3.4.Twisted-Pair Cable
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Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources.
Two categories of twisted-pair cable include :
shielded twisted pair (STP)
unshielded twisted pair (UTP)
Solution 1 : One option of supporting higher frequencies is to surround a twisted pair in a metallic shielding, similar to the outer conductor in a coaxial cable. This type of cable is referred to as a shielded twisted-pair (STP) cable .
Solution 2 : Another way to block EMI from the copper strands making up a twisted-pair cable is to twist the strands more tightly (that is, more twists per centimeters [cm]). By wrapping these strands around each other, the wires insulate each other from EMI.
Figure below shows an example of STP cable. These outer conductors shield the copper strands from EMI; however, the addition of the metallic shielding adds to the expense of STP.
Figure below illustrates an example of UTP cable. Because UTP is less expensive than STP, it has grown in popularity since the mid 1990s to become the media of choice for most LANs.
A type 45 registered jack (RJ-45) is an eight-pin connector found in most Ethernet networks. However, most Ethernet implementations only use four of the eight pins.
A type 11 registered jack (RJ-11) has the capacity to be a six-pin connector. However, most RJ-11 connectors have only two or four conductors. An RJ-11 connector is found in most home telephone networks. However, most home phones only use two of the six pins.
A 9-pin D-subminiature (DB-9) connector is commonly used as a connector for asynchronous serial communications. One of the more popular uses of a DB-9 connector is to connect the serial port on a computer with an external modem.
