TY - GEN

T1 - Optimal clock synchronization under different delay assumptions

AU - Attiya, Hagit

AU - Herzberg, Amir

AU - Rajsbaum, Sergio

PY - 1993

Y1 - 1993

N2 - The problem of achieving optimal clock synchronization in a communication network with arbitrary topology and perfect clocks (that do not drift) is studied. A novel modular presentation of the problem is described which allows to deal with different assumptions for the delay of messages. We present a definition of clock synchronization under arbitrary delay assumptions, and present an optimal clock synchronization algorithm for general systems. We then show that in local systems (where delays on each link are independent of the other links) the inputs for the clock synchronization algorithm can be computed from the maximum local shifts for each pair of processors sharing a link. The maximum local shift for two processors depends only on their views. This allows our theory to deal with systems where different links adhere to different assumptions, or the same link satisfies several sets of assumptions; such mixtures are quite likely in practice. In particular, we show how to compute the maximum local shifts from the views, and hence provide optimal algorithms for systems where some links may have upper and/or lower bounds on the delay, some may have a bound on the difference between the delay in both directions, some may have both kinds of bounds and some may have no bounds. Previous results dealt only with the case where upper and lower bounds were known for all links. We introduce a new notion of optimality, that requires an algorithm to achieve the best possible precision on each instance; this notion is stronger than the previously used notion of worst case optimality. In contrast to the worst case approach, the new notion handles models where the worst-case behavior of any clock synchronization algorithm is inherently unbounded.

AB - The problem of achieving optimal clock synchronization in a communication network with arbitrary topology and perfect clocks (that do not drift) is studied. A novel modular presentation of the problem is described which allows to deal with different assumptions for the delay of messages. We present a definition of clock synchronization under arbitrary delay assumptions, and present an optimal clock synchronization algorithm for general systems. We then show that in local systems (where delays on each link are independent of the other links) the inputs for the clock synchronization algorithm can be computed from the maximum local shifts for each pair of processors sharing a link. The maximum local shift for two processors depends only on their views. This allows our theory to deal with systems where different links adhere to different assumptions, or the same link satisfies several sets of assumptions; such mixtures are quite likely in practice. In particular, we show how to compute the maximum local shifts from the views, and hence provide optimal algorithms for systems where some links may have upper and/or lower bounds on the delay, some may have a bound on the difference between the delay in both directions, some may have both kinds of bounds and some may have no bounds. Previous results dealt only with the case where upper and lower bounds were known for all links. We introduce a new notion of optimality, that requires an algorithm to achieve the best possible precision on each instance; this notion is stronger than the previously used notion of worst case optimality. In contrast to the worst case approach, the new notion handles models where the worst-case behavior of any clock synchronization algorithm is inherently unbounded.

UR - http://www.scopus.com/inward/record.url?scp=0027802102&partnerID=8YFLogxK

U2 - 10.1145/164051.164067

DO - 10.1145/164051.164067

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AN - SCOPUS:0027802102

SN - 0897916131

SN - 9780897916134

T3 - Proceedings of the Annual ACM Symposium on Principles of Distributed Computing

SP - 109

EP - 120

BT - Proceedings of the Annual ACM Symposium on Principles of Distributed Computing

PB - Publ by ACM

T2 - Proceedings of the 12th Annual ACM Symposium on Principles of Distributed Computing

Y2 - 15 August 1993 through 18 August 1993

ER -