CPSC 155b, Spring 2003 Homework 1 E-Commerce: Doing Business on the Internet Page 1 of 6 Homework 1 This assignment is due in class on Tuesday, January 28. It covers readings and lectures through Thursday, January 23. Late homeworks will not be accepted. Write your name, your e-mail address, and the date on the paper that you hand in. 1. MASS-MARKET BUSINESSES AND NETWORK EFFECTS (10 points) A. (6 points) Explain briefly the difference between a mass-market business and a business that exhibits network effects. B. (4 points) Give two examples of mass-market businesses that were discussed in class, one of which relies much more heavily on network effects than the other; identify which of the two relies much more heavily on network effects. 2. INTERNET ARCHITECTURE AND PROTOCOLS (10 points) A. (2 points) What type of number must your browser translate the name www.microsoft.com into so that you can view a page on the Microsoft website? B. (4 points) If the correct translation of www.microsoft.com is not already known to your browser, which Internet service is used to look it up? Briefly explain the lookup process. C. (4 points) For one point each, identify the Internet layer that is most closely associated with each of: (i) Retransmission of dropped packets (ii) Congestion control (iii) Interdomain routing (iv) Ethernet connection 3. OSPF ROUTING (22 points) Open Shortest Path First (OSPF) routing is used to determine best routes within a single administrative domain. Because the routers involved are in the same domain, they can work together towards a common, simple goal, which is choosing the lowest-cost path available. In addition, because domains are relatively small compared to the Internet, it is possible to share more information about the network without causing congestion. Thus, OSPF works by sending information about the network topology throughout the network so that each node can calculate the lowest-cost path to reach a destination. For example, consider a node A that has two neighbors: A would then broadcast the following link-state packet (LSP): Link Weight A→B 2 A→C 5 A BC25CPSC 155b, Spring 2003 Homework 1 E-Commerce: Doing Business on the Internet Page 2 of 6 Suppose A receives the following LSPs from other nodes: Link Weight B→A 2 B→C 1 B→D 3 Link Weight C→A 5 C→B 1 C→D 4 Link Weight D→B 3 D→C 4 From this information, we can deduce the topology of the network, calculate the shortest paths to the other nodes, and construct a forwarding table. Here is what the whole network looks like, based on the above: The shortest paths (paths of minimum total weight) from A to the other nodes are: Destination Path Total Cost A→B A→B 2 A→C A→B→C 3 A→D A→B→D 5 Then the forwarding table for A, which indicates where next to send packets for a given destination, is: Destination Next Hop B B C B D B When A receives updated LSPs from new or existing nodes on the network, it recalculates its forwarding table to reflect the new shortest paths. Now consider a new network in which node A has three neighbors: A BCD25134AC D 14 B 2CPSC 155b, Spring 2003 Homework 1 E-Commerce: Doing Business on the Internet Page 3 of 6 and A receives the following LSPs: Link Weight B→A 2 B→E 2 Link Weight C→A 1 C→E 3 Link Weight D→A 4 Link Weight E→B 2 E→C 3 A (4 points). Give the forwarding table for A. B (5 points). Assume that a new node, F, joins the network. A receives the following updated LSPs: Link Weight C→A 1 C→E 3 C→F 1 Link Weight D→A 4 D→F 1 Link Weight E→B 2 E→C 3 E→F 3 Link Weight F→C 1 F→D 1 F→E 3 Give the new forwarding table for A (including the new entry for destination F). C (13 points). Assume that the link between A and C fails and must be withdrawn. Assume further that the link between A and D becomes less congested, and so both A and D recalculate the cost of the A↔D link to be 1. (i) Give the updated LSPs that A, C, and D send (3 points). (ii) Give the updated forwarding table for C (5 points). (iii) Give the updated forwarding table for D (5 points).CPSC 155b, Spring 2003 Homework 1 E-Commerce: Doing Business on the Internet Page 4 of 6 4. BUSINESS ON THE INTERNET (12 points) In Trust and Risk in Internet Commerce, Camp identifies the following stages of a commercial transaction: account acquisition, browsing or discovery, price negotiation, payment, merchandise delivery, dispute resolution, and collection and final settlement. For simplicity, restrict your attention in this question to business-to-consumer transactions (e.g., those on Amazon) or consumer-to-consumer transactions (e.g., those on eBay), and ignore business-to-business transactions. Choose three of these stages and, for each, state whether you think that the use of the Internet enables a unique type of consumer experience in that stage. If you think that it does, briefly explain what is unique about the consumer experience and what property of the Internet enables this unique experience. If you think that it does not, give another example of a communication system or environment in which a consumer can have a similar experience. (You will get 4 points for each correct answer.) 5. INFORMATION ECONOMY (12 points) Recall that information goods often have high fixed costs and low marginal costs; furthermore, it is often the case that anyone (i.e., not only the creator or authorized manufacturer) can reproduce them. Briefly describe three techniques that can be used to build effective information businesses despite this fundamental fact about information goods. (You will get 4 points for each correct answer.) 6. BGP ROUTING (34 points) The Border Gateway Protocol (BGP) is used to determine best routes between sources and destinations that are not in the same autonomous system (AS), i.e., administrative domain. Because paths often traverse networks managed by separate companies, route choices are often determined by a combination of factors, possibly including specific local preferences at each router, business relationships with neighbors, and path length. BGP accommodates these complex routing policies that are not uniform throughout the Internet. Because BGP performs interdomain routing (i.e., between domains), it is primarily concerned with reaching an AS containing a specific host destination, not with reaching the host itself. Once the
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