AT&T 2500 series User Manual
8-14
LOCAL 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:
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
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Coaxial cable
50 Mbps
100 km
10,000
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Twisted pair
16 Mbps
5 km
100
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Fiber optic cable
1.7 Gbps
200 km
100
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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.
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.)
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.)
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Bridges translate data-link layer (layer 2) messages.
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Routers translate network layer (layer 3) messages.
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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.
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:
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