CS 357 - Computer Networks I

Assignments 2

Due Wednesday May 29, 2002 @ 8:30 a.m.
Due on the CS 357 locker No. 103, MC building, ground floor (beside the elevator)
Do not forget to write CLEARLY your name, your student number, and sign the submission form

  1. What is the maximum reliable bit rate possible over a telephone channel with the following parameters:
    (a) bandwidth = 2400 Hz and SNR = 30 dB
    (b) bandwidth = 2400 Hz and SNR = 40 dB

  2. Suppose we wish to transmit at a rate of 64 kbps over a 2400 Hz telephone channel. What is the minimum SNR required to accomplish this?

  3. A digital system is required to operate at 38400 bps. If this system can encode 64 different levels per change,
    (a) What is the minimum required bandwidth for the channel?
    (b) What is the minimum required signal-to-noise ratio (in dB) for this channel?

  4. Given a 64-bit data-sequence 10111101 10110110 11000111 10101111 11111001 10111011 10000110 01001010.
    Find the 16-bit checksum for this data-sequence.
    Include in your answer ALL calculations you did.

  5. Given a 10-bit data-sequence 1000011110 and a divisor of 1101, find the CRC value using:
    (a) The long division scheme (do not forget to add 000 to the right of the message before starting)
    (b) The shift registers/XORs scheme (sketch the circuit first, and do not forget to add 000 to the right of the message before starting)
    (c) What is the data-sequence which will be sent?

  6. In the previous problem, check the correctness of the received message using both the long division and the shift registers/XORs schemes, if:
    (a) The data was transmitted without any error
    (b) The second bit (counting from the MSB) was in error, i.e., it was flipped from ``0'' to ``1''.