Theory of Computing Systems

, Volume 49, Issue 4, pp 781–816

Gradient Clock Synchronization in Dynamic Networks

Article

Abstract

Over the last years, large-scale decentralized computer networks such as peer-to-peer and mobile ad hoc networks have become increasingly prevalent. The topologies of many of these networks are often highly dynamic. This is especially true for ad hoc networks formed by mobile wireless devices.

In this paper, we study the fundamental problem of clock synchronization in dynamic networks. We show that there is an inherent trade-off between the skew \(\mathcal{S}\) guaranteed along sufficiently old links and the time needed to guarantee a small skew along new links: for any sufficiently large initial skew on a new link, there are executions in which the time required to reduce the skew on the link to \(O(\mathcal{S})\) is at least \(\Omega(n/\mathcal{S})\).

We show that this bound is tight for moderately small values of \(\mathcal{S}\). Assuming a fixed set of n nodes, an arbitrary pattern of edge insertions and removals, and a weak dynamic connectivity requirement, we present an algorithm that always maintains a skew of O(n) between any two nodes in the network. For a parameter \(\mathcal{S}=\Omega(\sqrt{\rho n})\), where ρ is the maximum hardware clock drift, it is further guaranteed that if a communication link between two nodes u,v persists in the network for \(\Theta(n/\mathcal{S})\) time, the clock skew between u and v is reduced to no more than \(O(\mathcal{S})\).

Keywords

Distributed algorithms Dynamic networks Gradient clock synchronization Lower bound 

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Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  1. 1.Faculty of InformaticsUniversity of LuganoLuganoSwitzerland
  2. 2.Computer Engineering and Networks LaboratoryETH ZurichZurichSwitzerland
  3. 3.Computer Science and Artificial Intelligence LaboratoryMITCambridgeUSA

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