Results 11  20
of
101
Distributed metric calibration of large camera networks
 in Proc. 1st Workshop on Broadband Advanced Sensor Networks
, 2004
"... Motivated by applications in surveillance sensor networks, we present a distributed algorithm for the automatic, external, metric calibration of a network of cameras with no centralized processor. We model the set of uncalibrated cameras as nodes in a communication network, and propose a distributed ..."
Abstract

Cited by 11 (3 self)
 Add to MetaCart
(Show Context)
Motivated by applications in surveillance sensor networks, we present a distributed algorithm for the automatic, external, metric calibration of a network of cameras with no centralized processor. We model the set of uncalibrated cameras as nodes in a communication network, and propose a distributed algorithm in which each camera only communicates with other cameras that image some of the same scene points. Each node independently forms a neighborhood cluster on which the local calibration takes place, and calibrated nodes and scene points are incrementally merged into a common coordinate frame. The accurate performance of the algorithm is illustrated using examples that model realworld sensor networking situations.
Gossiping in Cayley Graphs by Packets
 In Conf. CCS95 (8 th FrancoJapanese and 4 th FrancoChinese Conf. Combin. Comput. Sci
, 1995
"... . Gossiping (also called total exchange or alltoall communication) is the process of information diffusion in which each node of a network holds a packet that must be communicated to all other nodes in the network. We consider here gossiping in the storeandforward, fullduplex and \Deltaport (o ..."
Abstract

Cited by 10 (4 self)
 Add to MetaCart
(Show Context)
. Gossiping (also called total exchange or alltoall communication) is the process of information diffusion in which each node of a network holds a packet that must be communicated to all other nodes in the network. We consider here gossiping in the storeandforward, fullduplex and \Deltaport (or shouting) model. In such a model, the protocol consists of a sequence of rounds and during each round, each node can send (and receive) messages from all its neighbors. The great majority of the previous works on gossiping problems allows the messages to be freely concatenated and so messages of arbitrary length can be transmitted during a round. Here we restrict the problem to the case where at each round communicating nodes can exchange exactly one packet. We give a lower bound of N \Gamma1 ffi , where ffi is the minimum degree, and show that it is attained in Cayley symmetric digraphs with some additional properties. That implies the existence of an optimal gossiping protocol for clas...
Robust gossiping with an application to consensus
 Journal of Computer and System Sciences
"... We study deterministic gossiping in synchronous systems with dynamic crash failures. Each processor is initialized with an input value called rumor. In the standard gossip problem, the goal of every processor is to learn all the rumors. When processors may crash, then this goal needs to be revised, ..."
Abstract

Cited by 9 (5 self)
 Add to MetaCart
(Show Context)
We study deterministic gossiping in synchronous systems with dynamic crash failures. Each processor is initialized with an input value called rumor. In the standard gossip problem, the goal of every processor is to learn all the rumors. When processors may crash, then this goal needs to be revised, since it is possible, at a point in an execution, that certain rumors are known only to processors that have already crashed. We define gossiping to be completed, for a system with crashes, when every processor knows either the rumor of processor v or that v has already crashed, for any processor v. We design gossiping algorithms that are efficient with respect to both time and communication. Let t < n be the number of failures, where n is the number of processors. If n − t = Ω(n/polylog n), then one of our algorithms completes gossiping in O(log 2 t) time and with O(n polylog n) messages. We develop an algorithm that performs gossiping with O(n 1.77) messages and in O(log 2 n) time, in any execution in which at least one processor remains nonfaulty. We show a tradeoff between time and communication in gossiping algorithms: if the number of messages is at most O(n polylog n), then the time has to be at least Ω ( log n. By way of application, we show that if n − t = Ω(n), then log(n log n)−log t consensus can be solved in O(t) time and with O(n log 2 t) messages.
Optimal Broadcasting in Hypercubes with Dynamic Faults
 INFORMATION PROCESSING LETTERS
, 1999
"... We consider the broadcasting problem in the shouting communication mode in which any node of a network can inform all its neighbours in one time step. In addition, during any time step a number of links less than the edgeconnectivity of the network can be faulty. The problem is to find an upper bou ..."
Abstract

Cited by 9 (2 self)
 Add to MetaCart
We consider the broadcasting problem in the shouting communication mode in which any node of a network can inform all its neighbours in one time step. In addition, during any time step a number of links less than the edgeconnectivity of the network can be faulty. The problem is to find an upper bound on the number of time steps necessary to complete broadcasting under this additional assumption. Fraigniaud and Peyrat proved for the ndimensional hypercube that n + O(log n) time steps are sufficient. De Marco and Vaccaro decreased the upper bound to n+7 and showed a worst case lower bound n + 2 for n 3. We prove that n + 2 time steps are sufficient. Our method is related to the isoperimetric problem in graphs and can be applied to other networks.
Optimal Algorithms for Broadcast and Gossip in the EdgeDisjoint Path Modes (Extended Abstract)
 INFORMATION AND COMPUTATION
, 1994
"... The communication power of the oneway and twoway edgedisjoint path modes for broadcast and gossip is investigated. The complexity of communication algorithms is measured by the number of communication steps (rounds). The main results achieved are the following: 1. For each connected graph Gn of ..."
Abstract

Cited by 8 (1 self)
 Add to MetaCart
The communication power of the oneway and twoway edgedisjoint path modes for broadcast and gossip is investigated. The complexity of communication algorithms is measured by the number of communication steps (rounds). The main results achieved are the following: 1. For each connected graph Gn of n nodes, the complexity of broadcast in Gn , Bmin(Gn ), satisfies dlog 2 ne Bmin(Gn) dlog 2 ne + 1. The complete binary trees meet the upper bound, and all graphs containing a Hamiltonian path meet the lower bound. 2. For each connected graph Gn of n nodes, the oneway (twoway) gossip complexity R(Gn ) (R 2 (Gn)) satisfies dlog 2 ne R 2 (Gn) 2 \Delta dlog 2 ne + 1, 1:44 : : : log 2 n R(Gn) 2 \Delta dlog 2 ne + 2. All these lower and upper bounds a...
Gossiping in VertexDisjoint Paths Mode in dDimensional Grids and Planar Graphs (Extended Abstract)
 Information and Computation
, 1993
"... Juraj Hromkovic y , Ralf Klasing, Elena A. Stohr, Hubert Wagener z Department of Mathematics and Computer Science University of Paderborn, 33095 Paderborn, Germany Abstract The communication modes (oneway and twoway mode) used for sending messages to processors of interconnection networks via ..."
Abstract

Cited by 8 (2 self)
 Add to MetaCart
Juraj Hromkovic y , Ralf Klasing, Elena A. Stohr, Hubert Wagener z Department of Mathematics and Computer Science University of Paderborn, 33095 Paderborn, Germany Abstract The communication modes (oneway and twoway mode) used for sending messages to processors of interconnection networks via vertexdisjoint paths in one communication step are investigated. The complexity of communication algorithms is measured by the number of communication steps (rounds). Here, the complexity of gossiping in grids and in planar graphs is investigated. The main results are the following: 1. Effective oneway and twoway gossip algorithms for ddimensional grids, d 2, are designed. 2. The lower bound 2 log 2 n \Gamma log 2 k \Gamma log 2 log 2 n \Gamma 2 is established on the number of rounds of every twoway gossip algorithm working on any graph of n nodes and vertex bisection k. This proves that the designed twoway gossip algorithms on ddimensional grids, d 3, are almost optimal, and it al...
Dissemination of Information in VertexDisjoint Paths Mode, Part 2: Gossiping in dDimensional Grids and Planar Graphs
 COMPUTER AND ARTI INTELLIGENCE
, 1993
"... This paper continues with the study of the communication modes introduced in [J. Hromkovic, R. Klasing, E.A. St¨ohr, "Dissemination of Information in VertexDisjoint Paths Mode, Part 1: General Bounds and Gossiping in HypercubeLike Networks", submitted to Information and Computation. (Ext ..."
Abstract

Cited by 8 (1 self)
 Add to MetaCart
This paper continues with the study of the communication modes introduced in [J. Hromkovic, R. Klasing, E.A. St¨ohr, "Dissemination of Information in VertexDisjoint Paths Mode, Part 1: General Bounds and Gossiping in HypercubeLike Networks", submitted to Information and Computation. (Extended abstract presented at WG'93.)] as a generalization of the standard oneway and twoway modes allowing to send messages between processors of interconnection networks via vertexdisjoint paths in one communication step. The complexity of communication algorithms is measured by the number of communication steps (rounds). Here, the complexity of gossiping in grids and in planar graphs is investigated. The main results are the following: 1. Effective oneway and twoway gossip algorithms for ddimensional grids, d 2, are designed. 2. The lower bound 2 log 2 n \Gamma log 2 k \Gamma log 2 log 2 n \Gamma 2 is established on the number of rounds of every twoway gossip algorithm working on any graph...
Scheduling Calls for Multicasting in TreeNetworks
, 1998
"... In this paper, we show that the multicast problem in trees can be expressed in term of arranging rows and columns of boolean matrices. Given a p \Theta q matrix M with 01 entries, the shadow of M is defined as a boolean vector x of q entries such that x i = 0 if and only if there is no 1entry in ..."
Abstract

Cited by 7 (4 self)
 Add to MetaCart
In this paper, we show that the multicast problem in trees can be expressed in term of arranging rows and columns of boolean matrices. Given a p \Theta q matrix M with 01 entries, the shadow of M is defined as a boolean vector x of q entries such that x i = 0 if and only if there is no 1entry in the ith column of M , and x i = 1 otherwise. (The shadow x can also be seen as the binary expression of the integer x = P q i=1 x i 2 q\Gammai . Similarly, every row of M can be seen as the binary expression of an integer.) According to this formalism, the key for solving a multicast problem in trees is shown to be the following. Given a p \Theta q matrix M with 01 entries, finding a matrix M such that: 1. M has at most one 1entry per column; 2. every row r of M (viewed as the binary expression of an integer) is larger than the corresponding row r of M , 1 r p; and 3. the shadow of M (viewed as an integer) is minimum. We show that there is an O(q(p + q)) algorithm that fin...
Optimal Odd Gossiping
 PROC. 6TH COLLOQUIUM ON STRUCTURAL INFORMATION & COMMUNICATION COMPLEXITY, PROCEEDINGS IN INFORMATICS 5
, 1998
"... In the gossiping problem, each node in a network starts with a unique piece of information and must acquire the information of all other nodes using twoway communications between pairs of nodes. In this paper we investigate gossiping in nnode networks with n odd. We use a linear cost model in whic ..."
Abstract

Cited by 7 (4 self)
 Add to MetaCart
In the gossiping problem, each node in a network starts with a unique piece of information and must acquire the information of all other nodes using twoway communications between pairs of nodes. In this paper we investigate gossiping in nnode networks with n odd. We use a linear cost model in which the cost of communication is proportional to the amount of information transmitted. In synchronous gossiping, the pairwise communications are organized into rounds, and all communications in a round start at the same time. We present optimal synchronous algorithms for all odd values of n. In asynchronous gossiping, a pair of nodes can start communicating while communications between other pairs are in progress. We provide a short intuitive proof that an asynchronous lower bound due to Peters, Raabe, and Xu is not tight.
Approximation algorithms for minimumtime broadcast under the vertexdisjoint paths mode
 In 9th Annual European Symposium on Algorithms (ESA '01), volume 2161 of LNCS
, 2001
"... We give a polynomialtime O( log n log OPT)approximation algorithm for minimumtime broadcast and minimumtime multicast in nnode networks under the singleport vertexdisjoint paths mode. This improves a previous approximation algorithm by Kortsarz and Peleg. In contrast, we give an (log n) lower ..."
Abstract

Cited by 7 (1 self)
 Add to MetaCart
(Show Context)
We give a polynomialtime O( log n log OPT)approximation algorithm for minimumtime broadcast and minimumtime multicast in nnode networks under the singleport vertexdisjoint paths mode. This improves a previous approximation algorithm by Kortsarz and Peleg. In contrast, we give an (log n) lower bound for the approximation ratio of the minimumtime multicast problem in directed networks. This lower bound holds unless NP Dtime(n log log n). An important consequence of this latter result is that the Steiner version of the Minimum Degree Spanning Tree (MDST) problem in digraphs cannot be approximated within a constant ratio, as opposed to the undirected version. Finally, we give a polynomialtime O(1)approximation algorithm for minimumtime gossip (i.e., alltoall broadcast).