The fault tolerant ring topology of FDDI accommodates the campus backbone well. These two approaches are pictured in Figure B-2. A backbone can link multiple networks in the campus environment or connect networks over wide area network links. So far, our backbone has been limited to a single building. It is usually just the high-speed switches that aggregates traffic from attached networks. In a switched network design, a backbone is not as clearly defined. The hub or switch uses a variety of architectural designs, such as bus, shared memory, or matrix-as discussed under " Switch Fabrics and Bus Design." A backbone is typically a network that interconnects other networks. The backbone is reduced to a hub or switch and the network is configured with a star- wired topology. In the collapsed backbone shown on the right, a cable runs from each department (or floor) network to a central hub or switch, usually located in a building wiring closet or management center. If one of the routers fails, the rest of the network stays connected. FDDI adds fault tolerance due to its ring topology. Each network is connected via a router to the backbone network. The distributed backbone on the left in Figure B-1 shows how the network (in this case, an FDDI ring) extends to each department or floor in a building. A hybrid configuration ties together several collapsed backbone hubs or switches with a distributed backbone. The two topologies are illustrated in Figure B-1. There are distributed backbones that snake throughout a building or campus to provide a connection point for LANs, and there are collapsed backbones that exist as wiring hubs and switches. Generally, the backbone's capacity is greater than the networks connected to it. A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. It provides a path for the exchange of information between different LANs or subnetworks. The backbone network is an important architectural element for building enterprise networks. Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM. Related Entries Web Links New/Updated Information Get info about the Encyclopedia of NetworkingĪnd Telecommunicatons, 3rd edition (2001)Äownload the electronic version of the Encyclopedia
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