Two neighbors, who live on the same street, both use ADSL service, but measurements show that one subscriber can download at approximately 1.5 Mbps and the other can download at 2.0 Mbps. Explain.
What will be an ideal response?
ADSL is adaptive. That is, when a pair of ADSL modems are powered on, they probe the line
between them to find its characteristics, and then agree to communicate using techniques that are
optimal for the line. When ADSL starts, both ends probe the available frequencies to determine which
frequencies work well and which experience interference. Also, the two ends assess the signal quality
at each frequency, and use the quality to select a modulation scheme. If a particular frequency has a high signal-to-noise ratio, ADSL selects a modulation scheme that encodes many bits per baud; if the
quality on a given frequency is low, ADSL selects a modulation scheme that encodes fewer bits per
baud.
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Discuss the advantages and disadvantages of using sampling to reduce the number of data objects that need to be displayed. Would simple random sampling (without replacement) be a good approach to sampling? Why or why not?
What will be an ideal response?