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hw3-sol

# hw3-sol - ECE 407 Introduction to Computer Communications...

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ECE 407: Introduction to Computer Communications Homework #3 - Solutions Problem 1 Solution: a. A to S : source port 1467, destination port 23 b. B to S : source port 1513, destination port 23 c. S to A : source port 23, destination port 1467 d. S to B : source port 23, destination port 1513 e. Yes f. No Problem 2 Solution: Suppose the IP addresses of the hosts A, B, and C are a, b, c, respectively. (Note that a,b,c are distinct.) a. To host A: Source port=80, source IP address=b, dest port=26145, dest IP address=a b. To host C, left process: Source port=80, source IP address=b, dest port=7532, dest IP address=c c. To host C, right process: Source port=80, source IP address=b, dest port=26145, dest IP address=c Problem 8 Solution: The sender side of protocol rdt3.0 differs from the sender side of protocol 2.2 in that timeouts have been added. We have seen that the introduction of timeouts adds the possibility of duplicate packets into the sender-to-receiver data stream. However, the receiver in protocol rdt.2.2 can already handle duplicate packets. (Receiver-side duplicates in rdt 2.2 would arise if the receiver sent an ACK that was lost, and the sender then retransmitted the old data). Hence the receiver in protocol rdt2.2 will also work as the receiver in protocol rdt 3.0. 1

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Problem 12 Solution: Figure 1: Example scenario where the alternating bit protocol will not work correctly.
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