Computer Science 825
                         Quiz 2              Name _______________________

1. a. What is the minimum SNR (in db) that will sustain a data rate of
      100,000 bits per second on a 10000hz channel?










   b. How signalling states must be employed?





2. The general form of a modulated sine wave carrier is
   f(t) = A sin(Wt + H).

   a. Which of the three parameters is varied in frequency modulation?
      Hint: the correct answer is "A", "W", or "H"



   b. Which of the three parameters was NOT varied in either of the
      1200 bps or 9600 bps modulation schemes discussed in class.
      Hint: the correct answer is "A", "W", or "H"




3. Diagram an example of a 1 (ONE!) bit per baud phase shift modulation
   scheme which is self clocking and one which is not.

   a. Self clocking:





   b. Not self clocking:






4. A modulation scheme is said to be self-clocking (i.e. able to
   carry a clock signal) if:

   a. it uses phase modulation       b. it doesn't use frequency
                                        modulation

   c. the signalling function        d. the signalling function
      may change state every baud       does change state every baud
      time.                             time.


5. In the models of synchronous and asynchonous transmission
   signalling between the U(S)ART and modem using the RS-232 interface
   is best described as:

   a. Base band and parallel          b. Base band and serial

   c. Modulated carrier and parallel  d. Modulated carrier and serial.


6. Suppose a channel is equipped with high and low pass filters
   that pass only harmonics in the range 60,000 hz to 68,000 hz.
   On this channel the MINIMUM sampling rate required to reconstruct
   the exact signalling function is closest to:

   a. 4000 samples / sec               b. 24000 samples / sec

   c. 16000 samples / sec              d. 48000 samples / sec.


7. What bit rate is required to support a new "hi-fi" PCM phone
   that supports frequencies to 32Khz and quantizes the signal
   into 512 discrete levels.






8. Suppose a network has links that carry data at a rate of 10,000
   bits per second.  Suppose Node A and Node B are connected by a
   path that requires 20 hops (transmissions).

   a. What is the minimum time required to send a 400,000 bit message
      if message switching is used.







   b. Suppose packet switching is used and no additional bits are
      required for headers. How long will it take to send the entire
      message if 2000 bit packets are used.






 9. The use of very small slot sizes in TDM is

    a. Inefficient and shouldn't       b. Generally shouldn't be used for
       be used in either STDM or ATDM     SDTM but is OK for ATDM

    c. Generally shouldn't be used     d. Perfectly OK for both
       for ATDM but is OK for STDM