Showing papers by "Yehuda Afek published in 1987"

Applying static network protocols to dynamic networks

Abstract: This paper addresses the problem of how to adapt an algorithm designed for fixed topology networks to produce the intended results, when run in a network whose topology changes dynamically, in spite of encountering topological changes during its execution. We present a simple and unified procedure, called a reset procedure, which, when combined with the static algorithm, achieves this adaptation. The communication and time complexities of the reset procedure, per topological change, are independent of the number of topological changes and are linearly bounded by the size of the subset of the network which participates in the algorithm.

Local management of a global resource in a communication network

Abstract: We introduce a new primitive, the Resource Controller, which abstracts the problem of controlling the total amount of resources consumed by a distributed algorithm. We present an efficient distributed algorithm to implement this abstraction. The message complexity of our algorithm per participating node is polylogarithmic in the size of the network, compared to the linear cost per node of the naive algorithm. The implementation of our algorithm is simple and practical and the techniques used are interesting because a global quantity is managed in a distributed way. The Resource Controller can be used to construct efficient algorithms for a number of important problems, such as the problem of bounding the worst-case message complexity of a protocol and the problem of dynamically assigning unique names to nodes participating in a protocol.

Detecting global termination conditions in the face of uncertainty

Abstract: We introduce a new problem, the Tokelz Collectiort Problem for distributed networks, \vhich models the general problem of detecting termination conditions in systems which contain uncertainty. We consider a rooted tree in kvhich tokens appear spontaneously at the nodes at arbitrary times. The Token Collection Problem with threshold t. (TCP(i)j. 1s LU collect t tokens at the root. Besides modeling fault-tolerant termination detection. this problem arises in other distributed algorithms. such as. fnult-roleram eiectiolt. reliotfi d ncquisiriofz. nem*ork reco\‘erJ. and token d -ributiorl. A message-efficient distributed algorithm for the TCP(t) i\ prsrenced. wh: ch uses 0(1r .log’t . log’r) msssages \vhere II is the total number of nodes. and r is the height of the tree. Using the algorithm as a mechanism for termination detection we establish an 0 (111 f/z .logjn) messages upper bound on the problem of fault-tolerant electiorz. where III is the total number of links in the network. This improves on the previous upper Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission.

Local Fail-safe Network Reset Procedure

Abstract: A simple, general and optimal procedure to adapt algorithms designed for fixed topology networks to run on a network with dynamically changing topology is presented. The communication and time complexities of the procedure, per topological change, are independent of the number of topological changes and are linearly bounded by the size of the subnetwork over which the algorithm is running.