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HW3FailureDetectionConsensusPeerToPeer-solution

# HW3FailureDetectionConsensusPeerToPeer-solution - Homework...

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Homework 3 (Failure Detection, Consensus, Peer to Peer, Routing, Distributed Object) 100 Points CS425/ECE 428 Distributed Systems, Fall 2009, Instructor: Klara Nahrstedt Out: Thursday, October 15, Due Date : Thursday, October 29 Instructions: (1) Please, hand in hardcopy solutions that are typed (you may use your favorite word processor). We will not accept handwritten solutions. Figures and equations (if any) may be drawn by hand. (2) Please, start each problem on a fresh sheet and type your name at the top of each sheet. (3) Homework will be due at the beginning of class on the day of the deadline. Relevant Reading for this Homework: Chapter 3 Problem 1: Failure Detection (20 Points) Centralized heart-beating and ring heart-beating may not detect simultaneous multiple failures of processes, while all-to-all heart-beating is too expensive (in terms of messages sent per time unit). Suppose, in an asynchronous system that initially has N processes, you are given that at most N/4 processes may crash. (a) Design an efficient failure detector algorithm for this system. Your failure detector should satisfy completeness. Either give pseudo-code for your algorithm, or explain it using a figure. (b) How many failure detector messages are sent by your algorithm if no failures occur? (c) Calculate the best-case and worst-case detection times for your failure detector (hint: These are likely to occur with 1 and N/4 simultaneous failures respectively.) Solutions: ( a) Ring-heart-beating can be modified to design a fault detector that can detect simultaneous failures, where at most N/4 simultaneous failures can occur. Processes form a ring, ordered using

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