Computer Science 825
                         Quiz 6              Name _______________________


1. Consider the following shift register:




   a. What will be the contents of the shift register after the
      input digits 0 and 1 are processed.









   b. What generator polynomial is represented by this shift register.






   c. Does this shift register represent standard long division  or
      is it the pre-multiplying version? (Yes is not the correct answer).


2. For the premultiplying version of a 4 stage shift register to work
   correctly, the register must be initialized to

   a. 0                           b. The first 4 bits of the message

   c. The last 4 bits of the      d. Either a. or b. will work
      message

3. Suppose A generator polynomial of x + 1 is used.  Answer the
   following T or F


 ___ a. Some, but not all, double bit errors in which the 2 error bits are
        not adjacent in the message will be detected.

 ___ b. Some, but not all, double bit errors in which the 2 error bits are
        separated by 1 correct bit will be detected.

 ___ c. All triple (not necessarily adjacent) bit errors can be caught.


4. In protocol 2, ACK's were used but no sequence numbers were used
   on frames or ACK's.  Which of the following problems could occur.

   a. Lost frames would go          b. Lost ACK's would result in
      undetected.                      lost frames

   c. Lost acks would result in     d. Lost frames would result in
      duplicate frames.                duplicate frames.

5. In protocol 3, frames's had sequence numbers but ACKS did not.
   Protocol 3 could fail in the presence of:

   a. ACK's that were lost          b. ACK's that were excessively
                                       delayed

   c. Frames that were lost.        d. Either a or b


6. When protocol 3 failed, the failure resulted in:

   a. The loss of 2 frames          b. The loss of 1 frame and
                                       the duplication of 1 frame.

   c. The duplication of 2          d. The loss of 1 frame
      frames.

7. The bisynch protocol introduced the use of the ENQ packet.
   An ENQ is used

   a. by the sender to request      b. Used by the receiver to
      that the last ACK be             request that the last
      retransmitted.                   packet be retransmitted

   c. Both of the above             d. Neither of the above.

9. Suppose two stations A and B are communicating using a sliding
   window protocol.  The value of "nxtrecv" at B should always be

   a. Between B's value of            b. Not between B's value of
      nxtack and nxtsend                 nxtack and nxtsend.

   c. Between A's value of            d. Not between A's value of
      nxtack and nxtsend                 nxtack and nxtsend.

   e. None of the above... there
      is no relation between
      sender window and receiver
      windows.

10. Match the amount of channel time lost each time an isolated
     error occurs in each of the following environments:

   ____ a. Go Back N            1. The two way propogation delay

   ____ b. Selective repeat     2. One way propogation delay.

   ____ c. Selective reject     3. One packet time

   ____ d. Stop and Wait.       4. The timeout interval

                                5. Two times the timeout interval

11. In going from a S&W protocol to a Go Back N protocol the
   main change is:

   a. Adding the capability      b. Adding the capability
      for the sender to retain      for the sender to retain
      multiple buffered packets     multiple buffered packets

   c. Both a. and b.