Distributed systems UE Past Papers Questions.

Why is computer clock synchronization necessary ?

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What is a leap second and why is it used ?

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Explain Cristian`s algorithm for clock synchronisation

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Suppose there are three processses A ,B  and C. All clock runs at the same rate but initially A`s clock reads 10, B`s clock reads 0 and C`s clock reads 5. At time 10 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 illustrating the timestamps for the messages and explain how the timestamps are obtained.
• What does it mean for two events to be concurrent and what is the relation of the Lamport timestamps of the two events.

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Explain in detail the Bully algorithm for electing a leader.

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