L. Lamport and P. Melliar-Smith, "Synchronizing clocks in the presence of faults," J. ACM, vol. 32, no. 1, pp. 52--78, 1985.  Home/Search   Document Not in Database   Summary   ACM   TOC   Related Articles   Check

....xx requires synchronized clocks with precision . are commonly used in modern textbooks on very different subjects, like communication protocols and data base systems. The clock synchronization algorithms of Halpern Simons Strong Dolev [3] Lundelius Lynch [5] Lamport Melliar Smith [4], Mahaney Schneider [6] Cristian Aghili Strong [1] Srikant Toueg [7] and the many variants derived from them) but also related theoretical work form a well established basis for applications that require synchronized clocks. So why wasting time and money by publishing a 1997 special issue ....

L. Lamport, P.M. Melliar-Smith. Synchronizing Clocks in the Presence of Faults, Journal of the ACM, 32(1), January 1985, p. 52--78.

....of the synchronized clocks are proven to be optimal. 1 Introduction Most distributed systems encountered in practice are asynchronous, in that they do not guarantee a bound on message communication delays. Traditional deterministic, fault tolerant clock synchronization algorithms such as those of [2, 3] assume bounded communication delays. Thus, they cannot be directly used to synchronize clocks in asynchronous systems. Moreover, these protocols typically require the transmission of at least messages each time clocks are synchronized and all messages are exchanged in a bursty manner within a ....

....can be used to synchronize clocks despite unbounded communication delays. Since probabilistic reading achieves higher precisions than deterministic reading, the protocols achieve synchronization precisions better than those achievable by previously known deterministic algorithms, such as those of [2, 3, 7, 8]. Our algorithms use several new midpoint convergence functions, derived from the original fault tolerant midpoint convergence function of [3] These new convergence functions achieve optimal accuracy: the drift rate of the synchronized clocks is bounded by the maximum drift rate of correct ....

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, Jan 1985.

....of California San Diego, La Jolla, CA 92093 0114. This research was partially supported by a grant from the Air Force Office of Scientific Research. quired to meet their deadlines, provided no more than a bounded number of failures occur [9] Examples are internal clock synchronization [18] and synchronous atomic broadcast [7] and membership services [8] The implementation of such services depends critically on the existence of an upper bound for message transmission and process scheduling delays. Synchronous fault tolerant services cannot be implemented in asynchronous systems ....

....fail aware distributed service. An example of the usage of an indicator in distributed services are the membership services of [8, 11] each of which has a joined indicator telling the service clients whether they are joined to a group or not. Most internal clock synchronization protocols, e.g. [18, 19], mask arbitrary failures, in the sense that correct clocks are synchronized when less than a third of the clocks suffer failures. Our proposed fail aware clock synchronization service handles performance, omission, and crash failures but does not tolerate arbitrary failures. An extension to mask ....

[Article contains additional citation context not shown here]

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, Jan 1985.

....is ambiguity as to which clock a process should use when an external application requests the time. Moreover, setting the clock forward at each resynchronization introduces a discontinuity in the logical time (when a process switches to a new logical clock) As Lamport and Melliar Smith noted in [9], an algorithm for discontinuously resynchronizing clocks can be easily transformed into one where logical clocks are continuous. This can be achieved by spreading out each resynchronization adjustment over the next resynchronization period. In this section we provide details on how to modify our ....

....averaging, and for the nonauthenticated case, given Dmx, the maximum permitted deviation between correct clocks, our algorithm needs about half as many resynchronizations as in the best previous result [ 10] The minimum value olDmax that our algorithm can achieve depends only on 9 and tdel. In [9], the minimum Dmax possible is proportional to the number of processes in the system. In the preceding sections, we have assumed a completely connected network. This assumption can be relaxed using well known techniques. For an authenticated system, node connectivity off 1 is sufficient. This ....

LAMPORT, L., AND MELLIAR-SMITH, P.M. Synchronizing clocks in the presence of faults. J. ACM 32, I (Jan. 1985), 52-78.

....total number of processes. The closeness of synchronization achi.eved depends only on the initial closeness of synchronization, the message delivery time and its uncertainty, and the drift rate. Since the closeness of synchronization depends on the initial closeness, this is, in the terminology of [LM], an interactive convergence algorithm. We give explicit bounds on how the difference between the clock values and real time grows. The algorithm can be easily adapted to become a reintegration procedure for repaired processes. Lamport and Melttar Smith [LM] Halpern, Simons and Strong [HSS] and ....

....this is, in the terminology of [LM] an interactive convergence algorithm. We give explicit bounds on how the difference between the clock values and real time grows. The algorithm can be easily adapted to become a reintegration procedure for repaired processes. Lamport and Melttar Smith [LM], Halpern, Simons and Strong [HSS] and Marzullo [M] also have clock synchronization algorithms that run in rounds. The three algorithms in [LM] as do ours, require a reliable, completely connected communication network and handle arbitrary faults. However, the closeness of synchronization ....

[Article contains additional citation context not shown here]

L. Lamport and P.M. Melliar-Smith, Synchronizing clocks in the presence of faults, SRI International Report (March 1982).

....at slightly different rates) The restart problem is to reestablish synchronization after transient faults have afflicted one or more (or all) controllers. The synchronization problem is well understood and many algorithms to solve it have been developed, analyzed, and formally verified [LMS85, Min93, Sha92, WL88] The algorithm employed in TTA belongs to the general class of averaging synchronization algorithms [Sch87] each controller i estimates its skew relative to each controller p by comparing the reading of its local clock at the instant when the message in slot p arrives ....

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, January 1985. 23

....in the full version of the paper. 5. FUTURE DIRECTIONS Our results require that at most a third of the processors are faulty during each period. Previous clock synchronization protocols assuming authenticated channels (as we do) were able to require only a majority of non faulty processors [19, 27]. It is interesting to close this gap. In [10] there is another weaker requirement: only that subnetwork containing non faulty processors remain connected (but [10] also assumes signatures) It may be possible to prove a variant of this for our protocol, in particular it would be interesting to ....

L. Lamport and P.M. Melliar-Smith, Synchronizing clocks in the presence of faults, JACM Vol. 32, No. 1, Jan. 1985, pp. 52--78.

....O(t 1) rounds of message exchange. Since our implementation of a k fail stop processor need tolerate at most k failures and involves at least 2k 1 processors for running s processes, IC1 and IC2 can be achieved. Protocols to achieve clock synchronization, as required by IC3, are described in [LM82] These protocols require at least 2t 1 processors in order to tolerate at most t faulty ones, if the origin of messages can be authenticated. For a single k fail stop pro cessor, IC3 requires the k 1 processors running p processes to have synchronized clocks. However, it is impossible to use ....

Lamport, L., P.M. Melliar-Smith. Synchronizing Clocks in the Presence of Faults. Op. $0, Com- puter Science Laboratory, SRI International, Menlo Park, California, March I982.

....on FCA. This provides the background necessary for understanding the modifications required to CCA so that it can be used for clock synchronization. We next sketch that. A detailed analysis of the performance of our clock synchronization protocols is not given here, since it differs from that in [LM85] only in the use of a different value for precision. 4.1. Using FCA to Synchronize Clocks Each processor p is assumed to have a real time clock which we model as a function c p from real time to clock time. Correct real time clocks satisfy Rate Restriction: dc p (t ) 1 for some ....

Lamport, L. and P.M. Melliar-Smith. Synchronizing clocks in the presence of faults. JACM 32, 1 (Jan. 1985), 52-78.

....CF Avg (x p , x 1, x N ) is the average of arguments x 1 through x N after the k highest and k lowest values have been discarded. The degree k of fault tolerance for CF Avg is characterized by 3k 1 = N . Precision p is N 2k f d a(d) d. CF EA was first proposed and analyized in [Lamport Milliar Smith 85] in connection with a clock synchronization algorithm. CF FCA is discussed in [Mahaney Schneider 85] who were the first to view convergence functions (there, called inexact agreement protocols) in terms of accuracy and precision. CF Mid and CF Avg are given in [Dolev et al. 83] CF Avg is the ....

....Message delivery times are typically non trivial and unpredictable. Thus, it is impossible for a single processor in a distributed system to compute CF (c p (t T ) c p (t T ) as required by the resynchronization protocol outlined in section 2. 6 A technique originally proposed in [Lamport Milliar Smith 85] allows one processor to compute an approximation for a virtual clock at another. Each processor p maintains a collection of tables t p [1 . N ] containing values that transform c p (t ) into an approximation for c q (t ) Processor p approximates c q (t ) by c p (t ) t p [q ] To ....

[Article contains additional citation context not shown here]

Lamport, L. and P.M. Milliar-Smith. Synchronizing clocks in the presence of faults. J. ACM 32, 1 (Jan. 1985), 52-78.

No context found.

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, 1985.

No context found.

L. Lamport and P. Melliar-Smith, "Synchronizing clocks in the presence of faults," J. ACM, vol. 32, no. 1, pp. 52--78, 1985.

No context found.

L. Lamport, P. Melliar-Smith, Synchronizing clocks in the presence of faults, J. ACM 32 (1) (1985) 52--78.

No context found.

Lamport, L., and P.M. Melliar-Smith. Synchronizing clocks in the presence of faults. JACM 32, 1 (January 1985), 52-78.

No context found.

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, Jan. 1985.

No context found.

Lamport, L., and P.M. Melliar-Smith. Synchronizing clocks in the presence of faults. JACM 32, 1 (January 1985), 52-78.

No context found.

Leslie Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, January 1985.

No context found.

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1):52--78, January 1985.

No context found.

Lamport, L., and P. Melliar-Smith "Synchronizing Clocks in the Presence of Faults", JACM 32, No. 1, pgs. 52-78, January 1985.

No context found.

L.Lamport and P.M. Mellair-Smith, "Synchronizing Clocks in the Presence of Faults", In Journal of the ACM, Vol. 32, No. 1, pp. 1-36, 1985

No context found.

L. Lamport and P. Melliar-Smith. Synchronizing clocks in the presence of faults. J. ACM, 32(1):52--78, 1985.

No context found.

L. Lamport and P. M. Melliar-Smith. Synchronizing clocks in the presence of faults. Journal of the ACM, 32(1), pages 52--78, 1985.

No context found.

L. Lamport and M. Melliar-Smith, `Synchronizing clocks in the presence of faults', Journal of the ACM, 32, (l), 52--78 (1985).

No context found.

L. Lamport and P. J. Melliar-Smith, "Synchronizing clocks in the presence of faults," Journal of the ACM, vol. 32, no. 1, pp. 52--78, 1985.

No context found.

Lamport, L. and P.M. Melliar-Smith. Synchronizing clocks in the presence of faults. J. ACM 32, 1 (lan. 1985), 52-78.

First 50 documents  Next 50

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC