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Unformatted text preview: CS 118 Spring 2008 : Homework 4 Problem 1 Problem 1
Given a buffer O = 100 Kbytes, sent from server to client. If S = 536 bytes and RTT = 100 msec, and the transport protocol uses static windows with size W : a For a transmission rate of 28 kbps, determine the minimum possible latency. Determine the minimum window size that achieves this latency. b Repeat (a) for 100 kbps. c Repeat (a) for 1 Mbps. d Repeat (a) for 10 Mbps. Problem 2
Trying to estimate RTTs Given = 0.1, and let: SampleRTT1 be the most recent sample RTT, and SampleRTT2 be the next most recent sample RTT, and so on. a In a TCP connection, suppose four acknowledgments have been returned with corresponding sample RTTs: SampleRTT1 SampleRTT2 SampleRTT3 SampleRTT4 . Express EstimatedRTT in terms of the four sample RTTs. b Express this as a general formula for n sample RTTs. c Using your formula (from part b) let n approach infinity. Comment on why this averaging procedure is called an exponential moving average. Problem 3
Consider a simple UDP based protocol for requesting files (based somewhat loosely on the Trivial File Transfer Protocol, TFTP). The client sends an initial file request, and the server answers (if the file can be sent) with the first data packet. Client and server then continue with a stop and wait transmission mechanism. a Describe a scenario by which a client might request one file but get another; you may allow the client application to exit abruptly and restarted with the same port. b Propose a change in the protocol that will make this situation much less likely. Problem 4
Host A and B are directly connected with a 200 Mbps link. There is one TCP connection between the two hosts, and Host A is sending to Host B an enormous file over this connection. Host A can send application data into the link at 100 Mbps but Host B can read out of its TCP receive buffer at a maximum rate of 50 Mbps. Describe the effect of TCP flow control. Page 1 of 1 ...
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- Spring '08