8,234 research outputs found
A Process Calculus for Dynamic Networks
In this paper we propose a process calculus framework for dynamic networks in which the network topology may change as computation proceeds. The proposed calculus allows one to abstract away from neighborhood-discovery computations and it contains features for broadcasting at multiple transmission ranges and for viewing networks at different levels of abstraction. We develop a theory of confluence for the calculus and we use the machinery developed towards
the verification of a leader-election algorithm for mobile ad hoc networks
Robust Leader Election in a Fast-Changing World
We consider the problem of electing a leader among nodes in a highly dynamic
network where the adversary has unbounded capacity to insert and remove nodes
(including the leader) from the network and change connectivity at will. We
present a randomized Las Vegas algorithm that (re)elects a leader in O(D\log n)
rounds with high probability, where D is a bound on the dynamic diameter of the
network and n is the maximum number of nodes in the network at any point in
time. We assume a model of broadcast-based communication where a node can send
only 1 message of O(\log n) bits per round and is not aware of the receivers in
advance. Thus, our results also apply to mobile wireless ad-hoc networks,
improving over the optimal (for deterministic algorithms) O(Dn) solution
presented at FOMC 2011. We show that our algorithm is optimal by proving that
any randomized Las Vegas algorithm takes at least omega(D\log n) rounds to
elect a leader with high probability, which shows that our algorithm yields the
best possible (up to constants) termination time.Comment: In Proceedings FOMC 2013, arXiv:1310.459
Rational Fair Consensus in the GOSSIP Model
The \emph{rational fair consensus problem} can be informally defined as
follows. Consider a network of (selfish) \emph{rational agents}, each of
them initially supporting a \emph{color} chosen from a finite set .
The goal is to design a protocol that leads the network to a stable
monochromatic configuration (i.e. a consensus) such that the probability that
the winning color is is equal to the fraction of the agents that initially
support , for any . Furthermore, this fairness property must
be guaranteed (with high probability) even in presence of any fixed
\emph{coalition} of rational agents that may deviate from the protocol in order
to increase the winning probability of their supported colors. A protocol
having this property, in presence of coalitions of size at most , is said to
be a \emph{whp\,--strong equilibrium}. We investigate, for the first time,
the rational fair consensus problem in the GOSSIP communication model where, at
every round, every agent can actively contact at most one neighbor via a
\emph{pushpull} operation. We provide a randomized GOSSIP protocol that,
starting from any initial color configuration of the complete graph, achieves
rational fair consensus within rounds using messages of
size, w.h.p. More in details, we prove that our protocol is a
whp\,--strong equilibrium for any and, moreover, it
tolerates worst-case permanent faults provided that the number of non-faulty
agents is . As far as we know, our protocol is the first solution
which avoids any all-to-all communication, thus resulting in message
complexity.Comment: Accepted at IPDPS'1
Dynamic sharing of a multiple access channel
In this paper we consider the mutual exclusion problem on a multiple access
channel. Mutual exclusion is one of the fundamental problems in distributed
computing. In the classic version of this problem, n processes perform a
concurrent program which occasionally triggers some of them to use shared
resources, such as memory, communication channel, device, etc. The goal is to
design a distributed algorithm to control entries and exits to/from the shared
resource in such a way that in any time there is at most one process accessing
it. We consider both the classic and a slightly weaker version of mutual
exclusion, called ep-mutual-exclusion, where for each period of a process
staying in the critical section the probability that there is some other
process in the critical section is at most ep. We show that there are channel
settings, where the classic mutual exclusion is not feasible even for
randomized algorithms, while ep-mutual-exclusion is. In more relaxed channel
settings, we prove an exponential gap between the makespan complexity of the
classic mutual exclusion problem and its weaker ep-exclusion version. We also
show how to guarantee fairness of mutual exclusion algorithms, i.e., that each
process that wants to enter the critical section will eventually succeed
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