EE122 Communication Networks Homework Assignment 2 Prof Ion Stoica and Dr Kevin Lai Due Date Monday October 7 15 50 Name SID EE122 login Discussion Section Problem 1 2 3 4 5 6 Total Points EE122 Communication Networks Homework Assignment 2 Prof Ion Stoica and Dr Kevin Lai September 23 2002 Due Date Monday October 7 15 50 1 2 151 Suppose we want to transmit the message 11001001 and protect it from errors using the CRC polynomial x3 1 a Use polynomial long division to determine the message that should be transmitted b Suppose the leftmost bit of the message is inverted due to noise on the transmission link What is the result of the receiver s CRC calculation How does the receiver know that an error has occurred 2 2 36 Suppose the round trip propagation delay for Ethernet is 46 4 s This yields a minimum packet size of 512 bits 464 bits corresponding to propagation delay 48 bits of jam signal a What happens to the minimum packet size if the delay time is held constant and the signaling rate rises to 100 Mbps b What are the drawbacks to so large a minimum packet size c If compatibility were not an issue how might the specifications be written so as to permit a smaller minimum packet size 3 3 1 Using the example network given in Figure 1 give the virtual circuit tables for all the switches after each of the following connections is established Assume that the sequence of connections is cumulative that is the first connection is still up when the second connection is established and so on Also assume that the VCI assignment always picks the lowest unused VCI on each link starting with 0 a Host A connects to host B b Host C connects to host G 1 This indicates that it is Problem 15 in Chapter 2 in Peterson and Davie s book The left has the same meaning 1 Host F Host D Switch 4 0 Switch 1 1 3 Host C Host E 2 2 3 2 Switch 2 1 3 Host A 0 Host H 0 1 Host J 0 Switch 3 3 2 Host B Host I Figure 1 Example network for Problem 3 c Host E connects to host I d Host D connects to host B e Host F connects to host J f Host H connects to host A 4 4 12 and 4 15 Consider the network given in Figure 2 3 A C 6 F B 8 1 2 D E 2 Figure 2 Example network for Problem 4 a Give the global distance vector tables2 when 2 Refer to Tables 4 5 and 4 8 in Pages 285 and 286 in Peterson and Davie s book 2 1 Host G i Each node knows only the distances to its immediate neighbors ii Each node has reported the information it had in the preceding step to its immediate neighbors iii The second step above happens a second time b Show how the link state algorithm builds the routing table for node D3 5 4 15 For the network in Figure 2 suppose the forwarding tables are all established as in Problem 4 a and then the C E link fails Give a the tables of A B D and F after C and E have reported the news b the tables of A and D after their next mutual exchange c the table of C after A exchanges with it 6 What are the differences between a distance vector and a link state routing protocol Enumerate at least two of them 3 Refer to Table 4 9 in Page 297 in Peterson and Davie s book 3
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