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Efficiency of semisynchronous versus asynchronous networks

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Abstract

Thes-session problem is studied inasynchronous andsemisynchronous networks. Processes are located at the nodes of an undirected graphG and communicate by sending messages along links that correspond to the edges ofG. A session is a part of an execution in which each process takes at least one step; an algorithm for thes-session problem guarantees the existence of at leasts disjoint sessions. The existence of many sessions guarantees a degree of interleaving which is necessary for certain computations. It is assumed that the (real) time for message delivery is at mostd. In the asynchronous model it is assumed that the time between any two consecutive steps of any process is in the interval [0, 1]; in the semisynchronous model the time between any two consecutive steps of any process is in the interval [c, 1] for somec such that 0 <c ≤ 1,the synchronous model being the special case wherec = 1. All processes are initially synchronized and take a step at time 0.

For the asynchronous model, an upper bound ofdiam(G)(d + l)(s − 1) and a lower bound ofdiam(G)d(s − 1) are presented;diam(G) is thediameter ofG. For the semisynchronous model, an upper bound of 1 + min{⌊1/c⌋ + 1,diam(G)(d + 1)}(s − 2) is presented. The main result of the paper is a lower bound of 1 + min{⌊1/2c⌋,diam(G)d}(s − 2) for the time complexity of any semisynchronous algorithm for thes-session problem, under the assumption thatd ≥ (d/min{⌊1/2c⌋, diam(G)d}) + 2. These results imply a time separation between semisynchronous (in particular, synchronous) and asynchronous networks. Similar results are proved for the case where delays are not uniform.

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A preliminary version of this paper appeared in theProceedings of the 28th Annual Allerton Conference on Communication, Control, and Computing, October 1990, pp. 578–587. H. Attiya was partially supported by B. and G. Greenberg Research Fund (Ottawa) and by Techion V.P.R. funds. Part of this work was performed when she was at the Laboratory for Computer Science, MIT, supported by ONR Contract N00014-85-K-0168, by NSF Grant CCR-8915206, and by DARPA Contract N00014-87-K-0825. M. Mavronicolas was supported by ONR Contract N00014-91-J-1981. His current address is: Department of Computer Science, University of Cyprus, Cyprus, and Institute of Computer Science, Foundation of Research and Technology, Hellas, Greece.

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Attiya, H., Mavronicolas, M. Efficiency of semisynchronous versus asynchronous networks. Math. Systems Theory 27, 547–571 (1994). https://doi.org/10.1007/BF01191625

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  • DOI: https://doi.org/10.1007/BF01191625

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