Shielded Twisted-Pair Cable
STP is a version of the 150 ohm twisted cable defined by International Business Machines (IBM) Cabling System specifications for use with Token Ring networks. This cable has a metal shield that covers each pair of insulated cable wires.
The twisted pairs are individually wrapped in a foil shield and then are enclosed in an overall outer braided wire shield. This type of shielding protects the cables from external electromagnetic interferences and crosstalk.
STP cable is available in various versions, which are identified by a Type number. Common Type numbers such as Type 1, 2, 6, 8, and 9 are described by IBM Cabling System specification. These Type numbers supports a frequency of 16 MHz. However, with the advancement in technology, IBM Cabling System defines the Type numbers for enhanced STP cable (STP-A). Common Type numbers defined are Type 1 A, 2A, 6A, and 9A which supports Fiber Distributed Data Interface (FDDI) as well as enhanced frequency of 300 MHz.