37,398 research outputs found
Termination Detection of Local Computations
Contrary to the sequential world, the processes involved in a distributed
system do not necessarily know when a computation is globally finished. This
paper investigates the problem of the detection of the termination of local
computations. We define four types of termination detection: no detection,
detection of the local termination, detection by a distributed observer,
detection of the global termination. We give a complete characterisation
(except in the local termination detection case where a partial one is given)
for each of this termination detection and show that they define a strict
hierarchy. These results emphasise the difference between computability of a
distributed task and termination detection. Furthermore, these
characterisations encompass all standard criteria that are usually formulated :
topological restriction (tree, rings, or triangu- lated networks ...),
topological knowledge (size, diameter ...), and local knowledge to distinguish
nodes (identities, sense of direction). These results are now presented as
corollaries of generalising theorems. As a very special and important case, the
techniques are also applied to the election problem. Though given in the model
of local computations, these results can give qualitative insight for similar
results in other standard models. The necessary conditions involve graphs
covering and quasi-covering; the sufficient conditions (constructive local
computations) are based upon an enumeration algorithm of Mazurkiewicz and a
stable properties detection algorithm of Szymanski, Shi and Prywes
Distributed Apportioning in a Power Network for providing Demand Response Services
Greater penetration of Distributed Energy Resources (DERs) in power networks
requires coordination strategies that allow for self-adjustment of
contributions in a network of DERs, owing to variability in generation and
demand. In this article, a distributed scheme is proposed that enables a DER in
a network to arrive at viable power reference commands that satisfies the DERs
local constraints on its generation and loads it has to service, while, the
aggregated behavior of multiple DERs in the network and their respective loads
meet the ancillary services demanded by the grid. The Net-load Management
system for a single unit is referred to as the Local Inverter System (LIS) in
this article . A distinguishing feature of the proposed consensus based
solution is the distributed finite time termination of the algorithm that
allows each LIS unit in the network to determine power reference commands in
the presence of communication delays in a distributed manner. The proposed
scheme allows prioritization of Renewable Energy Sources (RES) in the network
and also enables auto-adjustment of contributions from LIS units with lower
priority resources (non-RES). The methods are validated using
hardware-in-the-loop simulations with Raspberry PI devices as distributed
control units, implementing the proposed distributed algorithm and responsible
for determining and dispatching realtime power reference commands to simulated
power electronics interface emulating LIS units for demand response.Comment: 7 pages, 11 Figures, IEEE International Conference on Smart Grid
Communication
Byzantine-Tolerant Set-Constrained Delivery Broadcast
Set-Constrained Delivery Broadcast (SCD-broadcast), recently introduced at ICDCN 2018, is a high-level communication abstraction that captures ordering properties not between individual messages but between sets of messages. More precisely, it allows processes to broadcast messages and deliver sets of messages, under the constraint that if a process delivers a set containing a message m before a set containing a message m\u27, then no other process delivers first a set containing m\u27 and later a set containing m. It has been shown that SCD-broadcast and read/write registers are computationally equivalent, and an algorithm implementing SCD-broadcast is known in the context of asynchronous message passing systems prone to crash failures.
This paper introduces a Byzantine-tolerant SCD-broadcast algorithm, which we call BSCD-broadcast. Our proposed algorithm assumes an underlying basic Byzantine-tolerant reliable broadcast abstraction. We first introduce an intermediary communication primitive, Byzantine FIFO broadcast (BFIFO-broadcast), which we then use as a primitive in our final BSCD-broadcast algorithm. Unlike the original SCD-broadcast algorithm that is tolerant to up to t<n/2 crashing processes, and unlike the underlying Byzantine reliable broadcast primitive that is tolerant to up to t<n/3 Byzantine processes, our BSCD-broadcast algorithm is tolerant to up to t<n/4 Byzantine processes. As an illustration of the high abstraction power provided by the BSCD-broadcast primitive, we show that it can be used to implement a Byzantine-tolerant read/write snapshot object in an extremely simple way
Fast distributed almost stable marriages
In their seminal work on the Stable Marriage Problem, Gale and Shapley
describe an algorithm which finds a stable matching in communication
rounds. Their algorithm has a natural interpretation as a distributed algorithm
where each player is represented by a single processor. In this distributed
model, Floreen, Kaski, Polishchuk, and Suomela recently showed that for bounded
preference lists, terminating the Gale-Shapley algorithm after a constant
number of rounds results in an almost stable matching. In this paper, we
describe a new deterministic distributed algorithm which finds an almost stable
matching in communication rounds for arbitrary preferences. We
also present a faster randomized variant which requires rounds.
This run-time can be improved to rounds for "almost regular" (and in
particular complete) preferences. To our knowledge, these are the first
sub-polynomial round distributed algorithms for any variant of the stable
marriage problem with unbounded preferences.Comment: Various improvements in version 2: algorithms for general (not just
"almost regular") preferences; deterministic variant of the algorithm;
streamlined proof of approximation guarante
Distributed Interior-point Method for Loosely Coupled Problems
In this paper, we put forth distributed algorithms for solving loosely
coupled unconstrained and constrained optimization problems. Such problems are
usually solved using algorithms that are based on a combination of
decomposition and first order methods. These algorithms are commonly very slow
and require many iterations to converge. In order to alleviate this issue, we
propose algorithms that combine the Newton and interior-point methods with
proximal splitting methods for solving such problems. Particularly, the
algorithm for solving unconstrained loosely coupled problems, is based on
Newton's method and utilizes proximal splitting to distribute the computations
for calculating the Newton step at each iteration. A combination of this
algorithm and the interior-point method is then used to introduce a distributed
algorithm for solving constrained loosely coupled problems. We also provide
guidelines on how to implement the proposed methods efficiently and briefly
discuss the properties of the resulting solutions.Comment: Submitted to the 19th IFAC World Congress 201
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