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2012-05-24

A+: Cable and Connector Types

Network cards are designed to interface with one or more types of network cables. UTP and STP cable can be purchased in prebuilt assemblies or can be built from bulk cable and connectors. Four major types of network cables are:

    • Unshielded twisted pair (UTP)
    • Shielded twisted pair (STP)
    • Fiber-optic
    • Coaxial (rare now)

USB, serial (RS-232) null modem and parallel (LPT) crossover cables can be used with direct parallel or direct serial connections (also known as direct cable connection), which are special types of two-station networking included in Windows that use standard network protocols but do not use network cards. Infrared (IR) ports built into many notebook computers can also be used with direct serial connection.

Unshielded twisted pair (UTP) cabling is the most common of the major cabling types. The name refers to its physical construction: four twisted pairs of wire surrounded by a flexible jacket.   It comes in various grades, of which Category 5e is the most common of the standard cabling grades. Category 5e cabling is suitable for use with both standard 10BaseT and Fast Ethernet networking, and can also be used for Gigabit Ethernet networks if it passes compliance testing.

Shielded twisted pair (STP) cabling was originally available only in Category 4, which was used by the now largely outdated IBM Token-Ring Networks. STP uses the same RJ-45 connector as UTP, but includes a metal shield for electrical insulation between the wire pairs and the outer jacket. It’s stiffer and more durable, but also more expensive and harder to loop through tight spaces than UTP. Type 1 STP cable used by older token-ring adapters has a 9-pin connector. STP cabling is also available in Category 5, 5e, and 6 for use with Ethernet networks. It is used where electromagnetic interference (EMI) prevents the use of UTP cable.

The connector used by Ethernet cards that use UTP or STP cable is commonly known as an RJ45 connector. RJ stands for registered jack; the RJ45 has 8 contacts that accept 8 wires, also known as pins. It resembles a larger version of the RJ11 connector used for telephone cabling. UTP cabling runs between a computer on the network and a hub or switch carrying signals between the two. The hub or switch then sends signals to other computers (servers or workstations) on the network. When a computer is connected to a hub or switch, a straight through cable is used. This means that both ends of the cable are wired the same way. If a computer needs to be connected directly to another computer, a crossover cable, which has a different pin configuration on one end, is used. Keep in mind that between the computer and the hub or switch, there might be other wiring equipment involved, for example RJ45 jacks, patch panels, and so on. UTP and STP cable can be purchased in prebuilt form or as bulk cable with connectors, so you can build the cable to the length you need. 

Although RJ45 is the common name for the UTP Ethernet connector, this is a misnomer, the proper name is 8P8C (8 position, 8 contact). Don’t confuse it with the RJ45S connector, an eight-position connector, used for telephone rather than computer data. An RJ45S jack has a slightly different shape than the connector used for Ethernet, and includes a cutout on one side to prevent unkeyed connectors from being inserted into the jack.     To see drawings of the RJ45S jack and other telephone jacks, see http://www.siemon.com/us/standards/13-24_modular_wiring_reference.asp  .

A chart of wired cable categories follows below:


Category Type+ Speed LANs
'CAT' pairs (Mbps) using
--- --- --- ---
1 UTP 1 varies phone, DSL, HomePNA (up to 100Mbps)
2 UTP 1 4 max LocalTalk (Apple, obsolete)
3 UTP 4 10 max 10Base-T (repl w/ CAT5, CAT5e, CAT6)
4 STP 1 16 max Token ring (obsolete)
5 U/STP 4 1000 max 10Base-T, 100Base-T, 1000Base-T
5e U/STP 4 1000 max 10Base-T, 100Base-T, 1000Base-T enhanced CAT5
6 U/STP 4 1000 max 10Base-T, 100Base-T, 1000Base-T higher freqs than CAT5, CAT5e
7 U/STP 4 1000 max 10Base-T, 100Base-T, 1000Base-T uses 12 connector GG45 connector (backwards compatible w/ RJ45)

The outer jacket of UTP, STP, and coaxial cable is usually made of PVC (polyvinyl chloride), a low-cost durable vinyl compound. Unfortunately, PVC creates dense poisonous smoke when burned. If you need to run network cable through suspended ceiling or air vents, you should use more-expensive plenum cable, which produces less smoke and a lower level of toxic chemicals when burned.

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