Twisted pair cable, coaxial cable and fibre optic cable are three media commonly used in wired networks. The popularity of each type has varied over time. The most common form of cable currently in use in networks is the unshielded twisted pair.
Unshielded Twisted Pair
The most widely implemented standards for the physical properties of networks is the Ethernet set of standards published by the Institute of Electrical and Electronics Engineers. A number of hardware elements commonly used for networks often get tagged with the name "Ethernet." Unshielded twisted pair, or UTP, is so closely identified with Ethernet implementations that it is often called "Ethernet cable." This form of cable can contain any number of wires, but the most common form used for networks contains eight wires, configured as four pairs, with the two wires in each pair twisted around each other for the length of the cable. The configuration and performance expectation of different grades of UTP is defined by the Telecommunications Industry Association. It classifies cable as a category number. Cat 5 and Cat 5e (enhanced) are the most widely implemented grades of UTP. Cat 6 is recommended by the IEEE for its newest, faster standards for Ethernet networks.
Shielded Twisted Pair
Shielded twisted pair comes in a variety of configurations. The standard STP is categorised under the IBM cabling system specifications into a range of "types" suitable for use with token ring networks. The cable has two twisted pairs which means it is not suitable for Ethernet networks, which require four twisted pairs. In this configuration each pair is wrapped in foil and the entire bundle has a woven metal case beneath the outer jacket of the cable. A variant of STP is screened twisted pair, or ScTP. This category can be used as a substitute for UTP cable in Ethernet networks because it has four twisted pairs. Each has a foil, or woven metal shield beneath the plastic coating of the cable.
Coaxial, or coax cable was the original cable used by the first implementations of Ethernet networks. It is little used in networking nowadays and is more common in TV antenna connections. The coaxial cable has a solid metal core which is surrounded by a padding of insulator and then also has a metal shield beneath the outer plastic coating. Ethenet recommendations do include the use of tin-axial cable which is the same as coaxial, but it has two metal conductors rather than the one core of coaxial.
All the gigabit Ethernet recommendations include versions using two types of fibre optic cable. These are multi-mode fibre and single-mode fibre. Multi-mode is the more common of the two types because it transmits data as light coming from an LED source, which is cheaper to implement than single-mode fibre. The single-mode fibre is the most expensive medium of all network cables and so is less often implemented. It requires a small laser as a light source for data signals.
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