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Mohamed G. Gouda                                        CS 356
Summer 2006                                             Homework 2
Solution
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1.

process p

inp m : integer {m>0}

var conp: boolean,
    cansnd : 0..m

begin

    timeout ~conp ^ (#ch.p.q + #ch.q.p) -> send crqst to p

[]  rcv crply from q -> conp, cansnd := true, m

[]  conp  -> if cansnd > 0 -> send data  to q; cansnd := cansnd - 1
             [] true       -> send drqst to q; cansnd := 0;
             fi

[]  rcv fin from q -> conp := false

[]  rcv rst from q -> conp := false

end

process q

var conq   : boolean {false}
    sntrst : boolean {false}

begin

    rcv crqst from p -> if true -> conq, sndrst := true, false; 
                                   send crply to p
                        [] true -> conp:=false, send rst to p
                        fi

[]  conq -> conq := false; sndrst := true

[]  rcv data from p  -> if ~conp -> {discard data msg} send rst to p
                        [] conq  -> {store data msg} skip
                        fi

[]  rcv drqst from p -> if conq -> conp := false; send fin to p
                        [] ~ conp ^ ~sndrst -> send fin to p
                        [] ~ conp ^ sndrst  -> send rst to p
                        fi

end

2.

Process p[i] is as same as process p in the textbook.

process q

const n

var  conq : boolean  {false}
     pid  : 0..n-1
     sq   : integer
     x,y  : integer

par i: 0..n-1

begin

rcv crqst(x) from p[i] -> if ~conq -> conq, pid, y := true, i, sq;
                                      send crply(x,y) to p[i]
                          [] ~conq -> conq, sq, y := false, sq+1, sq
                                      send drply(x, y) to p[i]
                          [] conq ^ pid = i   -> y:=sq; send crply(x,y) to p[i]
			  [] conq ^ pid != i  -> y:=sq; send drply(x,y) to p[i]
                          fi

[] conq -> conq, sq := false, sq + 1

[] rcv data(x,y) from p[i] -> if sq!= y V pid != i -> {discard data msg}
                                                      send drply(x,y) to p[i]
                              [] sq = y ^ pid  = i -> {store data msg} skip
                              fi

[] rcv drqst(x, y) from p[i] -> if sq!= y V pid != i -> skip; 
                                [] sq = y ^ pid  = i -> conq, sq:= false, sq+1; 
                                                        send drply(x,y) to p[i]
                                fi;

end

3.

(m+1) * n

According to the definition of corruption burst, the longest corruption burst
happens when the first bit in the m*n block and the last bit in the n parity
bits corrupt.