Final Examination

CSci 555 / Neuman Fall 1994
Directions for completing exam

Answer the following three questions:

1. (45 points total) The recent acquisition of A Network Service provider by An On-Line system (OL) provides OL with an increased presence on the Internet. Many expect that OL will begin offering services over the Internet. In the short term, however, this acquisition is more likely play a role providing connectivity for customers to OL's computers. As is presently the case, users will dial in locally and be connected through the Network Service provider to the OL system, but where OL used to route the connection through another network service provider, the connections will now be routed over the Internet, using the facilities of the newly acquired network service provider.
   1. (10 points) OL is interested in making maximum use of the bandwidth they have acquired. At the present time all users connect from a local network port to the OL system in the State of Virginia. How might you redesign the system to reduce the communication load on cross-country links. What problems might this introduce.
   2. (10 points) One service provided by OL is a collection of user forums where users see all comments from other forum users as they are entered, in real-time. Comment on the scalability of this service in general, and how it is affected by your design.
   3. (10 points) OL requires a gateway to Internet information services. In your design how would you address problems of scale and heterogeneity with respect to accessing information provided by other organizations on the Internet.
   4. (15 points) Because OL is a commercial service, its users have a greater expectation of privacy than do (or should) users of the Internet. If successful, as OL begins to use the Internet for communication and other services, users won't notice the difference. What are the privacy and security issues that affect OL's use of the Internet. Compare them with the same issues on a proprietary (non-open) system and network. What measures might be taken to mitigate the problems that arise from use of an open network. Describe specifically how these measures would be applied in the OL system.

2. (10 points) Discuss the alternative approaches for synchronizing reads and writes in file systems. Consider the need to maintain state on the client and/or server, required network messages, user and application visible semantics of file operations, flexibility, reliability, correctness, and availability.
3. For this problem, you will need to refer to the following scenario which was distributed in class the week prior to the exam:
   The scenario for one of the final exam questions follows. You should think about the environment within which the system you would design will operate, consider the problems that might arise, and decide how you might deal with those problems. You are free to discuss the scenario and potential designs with others before the final exam. During the exam you will be presented with the scenario again, and you will be asked to answer several specific questions about your design. You will be free to modify your design once you know the questions, but the better thought through your design is to begin with, the easier it will be to answer the questions.

   Once the exam begins, you will not be allowed to receive help, though the test will be open book and you will be allowed to refer to your notes, papers, or textbooks. If you want, you can write about your design before the final and turn it in with the exam question (as long as it is typed, not handwritten). As long as your assumptions are stated in what you write in advance, you will not have to repeat your assumptions in the answer to the question.

   This scenario applies to only one of the questions on the final exam. There will be one or two additional questions.

   • The Republican party took control of both houses of congress in the November elections. In compliance with the terms of their Contract with America, and in ``cooperation'' with the Clinton administration, the new congress will attempt to pass legislation to reduce the size of government. As part of this legislation they are likely to eliminate several government agencies.
   • One agency that is a strong candidate for elimination is the Department of Energy (DOE). The DOE plays an important role in several areas. Thus, if eliminated, parts of the DOE will be reorganized and become part of other agencies, perhaps parts moving to the Department of Defense, some to Commerce, some to the Environmental Protection Agency, etc.
   • In the past, the Department of Energy has developed many of their own networking and computer system technologies, separately from the commercial sector and other government agencies. You have been hired by the Department of Energy (don't expect to be employed for very long!) to develop a plan to ease the transition of their information systems into their new homes in other agencies.
   • The goal of reducing waste, and the future cost of computing operations is paramount in the design of the system. It is extremely important that the existing base of DOE users is able to share information and resources with the new agencies. Ideally, the measures taken will not be cumbersome for the users, nor would they be disruptive of the existing activities of the users of any of the systems. There are other concerns that apply, but which were not thought of when the legislation was introduced (as usual). You are expected to recognize these issues and consider them in your design.

   (45 points total) These questions apply to the advance scenario distributed in class (which appears above).

   1. (10 points) As operations are moved from the DOE to other agencies, names of documents and other items will change. What measures can be taken before the transition to ease the transition. Although you didn't get to pick the form of naming used originally, discuss the tradeoffs of the different approaches to naming with respect to such a transition.
   2. (10 points) During the life of the Department of Energy, many online documents were written that referenced files stored on DOE computer systems. As the names of files change, how might you prevent the old references from breaking. Discuss alternative approaches and how each might work in your design.
   3. (25 points) Of the topics/issues we discussed in class, and which have not already been covered by parts a and b, what critical issues will affect the cost and the success or failure of the system after the transition (this is an open ended question, be sure to leave time to answer all the other questions on the exam).

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