hw1-2-soln - CS536 Partial Homework Answers March 12, 2009...

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CS536 Partial Homework Answers March 12, 2009 HW1: Problem 6 For the short link, propagation delay is assumed to be negligible. So we only worry about transmission delay. We need to transmit 11 objects, each 120,000 bits long. The transmission delay is this 120,000 bits / 120 (bits/s) = 1000 sec / object. (Note that the question is somewhat confusing: if you took 150,000 bits here that was okay). For 11 objects, that’s a total of 11,000 seconds. Re: persistent connections vs. non-persistent connections, the TCP connection establishment can be avoided, which reduces up to 2 control packets [syn/synack] (4 seconds/object). The final ack in the 3-way handshake can also contain the request, and must be sent in all cases). We cannot eliminate one for the first socket, of course, but I’m looking at the big picture. Compare 11,000 seconds of data transmission to up to 66 seconds of control. Now, of the 6 seconds of control (syn, syn-ack, ack/request), 4 are client-server, and 2 are server-client. The client is not using much bw, so parallelizing these can hide the client-server ones. But the 2 server-client seconds will add additional delay for each object. Persistent connections can remove this 2-second delay per object. But we’re talking about 11,000 seconds wrt 66 seconds of control, and there is little difference regardless. HW1: Problem 8 Thanks to Long Van Nguyen Dinh for agreeing to distribute this answer! Denote s i ( t ) be the rate at which the server sends bits to peer i at time t. As soon as each peer i begins to receive its bits from the server, it forwards the received bits to each of the other ( N - 1) peers. In each distribution scheme, we need to show that 1
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The server rate s i ( t ) is non-negative and the aggregate server up- load rate does not exceed the total server upload bandwidth, that is, N i =1 s i ( t ) u s .
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This note was uploaded on 10/24/2009 for the course CS 536 taught by Professor Sonia,f during the Spring '08 term at Purdue University-West Lafayette.

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hw1-2-soln - CS536 Partial Homework Answers March 12, 2009...

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