Hardware Reference
In-Depth Information
network. Therefore, although the physical wiring topology is a star, the data path is theor-
etically a ring. This is called a logical ring .
A logical ring that Token-Ring networks use is preferable to a physical ring network to-
pology 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 net-
work.FDDInetworksusetwophysicalringstoprovideabackupincaseoneringfails.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 .
Figure 17.16 The star topology, linking the LAN's computers and devices to one or more central hubs, or
access units.
Because each computer uses a separate cable, the failure of a network connection affects
onlythesinglemachineinvolved.Theothercomputerscancontinuetofunctionnormally.
Buscablingschemesuselesscablethanthestarbutarehardertodiagnoseorbypasswhen
problems occur. At this time, Fast Ethernet and Gigabit Ethernet in a star topology are the
most commonly implemented types of wired LAN.
Switches for Ethernet Networks
Asyouhaveseen,modernEthernetworkgroupnetworks—whetherwirelessorwiredwith
UTPcable—areusuallyarrangedinastartopology.Thecenterofthestarusesamultiport
connecting device that can be either a hub or a switch. Although both hubs and switches
 
 
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