Presence Of Clock Drift Research Articles

Cross-chain payment protocols with success guarantees

In this paper, we consider the problem of cross-chain payment whereby customers of different escrows—implemented by a bank or a blockchain smart contract—successfully transfer digital assets without trusting each other. Prior to this work, cross-chain payment problems did not require this success, or any form of progress. We introduce a new specification formalism called Asynchronous Networks of Timed Automata to formalise such protocols. We present the first cross-chain payment protocol that ensures termination in a bounded amount of time and works correctly in the presence of clock drift. We then demonstrate that it is impossible to solve this problem without assuming synchrony, in the sense that each message is guaranteed to arrive within a known amount of time. Yet, we solve an eventually terminating weaker variant of this problem, where success is conditional on the patience of the participants, without assuming synchrony, and in the presence of Byzantine failures. We also discuss the relation with the recently defined cross-chain deals.

Asynchronous Deterministic Network Based on the DiffServ Architecture

In this study, we propose a scalable framework that guarantees both latency and jitter bounds in large networks, including the Internet. The framework is composed of two parts: a latency-guaranteeing network and a jitter-guaranteeing end system. For latency bounds, we suggest regulators per class per input–output port pair of the DiffServ-type relay nodes. For jitter bounds, based on the guaranteed latency bounds, we suggest time-stamping and buffers at the network egress edge. The framework does not require network-wide time synchronization, frequency synchronization, flow state maintenance, or flow-level queuing/scheduling. Therefore, the complexity does not increase as the number of flows or network size increases. Moreover, the framework is based on the DiffServ architecture; therefore, it requires minimal modification to the current Internet. We demonstrate that the proposed regulators can achieve latency bounds comparable to the IEEE asynchronous traffic shaping technique. We prove that the jitter is bounded even with realistic limitations such as buffers without cut-through capability. We also prove that in the presence of clock drift, the jitter can still be upper bounded with a suggested compensation algorithm. We demonstrate through experiments on simple programmable microcontrollers that the jitter upper bound can be within a few tens of microseconds, even in a realistic situation with store-and-forward buffers, clock drift, and random network delays.

Distributed secondary frequency control in microgrids: Robustness and steady-state performance in the presence of clock drifts

Microgrids are distributed systems with high share of inverter-interfaced renewable energy sources where stable and reliable system operation is realized by suitably controlling the inverters. In this work, we focus on secondary frequency control, which is an important ancillary service provided by the inverters. In the literature on secondary frequency control, the effect of clock drifts has often been neglected. However, clock drifts are practically unavoidable parameter uncertainties in inverter-based microgrids and we show that the most commonly employed distributed secondary frequency controllers exhibit performance deteriorations when taking clock drifts explicitly into consideration. Motivated by this, we propose a novel alternative control law called generalized distributed averaging integral (GDAI) control, which achieves the secondary control objectives of steady-state accurate frequency restoration and proportional power sharing in the presence of clock drifts. In addition, we derive a sufficient tuning criterion in the form of a set of linear matrix inequalities (LMIs) which guarantees robust stability of the closed-loop equilibrium point in the presence of uncertain clock drifts. Finally, our analysis is validated extensively via simulation with comprehensive comparisons to other related distributed control approaches.

An improved asynchronous energy-saving mechanism for IEEE 802.15.5-based networks

IEEE 802.15.5 standard introduces the mesh routing which improves reliability and robustness of routing in wireless sensor network since there are multiple routes from source node to destination node. To achieve energy efficiency for a long network lifetime, the asynchronous energy saving is proposed in IEEE 802.15.5, which includes the receiver-initiated unicast mechanism and the sender-initiated broadcast mechanism. In this article, an improved asynchronous energy saving named semi-synchronous energy saving is proposed to deal with the energy inefficiency from idle listening existing in asynchronous energy saving. In semi-synchronous energy saving, every node maintains the wake/sleep schedule information of nodes in its two-hop neighborhood and uses this information to calculate the wake-up time of an interested neighbor that the data will be sent to, which reduces idle listening time in both unicast and broadcast mechanisms. A low delay routing mechanism is also proposed based on the wake/sleep schedule information of neighbors. Furthermore, the optimal guard time to guarantee receiving the wake-up notification from neighbor in the presence of clock drift is investigated for saving energy. The performance analysis and simulation evaluation show that semi-synchronous energy saving saves more than 80% of energy with less than 30% memory cost compared to asynchronous energy saving, and it also improves the time of completing broadcast and the end-to-end delay.

Communication with Crystal-Free Radios

We consider a communication channel where there is no common clock between the transmitter and the receiver. This is motivated by the recent interest in building system-on-chip radios for Internet of Things applications, which cannot rely on crystal oscillators for accurate timing. We identify two types of clock uncertainty in such systems: timing jitter, which occurs at a time scale faster than the communication duration (or equivalently blocklength), and clock drift, which occurs at a slower time scale. We study the zero-error capacity under both types of timing imperfections and obtain optimal zero-error codes for some cases. Our results show that, as opposed to common practice, in the presence of clock drift, it is highly suboptimal to try to learn and track the clock frequency at the receiver; rather, one can design codes that come close to the performance of perfectly synchronous communication systems without any clock synchronization at the receiver.

Analysis of quantities influencing the performance of time synchronization based on linear regression in low cost WSNs

Time synchronization is a key feature of Wireless Sensor Networks (WSNs). In low cost WSNs this is a very challenging issue since the general employment of a large number of nodes, characterized by low power and limited energy resources. Therefore, in such contexts, the adoption of synchronization algorithms is preferable to the adoption of GPS-based solution because of its high energy consumption, high cost and poor performance in indoor environment. An even increasing number of papers dealing with the design and the implementation of protocol-based techniques for synchronization can be found in literature.These synchronization algorithms can be divided into three main categories: one way messaging, two ways messaging and consensus based synchronization. Among the others, those based on the one way messaging and, in particular, on the adoption of regressive algorithms are widely used in many application contexts. Focusing the attention on this class of synchronization algorithms, this paper proposes a deep performance analysis aimed at highlighting the sensitivity of the regression-based algorithms to some factors that influence the accuracy in typical low cost applications, such as the finite resolution of the local timing clock, the presence of clock drift, clock high frequency noise and low frequency noise, the presence of latencies due to the radio devices, the presence of latencies due to the microcontroller device. The main goal is to evaluate the effect of each one of these factors of influence on the overall synchronization performance. To these aims, suitable analyses both in simulation environment and on real nodes have been carried out.

Mitigating Distributed Denial of Service Attacks in Multiparty Applications in the Presence of Clock Drifts

Network-based applications commonly open some known communication port(s), making themselves easy targets for (distributed) Denial of Service (DoS) attacks. Earlier solutions for this problem are based on port-hopping between pairs of processes which are synchronous or exchange acknowledgments. However, acknowledgments, if lost, can cause a port to be open for longer time and thus be vulnerable, while time servers can become targets to DoS attack themselves. Here, we extend port-hopping to support multiparty applications, by proposing the BIGWHEEL algorithm, for each application server to communicate with multiple clients in a port-hopping manner without the need for group synchronization. Furthermore, we present an adaptive algorithm, HOPERAA, for enabling hopping in the presence of bounded asynchrony, namely, when the communicating parties have clocks with clock drifts. The solutions are simple, based on each client interacting with the server independently of the other clients, without the need of acknowledgments or time server(s). Further, they do not rely on the application having a fixed port open in the beginning, neither do they require the clients to get a first-contact” port from a third party. We show analytically the properties of the algorithms and also study experimentally their success rates, confirm the relation with the analytical bounds.