2,672 research outputs found
Telecommunications Network Planning and Maintenance
Telecommunications network operators are on a constant challenge to provide new services which require ubiquitous broadband access. In an attempt to do so, they are faced with many problems such as the network coverage or providing the guaranteed Quality of Service (QoS). Network planning is a multi-objective optimization problem which involves clustering the area of interest by minimizing a cost function which includes relevant parameters, such as installation cost, distance between user and base station, supported traffic, quality of received signal, etc. On the other hand, service assurance deals with the disorders that occur in hardware or software of the managed network. This paper presents a large number of multicriteria techniques that have been developed to deal with different kinds of problems regarding network planning and service assurance. The state of the art presented will help the reader to develop a broader understanding of the problems in the domain
Iterative Approximate Consensus in the presence of Byzantine Link Failures
This paper explores the problem of reaching approximate consensus in
synchronous point-to-point networks, where each directed link of the underlying
communication graph represents a communication channel between a pair of nodes.
We adopt the transient Byzantine link failure model [15, 16], where an
omniscient adversary controls a subset of the directed communication links, but
the nodes are assumed to be fault-free.
Recent work has addressed the problem of reaching approximate consen- sus in
incomplete graphs with Byzantine nodes using a restricted class of iterative
algorithms that maintain only a small amount of memory across iterations [22,
21, 23, 12]. However, to the best of our knowledge, we are the first to
consider approximate consensus in the presence of Byzan- tine links. We extend
our past work that provided exact characterization of graphs in which the
iterative approximate consensus problem in the presence of Byzantine node
failures is solvable [22, 21]. In particular, we prove a tight necessary and
sufficient condition on the underlying com- munication graph for the existence
of iterative approximate consensus algorithms under transient Byzantine link
model. The condition answers (part of) the open problem stated in [16].Comment: arXiv admin note: text overlap with arXiv:1202.609
06371 Abstracts Collection -- From Security to Dependability
From 10.09.06 to 15.09.06, the Dagstuhl Seminar 06371 ``From Security to Dependability\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Solving k-Set Agreement with Stable Skeleton Graphs
In this paper we consider the k-set agreement problem in distributed
message-passing systems using a round-based approach: Both synchrony of
communication and failures are captured just by means of the messages that
arrive within a round, resulting in round-by-round communication graphs that
can be characterized by simple communication predicates. We introduce the weak
communication predicate PSources(k) and show that it is tight for k-set
agreement, in the following sense: We (i) prove that there is no algorithm for
solving (k-1)-set agreement in systems characterized by PSources(k), and (ii)
present a novel distributed algorithm that achieves k-set agreement in runs
where PSources(k) holds. Our algorithm uses local approximations of the stable
skeleton graph, which reflects the underlying perpetual synchrony of a run. We
prove that this approximation is correct in all runs, regardless of the
communication predicate, and show that graph-theoretic properties of the stable
skeleton graph can be used to solve k-set agreement if PSources(k) holds.Comment: to appear in 16th IEEE Workshop on Dependable Parallel, Distributed
and Network-Centric System
Deaf, Dumb, and Chatting Robots, Enabling Distributed Computation and Fault-Tolerance Among Stigmergic Robot
We investigate ways for the exchange of information (explicit communication)
among deaf and dumb mobile robots scattered in the plane. We introduce the use
of movement-signals (analogously to flight signals and bees waggle) as a mean
to transfer messages, enabling the use of distributed algorithms among the
robots. We propose one-to-one deterministic movement protocols that implement
explicit communication. We first present protocols for synchronous robots. We
begin with a very simple coding protocol for two robots. Based on on this
protocol, we provide one-to-one communication for any system of n \geq 2 robots
equipped with observable IDs that agree on a common direction (sense of
direction). We then propose two solutions enabling one-to-one communication
among anonymous robots. Since the robots are devoid of observable IDs, both
protocols build recognition mechanisms using the (weak) capabilities offered to
the robots. The first protocol assumes that the robots agree on a common
direction and a common handedness (chirality), while the second protocol
assumes chirality only. Next, we show how the movements of robots can provide
implicit acknowledgments in asynchronous systems. We use this result to design
asynchronous one-to-one communication with two robots only. Finally, we combine
this solution with the schemes developed in synchronous settings to fit the
general case of asynchronous one-to-one communication among any number of
robots. Our protocols enable the use of distributing algorithms based on
message exchanges among swarms of Stigmergic robots. Furthermore, they provides
robots equipped with means of communication to overcome faults of their
communication device
Stabilizing Server-Based Storage in Byzantine Asynchronous Message-Passing Systems
A stabilizing Byzantine single-writer single-reader (SWSR) regular register,
which stabilizes after the first invoked write operation, is first presented.
Then, new/old ordering inversions are eliminated by the use of a (bounded)
sequence number for writes, obtaining a practically stabilizing SWSR atomic
register. A practically stabilizing Byzantine single-writer multi-reader (SWMR)
atomic register is then obtained by using several copies of SWSR atomic
registers. Finally, bounded time-stamps, with a time-stamp per writer, together
with SWMR atomic registers, are used to construct a practically stabilizing
Byzantine multi-writer multi-reader (MWMR) atomic register. In a system of
servers implementing an atomic register, and in addition to transient failures,
the constructions tolerate t<n/8 Byzantine servers if communication is
asynchronous, and t<n/3 Byzantine servers if it is synchronous. The noteworthy
feature of the proposed algorithms is that (to our knowledge) these are the
first that build an atomic read/write storage on top of asynchronous servers
prone to transient failures, and where up to t of them can be Byzantine
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