Midterm Examination

CSci 555 / Neuman-Obraczka Fall 1996
Directions for completing exam

Answer the following three questions:

1. (45 points) Several large software, communications, and cable companies are currently marketing the idea that home entertainment and computing will be integrated into a single system. In other words, home users will have a single device that will serve as a TV set and a personal computer, where they will be able to watch their favorite TV programs as well as browse the Web. Satellite communication will be used: ground stations will transmit TV programs and Web pages to the satellite.

   You have been hired as a consultant to design an efficient and scalable architecture to support this system.

   1. Why would you use satellite communication for this type of interaction? What are the disadvantages? Consider the case of both TV and Web access. Assume that users have Internet connection through a modem which can be used as a back channel. (10 points)
   2. For traditional Web access, caching can be used to improve system's response time. Will caching help in the case of Web access over satellite? Why or why not? (10 points)
   3. If caching is to be used, where should you put caches: on the information provider premises, on the user premises, on the satellite, or on an intermediate site? Justify your solution. (10 points)
   4. Suppose CNN advertised that www.cnn.com will transmit the final 1996 presidential debate. What kind of problem(s) do you think happen? How would you solve it(them)? Explain your solution. (10 points)
   5. How would you support access to paid TV programs and paid Web pages? What are the security threats you need to address and how would you address them? (5 points)

2. (15 points) In a distributed whiteboard system, users collaborate by sharing a common work area, the distributed whiteboard. As a user writes on the whiteboard, all the other users sharing the whiteboard see what is being written. If you were assigned to implement this application for a distributed system, what communication paradigm would you choose and why? What are the advantages and disadvantages when compared to other communication paradigms?
3. (40 points) You have been hired by a company specializing in tools for finding information in distributed systems. You are assigned to a project that will develop applets - executable code that will move from server to server - looking for information that meets the user's requirements. As information is found, these applets will modify the user's directory to include references to the new information.
   1. What are the security implications of this system? What are the objects to be protected, and what permissions will users or processes have to these objects? (10 points)
   2. What form of access control is most appropriate for each of these objects. Would you use an access control list or a capability list? Why? (5 points)
   3. In your design, how will the credentials needed for authentication or authorization be made available to the applets, and how will they be protected from compromise? (10 points)
   4. Where are they vulnerable to compromise? What can be done to eliminate or reduce the potential consequence of such compromise? (15 points)

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