Twisted pair

Twisted pair cabling is a type of networking hardware formed by twisting two copper wires together in order to minimize electromagnetic interference (EMI) from outside sources as well as crosstalk between the two wires. Twisted pair cables are commonly used among small and medium-sized data networks because they are cheaper in comparison to other network mediums like coaxial and fiber-optic cabling.

tion of twisting two wires together was developed soon after the invention of the telephone in the 1870's. When open wire lines were used for transmission, the large loop area between the two wires caused them to receive a lot of EMI from the power lines that they were strung on.

Crosstalk also occurred, because the signals transmitted on each line caused an undesired effect or "noise" on the adjacent line. With greater loop area, the interference increased, thus limiting the length of the wires used. Engineers discovered that crossing the lines over each other once every several poles reduced the loop area, in effect reducing the crosstalk and EMI and allowing for greater wire lengths.

A typical twisted pair cable includes a number of pairs of copper wires twisted around each other. These twisted pairs are then twisted around other twisted pairs to form the whole cable.

Twist rate, usually measured in twists per meter, is a crucial aspect of cable installation. This factor determines how susceptible a cable is to EMI. For cables which have hundreds of pairs or more, the twist rate for each pair has to be specific.

Determining different twist rates for every pair would be difficult due to the quantity, so pairs are divided into smaller groups and assigned different twist rates. It is very important that the twisting remains intact during installation, so maximum pulling tension and minimum bend radius is required when devising the twisting schemes.

There are two main types of twisted pair cabling:

STP : Shielded Twisted Pair

UTP : Unshielded Twisted Pair

The difference between them being that UTP cables do not have any insulation or "shielding" surrounding them.

The lack of shielding in UTPs allows for greater flexibility and durability, and UTP cabling is the least expensive among all types of local area network (LAN) cables. Because of this, several Ethernet networks and telephone systems make use of UTP cables.

g provides greater protection against EMI, making STP the more ideal type of cabling for larger networks and businesses. In an STP cable, "shielding" refers to the metal wrapped around an individual twisted pair or wires.

"Screening" refers to the metal wrapped around the entire set of pairs. There are various combinations formed by the presence or absence of shielding and screening: STP, which has shielding but no screening; Screened Shielded Twisted Pair (S/STP), which has both shielding and screening and thus provides the best insulation from interference generated by outside sources; and Screened Unshielded Twisted Pair (S/UTP), which has screening but no shielding, basically making it a UTP with shielding. S/UTP may also be referred to as a Foiled Twisted Pair (FTP).