1 research outputs found
Tight Bounds for Black Hole Search in Dynamic Rings
In this paper, we start the investigation of distributed computing by mobile
agents in dangerous dynamic networks. The danger is posed by the presence in
the network of a black hole BH, a harmful site that destroys all incoming
agents without leaving any trace. The problem of determining the location of
the black hole in a network, known as black hole search BHS, has been
extensively studied in the literature, but always and only assuming that the
network is static. At the same time, the existing results on mobile agents
computing in dynamic networks never consider the presence of harmful sites.
In this paper we start filling this research gap by studying black hole
search in temporal rings, specifically focusing on 1-interval connectivity
adversarial dynamics. The problem is solved if within finite time at least one
agent survives and knows the location of BH. The main complexity parameters of
BHS is the number of agents (called size) needed to solve the problem, and the
number of moves (called cost) performed by the agents; in synchronous systems,
such as temporal rings, an additional complexity measure is the amount of time
until termination occurs.
Feasibility and complexity depend on many parameters; in particular: whether
the agents start from the same safe node or from possibly distinct safe
locations, the size of the ring, whether or not is known, and the type
of inter-agent communication (whiteboards, tokens, face-to-face, visual). In
this paper, we provide a complete feasibility characterization for all
instances of those parameters; all our algorithms are size optimal.
Furthermore, we establish lower bounds on the cost (i.e., the number of moves)
and time of size-optimal solutions for all instances of those parameters and
show that our algorithms achieve those bound