hw1key

hw1key - d prop = m s (b) d trans = L R (c) d end-end = d...

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EEE459 Homework 1 answer key 5 points/review question: 1,3,9 10 points/problem: 4,7,8,11 Review Questions 1. “Host” and “end system” are used interchangably, and can refer to PCs, servers, PDAs, cell phones, appliances, game consoles — anything on the “edge” of the network. This includes web servers. 3. When two hosts communicate, the one which initiates a request is traditionally called the client , and the one that responds is the server , although each may send data to the other. 9. A X B . . R 1 R 2 . In a store-and-forward packet-switching network, ignoring all others delays, the trans- mission delay is d trans = L R . Since there are two links, and the whole file must arrive at the router before it starts on the second link d = L R 1 + L R 2 Problems 4. propogation speed s = 100 km hr , distance d = 200 km , service time = 12 s/car , number of toll booths = 2. Only transmission and propogation delays apply here. d prop = d/s = 200 km/ 100 km hr = 2 hr . (a) d trans = 10 cars × 2 booths × 12 s = 240 s = 4 min . Total time = 2 hr, 4 min . (b) d trans = 7 cars × 2 booths × 12 s = 168 s = 2 min, 48 s . Total time = 2 hr, 2 min, 48 s . 6. (a)
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Unformatted text preview: d prop = m s (b) d trans = L R (c) d end-end = d prop + d trans = m s + L R (d) at t = d trans , the last bit is still at the beginning of the link, host A. (e) at t = d trans < d prop , the rst bit is on the link, in between hosts A and B. (f) at t = d trans > d prop , the rst bit is already at the end of the link, host B. (g) L = 100 bit , R= 28 10 3 bit/s , s= 2 . 5 10 8 m/s , m = ? given d trans = d prop m s = L R m = sL R 893 km 1 22. Form an expression for delay d trans in terms of segment size S , take the derivative with respect to S, and set it to 0 to nd the minimum. Total le size F = M S , where M is the number of packets. Total packet size L = S + H , where H is header size (in this case 40). Since there is one router in between the hosts, the total delay is d trans = ( M + 1) L R = ( F S + 1) H + S R = F + S S H + S R = HF SR + F + H + S R d S =-HF S 2 R + 1 R = 0 S 2 = HF S = l HF m 2...
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hw1key - d prop = m s (b) d trans = L R (c) d end-end = d...

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