Results 1  10
of
10
Hardness and approximation of gathering in static radio networks
 Parallel Processing Letters
, 2006
"... In this paper, we address the problem of gathering information in a specific node (or sink) of a radio network, where interference constraints are present. We take into account the fact that, when a node transmits, it produces interference in an area bigger than the area in which its message can act ..."
Abstract

Cited by 35 (7 self)
 Add to MetaCart
In this paper, we address the problem of gathering information in a specific node (or sink) of a radio network, where interference constraints are present. We take into account the fact that, when a node transmits, it produces interference in an area bigger than the area in which its message can actually be received. The network is modeled by a graph; a node is able to transmit one unit of information to the set of vertices at distance at most dT in the graph, but when doing so it generates interference that does not allow nodes at distance up to dI (dI ≥ dT) to listen to other transmissions. Time is synchronous and divided into timesteps in each of which a round (set of noninterfering radio transmissions) is performed. We give general lower bounds on the number of rounds required to gather into a sink of a general graph, and present an algorithm working on any graph, with an approximation factor of 4. We also show that the problem of finding an optimal strategy for gathering is NPhard, for any values of dI and dT. If dI> dT, we show that the problem remains hard when restricted to the uniform case where each vertex in the network has exactly one piece of information to communicate to the sink. 1
Algorithms for Data Migration with Cloning
, 2003
"... Our work is motivated by the problem of managing data on storage devices, typically a set of disks. Such high demand storage servers are used as web servers, or multimedia servers for handling high demand for data. As the system is running, it needs to dynamically respond to changes in demand for di ..."
Abstract

Cited by 32 (4 self)
 Add to MetaCart
Our work is motivated by the problem of managing data on storage devices, typically a set of disks. Such high demand storage servers are used as web servers, or multimedia servers for handling high demand for data. As the system is running, it needs to dynamically respond to changes in demand for di#erent data items. In this work we study the data migration problem, which arises when we need to quickly change one storage configuration into another. We show that this problem is NPhard. In addition, we develop polynomialtime approximation algorithms for this problem and prove a worst case bound of 9.5 on the approximation factor achieved by our algorithm. We also compare the algorithm to several heuristics for this problem.
On Generalized Gossiping and Broadcasting
 in Proceedings of the 11th Annual European Symposium on Algorithms (ESA), Lecture Notes in Comput. Sci. 2832
, 2003
"... The problems of gossiping and broadcasting have been widely studied. The basic gossip problem is defined as follows: there are n individuals, with each individual having an item of gossip. The goal is to communicate each item of gossip to every other individual. ..."
Abstract

Cited by 5 (1 self)
 Add to MetaCart
The problems of gossiping and broadcasting have been widely studied. The basic gossip problem is defined as follows: there are n individuals, with each individual having an item of gossip. The goal is to communicate each item of gossip to every other individual.
Optimal Gossiping in Paths and Cycles
, 1997
"... In the gossiping problem, each node in a network possesses a token initially; after gossiping, every node has a copy of every other node's token. The nodes exchange their tokens by packets. A solution to the problem is judged by how many rounds of packet sending it requires. In this paper, we consid ..."
Abstract

Cited by 2 (2 self)
 Add to MetaCart
In the gossiping problem, each node in a network possesses a token initially; after gossiping, every node has a copy of every other node's token. The nodes exchange their tokens by packets. A solution to the problem is judged by how many rounds of packet sending it requires. In this paper, we consider the version of the problem in which a packet is of limited size (a packet can hold up to p tokens), the links (edges) of the network are halfduplex (only one packet can flow through a link at a time), and the nodes are allport (a node's incident edges can all be active at the same time). This is also known as the H* model. We study the path and the cycle which are essential building blocks for more complex structures. We present tight lower bounds and matching algorithms. The results also lead to the conclusion that p = 2 is the optimal packet size. 1 Introduction In parallel and distributed computing, communication among the processors is an important issue. Gossiping, also known a...
Concurrent Multicast in Weighted Networks
 SWAT
, 1998
"... Concurrent multicast is the problem of information dissemination from a set of source nodes to a set of destination nodes in a network with cost function: Each source node s needs to multicast a block of data B(s) to the set of destinations. We are interested in protocols for this problem which have ..."
Abstract

Cited by 1 (0 self)
 Add to MetaCart
Concurrent multicast is the problem of information dissemination from a set of source nodes to a set of destination nodes in a network with cost function: Each source node s needs to multicast a block of data B(s) to the set of destinations. We are interested in protocols for this problem which have minimum communication cost. We consider both the usual case in which any transmitted message can consist of an arbitrary number of data blocks and the case in which each message must consist of exactly one block of data. The problem of determining the minimum cost to perform concurrent multicast from a given set of sources to a set of destinations is NPhard under both assumptions. We give approximation algorithms to efficiently perform concurrent multicast in arbitrary networks. We also analyze the communication time and communication complexity, i.e., the product of the communication cost and time, of our algorithms. A preliminary version of an extended abstract of this paper was presen...
unknown title
"... Abstract Our work was motivated by the problem of managing data on storage devices, typically a set of parallel disks. Due to dynamic changes in load, one needs to develop algorithms for quickly changing one storage configuration into another. We refer to this problem as the data migration problem. ..."
Abstract
 Add to MetaCart
Abstract Our work was motivated by the problem of managing data on storage devices, typically a set of parallel disks. Due to dynamic changes in load, one needs to develop algorithms for quickly changing one storage configuration into another. We refer to this problem as the data migration problem. 1 Introduction To handle high demand, especially for multimedia data, a common approach is to replicate data objects within the storage system. Typically, a large storage server consists of several disks connected using a dedicated network, called a Storage Area Network. Disks typically have constraints on storage as well as the number of clients that can access data from a single disk simultaneously.
1 Hardness and approximation of Gathering in static radio networks
"... Abstract — In this paper, we address the problem of gathering information in a central node of a radio network, where interference constraints are present. We take into account the fact that, when a node transmits, it produces interference in an area bigger than the area in which its message can act ..."
Abstract
 Add to MetaCart
Abstract — In this paper, we address the problem of gathering information in a central node of a radio network, where interference constraints are present. We take into account the fact that, when a node transmits, it produces interference in an area bigger than the area in which its message can actually be received. The network is modeled by a graph; a node is able to transmit one unit of information to the set of vertices at distance at most dT in the graph, but when doing so it generates interference that does not allow nodes at distance up to dI (dI ≥ dT) to listen to other transmissions. Time is synchronous and divided into timesteps in each of which a round (set of noninterfering radio transmissions) is performed. We give a general lower bound on the number of rounds required to gather on any graph, and present an algorithm working on any graph, with an approximation factor of 4. We also show that the problem of finding an optimal strategy for gathering (one that uses a minimum number of timesteps) does not admit a Fully Polynomial Time Approximation Scheme if dI> dT, unless P=NP, and in the case dI = dT the problem is NPhard. I.
❢c World Scientific Publishing Company HARDNESS AND APPROXIMATION OF GATHERING IN STATIC RADIO NETWORKS ∗
, 2009
"... In this paper, we address the problem of gathering information in a specific node (or sink) of a radio network, where interference constraints are present. We take into account the fact that, when a node transmits, it produces interference in an area bigger than the area in which its message can act ..."
Abstract
 Add to MetaCart
In this paper, we address the problem of gathering information in a specific node (or sink) of a radio network, where interference constraints are present. We take into account the fact that, when a node transmits, it produces interference in an area bigger than the area in which its message can actually be received. The network is modeled by a graph; a node is able to transmit one unit of information to the set of vertices at distance at most dT in the graph, but when doing so it generates interference that does not allow nodes at distance up to dI (dI ≥ dT) to listen to other transmissions. Time is synchronous and divided into timesteps in each of which a round (set of noninterfering radio transmissions) is performed. We give general lower bounds on the number of rounds required to gather into a sink of a general graph, and present an algorithm working on any graph, with an approximation factor of 4. We also show that the problem of finding an optimal strategy for gathering is NPHARD, for any values of dI and dT. If dI> dT, we show that the problem remains hard when restricted to the uniform case where each vertex in the network has exactly one piece of information to communicate to the sink.
Gathering radio messages in the path ∗
, 2011
"... In this paper, we address the problem of gathering information in one node (sink) of a radio network where interference constraints are present: when a node transmits, it produces interference in an area bigger than the area in which its message can actually be received. The network is modeled by a ..."
Abstract
 Add to MetaCart
In this paper, we address the problem of gathering information in one node (sink) of a radio network where interference constraints are present: when a node transmits, it produces interference in an area bigger than the area in which its message can actually be received. The network is modeled by a graph; a node is able to transmit one unit of information to the set of vertices at distance at most dT in the graph, but when doing so it generates interferences that do not allow nodes at distance up to dI (dI ≥ dT) to listen to other transmissions. We are interested in finding a gathering protocol, that is an ordered sequence of rounds (each round consists of noninterfering simultaneous transmissions) such that w(u) messages are transmitted from node u to a fixed node called the sink. Our aim is to find the minimum number of rounds called gathering time. In this article, we focus on the specific case where the network is a path and where the traffic is unitary (w(u) = 1 for all u); indeed this simple case appears to be already very difficult. We give for arbitrary location of the sink lower and upper bounds on the number of rounds that differ only by a constant independent of the length of the path. When the sink is an endvertex of the path, we present a method to construct incremental protocols. An incremental protocol for the path on n+1 vertices is obtained from a protocol for n vertices by adding new rounds and new calls to some rounds but without changing the calls of the original rounds. We conjecture that this incremental construction gives optimal protocols and prove it in some special cases (dT prime in particular). Radio networks, interference, paths, gathering, approximation algoKeywords: rithms.
Mention INFORMATIQUE
, 2009
"... pour obtenir le titre de Docteur en SCIENCES de l’Université de NiceSophia Antipolis ..."
Abstract
 Add to MetaCart
pour obtenir le titre de Docteur en SCIENCES de l’Université de NiceSophia Antipolis