CABLING

3/20/99

Cabling: Computers use a wide variety of cabling. Ignoring PC to peripheral cabling such as Printer and USB cables, about half a dozen varieties of intercomputer cabling are in common use:

Serial Cables: Three to 25 wire cables that connect serial ports and (usually) pay some lip service to the RS-232 standards. Serial cables operate at standardized data rates (multiples of 75 bits per second up to and beyond 115 thousand bits per second. Minimal wiring consists of two data wires and a ground. Three control signal pairs are often added. Additional wires usages are defined. Serial cables are generally not used between high end units but may be used with terminal emulators, remote printers, etc. Generally they use 25 or 9 pin D connectors. The socket on PCs is usually female. Sockets on other devices may be either male or female. In theory, there are two configurations DTE and DCE that match the sockets. Again, in theory cross over ("null modem") connectors should be used when both devices have the same polarity plug, straight through cables should be used when the devices have different polarity plugs. Don't bet on it.

RCA cables: Short patch cables terminated in a two wire lead with a center pin and outside ground. Sometimes used for audio or video.

ZIP cord: Two fairly heavy conductors in a single package. Sometimes used for power cords. Occasionally used for audio cabling to speakers, etc.

TV cables: 300 Ohm twin lead or 75 ohm Coaxial cable -- Often RG6 or RG59. Uses Type-F or screw type connectors. Used only with specialized peripherals.

Thicknet Ethernet Cables: Thicknet Ethernet uses a thick 50 Ohm cable and a 15 pin D "AUI connector". It is limited to 10MHz Ethernet. It must be terminated at each end by a 50 ohm terminator.

Thinnet Ethernet: RG58 Coaxial cable with BNC connectors. It is limited to 10MHz Ethernet. It has a maximum segment length of 135 meters. Units are daisychained along the cable. It must be terminated at each end by a 50 ohm terminator.

ArcNet: An obsolete networking technology that used 90 ohm (RG62 Coaxial cable) to transmit Ethernet signals. Unlike Thinnet and Thicknet, cables are directly connected, use hubs, and rarely use terminators except in conjunction with unused ports on "passive hubs".

Telephone wires: Two or four twisted or untwisted wire pairs. Generally 4 pin RJ11 telephone connectors are used. The primary line is on pins 2 and 3, the secondary is on 1 and 4. Signals have a defined polarity which usually doesn't matter to telephone equipment, but may to modems and computer related equipment. PBXes and other specialized equipments may use variants with the same plugs but with signals that won't work or may even damage conventional equipment.

Unshielded Twisted Pair: Various categories of four twisted "telephone wires" in a plastic wrapper. Uses RJ45 8-pin telephone connectors with one pair on pins 1&2 and the another pair on 3&6. Category 2 and above run at 10MHz. Category 5 and above are rated for 100MHz. Unlike coaxial cables, UTP is usually wired in a star pattern from "hubs". Crossover cables with pins 1&3, 2&6 reversed are occasionally used for direct connection in two station installations.

Fire retardant plenum cabling is used in air ducts -- including the above ceiling space in most offices used as a return "duct" by heating/cooling systems. Coaxial cable and UTP both are available as plenum cabling.

Return To Index Copyright 1994-2002 by Donald Kenney.