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Q17: What is Shielded Twisted Pair Cables (STP)?
A17:The 150 ohm twisted pair cabling defined by the IBM Cabling System
specifications for use with Token-Ring networks.The twisted pairs in 150
ohm STP are individually wrapped in a foil shield and enclosed in an ov
The term "shielded twisted pair" (STP) most often refers to
erall outer braided wire shield.The shielding is designed to minimize
EMI radiation and susceptibility to crosstalk.150 ohm STP is not generally
intended for use with Ethernet.However,the Ethernet standard does describe
how it can be adapted for use with 10Base-T,100Base-TX,and 100Base-T2.
Ethernet by installing special impedance matching transformers,or "baluns",that
convert the 100 ohm impedance of the Ethernet transceivers to the 150
ohm impedance of the STP cable.
The various versions of 150 ohm STP cable are identified by a "Type"
number.The original IBM Cabling System specifications defined STP cable
Types 1, 2, 6, 8, & 9 for support of Token-Ring frequencies up to
16 MHz. Later, an enhanced IBM Cabling System defined STP-A cable Types
1A, 2A, 6A, &9A for support of FDDI frequencies up to 100 MHz.The
"A" suffix denotes the enhanced IBM Cabling System.Type 1 is
the heavy black cable that is most commonly associated with the IBM Cabling
System.It contains only 2 twisted pairs as compared to UTP and ScTP which
typically contain 4 twisted pairs. Note that 100Base-T4 and 1000Base-T
cannot be adapted to use STP¡¡because they require a cable
with 4 twisted pairs.
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