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78
Object Replication Strategies in Content Distribution Networks
 Computer Communications
, 2001
"... content distribution networks (CDNs). In this paper we study the problem of optimally replicating objects in CDN servers. In our model, each Internet Au tonomous System (AS) is a node with finite storage ca pacity for replicating objects. The optimization problem is to replicate objects so that wh ..."
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Cited by 165 (0 self)
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content distribution networks (CDNs). In this paper we study the problem of optimally replicating objects in CDN servers. In our model, each Internet Au tonomous System (AS) is a node with finite storage ca pacity for replicating objects. The optimization problem is to replicate objects so that when clients fetch objects from the nearest CDN server with the requested object, the average number of ASs traversed is minimized. We formulate this problem as a combinatorial optimization problem. We show that this optimization problem is NP complete. We develop four natural heuristics and compare them numerically using real Internet topology data. We find that the best results are obtained with heuristics that have all the CDN servers cooperating in making the replication decisions. We also develop a model for studying the benefits of cooperation between nodes, which provides insight into peertopeer content distribution.
The Cache Location Problem
 IEEE/ACM Transactions on Networking
"... This paper studies the problem of where to place network caches. Emphasis is given to caches that are transparent to the clients since they are easier to manage and they require no cooperation from the clients. Our goal is to minimize the overall flow or the average delay by placing a given number o ..."
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Cited by 152 (6 self)
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This paper studies the problem of where to place network caches. Emphasis is given to caches that are transparent to the clients since they are easier to manage and they require no cooperation from the clients. Our goal is to minimize the overall flow or the average delay by placing a given number of caches in the network.
A new greedy approach for facility location problems
"... We present a simple and natural greedy algorithm for the metric uncapacitated facility location problem achieving an approximation guarantee of 1.61 whereas the best previously known was 1.73. Furthermore, we will show that our algorithm has a property which allows us to apply the technique of Lagra ..."
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Cited by 130 (9 self)
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We present a simple and natural greedy algorithm for the metric uncapacitated facility location problem achieving an approximation guarantee of 1.61 whereas the best previously known was 1.73. Furthermore, we will show that our algorithm has a property which allows us to apply the technique of Lagrangian relaxation. Using this property, we can nd better approximation algorithms for many variants of the facility location problem, such as the capacitated facility location problem with soft capacities and a common generalization of the kmedian and facility location problem. We will also prove a lower bound on the approximability of the kmedian problem.
Greedy Facility Location Algorithms analyzed using Dual Fitting with FactorRevealing LP
 Journal of the ACM
, 2001
"... We present a natural greedy algorithm for the metric uncapacitated facility location problem and use the method of dual fitting to analyze its approximation ratio, which turns out to be 1.861. The running time of our algorithm is O(m log m), where m is the total number of edges in the underlying c ..."
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Cited by 122 (13 self)
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We present a natural greedy algorithm for the metric uncapacitated facility location problem and use the method of dual fitting to analyze its approximation ratio, which turns out to be 1.861. The running time of our algorithm is O(m log m), where m is the total number of edges in the underlying complete bipartite graph between cities and facilities. We use our algorithm to improve recent results for some variants of the problem, such as the fault tolerant and outlier versions. In addition, we introduce a new variant which can be seen as a special case of the concave cost version of this problem.
Efficient and Adaptive Web Replication using Content Clustering
 IEEE Journal on Selected Areas in Communications
, 2003
"... Recently there has been an increasing deployment of content distribution networks (CDNs) that offer hosting services to Web content providers. In this paper, we first compare the uncooperative pulling of Web contents used by commercial CDNs with the cooperative pushing. Our results show that the lat ..."
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Cited by 45 (3 self)
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Recently there has been an increasing deployment of content distribution networks (CDNs) that offer hosting services to Web content providers. In this paper, we first compare the uncooperative pulling of Web contents used by commercial CDNs with the cooperative pushing. Our results show that the latter can achieve comparable users' perceived performance with only 4  5% of replication and update traffic compared to the former scheme. Therefore we explore how to efficiently push content to CDN nodes. Using tracedriven simulation, we show that replicating content in units of URLs can yield 60  70% reduction in clients' latency, compared to replicating in units of Web sites. However, it is very expensive to perform such a finegrained replication.
A Framework for Evaluating Replica Placement Algorithms
, 2002
"... This paper introduces a framework for evaluating replica placement algorithms (RPA) for content delivery networks (CDN) as well as RPAs from other fields that might be applicable to current or future CDNs. First, the framework classifies and qualitatively compares RPAs using a generic set of primiti ..."
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Cited by 42 (1 self)
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This paper introduces a framework for evaluating replica placement algorithms (RPA) for content delivery networks (CDN) as well as RPAs from other fields that might be applicable to current or future CDNs. First, the framework classifies and qualitatively compares RPAs using a generic set of primitives that capture problem definitions and heuristics. Second, it provides estimates for the decision times of RPAs using an analytic model. To achieve accuracy, the model takes into account disk accesses and message sizes, in addition to computational complexity and message numbers that have been considered traditionally. Third, it uses the "goodness" of produced placements to compare RPAs even when they have different problem definitions. Based on these evaluations, we identify open issues and potential areas for future research.
On the Optimization of Storage Capacity Allocation for Content Distribution
 Computer Networks
, 2003
"... The addition of storage capacity in network nodes for the caching or replication of popular data objects results in reduced enduser delay, reduced network tra#c, and improved scalability. ..."
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Cited by 22 (1 self)
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The addition of storage capacity in network nodes for the caching or replication of popular data objects results in reduced enduser delay, reduced network tra#c, and improved scalability.
Online Algorithms for Network Design
 IN PROCEEDINGS OF THE 16TH ACM SYMPOSIUM ON PARALLELISM IN ALGORITHMS AND ARCHITECTURES
, 2003
"... We give the first polylogarithmiccompetitive online algorithms for twometric network design problems. These problems are very general, including as special cases such problems as steiner tree, facility location, and concavecost single commodity flow. ..."
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Cited by 16 (1 self)
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We give the first polylogarithmiccompetitive online algorithms for twometric network design problems. These problems are very general, including as special cases such problems as steiner tree, facility location, and concavecost single commodity flow.
Clustering web content for efficient replication
 In Proceedings of 10th IEEE International Conference on Network Protocols (ICNP’02
, 2002
"... Recently there has been an increasing deployment of content distribution networks (CDNs) that offer hosting services to Web content providers. In this paper, we first compare the uncooperative pulling of Web contents used by commercial CDNs with the cooperative pushing. Our results show that the la ..."
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Cited by 15 (1 self)
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Recently there has been an increasing deployment of content distribution networks (CDNs) that offer hosting services to Web content providers. In this paper, we first compare the uncooperative pulling of Web contents used by commercial CDNs with the cooperative pushing. Our results show that the latter can achieve comparable users ’ perceived performance with only 4 5 % of replication and update traffic compared to the former scheme. Therefore we explore how to efficiently push content to CDN nodes. Using tracedriven simulation, we show that replicating content in units of URLs can yield 60 70 % reduction in clients ’ latency, compared to replicating in units of Web sites. However, it is very expensive to perform such a finegrained replication. To address this issue, we propose to replicate content in units of clusters, each containing objects which are likely to be requested by clients that are topologically close. To this end, we describe three clustering techniques, and use various topologies and several large Web server traces to evaluate their performance. Our results show that the clusterbased replication achieves 40 60 % improvement over the per Web site based replication. In addition, by adjusting the number of clusters, we can smoothly trade off the management and computation cost for better client performance. To adapt to changes in users ’ access patterns, we also explore incremental clusterings that adaptively add new documents to the existing content clusters. We examine both offline and online incremental clusterings, where the former assumes access history is available while the latter predicts access pattern based on the hyperlink structure. Our results show that the offline clusterings yield close to the performance of the complete reclustering at much lower overhead. The online incremental clustering and replication cut down the retrieval cost by 4.6 8 times compared to no replication and random replication, so it is especially useful to improve document availability during flash crowds. 1
HighDensity Model for Server Allocation and Placement
 in Proc. of ACM SIGMETRICS ’02
, 2002
"... It is well known that optimal server placement is NPhard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on highrate vector quantization theory. The key idea is to regard the location of a r ..."
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Cited by 13 (0 self)
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It is well known that optimal server placement is NPhard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on highrate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a joint server allocation and placement algorithm that has a timecomplexity that is linear in the number of clients. Simulations are presented to illustrate its performance.