Twisted pair cable installed in a star topology is used in LANs today. These pairs are called a Shielded Twisted Pair (STP) cable and Unshielded Twisted Pair (UTP) cable. LANs primarily use UTP cable.

UTP cable has eight separate conductors, as opposed only two in coaxial cable. The eight wires are placed in four pairs of twisted conductors, and each conductor is a single insulated wire. The twists inhibit interference from signals on other wire pairs and act as a buffer to outside interference.

The connectors used for twisted pair cables are called RJ-45; telephone cables use the same connectors (twisted pair cable has been used with telephone installations). With LAN, twisted pair cable usage is more recent.

Coaxial cable has been replaced by twisted pairs in the data networking world. The cable in twisted pair is more flexible than coaxial cable, making it easier to work with for installation. Qualified telephone cable installers would have a base knowledge for installing LAN cables.

UTP Cable Grades: UTP cable has different grades or “categories” formulated by the Electronics Industry Association (EIA) and the Telecommunications Industry Association (TIA). Category 3 and Category 5 are the two most significant UTP grades used for LAN.

  • Category 3 cable was designed for telephone networks and was eventually used for Ethernet. Category 3 cable is sufficient for 10 Mbps Ethernet networks, but not for Fast Ethernet, except under special conditions. While it’s feasible to use Category 3 cable installation to build a standard Ethernet network, most new UTP cable installations today use at least Category 5 cable.
  • Category 5 UTP is best suited for 100BaseTX Fast Ethernet networks running at 100 Mbps. Along with the formally ratified EIA/TIA categories, there are other UTP cable grades yet to be standardized. There’s a cable standard known as Level 5 that’s currently being marketed by the company Anixter, Inc. This cable grade is being tagged with names like Enhanced Category 5. It increases the bandwidth of Category 5 from 100 to 350 MHz, making it capable of running the most updated Gigabit Ethernet protocol at 1,000 Mbps (1 Gbps).

STP Cable Grades: Shielded twisted pair cable is similar in composition to UTP. There are two pairs of wires with a foil or mesh shielding around each pair. STP shielding is of better quality than shielding found in UTP, specifically with installations where electromagnetic interference is an issue due to the proximity of electrical equipment. The STP cable types were standardized by IBM, the developers of the Token Ring protocol. STP networks use Type 1A for longer length of cables and Type 6A for shorter patch cables. Type 1A has two pairs of 22 gauge wires with foil shielding, and Type 6A contains two pairs of 26 gauge wires with foil or mesh shielding. IBM data connectors (IDCs) are utilized in Token Ring STP networks. Most Token Ring LANs today use UTP cable.

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