Lan Transmission Media; Lan Connectors; Advantages Of A Communications System In A Lan Environment; Table 8-3. Lan Transmission Media Characteristics - AT&T DEFINITY 2500 series Network Manual

8-14
LOCAL AREA NETWORK CONNECTIONS
_ ___________________________________________________________________________________________________________________________
_ ___________________________________________________________________________________________________________________________
_ ___________________________________________________________________________________________________________________________

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:
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:

Table 8-3. LAN Transmission Media Characteristics

Transmission Maximum
Medium Data Rate
Coaxial cable 50 Mbps
Twisted pair 16 Mbps
Fiber optic cable 1.7 Gbps
Distance Node
Limit Capacity
100 km 10,000
5 km 100
200 km 100