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Yale CPSC 155 - Homework 1

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CPSC 155a, Fall 2001 Homework 1 E-Commerce: Doing Business on the Internet Page 1 of 6 Homework 1 This assignment is due in class on Tuesday, September 25. It covers readings and lectures through Thursday, September 20. Late homeworks will not be accepted. Write your name, your e-mail address, and the date on the paper that you hand in. 1. INTERNET ARCHITECTURE (30 points) For 5 points each, match each item in the left-hand column with the item in the right-hand column with which it is most closely associated. Browsers UDP Flexibility and empowerment IP layer Packet routing Increased core-network functionality Reliable byte streams Application layer Low prices and ease of use End-to-end arguments Nonreliable byte streams TCP 2. INFORMATION ECONOMY (20 points) a. (5 points) The basic technology for fax machines was patented in 1843, but fax machines remained rare until the mid-1980's. During the period from 1982 to 1987, fax usage experienced explosive growth because of positive feedback: As the number of fax owners increased, the usefulness of a fax machine grew; the more useful fax machines were, the more people bought them. What well-known property of communication technologies does this illustrate? b. (5 points) True or false: The vendor of a product that exhibits the phenomenon described in 2(a) can definitely maintain a large market share; once adoption reaches critical mass, the product is so useful that customers cannot bear the switching costs of abandoning it, even for something better. c. (5 points) Production of an information good exhibits high fixed costs and low marginal costs. Because creators of information goods can reproduce them cheaply, potential competitors can copy or imitate them cheaply. Nonetheless, some information businesses are long-lived and profitable. Give an example of a technique that allows information producers to succeed in spite of this inherent property of information goods. d. (5 points) Cable-TV subscription packages, Microsoft Office, and a discounted subscription to the online Wall Street Journal for subscribers to the printed version are all examples of a common strategy for pricing information goods that we discussed in class. What is the name of this strategy?CPSC 155a, Fall 2001 Homework 1 E-Commerce: Doing Business on the Internet Page 2 of 6 3. DIGITAL CONTENT DISTRIBUTION (20 points) a. (5 points) What do the following businesses have in common? • Traditional broadcast television • Training and support services for free software • Certain pairs of complementary software products, e.g., Adobe Acrobat Reader and the Adobe document-preparation software. b. (5 points) Technical protection measures: 1. Can help rights holders prevent unauthorized copying. 2. Can help verify legitimate provenance of digital documents. 3. Will probably be more effective against professional content pirates when implemented in special-purpose hardware for single-purpose devices than they are when implemented in software for general-purpose, networked PCs. 4. All of the above. c. (5 points) In the physical realm, the question of access to copyrighted works is cleanly separable from the question of reproduction of such works. For example, a single copy of a book can be read, a single copy of a music CD played, or a painting viewed by many people without any additional copies' being made. By contrast, in the digital realm, access usually entails reproduction. For example, software programs are copied from disk into RAM (random access memory) so that they can be run, and Web pages are copied from remote machines onto local machines so that they can be viewed. This fundamental difference between physically embodied copyrighted works and digitally embodied copyrighted works calls into question the continued applicability of one of the central elements of existing copyright law listed below. Which one? 1. The long duration of copyright ownership (e.g., the fact that copyrights last much longer than patents) 2. The copyright owner's exclusive right to reproduce the copyrighted work in copies or phonorecords (number 1 of Section 106 of U.S. Copyright Law) 3. The copyright owner's exclusive right to prepare derivative works based upon the copyrighted work (number 2 of Section 106 of U.S. Copyright Law) 4. "Fair use" limitations on exclusive rights of copyright owners (Section 107 of U.S. Copyright Law) d. (5 points) The widely held belief that virtually all non-commercial, private-use copying is lawful is wrong. However, in the physical realm, copyright owners do not suffer much from non-commercial, private-use copying, because it does not destroy their markets and because its private nature usually means that it is limited in scope. Is this true in the digital realm? (Answer yes or no.) 4. ROUTING (30 points) I. OSPF Routing Recall that, in OSPF routing, each node broadcasts the state of links physically connected to it, and nodes use this information to calculate shortest paths and forwarding tables. For example, consider a node A that has two neighbors: A BC2 5CPSC 155a, Fall 2001 Homework 1 E-Commerce: Doing Business on the Internet Page 3 of 6 A would then broadcast the following link-state packet (LSP): Link Weight A→B 2 A→C 5 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 the 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 A B C D2 5 1 34CPSC 155a, Fall 2001 Homework 1 E-Commerce: Doing Business on the Internet Page 4 of 6 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 two neighbors: and A


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Yale CPSC 155 - Homework 1

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