSAU, are sent out to the next computer, and then
go back to the MSAU again. The data is then passed to each system in turn until it arrives back at the
computer that originated it, where it is removed from the network. Therefore, although the physical
wiring topology is a star, the data path is theoretically a ring. This is called a
logical ring
.
A logical ring that Token-Ring networks use is preferable to a physical ring network topology
because it affords a greater degree of fault tolerance. As on a bus network, a cable break anywhere in
a physical ring network topology, such as FDDI, affects the entire network. FDDI networks use two
physical rings to provide a backup in case one ring fails. By contrast, on a Token-Ring network, the
MSAU can effectively remove a malfunctioning computer from the logical ring, enabling the rest of
the network to function normally.
Star Topology
By far the most popular type of topology in use today has separate cables to connect each computer to
a central wiring nexus, often called a
switch
or
hub
.
Figure 17.16
shows this arrangement, which is
called a
star topology
.
