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7 Cards in this Set
- Front
- Back
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What is the difference between guided and unguided transmission? |
Guided transmission refers to transmissions that occur over a physical medium such as copper wire or optical fiber. These provide a specific path to the for the transmission to follow. Unguided transmissions refer to radio wave or microwave transmissions that travel out in all directions through free space. |
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Explain how twisted pair cable reduces the effect of noise. |
When two wires are run in parallel this causes one wire to be closer to a source causing a large amount of noise. However when twisted a pair of wires alternates shielding each other from the source of the radiation leading to a much smaller amount of noise. |
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List and explain the three main sources of transmission errors? |
1) Interference causes noise in an electrical system caused by radiation being transmitted from the environment. This noise can also be a side effect of normal operations 2) Distortion is caused when the signal travels along a physical medium. The signal will be dispersed when traveling along an optical fiber or, have issues with the properties of capacitance and inductance. This can even be caused by large metal objects placed near a wire. 3) Attenuation is caused by signals passing over wires for long distances. When a signal has attenuated it has grown weaker as it passed over a physical medium such as wire or optical fiber. |
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What is the Hamming distance? And, compute the Hamming distance for the following pairs: (00000, 10001), (01010, 10111), (00111, 10000), and (01100, 00011). |
2 4 4 4 |
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For each 8-bit data frame the layer uses a generator polynomial G(x) = x4+x2+ x+1 to add redundant bits. What is the sequence of bits actually sent when the 8-bit data frame is “10011101”? |
100111011000 10111 ) 100111010000 10111 0010010 10111 0010110 10111 00001000 Now append remainder onto data as the CRC code. |
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What are the advantages of parallel transmission? What is the main disadvantage of parallel transmission? |
1) A parallel transmission has the benefit of being N times faster than serial transmission because it can send N bits at the same time. 2) The underlying hardware of a system runs in parallel so this lends itself to running transmissions in parallel as well. 3) Parallel transmissions have the downside of cost more than their serial transmission counterparts. |
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Of the four basic multiplexing techniques: FDM, WDM, TDM and CDM, is TDM always the best? Why/why not? Explain |
TDM not always the best it is only the best fit when all sources produce data at a uniform fixed rate of 1/N otherwise unfilled slots are produced. The statistical method can help to alleviate this issue however it then incurs additional overhead. |
