CSci 555 / Neuman-Obraczka Fall 1998
Directions for completing exam

Answer the following two questions:

• ( 50 points) Ubiquitous computing and communication motivated the idea of smart spaces, ie, (fixed or mobile) collection of devices with different processing and communication capabilities. As users move about, users and these collection of devices interact with one another. An interesting application of smart spaces is in disaster relief situations caused by natural catastrophes like earthquakes.

  For instance, buildings in an earthquake-prone area like Los Angeles could function as smart spaces. Seismic sensors could be built into the building infrastructure. These sensors serve two purposes: (1) collect ongoing seismic information and information on building structure behavior, and (2) provide information to search and rescue personnel in case a building collapses as result of an earthquake. Ongoing seismic and structural information is saved in a database kept by the construction company which may only be consulted by company personnel. Note that the construction company may have several offices located in different parts of the world.

  Other, more sophisticated devices (eg, special-purpose robots) can also access this information and automatically perform simple scheduled or on-demand maintenance procedures. These robots are also capable of participating in rescue efforts in case of fire or earthquake. All maintenance procedures are recorded in a company-wide maintenance log that can only be consulted by authorized personnel.

  Every once in a while, field technicians and building inspectors come on-site. They use their personal digital assistants (PDAs) or laptops to interact with the building. They are able to collect information emanating from sensors, as well as control a subset of them by adjusting their position (in case they are mobile), sensitivity, reporting threshold, etc. They can also interact with a subset of maintenance robots and request them to perform maintenance and inspection procedures on-the-fly. Control operations affecting sensors and robots can only be executed by authorized personnel. Furthermore, these operations must be done reliably and atomically. In case of fire or earthquake, rescue crews will use similar procedures to interact with the building.

  The wireless networking infrastructure provided by the building also allows maintenance and rescue crews to set up impromptu multimedia teleconferences. Besides audio and video conferencing tools, conference participants can also use a whiteboard tool to plan and report their activities.

  Given the above scenario, answer the following questions:

  • (10 points) List all possible interactions between the building and its "users". In case these interactions generate data, list the producer, consumer, and what type of data access can be performed including access control requirements.
  • (10 points) Given the communication models covered in class, discuss their use in implementing the interactions listed in item (a).
  • (10 points) How would you implement the control operations described above to guarantee they are performed reliably and atomically?
  • (10 points) Suppose the sensoring and maintenance log databases have been implemented in a centralized fashion. Discuss the advantages and disadvantages of this design decision. How could you improve the performance of these centralized databases and what cost does your modification incur?
  • (10 points) Suppose you could re-design these databases in a distributed fashion. How would you distribute them? Would your design still benefit from the same techniques you proposed to improve the performance of the centralized case?

• (50 points) In the past year we have seen an increase in deployment of home networking technologies supporting "always-on" personal connections to the Internet. These technologies include cable modems, ADSL, and wireless systems like Metricom's Ricochet modems. The increased use of such connection technologies will result in increased demand from users to access their "home" resources while at work, while traveling, or by friends and associates.

  In considering the questions that follow, keep in mind that even though the connection may be described as "always-on", the reliability of the connection might not be perfect. Systems will be occasionally disconnected due to line failures, power outages, or if users choose to turn off their home machines. The network addresses of these machines are also likely to change on an occasional basis for home machines, and on a more frequent basis for mobile machines connected through wireless connections.

  • (20 points) Naming: Discuss alternatives for naming in such a system. What are the resources to be named, when will names be used, and from where. For the four models of naming discussed in class, what are the characteristics of the system that make them more or less suitable. Which model of naming would you use for each kind of object to be named. Justify your choice. When implementing the chosen naming model for each kind of object, are there special steps you would take to improve the performance, reliability, availability, manageability, security or cost of the system?
  • ( 20 points) Security: What are the security implications for a system running in such an environment? Describe some of the vulnerabilities that will become more readily exploited on such systems. List the security services that must be provided on user machines, both as a client system, and as a repository for data. How would you implement these services? Justify your choice.
  • ( 10 points) Reliability and availability: Discuss the reliability and availability of the system you designed in items (a) and (b). Discuss some techniques you might use to improve the reliability and availability of the system (beyond what you described in part a).