NETWORK BACKBONES

Backbone cable refers to the cable that forms the main trunk, or backbone, of a network. Individual nodes and other devices may be connected to this cable using special adapters and a separate stretch of cable.

Backbone cable is defined by the Electronics Industries Association/Telecommunications Industry Association-568 (EIA/TIA-568) committee as any "behind the scenes" cable; that is, cable running behind walls, in shafts, or under the ground.

The EIA/TIA-568 recognizes four types of backbone cable; they are listed in table 2-3.

The use of a backbone network to tie together a number of small access networks offers several advantages over the construction of a single large LAN. The various LANs connected to the backbone are able to operate in parallel, providing greater processing efficiency. The multiple-network approach is also more reliable, since each individual LAN can continue operating if one of the access networks, or even the backbone, fails. The backbone network must also be highly reliable, since the greater distances covered may make it difficult to locate and repair faults. The LANs that connect to the backbone must be flexible and low-cost in terms of installation and user connection.

To connect a node directly to a backbone, you would use a drop cable for the connection. Nodes are normally connected to the backbone indirectly through a concentrator or a hub rather than with a drop cable.

The elements needed to connect a node to a network include the following:

e Cable: twisted-pair, coaxial, or fiber-optic

l Wiring centers: hubs or concentrators

l Intranetwork links: connectors, repeaters, and so on

l Internetwork links: bridges, routers, gateways, and so on

The cable provides a transmission medium, as well as the physical link between the nodes on the network. Connectors and repeaters attach cable sections to each other; connectors and transceivers attach NICs to a cable and, thereby, to the network. Transceivers enable different types of cable to be attached to each other. Terminators absorb a transmission at the end of a network, preventing the signal from traveling back in the other direction on the network. The types of intranetwork links allowed in the network depend on the type of cable used and on the network topology used.

Wiring centers serve as a focal point for network elements, and may influence the logical arrangement of nodes on the network.

Internetwork links may be bridges, routers, gateways, and soon. Such components serve to connect networks to each other. The type of internetwork link depends on whether the two networks are the same or not, and the amount of translation that is needed.

NETWORK SERVER

A server is the central computer in a network, and is responsible for managing the network. The server provides some type of network service. It may be hardware, such as a file server, or software, such as network level protocol for a transport level client.

The server provides its service to other workstations on the network or to other processes. In a server-based network, the most important hardware server is the fileserver, which controls access to the files and data stored on one or more hard disks.

Table 2-3.\Types of backbone cable.

Connection to the backbone network may require a bridge, router, gateway, concentrator or hub, depending on the architectures of the various LANs and the backbone itself. The connectors used will also depend on the type of cable used for the backbone. If the backbone is coaxial cable, you would use a T-connector and barrel connectors to make the connection to another cable or a hardware device.

The backbone manages the bulk of the traffic, and it may connect several different locations, buildings, and even smaller networks. The backbone often uses a higher-speed protocol than the individual local area network (LAN) segments.

One obstacle to a successful backbone network is the high bandwidth that may be required to handle potentially heavy traffic. Because of this consideration, fiber-optic cable is the most sensible cabling for backbone networks.