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Leader Election. Breaking the symmetry in a system. Ring based leader election. The network is known to be a ring Ring size is unknown. Chang-Robert’s algorithm. Every process sends an election message with its id to the left process if it has not seen a message from a higher process

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leader election

Leader Election

Breaking the symmetry in a system

ring based leader election
Ring based leader election
  • The network is known to be a ring
  • Ring size is unknown
chang robert s algorithm
Chang-Robert’s algorithm
  • Every process sends an election message with its id to the left process if it has not seen a message from a higher process
  • Forward any message with an id greater than own id to the left
  • If a process receives its own election message it is the leader
  • It then declares itself to be the leader by sending a leader message
chang roberts leader election
Chang Roberts Leader Election
  • Worst case message complexity

Best case

Worst case

hirschberg sinclair algorithm
Hirschberg-Sinclair algorithm
  • Assume ring is bidirectional
  • Carry out elections on increasingly larger sets
  • Algorithm works in asynchronous rounds
  • Only processes that win the election in round r can proceed to round r+1
  • Algorithm: Pi is the leader in round r iff it has the largest id of all nodes that are at a distance 2r or less from Pi
hirschberg sinclair algorithm6
Hirschberg-Sinclair algorithm
  • Initially:
    • All processes are leaders
  • Round 0:
    • 6 , 7 and 8 are leaders
  • Round 1:
    • 7, 8 are leaders
  • Round 2:
    • 8 is the only leader
  • At most log(N) rounds
election on general graphs
Election on general graphs
  • Totally connected graph – all nodes are mutually connected
  • Homework assignment:
    • Give a randomized algorithm to elect a leader
    • Analyze its message and time complexity