Network Design
5-18 The Workgroup in the Larger Network
The Distributed Backbone
One method of creating a backbone network is to sequentially string all of the
workgroup networks or hubs together. Cabling is run from one workgroup hub to
the next, providing the necessary connections. This method of configuring a
backbone network, as shown in Figure 5-5, may be used with any technology
except ATM, which requires a device backbone configuration (detailed later in
this chapter).
Figure 5-5. Distributed Backbone
A distributed backbone is usually the least expensive backbone network selection,
as the only products required is the cabling that runs from one workgroup
network to another. The problems inherent in the distributed backbone network
are somewhat limiting, however:
• Connectivity Requirements - FDDI and Token Ring networks must form a
complete, unbroken ring. Ethernet backbones are most effective if all
workgroup networks are attached to a shared bus, such as a thick coaxial cable.
• Limited Expandability - While it is possible to simply add stations to a thick
Ethernet backbone, the ring-dependent technologies (Token Ring and FDDI)
require that existing cable be cut and terminated or replaced with additional
cable runs when new workgroup networks are added to the backbone.
• Troubleshooting Complexity - If a distributed backbone suffers an error or a
faulty cable, locating the fault in the network often takes up much of the total
troubleshooting time. If a cable is at fault, the Network Manager may spend a
lot of time pulling and testing new cabling.
• Limited Control - The use of a distributed backbone makes the isolation of
workgroups from the rest of the overall network somewhat time-consuming.
If a workgroup in a distributed backbone must be disconnected from the other
networks physically, the distributed backbone requires that a Network
Manager go out to the physical location of the workgroup network and
disconnect the required cables, making any additions or changes necessary to
keep the backbone network whole and operating.
hub
hub
hub
hub
2094n10