SYSC4502 Midterm

SYSC4502 Midterm - messages to hosts B and C. A is...

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2005 SYSC 4502 Midterm 80 Minutes Close book 1. (50%) Provide simple and straight answers to the following questions. a. Name two benefits of layered protocol architecture. b. What factor decides the cost of packet forwarding? c. What are the major advantage and disadvantage of designing a protocol software package as an application program? d. What are the major advantage and disadvantage of one thread per protocol in comparison with one thread per packet? e. What factor decides the cost of error detection and correction for a packet? f. What does a socket do with the following line of code? Socket clientSocket = new Socket(“hostname”,6789); g. Which transport protocol does SMTP use? h. What are the typical events in a FSM for communications software? i. What is the purpose of FIN_WAIT_1 state in the FSM for TCP protocol? j. What are the different types of messages in HTTP protococol. 2. (50%) Consider a scenario in which a host, A, wants to simultaneously send
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Unformatted text preview: messages to hosts B and C. A is connected to B and C via a broadcast channel-a packet sent by A is carried by the channel to both B and C. Suppose that the broadcast channel connecting A, B, and C can independently lose and corrupt messages (and so, for example, a message sent from A might be correctly received by B, but not by C). Design a stop-and-wait-like error-control protocol for reliably transferring packets from A to B and C, such that A will not get new data from the upper layer until it knows that both B and C have correctly received the current packet. a) Give FSM descriptions of A and C. (Hint: The FSM for B should be essentially the same as for C.) b) Give a description of the packet formats used. You should try to minimize the overhead. c) Gives a trace of the scenario that B loses a packet while C receives the packet correctly using MSC....
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