|  | 5.1 | Most Common LAN Media
| 5.1.1 | STP

Shielded twisted-pair cable (STP) combines the techniques of shielding, cancellation, and twisting of wires . Each pair of wires is wrapped in metallic foil. The 4 pairs of wires are wrapped in an overall metallic braid or foil. It is usually 150 Ohm cable. As specified for use in Ethernet network installations, STP reduces electrical noise, both within the cable (pair to pair coupling, or crosstalk) and from outside the cable (electromagnetic interference -- EMI -- and radio frequency interference -- RFI). Shielded twisted-pair cable shares many of the advantages and disadvantages of unshielded twisted-pair cable (UTP). STP affords greater protection from all types of external interference, but is more expensive and difficult to install than UTP.

A new hybrid of UTP with traditional STP is Screened UTP (ScTP), also known as Foil Twisted Pair (FTP) . ScTP is essentially UTP wrapped in a metallic foil shield, or "screen". It is usually 100 or 120 Ohm cable.

The metallic shielding materials in STP and ScTP need to be grounded at both ends. If improperly grounded (or if there are any discontinuities in the entire length of the shielding material, for example due to poor termination or installation), STP and ScTP become susceptible to major noise problems, because they allow the shield to act like an antenna picking up unwanted signals. However, this effect works both ways. Not only does the foil (shield, screen) prevent incoming electromagnetic waves from causing noise on our data wires, but it minimizes the outgoing radiated electromagnetic waves, which could cause noise in other devices. STP and ScTP cable cannot be run as far as other networking media (coaxial cable, optical fiber) without the signal being repeated. More insulation and shielding combine to considerably increase the size, weight, and cost of the cable. And the shielding materials make terminations more difficult and susceptible to poor workmanship. However STP and ScTP still have their role, especially in Europe.

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