NETWORK CABLING

10/2/98

Network Cabling: PC networks are generally wired with one of three types of cabling--

Thinnet Ethernet uses 50 ohm coaxial cable (RG-58 usually) with BNC connectors. Devices are "T-ed" off a backbone terminated with a 50 ohm resister at each end. Devices must be separated by .5 meters of cable. Maximum cable length is 185 meters -- 925 meters with repeaters. A maximum of 30 taps are permitted off the cable and more than one device can be connected to a tap. In general, any defect in the cabling will bring the entire network down. Thinnet will support 10MHz signaling, but not the more recent 100MHz version.

Thicknet Ethernet is similar to Thinnet, but uses a 1cm diameter coaxial cable with no RG designation. A 15 pin DIN connector (AUI connector) is used. Different AUI pinout is used on transmitters (DCE) and receivers(DTE) and direct connections are not permitted between two DTE devices or two DCE devices. Terminations are 50 ohms using an N-connector. Maximum cable length is 500 meters -- 2500 meters with repeaters. Maximum signal speed is 10MHz. Thicknet is rarely encountered except in older installations or sometimes as a network backbone.

Unshielded Twisted Pair (UTP) uses 4 wires (2 pairs out of 4 pairs in the cable) connected to pins 1-2 and 3-6 of an RJ-45 connector. 10BaseT uses hubs in a star configuration. Maximum cable length is 100 meters between a device and a hub or a hub and another hub. Cabling is generally straight through, although "crossover cables" (with pins 2 and 6 reversed) are sometimes used to connect two devices directly without a hub. UTP comes in various categories. Cat 5 or above are needed for 100MHz and it is recommended that unused pairs be terminated. (How?)

Other types of wiring may be encountered. For example, ARCnet uses 90 ohm coaxial cable (RG-62 or CL/2) with BNC connectors. Arcnet is arranged in a star network with hubs distributing signals to the individual devices. Terminators are not required except possibly where passive signal splitting ("passive hubs") are used.

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