Answer to Question 1
Manchester is used in Ethernet and other LANs, whereas Differential Manchester is used in token ring LANs. With Manchester, the direction of the transition in mid-interval, negative to positive or positive to negative, indicates the binary bit value. For a 1 bit, the transition is always from negative to positive; for a 0 bit, it is from positive to negative. This mid-bit transition serves not only to represent data, but also provides clocking. With Differential Manchester, the presence or absence of a transition at the beginning of a bit interval indicates the bit value. The transition in mid-interval is used only for self-clocking, not to provide data, which is an advantage.
Answer to Question 2
Digital signaling uses only two values: 0 and 1. These values are represented electronically. Because digital signals are one value or the other, with no variance in between, they are a discrete representation. This discrete representation means that digital signals have only a given, specific value. Digital signaling is usually less expensive than analog signaling because it requires less complex circuitry. Noise interference is less of a problem in digital signaling, making error detection and correction easier. A disadvantage is that digital signals are more susceptible to attenuation. This weakening of the signal is caused by friction. The longer the distance that a signal needs to travel though a circuit the more probable attenuation becomes. Different media, however, will suffer from attenuation at varying distances. Digital signals can be carried over copper or fiber-optic cables.
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