TRANSMISSION MEDIA
A transmission medium can be broadly defined as anything that can carry information from a source to a destination. For example, the transmission medium for two people having a dinner conversation is the air. The air can also be used to convey the message in a smoke signal or semaphore. For a written message, the transmission medium might be a mail carrier, a truck, or an airplane. In data communications the definition of the information and the transmission medium is more specific. The transmission medium is usually free space, metallic cable, or fiber-optic cable. The information is usually a signal that is the result of a conversion of data from another form.
Guided Media:
Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. A signal traveling along any of these media is directed and contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current. Optical fiber is a cable that accepts and transports signals in the form of light.
1. Twisted-Pair Cable
A twisted pair consists of two conductors (normally copper), each with its own plastic insulation,
twisted together, as shown in Figure 7.3.
One of the wires is used to carry signals to the receiver, and the other is used only as a ground
reference. The receiver uses the difference between the two. In addition to the signal sent by the
sender on one of the wires, interference (noise) and crosstalk may affect both wires and create
unwanted signals. If the two wires are parallel, the effect of these unwanted signals is not the
same in both wires because they are at different locations relative to the noise or crosstalk
sources (e,g., one is closer and the other is farther). This results in a difference at the receiver. By
twisting the pairs, a balance is maintained. For example, suppose in one twist, one wire is closer
to the noise source and the other is farther; in the next twist, the reverse is true. Twisting makes it
probable that both wires are equally affected by external influences (noise or crosstalk). This
means that the receiver, which calculates the difference between the two, receives no unwanted
signals. The unwanted signals are mostly canceled out. From the above discussion, it is clear that
the number of twists per unit of length (e.g., inch) has some effect on the quality of the cable.
Applications
Twisted-pair cables are used in telephone lines to provide voice and data channels. The local
loop-the line that connects subscribers to the central telephone office-commonly consists of
unshielded twisted-pair cables. The DSL lines that are used by the telephone companies to
provide high-data-rate connections also use the high-bandwidth capability of unshielded twistedpair cables. Local-area networks, such as lOBase-T and lOOBase-T, also use twisted-pair cables.
A transmission medium can be broadly defined as anything that can carry information from a source to a destination. For example, the transmission medium for two people having a dinner conversation is the air. The air can also be used to convey the message in a smoke signal or semaphore. For a written message, the transmission medium might be a mail carrier, a truck, or an airplane. In data communications the definition of the information and the transmission medium is more specific. The transmission medium is usually free space, metallic cable, or fiber-optic cable. The information is usually a signal that is the result of a conversion of data from another form.
Guided Media:
Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. A signal traveling along any of these media is directed and contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current. Optical fiber is a cable that accepts and transports signals in the form of light.
1. Twisted-Pair Cable
A twisted pair consists of two conductors (normally copper), each with its own plastic insulation,
twisted together, as shown in Figure 7.3.
One of the wires is used to carry signals to the receiver, and the other is used only as a ground
reference. The receiver uses the difference between the two. In addition to the signal sent by the
sender on one of the wires, interference (noise) and crosstalk may affect both wires and create
unwanted signals. If the two wires are parallel, the effect of these unwanted signals is not the
same in both wires because they are at different locations relative to the noise or crosstalk
sources (e,g., one is closer and the other is farther). This results in a difference at the receiver. By
twisting the pairs, a balance is maintained. For example, suppose in one twist, one wire is closer
to the noise source and the other is farther; in the next twist, the reverse is true. Twisting makes it
probable that both wires are equally affected by external influences (noise or crosstalk). This
means that the receiver, which calculates the difference between the two, receives no unwanted
signals. The unwanted signals are mostly canceled out. From the above discussion, it is clear that
the number of twists per unit of length (e.g., inch) has some effect on the quality of the cable.
Applications
Twisted-pair cables are used in telephone lines to provide voice and data channels. The local
loop-the line that connects subscribers to the central telephone office-commonly consists of
unshielded twisted-pair cables. The DSL lines that are used by the telephone companies to
provide high-data-rate connections also use the high-bandwidth capability of unshielded twistedpair cables. Local-area networks, such as lOBase-T and lOOBase-T, also use twisted-pair cables.
Newage Cables (Private) Limited is the largest copper wire cable manufacturer of Pakistan and the 1st in its category to be accredited with ISO 9000 certification. Newage was established in 1956 by Mr. Mir Muhammad Azam with the vision of self reliance of a nascent nation and commitment to contribute country’s development by supplying high quality indigenous products to the electrical and industrial infrastructure at competitive rates.
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