On the bit communication complexity of randomized rumor spreading

  • Authors:
  • Pierre Fraigniaud;George Giakkoupis

  • Affiliations:
  • CNRS and Univ. Paris Diderot, Paris, France;CNRS and Univ. Paris Diderot, Paris, France

  • Venue:
  • Proceedings of the twenty-second annual ACM symposium on Parallelism in algorithms and architectures
  • Year:
  • 2010

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Abstract

We study the communication complexity of rumor spreading in the random phone-call model. Suppose nplayers communicate in parallel rounds, where in each round every player calls a randomly selected communication partner. A player u is allowed to exchange messages during a round only with the player that u called, and with all the players that $u$ received calls from, in that round. In every round, a (possibly empty) set of rumors to be distributed among all players is generated, and each of the rumors is initially placed in a subset of the players. Karp et. al \cite{Karp2000} showed that no rumor-spreading algorithm that spreads a rumor to all players with constant probability can be both time-optimal, taking O(lg n) rounds, and message-optimal, using O(n) messages per rumor. For address-oblivious algorithms, in particular, they showed that Ω(n lg lg n) messages per rumor are required, and they described an algorithm that matches this bound and takes O(lg n) rounds. We investigate the number of communication bits required for rumor spreading. On the lower-bound side, we establish that any address-oblivious algorithm taking O(lg n) rounds requires Ω(n (b+ lg lg n)) communication bits to distribute a rumor of size b bits. On the upper-bound side, we propose an address-oblivious algorithm that takes O(lg n) rounds and uses O(n(b+ lg lg n lg b)) bits. These results show that, unlike the case for the message complexity, optimality in terms of both the running time and the bit communication complexity is attainable, except for very small rumor sizes b n lg lg lg n.