AT&T 7500 series, 7100 series, 2500 series, 7200 series manual LAN Transmission Media, LAN Connectors

8-14LOCAL AREA NETWORK CONNECTIONS

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LAN TRANSMISSION MEDIA

The transmission media through which LAN nodes are linked may be fiber optic cable, coaxial cable, twisted-pair, or a combination of these. Each transmission medium has a maximum data rate, and distance and capacity limits that characterize it:

	Table 8-3.LAN Transmission Media Characteristics
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⎜		⎜		⎜		⎜		⎜
⎜	Transmission	⎜ Maximum		⎜	Distance	⎜	Node	⎜
⎜	Medium	⎜ Data Rate		⎜	Limit	⎜ Capacity ⎜
⎜		⎜		⎜		⎜		⎜
⎜		⎜	50 Mbps	⎜	100 km	⎜	10,000	⎜
⎜ Coaxial cable		⎜		⎜		⎜		⎜
_______________________________________________								⎜
⎜		⎜		⎜		⎜
⎜ Twisted pair		⎜	16 Mbps	⎜	5 km	⎜	100	⎜
⎜		⎜		⎜		⎜		⎜
⎜		⎜		⎜	200 km	⎜	100	⎜
⎜ Fiber optic cable		⎜ 1.7 Gbps		⎜		⎜		⎜
⎜		⎜		⎜		⎜		⎜

Diverse transmission media along LAN communications paths are linked through adapters or connectors. Adapters allow the transmission media along the same LAN to change, for example, from fiber optic cable to twisted pair. Connectors can provide changes in the transmission media, but their major purpose is to provide LAN access to outside networks and terminals.

LAN CONNECTORS

Generally, three types of connectors — bridges, routers, and gateways — link LANs to outside terminals or networks. These connectors provide external access and translate messages between protocols. The kind of connector that is appropriate for a configuration depends upon where the differing protocols fall in the Open System Interface (OSI) hierarchy. (See appendix D for an explanation of the OSI hierarchy.)

∙Bridges translate data-link layer (layer 2) messages.

∙Routers translate network layer (layer 3) messages.

∙Gateways translate messages at layers higher than the network layer.

Most often, the installation of a circuit-board, along with specialized communications software, transforms a LAN node into a LAN connector that functions as a bridge, router, or gateway for outside access to the LAN.

ADVANTAGES OF A COMMUNICATIONS SYSTEM IN A LAN ENVIRONMENT

Linking a LAN to a communications system can offer three distinct advantages to the LAN user:

∙First, it can let LAN nodes and outside (both on-premises and off-premises) DTEs communicate with each other. This means: