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19
The Load, Capacity and Availability of Quorum Systems
, 1998
"... A quorum system is a collection of sets (quorums) every two of which intersect. Quorum systems have been used for many applications in the area of distributed systems, including mutual exclusion, data replication and dissemination of information Given a strategy to pick quorums, the load L(S) is th ..."
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Cited by 89 (12 self)
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A quorum system is a collection of sets (quorums) every two of which intersect. Quorum systems have been used for many applications in the area of distributed systems, including mutual exclusion, data replication and dissemination of information Given a strategy to pick quorums, the load L(S) is the minimal access probability of the busiest element, minimizing over the strategies. The capacity Cap(S) is the highest quorum accesses rate that S can handle, so Cap(S) = 1=L(S).
Towards an Archival Intermemory
 In Proc. of IEEE ADL
, 1998
"... We propose a selforganizing archival Intermemory. That is, a noncommercial subscriberprovided distributed information storage service built on the existing Internet. Given an assumption of continued growth in the memory's total size, a subscriber's participation for only a finite time can neverthe ..."
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Cited by 88 (1 self)
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We propose a selforganizing archival Intermemory. That is, a noncommercial subscriberprovided distributed information storage service built on the existing Internet. Given an assumption of continued growth in the memory's total size, a subscriber's participation for only a finite time can nevertheless ensure archival preservation of the subscriber's data. Information disperses through the network over time and memories become more difficult to erase as they age. The probability of losing an old memory given random node failures is vanishingly small  and an adversary would have to corrupt hundreds of thousands of nodes to destroy a very old memory. This paper presents a framework for the design of an Intermemory, and considers certain aspects of the design in greater detail. In particular, the aspects of addressing, space efficiency, and redundant coding are discussed. Keywords: Archival Storage, Distributed Redundant Databases, Electronic Publishing, Distributed Algorithms, Error ...
A constantfactor approximation algorithm for packet routing, and balancing local vs. global criteria
 In Proceedings of the ACM Symposium on the Theory of Computing (STOC
, 1997
"... Abstract. We present the first constantfactor approximation algorithm for a fundamental problem: the storeandforward packet routing problem on arbitrary networks. Furthermore, the queue sizes required at the edges are bounded by an absolute constant. Thus, this algorithmbalances a global criterio ..."
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Cited by 46 (5 self)
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Abstract. We present the first constantfactor approximation algorithm for a fundamental problem: the storeandforward packet routing problem on arbitrary networks. Furthermore, the queue sizes required at the edges are bounded by an absolute constant. Thus, this algorithmbalances a global criterion (routing time) with a local criterion (maximum queue size) and shows how to get simultaneous good bounds for both. For this particular problem, approximating the routing time well, even without considering the queue sizes, was open. We then consider a class of such local vs. global problems in the context of covering integer programs and show how to improve the local criterion by a logarithmic factor by losing a constant factor in the global criterion.
Improved Approximation Guarantees for Packing and Covering Integer Programs
 SIAM J. Comput
, 1995
"... Several important NPhard combinatorial optimization problems can be posed as packing/covering integer programs; the randomized rounding technique of Raghavan & Thompson is a powerful tool to approximate them well. We present one elementary unifying property of all these integer programs (IPs), and ..."
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Cited by 43 (6 self)
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Several important NPhard combinatorial optimization problems can be posed as packing/covering integer programs; the randomized rounding technique of Raghavan & Thompson is a powerful tool to approximate them well. We present one elementary unifying property of all these integer programs (IPs), and use the FKG correlation inequality to derive an improved analysis of randomized rounding on them. This also yields a pessimistic estimator, thus presenting deterministic polynomialtime algorithms for them with approximation guarantees significantly better than those known. Keywords.Approximation Algorithms, Combinatorial Optimization, Correlation Inequalities, Covering Integer Programs, Derandomization, Integer Programming, Linear Programming, Linear Relaxations, Packing Integer Programs, Positive Correlation, Randomized Rounding, Rounding Theorems. 1 Preliminary versions of this work appeared in the Proc. ACM Symposium on the Theory of Computing, pages 268276, 1995, and as DIMACS Te...
Network Coding for Joint Storage and Transmission with Minimum Cost
 In ISIT
, 2006
"... Abstract — Network coding provides elegant solutions to many data transmission problems. The usage of coding for distributed data storage has also been explored. In this work, we study a joint storage and transmission problem, where a source transmits a file to storage nodes whenever the file is upd ..."
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Cited by 20 (0 self)
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Abstract — Network coding provides elegant solutions to many data transmission problems. The usage of coding for distributed data storage has also been explored. In this work, we study a joint storage and transmission problem, where a source transmits a file to storage nodes whenever the file is updated, and clients read the file by retrieving data from the storage nodes. The cost includes the transmission cost for file update and file read, as well as the storage cost. We show that such a problem can be transformed into a pure flow problem and is solvable in polynomial time using linear programming. Coding is often necessary for obtaining the optimal solution with the minimum cost. However, we prove that for networks of generalized tree structures, where adjacent nodes can have asymmetric links between them, file splitting — instead of coding — is sufficient for achieving optimality. In particular, if there is no constraint on the numbers of bits that can be stored in storage nodes, there exists an optimal solution that always transmits and stores the file as a whole. The proof is accompanied by an algorithm that optimally assigns file segments to storage nodes. I.
Contentaccess QoS in peertopeer networks using a fast MDS erasure code
 ERASURE CODE,” ELSEVIER COMPUTER COMMUNICATIONS
, 2005
"... This paper describes an enhancement of content access Quality of Service in peer to peer (P2P) networks. The main idea is to use an erasure code to distribute the information over the peers. This distribution increases the users ’ choice on disseminated encoded data and therefore statistically enhan ..."
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Cited by 10 (2 self)
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This paper describes an enhancement of content access Quality of Service in peer to peer (P2P) networks. The main idea is to use an erasure code to distribute the information over the peers. This distribution increases the users ’ choice on disseminated encoded data and therefore statistically enhances the overall throughput of the transfer. A performance evaluation based on an original model using the results of a measurement campaign of sequential and parallel downloads in a real P2P network over Internet is presented. Based on a bandwidth distribution, statistical contentaccess QoS are guaranteed in function of both the content replication level in the network and the file dissemination strategies. A simple application in the context of media streaming is proposed. Finally, the constraints on the erasure code related to the proposed system are analysed and a new fast MDS erasure code is proposed, implemented and evaluated.
Network file storage with graceful performance degradation
 ACM Transactions on Storage
, 2005
"... A file storage scheme is proposed for networks containing heterogeneous clients. In the scheme, the performance measured by fileretrieval delays degrades gracefully under increasingly serious faulty circumstances. The scheme combines coding with storage for better performance. The problem is NPhar ..."
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Cited by 8 (3 self)
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A file storage scheme is proposed for networks containing heterogeneous clients. In the scheme, the performance measured by fileretrieval delays degrades gracefully under increasingly serious faulty circumstances. The scheme combines coding with storage for better performance. The problem is NPhard for general networks; and this paper focuses on tree networks with asymmetric edges between adjacent nodes. A polynomialtime memoryallocation algorithm is presented, which determines how much data to store on each node, with the objective of minimizing the total amount of data stored in the network. Then a polynomialtime datainterleaving algorithm is used to determine which data to store on each node for satisfying the qualityofservice requirements in the scheme. By combining the memoryallocation algorithm with the datainterleaving algorithm, an optimal solution to realize the file storage scheme in tree networks is established.
Approximation Algorithms for Stochastic and RiskAverse Optimization
, 2007
"... We present improved approximation algorithms in stochastic optimization. We prove that the multistage stochastic versions of covering integer programs (such as set cover and vertex cover) admit essentially the same approximation algorithms as their standard (nonstochastic) counterparts; this impro ..."
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Cited by 8 (0 self)
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We present improved approximation algorithms in stochastic optimization. We prove that the multistage stochastic versions of covering integer programs (such as set cover and vertex cover) admit essentially the same approximation algorithms as their standard (nonstochastic) counterparts; this improves upon work of Swamy & Shmoys that shows an approximability which depends multiplicatively on the number of stages. We also present approximation algorithms for facility location and some of its variants in the 2stage recourse model, improving on previous approximation guarantees.
Multicluster interleaving on paths and cycles
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2005
"... Interleaving codewords is an important method not only for combatting bursterrors, but also for distributed data retrieval. This paper introduces the concept of MultiCluster Interleaving (MCI), a generalization of traditional interleaving problems. MCI problems for paths and cycles are studied. T ..."
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Cited by 4 (3 self)
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Interleaving codewords is an important method not only for combatting bursterrors, but also for distributed data retrieval. This paper introduces the concept of MultiCluster Interleaving (MCI), a generalization of traditional interleaving problems. MCI problems for paths and cycles are studied. The following problem is solved: how to interleave integers on a path or cycle such that any m (m ≥ 2) nonoverlapping clusters of order 2 in the path or cycle have at least 3 distinct integers. We then present a scheme using a ‘hierarchicalchain structure’ to solve the following more general problem for paths: how to interleave integers on a path such that any m (m ≥ 2) nonoverlapping clusters of order L (L ≥ 2) in the path have at least L + 1 distinct integers. It is shown that the scheme solves the second interleaving problem for paths that are asymptotically as long as the longest path on which an MCI exists, and clearly, for shorter paths as well.