Computer Science 825
                           Quiz 1           Name _______________________

Terminology:  the very highest layer is the APPLICATION LAYER = Layer N
              the very lowest  layer is the PHYSICAL LAYER    = Layer 1

1. a. Which of the seven layers of the ISO-OSI model is the LOWEST
      layer that is typically found in each host computer but not
      found in an IMP.


   b. Which of the seven layers of the ISO-OSI model was
      originally designated as responsible for data encryption.


   c. At which layer is it necessary that a common protocol
      be supported within all hosts and IMPs of a network.



2. For two separate implementations of a specific network
   architecture to interoperate correctly it is necessary that:

   a. Intra-level peer protocols  b. Internal inter-level interface
      be compatible                  definitions be compatible at
                                     both end-points.

   c. Both a and b.               d. Neither a or b.

3. Protocol headers used by a layer N are handled by layer K (K > N)
   as follows:

   a. The are removed before  b. They are treated as user data.
      the packet arrives at
      Layer K

   c. They are deleted by layer K.

4. In the "apocalypse of the two elephants"

   a. what do the X and Y axes represent:

      X -


      Y -


   b. In what way does the apocalypse explain the failure of the
      world to adopt the ISO/OSI network architecture when it became
      standardized.





5. Suppose a channel is equipped with high and low pass filters
   that pass only harmonics in the range 80,000 hz to 96,000 hz.
   On this channel what is the  MINIMUM sampling rate required
   to reconstruct the exact signalling function.


6. Suppose that you have trained a carrier pigeon to transport a
   single, small cartridge tape that hold 10 ^ 9 Bytes of data.
   The pigeon can fly at a speed of 40 Km / hour.   For what range
   of distances (in Km) does the pigeon provide a faster way to
   transmit 10 ^ 9 bytes than a 128 * 10^3 bit / second ISDN link
   provided by your friendly local telco at only $100 / month.








7. Two things that a protocol can do to earn the term "unreliable"
   are (1) deliver packets with bits that have been inverted and
   (2) lose packets.  Identify two others (Hint: losing bits is
   NOT one of the answers).

   a.


   b.



8. a. What is the minimum number of signalling states necessary to transmit
      100,000 bits per second on a noise free channel that has a bandwidth of
      10000hz.








    b. What would be the BAUD rate of a modem performing this function.





9. What is the minimum SNR (in db) that will support a data rate of
   100,000 bits per second on a 5000hz channel?