In this paper, we develop an analytical framework to explain the appearance of bimodal degree distribution in existing popular superpeer networks like Gnutella. The framework leads to several interesting and important inferences related to network topology and node/link dynamics. Beyond the simulation based study, we validate our framework through almost exact matching of the topological structure of Gnutella network constructed from real data.
{"title":"Brief announcement: superpeer formation amidst churn and rewiring","authors":"Bivas Mitra, S. Ghose, Niloy Ganguly","doi":"10.1145/1835698.1835733","DOIUrl":"https://doi.org/10.1145/1835698.1835733","url":null,"abstract":"In this paper, we develop an analytical framework to explain the appearance of bimodal degree distribution in existing popular superpeer networks like Gnutella. The framework leads to several interesting and important inferences related to network topology and node/link dynamics. Beyond the simulation based study, we validate our framework through almost exact matching of the topological structure of Gnutella network constructed from real data.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129023656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present view transactions, a model for relaxed consistency checks in software transactional memory (STM). View transactions always operate on a consistent snapshot of memory but may commit in a different snapshot. They are therefore simpler to reason about, provide opacity and maintain composability. In addition, view transactions avoid many of the overheads associated with previous approaches for relaxing consistency checks. As a result, view transactions outperform the prior approaches by 1.13x to 2x on various benchmarks.
{"title":"Brief announcement: view transactions: transactional model with relaxed consistency checks","authors":"Y. Afek, Adam Morrison, Moran Tzafrir","doi":"10.1145/1835698.1835711","DOIUrl":"https://doi.org/10.1145/1835698.1835711","url":null,"abstract":"We present view transactions, a model for relaxed consistency checks in software transactional memory (STM). View transactions always operate on a consistent snapshot of memory but may commit in a different snapshot. They are therefore simpler to reason about, provide opacity and maintain composability. In addition, view transactions avoid many of the overheads associated with previous approaches for relaxing consistency checks. As a result, view transactions outperform the prior approaches by 1.13x to 2x on various benchmarks.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129658643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper deals with pipelined queries over services. The execution plan of such queries defines an order in which the services are called. We present the theoretical underpinnings of a newly proposed algorithm that produces the optimal linear ordering corresponding to a query being executed in a decentralized manner, i.e., when the services communicate directly with each other. The optimality is defined in terms of query response time, which is determined by the bottleneck service in the plan. The properties discussed in this work allow a branch-and-bound approach to be very efficient.
{"title":"Brief announcement: on the quest of optimal service ordering in decentralized queries","authors":"Efthymia Tsamoura, A. Gounaris, Y. Manolopoulos","doi":"10.1145/1835698.1835763","DOIUrl":"https://doi.org/10.1145/1835698.1835763","url":null,"abstract":"This paper deals with pipelined queries over services. The execution plan of such queries defines an order in which the services are called. We present the theoretical underpinnings of a newly proposed algorithm that produces the optimal linear ordering corresponding to a query being executed in a decentralized manner, i.e., when the services communicate directly with each other. The optimality is defined in terms of query response time, which is determined by the bottleneck service in the plan. The properties discussed in this work allow a branch-and-bound approach to be very efficient.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128941251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Session details: Regular papers","authors":"F. Petit","doi":"10.1145/3258218","DOIUrl":"https://doi.org/10.1145/3258218","url":null,"abstract":"","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"145 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122413743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Bar-Noy, Panagiotis Cheilaris, Yi Feng, Asaf Levin
A token is hidden in one of several boxes and then the boxes are locked. The probability of placing the token in each of the boxes is known. A searcher is looking for the token by unlocking boxes where each box is associated with an unlocking cost. The searcher conducts its search in rounds and must find the token in a predetermined number of rounds. In each round, the searcher may unlock any set of locked boxes concurrently. The optimization goal is to minimize the expected cost of unlocking boxes until the token is found. The motivation and main application of this game is the task of paging a mobile user (token) who is roaming in a zone of cells (boxes) in a cellular network system. Here, the unlocking costs reflect cell congestions and the placing probabilities represent the likelihood of the user residing in particular cells. Another application is the task of finding some data (token) that may be known to one of the sensors (boxes) of a sensor network. Here, the unlocking costs reflect the energy consumption of querying sensors and the placing probabilities represent the likelihood of the data being found in particular sensors. In general, we call mobile data any entity that has to be searched for. The special case, in which all the boxes have equal unlocking costs has been well studied in recent years and several optimal polynomial time solutions exist. To the best of our knowledge, this paper is the first to study the general problem in which each box may be associated with a different unlocking cost. We first present three special interesting and important cases for which optimal polynomial time algorithms exist: (i) There is no a priori knowledge about the location of the token and therefore all the placing probabilities are the same. (ii) There are no delay constraints so in each round only one box is unlocked. (iii) The token is atypical in the sense that it is more likely to be placed in boxes whose unlocking cost is low. Next, we consider the case of a typical token for which the unlocking cost of any box is proportional to the probability of placing the token in this box. We show that computing the optimal strategy is strongly NP-Hard for any number of unlocking rounds, we provide a PTAS algorithm, and analyze a greedy solution. We propose a natural dynamic programming heuristic that unlocks the boxes in a non-increasing order of the ratio probability over cost. For two rounds, we prove that this strategy is a 1.143-approximation solution for an arbitrary token and a 1.108-approximation for a typical token and that both bounds are tight. For an arbitrary token, we provide a more complicated PTAS
{"title":"Finding mobile data under delay constraints with searching costs","authors":"A. Bar-Noy, Panagiotis Cheilaris, Yi Feng, Asaf Levin","doi":"10.1145/1835698.1835774","DOIUrl":"https://doi.org/10.1145/1835698.1835774","url":null,"abstract":"A token is hidden in one of several boxes and then the boxes are locked. The probability of placing the token in each of the boxes is known. A searcher is looking for the token by unlocking boxes where each box is associated with an unlocking cost. The searcher conducts its search in rounds and must find the token in a predetermined number of rounds. In each round, the searcher may unlock any set of locked boxes concurrently. The optimization goal is to minimize the expected cost of unlocking boxes until the token is found. The motivation and main application of this game is the task of paging a mobile user (token) who is roaming in a zone of cells (boxes) in a cellular network system. Here, the unlocking costs reflect cell congestions and the placing probabilities represent the likelihood of the user residing in particular cells. Another application is the task of finding some data (token) that may be known to one of the sensors (boxes) of a sensor network. Here, the unlocking costs reflect the energy consumption of querying sensors and the placing probabilities represent the likelihood of the data being found in particular sensors. In general, we call mobile data any entity that has to be searched for. The special case, in which all the boxes have equal unlocking costs has been well studied in recent years and several optimal polynomial time solutions exist. To the best of our knowledge, this paper is the first to study the general problem in which each box may be associated with a different unlocking cost. We first present three special interesting and important cases for which optimal polynomial time algorithms exist: (i) There is no a priori knowledge about the location of the token and therefore all the placing probabilities are the same. (ii) There are no delay constraints so in each round only one box is unlocked. (iii) The token is atypical in the sense that it is more likely to be placed in boxes whose unlocking cost is low. Next, we consider the case of a typical token for which the unlocking cost of any box is proportional to the probability of placing the token in this box. We show that computing the optimal strategy is strongly NP-Hard for any number of unlocking rounds, we provide a PTAS algorithm, and analyze a greedy solution. We propose a natural dynamic programming heuristic that unlocks the boxes in a non-increasing order of the ratio probability over cost. For two rounds, we prove that this strategy is a 1.143-approximation solution for an arbitrary token and a 1.108-approximation for a typical token and that both bounds are tight. For an arbitrary token, we provide a more complicated PTAS","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"152 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122497313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Kuhn, N. Lynch, Calvin C. Newport, R. Oshman, A. Richa
Practitioners agree that unreliable links, which sometimes deliver messages and sometime do not, are an important characteristic of wireless networks. In contrast, most theoretical models of radio networks fix a static set of links and assume that these links are reliable. This gap between theory and practice motivates us to investigate how unreliable links affect theoretical bounds on broadcast in radio networks. To that end we consider a model that includes two types of links: reliable links, which always deliver messages, and unreliable links, which sometimes fail to deliver messages. We assume that the reliable links induce a connected graph, and that unreliable links are controlled by a worst-case adversary. In the new model we show an Ω(n log n) lower bound on deterministic broadcast in undirected graphs, even when all processes are initially awake and have collision detection, and an Ω(n) lower bound on randomized broadcast in undirected networks of constant diameter. This separates the new model from the classical, reliable model. On the positive side, we give two algorithms that tolerate unreliability: an O(n3/2 √log n)-time deterministic algorithm and a randomized algorithm which terminates in O(n log2 n) rounds with high probability.
{"title":"Broadcasting in unreliable radio networks","authors":"F. Kuhn, N. Lynch, Calvin C. Newport, R. Oshman, A. Richa","doi":"10.1145/1835698.1835779","DOIUrl":"https://doi.org/10.1145/1835698.1835779","url":null,"abstract":"Practitioners agree that unreliable links, which sometimes deliver messages and sometime do not, are an important characteristic of wireless networks. In contrast, most theoretical models of radio networks fix a static set of links and assume that these links are reliable. This gap between theory and practice motivates us to investigate how unreliable links affect theoretical bounds on broadcast in radio networks. To that end we consider a model that includes two types of links: reliable links, which always deliver messages, and unreliable links, which sometimes fail to deliver messages. We assume that the reliable links induce a connected graph, and that unreliable links are controlled by a worst-case adversary. In the new model we show an Ω(n log n) lower bound on deterministic broadcast in undirected graphs, even when all processes are initially awake and have collision detection, and an Ω(n) lower bound on randomized broadcast in undirected networks of constant diameter. This separates the new model from the classical, reliable model. On the positive side, we give two algorithms that tolerate unreliability: an O(n3/2 √log n)-time deterministic algorithm and a randomized algorithm which terminates in O(n log2 n) rounds with high probability.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"191 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122858829","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Session details: Brief announcements","authors":"C. Cachin","doi":"10.1145/3258215","DOIUrl":"https://doi.org/10.1145/3258215","url":null,"abstract":"","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121429994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Consider a distributed network in which events occur at arbitrary nodes and at unpredicted times. An event occurring at node u is sensed only by u which in turn may invoke a communication protocol that allows nodes to exchange messages with their neighbors. We are interested in the following threshold detection (TD) problem inherent to distributed computing: Given some threshold k, the goal of a TD protocol is to broadcast a termination signal when at least k events have occurred (throughout the network). In this paper we develop a randomized TD protocol that may fail with negligible probability but which significantly improves previous results in terms of the message complexity, namely, the total number of messages sent by all participating nodes. With the right choice of parameters our randomized protocol turns into a deterministic one that guarantees low communication burden for any node. This is a principal complexity measure in many applications of wireless networks and which, to the best of our knowledge, has not been bounded before in the context of such problems.
{"title":"Efficient threshold detection in a distributed environment: extended abstract","authors":"Y. Emek, Amos Korman","doi":"10.1145/1835698.1835742","DOIUrl":"https://doi.org/10.1145/1835698.1835742","url":null,"abstract":"Consider a distributed network in which events occur at arbitrary nodes and at unpredicted times. An event occurring at node u is sensed only by u which in turn may invoke a communication protocol that allows nodes to exchange messages with their neighbors. We are interested in the following threshold detection (TD) problem inherent to distributed computing: Given some threshold k, the goal of a TD protocol is to broadcast a termination signal when at least k events have occurred (throughout the network). In this paper we develop a randomized TD protocol that may fail with negligible probability but which significantly improves previous results in terms of the message complexity, namely, the total number of messages sent by all participating nodes. With the right choice of parameters our randomized protocol turns into a deterministic one that guarantees low communication burden for any node. This is a principal complexity measure in many applications of wireless networks and which, to the best of our knowledge, has not been bounded before in the context of such problems.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116212930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We consider the rational secret sharing problem introduced by Halpern and Teague [1]. Some positive results have been derived by Kol and Naor[3] by considering that players only prefer to learn.The solution considers that players are of two types; one player is the short player and the rest of the players are long players. But their protocol is susceptible to coalitions if the short player colludes with any of the long players. We extend their protocol, and propose a completely collusion free, &3949;-Nash equilibrium protocol, when n ≥ 2m-1, where n is the number of players and m is the number of shares needed to construct the secret.
{"title":"Brief announcement: collusion free protocol for rational secret sharing","authors":"A. Shareef","doi":"10.1145/1835698.1835792","DOIUrl":"https://doi.org/10.1145/1835698.1835792","url":null,"abstract":"We consider the rational secret sharing problem introduced by Halpern and Teague [1]. Some positive results have been derived by Kol and Naor[3] by considering that players only prefer to learn.The solution considers that players are of two types; one player is the short player and the rest of the players are long players. But their protocol is susceptible to coalitions if the short player colludes with any of the long players. We extend their protocol, and propose a completely collusion free, &3949;-Nash equilibrium protocol, when n ≥ 2m-1, where n is the number of players and m is the number of shares needed to construct the secret.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"14 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126118213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Session details: Regular papers","authors":"Luís Rodrigues","doi":"10.1145/3258208","DOIUrl":"https://doi.org/10.1145/3258208","url":null,"abstract":"","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124664965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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