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Mohamed G. Gouda                                        CS 356
Spring 2008                                             Midterm 3
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Open Book						Time: 1 hour
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1. (10 points)
In a process array p[i : 0..n-1], process p[0] periodically initiates a flood
by sending a copy of the message data(t, txt, d) to each one of its up 
neighbors, where t is the integer timestamp of the message, txt is the integer
text of the message, and d is the "destination indicator" of the message in 
the range 0..1: 

	If d=0 then every process p[i], where i is even and larger than 0, 
	should accept the message text and every process p[i], where i is odd,
	should ignore the message text. 

	If d=1 then every process p[i], where i is odd, should accept the 
	message text and every process p[i], where i is even, should ignore
	the message text.

When a process p[i : 1..n-1] receives a message data(t, txt, d) from a neighbor
p[g], p[i] first checks whether it has received this message earlier and, if 
so, it discards the message. Otherwise, p[i] checks whether or not to accept 
txt and then p[i] forwards a copy of the received message to each one of its 
up neighbors, other than p[g] and p[0].

Specify process p[i : 1..n-1] in this protocol. Add the two comments {accept
txt} and {ignore txt} where appropriate in your specification.

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2. (10 points):

Consider a process array p[i : 0..4] where each of the following two
processes are neighbors:
 
	{p[0], p[1]}, {p[0], p[2]}, {p[1], p[2]}, 
	{p[1], p[3]}, {p[2], p[3]}, {p[2], p[4]}, 
	{p[3], p[4]}.

Each process p[i] in this array has a random routing table rtb that is 
declared as follows.

	inp N   : set { g | p[g] is a neighbor of p[i]},
	    rtb : array [0..4, 0..1] of N

(Recall that rtb[d, 0] and rtb[d, 1] store the two best neighbors of p[i] for 
reaching the ultimate destination p[d].) Specify what should be stored in 
rtb[0, 0..1] in each process in the process array so that no routed data 
message whose ultimate destination is p[0] ever go through a cycle.

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