CS6/73201 "Advanced Operating Systems" 

            HOMEWORK #3
	
        Due in class 10/31/00


The numbers in parenthesis refer to "Introduction to Distributed
Algorithms" (IDA) textbook. Each question is worth 5 points.


1. Suppose the code for the ring algorithm (Picture 6.2)
   is changed as follows. The code for the initiator is
   the same. The code for non-initiators is as follows:

	begin receive <tok>; send <tok> to NEXTp; receive <tok>; decide end

   Is the modified version of the algorithm a wave algorithm?
   Is there a computation of the algorithm where a non-initiator 
   decides? Explain your answers.

2. For the tree algorithm  (Picture 6.3), provide an example
   where the first node to decide is a leaf node
   (there has to be at least two non-leaf nodes in your example)

3. (IDA 6.5)

4. (IDA 6.12)

5. Explain why Classical depth-first search algorithm (unlike Tarry's)
   algorithm always computes a depth-first tree.

6. in Auerbach's algorithm. When a process P receives <tok> message
   it first sends <vis> message to every neighbor, waits for <ack>
   from every neighbor and then proceeds to forward <tok>.

   Would the algorithm be correct if a process does not wait for <ack>s to
   come back but forwards <tok> immediately after <vis> messages are sent?
   If yes, explain why; if no, explain why and provide a counter-example.

7. Modify LeLann's election algorithm (Picture 7.2) such that
   the winner is the node with the lowest identity in the system
   not only the lowest among the initiators.

8. (IDA 7.2)

9. (IDA 7.5)

10.(IDA 7.9)