472 research outputs found
Doing-it-All with Bounded Work and Communication
We consider the Do-All problem, where cooperating processors need to
complete similar and independent tasks in an adversarial setting. Here we
deal with a synchronous message passing system with processors that are subject
to crash failures. Efficiency of algorithms in this setting is measured in
terms of work complexity (also known as total available processor steps) and
communication complexity (total number of point-to-point messages). When work
and communication are considered to be comparable resources, then the overall
efficiency is meaningfully expressed in terms of effort defined as work +
communication. We develop and analyze a constructive algorithm that has work
and a nonconstructive
algorithm that has work . The latter result is close to the
lower bound on work. The effort of each of
these algorithms is proportional to its work when the number of crashes is
bounded above by , for some positive constant . We also present a
nonconstructive algorithm that has effort
EESMR: Energy Efficient BFT-SMR for the masses
Modern Byzantine Fault-Tolerant State Machine Replication (BFT-SMR) solutions
focus on reducing communication complexity, improving throughput, or lowering
latency. This work explores the energy efficiency of BFT-SMR protocols. First,
we propose a novel SMR protocol that optimizes for the steady state, i.e., when
the leader is correct. This is done by reducing the number of required
signatures per consensus unit and the communication complexity by order of the
number of nodes n compared to the state-of-the-art BFT-SMR solutions.
Concretely, we employ the idea that a quorum (collection) of signatures on a
proposed value is avoidable during the failure-free runs. Second, we model and
analyze the energy efficiency of protocols and argue why the steady-state needs
to be optimized. Third, we present an application in the cyber-physical system
(CPS) setting, where we consider a partially connected system by optionally
leveraging wireless multicasts among neighbors. We analytically determine the
parameter ranges for when our proposed protocol offers better energy efficiency
than communicating with a baseline protocol utilizing an external trusted node.
We present a hypergraph-based network model and generalize previous fault
tolerance results to the model. Finally, we demonstrate our approach's
practicality by analyzing our protocol's energy efficiency through experiments
on a CPS test bed. In particular, we observe as high as 64% energy savings when
compared to the state-of-the-art SMR solution for n=10 settings using BLE.Comment: Appearing in Middleware 202
Robust Decentralized Secondary Frequency Control in Power Systems: Merits and Trade-Offs
Frequency restoration in power systems is conventionally performed by
broadcasting a centralized signal to local controllers. As a result of the
energy transition, technological advances, and the scientific interest in
distributed control and optimization methods, a plethora of distributed
frequency control strategies have been proposed recently that rely on
communication amongst local controllers.
In this paper we propose a fully decentralized leaky integral controller for
frequency restoration that is derived from a classic lag element. We study
steady-state, asymptotic optimality, nominal stability, input-to-state
stability, noise rejection, transient performance, and robustness properties of
this controller in closed loop with a nonlinear and multivariable power system
model. We demonstrate that the leaky integral controller can strike an
acceptable trade-off between performance and robustness as well as between
asymptotic disturbance rejection and transient convergence rate by tuning its
DC gain and time constant. We compare our findings to conventional
decentralized integral control and distributed-averaging-based integral control
in theory and simulations
Narwhal and Tusk: A DAG-based Mempool and Efficient BFT Consensus
We propose separating the task of reliable transaction dissemination from
transaction ordering, to enable high-performance Byzantine fault-tolerant
quorum-based consensus. We design and evaluate a mempool protocol, Narwhal,
specializing in high-throughput reliable dissemination and storage of causal
histories of transactions. Narwhal tolerates an asynchronous network and
maintains high performance despite failures. Narwhal is designed to easily
scale-out using multiple workers at each validator, and we demonstrate that
there is no foreseeable limit to the throughput we can achieve. Composing
Narwhal with a partially synchronous consensus protocol (Narwhal-HotStuff)
yields significantly better throughput even in the presence of faults or
intermittent loss of liveness due to asynchrony. However, loss of liveness can
result in higher latency. To achieve overall good performance when faults occur
we design Tusk, a zero-message overhead asynchronous consensus protocol, to
work with Narwhal. We demonstrate its high performance under a variety of
configurations and faults. As a summary of results, on a WAN, Narwhal-Hotstuff
achieves over 130,000 tx/sec at less than 2-sec latency compared with 1,800
tx/sec at 1-sec latency for Hotstuff. Additional workers increase throughput
linearly to 600,000 tx/sec without any latency increase. Tusk achieves 160,000
tx/sec with about 3 seconds latency. Under faults, both protocols maintain high
throughput, but Narwhal-HotStuff suffers from increased latency
- …