Tutorial 7

1. Suppose there are three processes A, B and C. All clocks run at the same rate (1 unit of time) but initially A’s clock reads 12, B’s clock reads 0 and C’s clock reads 5. At time 12 by A’s clock, A sends a message to B, this message takes 4 units of time to reach B. B then waits one unit of time and then sends a message onto C which takes 2 units of time to reach C. Assuming that the system implements Lamport’s timestamps, draw a picture to illustrate the timestamps for the messages and how the timestamps are obtained.

2. Three clocks X, Y and Z are performing internal synchronization by using Berkeley algorithm. X is reading 15:00:00.0 (hr:min:sec) when it is chosen as the master clock. Y and Z are reading 15:50:00.0 and 14:40:00.0, respectively. Illustrate the clock synchronization process with diagrams (initialization, polls the times, adjust the times) and calculations.

3. You are on a network with a 9 Mbps downstream bandwidth and a 1 Mbps upstream bandwidth. Your client makes a request at 9:10:00.0 and gets a response 200 msec later. If the time on the server is 8:42:00.0, what would the time be set to on your client?