Homework 2

Homework 2 is to be done on your own. This homework is divided into two sections. Part A must be word-processed. Use good writing skills in your answer. Part B may be handwritten in your best handwriting. If it cannot be read it will not be graded. Be sure to show your work for full credit. Point values are estimated and may change up or down by a point or so at the time of grading. This homework is due at the start of class on Friday, February 25.

Part A

(15 points) Read the Southwestern Bell Internet at Home products pages, including the current information about dialup access, ISDN, and DSL Internet access services. For each of the three services, answer the following questions:

  1. Is the data sent using a digital or analog signal? Include in your answer a basic description of how the signal is encoded.
  2. What is the basic data rate? Is the rate the same in both directions?
  3. Will you need a separate phone line for voice with this service (and under what circumstances might you not) ?
  4. Are there extra features provided that you would find useful?
  5. Not including setup fees, what is the best price per month that you can get for each service from Southwestern Bell? Be sure to note if this price includes unlimited access or not.
Ignoring for the time being any other prices or services that may be available from Southwestern Bell or another provider, if you were going to purchase one of these Internet access services from Southwestern Bell, which of them would you purchase? Justify your answer with both technical and cost arguments. (For example, don't just say "I want the fastest and so I'll get XXX.") Explain your choice on the basis of the cost, the expected performance of the service, and your expected Internet use.

Part B

  1. (3 points) Consider a LAN with a maximum distance of 2 km. At what bandwidth would propagation delay (at a speed of 200m/usec) equal transmit delay of 100-byte packets?

  2. (2 points) A noiseless 6-kHz channel is sampled every 1msec. What is the maximum data rate?

  3. (3 points) If a binary signal is sent over a 5Khz channel whose signal to noise ratio is 25dB, what is the maximum achievable data rate?

  4. (2 points) What is the difference between a passive star and an active repeater in a fiber optic network?

  5. (2 points) Is the Nyquist theorem true for optical fiber, or only for copper wire?

  6. (2 points) Suppose that a signal is received at 90% of its original transmitted power. What is its attenuation in decibels?

  7. (3 points) Radio antennas often work best when the diameter of the antenna is equal to the wavelength of the radio wave. Reasonable antenna range from 1 cm to 5 meters in diameter. What frequency range does this cover?

  8. (4 points) Some cable channels used for distributing multimedia to homes will be modulated using quadrature amplitude modulation. Suppose that the bandwidth supplied is 48Mbps over a 6MHz channel. What is the number of points in the constellation diagram for QAM? Draw a sample QAM constellation pattern (that you make up).

  9. (3 points) What is the percent overhead on a T1 carrier. That is, what percent of the 1.544 Mbps are not delivered to the end user?

  10. (2 points) If the bit string 0 1 1 1 1 1 1 0 0 1 1 1 1 1 0 1 1 1 1 0 is bit stuffed, what is the output string?

  11. (3 points) What is the remainder obtained by dividing x7 + x5 + 1 by the generator polynomial x3 + 1 ?

  12. (4 points) A channel has a bit rate of 4Kbps and a propagation delay of 20msec. For what range of frame sizes does stop-and-wait give an efficiency of at least 50 percent?

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