454 E&CE Distributed and Network-Centric Computing
Final Examination Spring 2000 Thursday, August 3, 2000 Instructor Kostas Kontogiannis
Notes: This is a closed book exam. Total exam time is 3 hours. No programmable electronic storage-capable devices are allowed. You may only use simple calculators. This exam has in total 115 marks. If information seems to be missing, state your assumptions and proceed for a solution.
Question 1 [10 marks] Pertaining to Networking
1. [5 marks] Discuss how Naming, Addressing and, Routing is handled in the TCP/IP protocol. 2. [5 marks] List and briefly discuss the most important differences between connectionless and connection-oriented computer communication protocols.
Question 2 [10 marks] Pertaining to RPC and Distributed Operating Systems
1. [4 marks] List and briefly discuss (one sentence) each of the critical path steps in an RPC call 2. [6 marks] Discuss the copy-on-write technique for the creation of new execution environments
Question 3 [20 marks] Pertaining to Time and Coordination
1. [5 marks] Discuss Cristian's algorithm for time coordination with respect to its behavior and
accuracy.
2. [5 marks] Discuss the Berkley algorithm for clock synchronization. 3. [10 marks] Adapt the central server model for mutual exclusion to handle the following failure conditions: i. the failure of a token-holding client ii. the failure of a client that has requested but not yet received a token iii. the failure of a mutual exclusion server
Question 4 [10 marks] Pertaining to Processes and Scheduling
Explain and give an example for each of: a) [5 marks] The ring-based election algorithm, and b) [5 marks] The bully election algorithm
Question 5 [15 marks] Pertaining to synchronization
A server manages the data items a1, a2, ... an.. The server provides two operations for its clients: Read(i) : returns the value of ai Write(i, value) : assigns value to ai The transactions T and U are defined as follows: T: x = Read(i); y = Read(i); Write(j, 44); Write(i, 33) U: x = Read(k); Write(i, 55); y = Read(j); Write(k, 66) Give three serially equivalent of interleavings the transactions T and U.
Question 6 [15 marks] Pertaining to synchronization
Give a serially equivalent interleaving of T and U, with the following properties: a) that is strict b) that is not strict but could not produce cascading aborts c) that could produce cascading aborts The transactions T and U are defined as follows: T: x = Read(i); y = Read(i); Write(j, 44); Write(i, 33) U: x = Read(k); Write(i, 55); y = Read(j); Write(k, 66)
Question 7 [15 marks] Pertaining to synchronization
Consider the following sequences of operations of the transactions T and U: T OpenTransaction y = Read(k) U Open Transaction Write(i, 55) Write(j, 66) Commit x = Read(i) Write(j, 44)
The outcome of optimistic concurrency control with backward validation is that T will be aborted, because its Read operation conflicts with U's Write operation on j, although the interleavings are serially equivalent. Suggest a modification to the algorithm that deals with such cases.
Question 8 [20 marks] Pertaining to Distributed Transactions
Consider the use of timestamp ordering with the interleavings of transactions T and U given below. Initial values of i and j are 10 and 20 and initial read and write timestamps are t0. Assume each transaction opens and obta...