Computer Science 825
                         Quiz 4              Name _______________________


1. Measurements of an infinite user slotted aloha channel show that 10%
   of the slots are idle.

   a. What is the total load (mean number of transmission attempts per
      packet time) = G.




   b. What is the throughput??


2. The maximum througput of a pure aloha channel is:

   a. 1 Packet / packet time.         c. .18 Packet / Packet time.

   b. .5 Packet / packet time.        d. .5 Packets / Second.

3. The window of collision vulnerability for slotted aloha is:

   a. 1 Packet transmission time.     c. 1 Signal Propogation time.

   b. 2 Packet transmission times.    d. 2 Signal Propogation times.

4. We described three distinct situtations in which a CSMA station
   might act with some form of "persistence". One was after a collision
   had occurred. What were the other two.

   a.


   b.


   c. For which of the three cases was 1 - persistent behavior LEAST
      likely to cause a problem.





5. Suppose a satellite channels supports a 200,000 bit/second bit rate.
   Suppose slotted aloha ground stations generate a 500 bit packet every 50
   seconds on average.

   a. What average bit rate in bit/second is each station generating?


   b. What is the maximum throughput in bits/second that the channel can
      sustain on average.



   c. What is the maximum number of stations the network can sustain.