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Mohamed G. Gouda						Homework 1
CS 356: Computer Networks					Summer 2007
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1. (3 Points):

It is required to design a network p[i : 0..3] as follows. At any time, process
p[0] sends a rqst message to process p[1] then waits to receive a rply message 
from any of the processes p[i : 1..3] before it can send the next rqst message 
to process p[1]. When a process p[i], where i=1..3, receives a rqst message 
from process p[i-1], p[i] either forwards the rqst message to p[i+1], provided 
that i<3, or sends a rply message to process p[0]. Assuming that the 
communication in this network is error-free, specify process p[0] and processes
p[i : 1..3]. 

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2. (3 Points):

Assuming that the communication in the network in problem 1 is error-prone, 
modify the processes in this network to ensure that the processes tolerate
message corruption, message loss, and message re-order.
 
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3. (4 Points):

Consider a network p[i : 0..n-1]. In this network, any two processes p[i] and 
p[g] are "neighbors" iff there are two oposite-direction channels between them
and so they can exchange messages. At any time, a process p[i] in this network 
can attempt to start a "connection" with anyone of its neighbors p[g]. In this 
case, p[i] sends a rqst message to p[g], and p[g] either rejects the connection
by sending message no to p[i], or accepts the connection by sending message yes
to p[i]. Neighbor p[g] rejects the connection with p[i] if p[g] is already in 
an established connection with another neighbor (other than p[i]) or is 
attempting to start a connection with anyone of its neighbors. If p[g] accepts 
the connection with p[i], then the connection between p[i] and p[g] remains 
established until p[i] sends a done message to p[g] to terminate the 
connection. Each process in this network can be in at most one established 
connection at a time. Specify the actions of each process p[i] in this network 
assuming that the communication in the network is error-free and that the 
input, variables, and parameter in p[i] is as follows.
 
process p[i : 0..n-1]

inp N : set {g | p[g] is a neighbor of p[i]}

var s : boolean,  {p[i] is attempting to start a connection with p[g] or 
		   has started the current connection with p[g], init. false}
    e : boolean,  {There is an established connection between p[i] and p[g], 
		   init. false}
    g : N

par j : N

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