Asynchronous Communication Model Research Articles

Special Delivery: Programming with Mailbox Types

The asynchronous and unidirectional communication model supported by mailboxes is a key reason for the success of actor languages like Erlang and Elixir for implementing reliable and scalable distributed systems. While many actors may send messages to some actor, only the actor may (selectively) receive from its mailbox. Although actors eliminate many of the issues stemming from shared memory concurrency, they remain vulnerable to communication errors such as protocol violations and deadlocks. Mailbox types are a novel behavioural type system for mailboxes first introduced for a process calculus by de’Liguoro and Padovani in 2018, which capture the contents of a mailbox as a commutative regular expression. Due to aliasing and nested evaluation contexts, moving from a process calculus to a programming language is challenging. This paper presents Pat, the first programming language design incorporating mailbox types, and describes an algorithmic type system. We make essential use of quasi-linear typing to tame some of the complexity introduced by aliasing. Our algorithmic type system is necessarily co-contextual, achieved through a novel use of backwards bidirectional typing, and we prove it sound and complete with respect to our declarative type system. We implement a prototype type checker, and use it to demonstrate the expressiveness of Pat on a factory automation case study and a series of examples from the Savina actor benchmark suite.

Strategies used throughout the scaling-up process of eConsult – Multiple case study of four Canadian Provinces

BackgroundeConsult is a model of asynchronous communication connecting primary care providers to specialists to discuss patient care. This study aims to analyze the scaling-up process and identify strategies used to support scaling-up efforts in four provinces in Canada. MethodsWe conducted a multiple case study with four cases (ON, QC, MB, NL). Data collection methods included document review (n = 93), meeting observations (n = 65) and semi-structured interviews (n = 40). Each case was analyzed based on Milat’s framework. ResultsThe first scaling-up phase was marked by the rigorous evaluation of eConsult pilot projects and the publication of over 90 scientific papers. In the second phase, provinces implemented provincial multi-stakeholder committees, institutionalized the evaluation, and produced documents detailing the scaling-up plan. During the third phase, efforts were made to lead proofs of concept, obtain the endorsement of national and provincial organizations, and mobilize alternate sources of funding. The last phase was mainly observed in Ontario, where the creation of a provincial governance structure and strategies were put in place to monitor the service and manage changes. ConclusionsVarious strategies need to be used throughout the scaling-up process. The process remains challenging and lengthy because health systems lack clear processes to support innovation scaling-up.

Edge-Based Sender-Receiver Event-Triggered Schemes for Distributed Filtering

This paper investigates the distributed filtering problem for a class of nonlinear systems under edge-based event-triggered (ET) communication. A dynamic edge-based ET mechanism for the sender-receiver ET scheme is proposed. The triggering depends on the relative state information over the edge between the sender and receiver nodes. Compared with the existing synchronous transmission protocols, the sender-receiver ET scheme leads to a more flexible asynchronous communication model by utilizing edge-related triggering parameters. Moreover, this allows the receiver node to be privileged to receive or reject the incoming state information, which is more conducive to reducing the transmission of redundant state information from the sender. If the receiver’s privilege to reject information is not considered, the sender-receiver scheme is further simplified to the sender ET scheme. In the sender ET scheme, the triggering of an edge is only determined by the sender node of the corresponding edge. Both edge-based ET schemes are applied to a unified fully distributed filter design. It is proved that the estimation errors of the proposed distributed filtering algorithm under both schemes are exponentially bounded in the mean square. A simulation example concerning target tracking is given to demonstrate the validity of the main results.

Asynchronous Remote Communication as a Tool for Care Management in Primary Care: A Rapid Review of the Literature.

Aim:To review the available evidence on asynchronous communication models between primary care professionals and patients in different countries around the world in order to analyse the added value that this model brings to patients and professionals.Design:A rapid literature review was conducted using the World Health Organisation guidance to include a variety of studies on the concept of asynchronous communications between primary care and patients in different countries.Data sources:The search for articles was carried out in PubMed and Google Academics and with the contribution of telemedicine experts from the Catalan Institute of Health.Selection of studies:The review included 271 articles. The inclusion criteria were: publications from 2010 onwards, in English, Spanish or Catalan, focused on asynchronous communications between primary care professionals and patients to improve patient management. After discarding duplicates and applying the exclusion criteria (255 articles), 16 were included for further review.Data extraction:The rapid literature review was conducted by an evaluator; detecting 5 main general themes: reduction of face-to-face visits, available services and most frequent uses, characteristics and perceptions of primary care professionals, characteristics and perceptions of users, and barriers and facilitators for the implementation of asynchronous teleconsultation.Results:A total of sixteen studies were included, including seven quantitative studies, seven qualitative studies and two mixed studies.Conclusions:The high degree of satisfaction of both users and professionals, the outbreak of COVID-19 and the effectiveness and efficiency of asynchronous remote communications are key factors for the implementation and improvement in the management of the different healthcare systems across the world.

An efficient distributed algorithm for economic dispatch considering communication asynchrony and time delays

The increasing integration of distributed energy resources (DERs) to power grids has fostered the emergence of advanced control technologies for energy management. This study focuses on distributed solutions to economic dispatch considering asynchrony and non-ideal communications. A distributed consensus-based algorithm is developed for general directed networks, where heavy-ball momentum is incorporated into the algorithm design to accelerate convergency. Subsequently, an asynchronous version is proposed based on a general asynchronous communication model with unpredictable, non-uniform, and bounded time delays. Without a global clock in conventional synchronous distributed algorithms, distributed generators (DGs) are allowed to exchange information through local communications at any moment and use out-sync information to execute new updates. Simulations are presented to demonstrate the performance of the proposed algorithm and verify its robustness against time delays.

Tangle 2.0 Leaderless Nakamoto Consensus on the Heaviest DAG

We introduce the theoretical foundations of the Tangle 2.0, a probabilistic leaderless consensus protocol based on a directed acyclic graph (DAG) called the Tangle. The Tangle naturally succeeds the blockchain as its next evolutionary step as it offers features suited to establish more efficient and scalable distributed ledger solutions. Consensus is no longer found in the longest chain but on the heaviest DAG, where PoW is replaced by a stake- or reputation-based weight function. The DAG structure and the underlying Reality-based UTXO Ledger allow parallel validation of transactions without the need for total ordering. Moreover, it enables the removal of the intermediary of miners and validators, allowing a pure two-step process that follows the \emph{propose-vote} paradigm at the node level and not at the validator level. We propose a framework to analyse liveness and safety under different communication and adversary models. This allows providing impossibility results in some edge cases and in the asynchronous communication model. We provide formal proof of the security of the protocol assuming a common random coin.

Cryptanalysis and Improvement of a Group Authentication Scheme with Multiple Trials and Multiple Authentications

Authentication is one of the most fundamental services in cryptography and information security. Compared with the traditional authentication methods, group authentication allows a group of users to be authenticated at once rather than authenticating each of these users individually. Therefore, it is more desirable in the group oriented environment, such as multicast/conference communications. In this paper, we first demonstrate that a recent group authentication scheme by Chien (Security and Communication Networks, 2017) suffers some security flaws, i.e. an adversary in the asynchronous communication model can pretend to be a legitimate group member without being detected. We then use the Anonymous Veto Networks (AV-net) to patch Chien’s scheme, so that its security can be rigorously proved in a well-defined security model.

Scaling up eConsult for access to specialists in primary healthcare across four Canadian provinces: study protocol of a multiple case study

BackgroundCanada has been referred to as the land of ‘perpetual pilot projects’. Effective innovations often remain small in scale, with limited impact on health systems. Several innovations have been developed in Canada to tackle important challenges such as poor access to services and excessive wait times – one of the most promising innovations that has been piloted is eConsult, which is a model of asynchronous communication that allows primary care providers to electronically consult with specialists regarding their patients’ medical issues. eConsult pilot projects have been shown to reduce wait times for specialist care, prevent unnecessary referrals and reduce health system costs. eConsult has been spread throughout Ontario as well as to certain regions in Manitoba, Quebec, and Newfoundland and Labrador.Our aim is to understand and support the scale-up process of eConsult in Ontario, Quebec, Manitoba, and Newfoundland and Labrador. Our specific objectives are to (1) describe the main components of eConsult relevant to the scale-up process in each province; (2) understand the eConsult scale-up process in each province and compare across provinces; (3) identify policy issues and strategies to scaling up eConsult in each province; and (4) foster cross-level and cross-jurisdictional learning on scaling up eConsult.MethodsWe will conduct a qualitative multiple case study to investigate the scaling up of eConsult in four Canadian provinces using a grey literature review, key stakeholder interviews (10 interviews/province), non-participant observations, focus groups and deliberative dialogues. We will identify the main components of eConsult to be scaled up using logic models (obj. 1). Scaling up processes will be analysed using strategies adapted from process research (obj. 2). Policy issues and strategies to scale-up eConsult will be analysed thematically (obj. 3). Finally, a symposium will foster pan-Canadian learning on the process of scaling up eConsult (obj. 4).DiscussionThis study will likely increase learning and support evidence-based policy-making across participating provinces and may improve the capacity for a pan-Canadian scale-up of eConsult, including in provinces where eConsult has not yet been implemented. This work is essential to inform how similar innovations can reshape our health systems in the evolving information age.

An Energy Efficiency Study of Web-Based Communication in Android Phones

Currently, mobile devices are the most popular pervasive computing devices, and they are becoming the primary way for accessing Internet. Battery is a critical resource in such personal computing gadgets, network communications being one of the primary energy consuming activities in any mobile app. Indeed, as web-based communication is the most used explicitly or implicitly by mobile devices, HTTP-based traffic is the most power demanding one. So, mobile web developers should be aware of how much energy demands the different web-based communication alternatives. The goal of this paper is to measure and compare the energy consumption of three asynchronous HTTP-based methods in mobile devices in different browsers. Our experiments focus on three HTTP-based asynchronous communication models that allow a web server to push data to a client browser through a HTTP/1.1 interaction: Polling, Long Polling, and WebSockets. The resulted measurements are then analysed to get more accurate understanding of the impact of the selected method, and the mobile browser, in the energy consumption of the asynchronous HTTP-based communication. The utility of these experiments is to show developers what are the factors and settings that mostly influence the energy consumption when different web-based asynchronous communication methods are used, helping them to choose the most beneficial solution if possible. With this information, mobile web developers should be able to reduce the power consumption of the front-end of web applications for mobile devices, just selecting and configuring the best asynchronous method or mobile browser, improving the performance of HTTP-based communication in terms of energy demand.

A distributed and asynchronous approach for optimizing weighted graph matchings in wireless network services

Weighted graph matching is one of the most fundamental graph theoretical problems used in network design, especially in wireless network services such as radio resource allocation, physical layer security, energy-efficient partner selection and optimizing storage capacity. In this paper we present a distributed heuristic which provides nearly-optimal weighted matchings in polynomial time. We also propose an algorithm to decrease the number of transmitted messages to provide energy-efficient operation. Our approaches assume the asynchronous communication model and small messages having O(log (n)) bits. These assumptions directly fit the battery powered wireless networks such as wireless ad hoc and sensor networks. To the best of our knowledge, we propose the first distributed weighted matching algorithm which benefits from augmentation of augmenting paths having size larger than 3 for these networks. We also provide results of our simulations on synthetic geometric graphs to model wireless networks. Extensive simulations reveal that our algorithm improves the approximation performances of the other weighted matching algorithms and closes the gap between the approximation ratio and the optimum up to 32%.

GPUDirect Async: Exploring GPU synchronous communication techniques for InfiniBand clusters

NVIDIA GPUDirect is a family of technologies aimed at optimizing data movement among GPUs (P2P) or among GPUs and third-party devices (RDMA). GPUDirect Async, introduced in CUDA 8.0, is a new addition which allows direct synchronization between GPU and third party devices. For example, Async allows an NVIDIA GPU to directly trigger and poll for completion of communication operations queued to an InfiniBand Connect-IB network adapter, with no involvement of CPU in the critical communication path of GPU applications. In this paper we describe the motivations and the building blocks of GPUDirect Async. After an initial analysis with a micro-benchmark, by means of a performance model, we show the potential benefits of using two different asynchronous communication models supported by this new technology in two MPI multi-GPU applications: HPGMG-FV, a proxy for real-world geometric multi-grid applications and CoMD-CUDA, a proxy for Classical Molecular Dynamics codes. We also report a test case in which the use of GPUDirect Async does not provide any advantage, that is an implementation of the Breadth First Search algorithm for large scale graphs.

Secure multi-party computation in large networks

We describe scalable protocols for solving the secure multi-party computation (MPC) problem among a significant number of parties. We consider both the synchronous and the asynchronous communication models. In the synchronous setting, our protocol is secure against a static malicious adversary corrupting less than a 1/3 fraction of the parties. In the asynchronous environment, we allow the adversary to corrupt less than a 1/8 fraction of parties. For any deterministic function that can be computed by an arithmetic circuit with m gates, both of our protocols require each party to send a number of messages and perform an amount of computation that is $$\tilde{O}(m/n + \sqrt{n})$$O~(m/n+n). We also show that our protocols provide statistical and universally-composable security. To achieve our asynchronous MPC result, we define the threshold counting problem and present a distributed protocol to solve it in the asynchronous setting. This protocol is load balanced, with computation, communication and latency complexity of $$O(\log {n})$$O(logn), and can also be used for designing other load-balanced applications in the asynchronous communication model.

On the diversity of asynchronous communication

Abstract Asynchronous communication is often viewed as a single entity, the counterpart of synchronous communication. Although the basic concept of asynchronous communication is the decoupling of send and receive events, there is actually room for a variety of additional specification of the communication, for instance in terms of ordering. Yet, these different asynchronous communications are used interchangeably and seldom distinguished. This paper is a contribution to the study of these models, their differences, and how they are related. In this paper, the variety of point-to-point asynchronous communication paradigms is considered with two approaches. In the first and theoretical one, communication models are specified as properties on the ordering of events in distributed executions. In the second and more practical approach that involves composition of peers, they are modeled with transition systems and message histories as part of a framework. The described framework enables to model peer composition and compatibility properties. Besides, an implemented tool chain based on the TLA + formalism and model checking is also proposed and illustrated. The conformance of the two approaches is highlighted. A hierarchy is established between the studied communication models. From the execution viewpoint, it completes existing work in the area by introducing more asynchronous communication models and showing their differences. The framework is shown to offer abstract implementations of the communication models. Both the correctness and the completeness of the descriptions in the framework are studied. This reveals necessary restrictions on the behavior of the peers so that the communication models are actually implementable.

Deciding Determinism with Fairness for Simple Transducer Networks

A distributed database system often operates in an asynchronous communication model where messages can be arbitrarily delayed. This communication model causes nondeterministic effects like unpredictable arrival orders of messages. Nonetheless, in general we want the distributed system to be deterministic; the system should produce the same output despite the nondeterministic effects on messages. Previously, two interpretations of determinism have been proposed. The first says that all infinite fair computation traces produce the same output. The second interpretation is a confluence notion, saying that all finite computation traces can still be extended to produce the same output. A decidability result for the confluence notion was previously obtained for so-called simple transducer networks, a model from the field of declarative networking. In the current article, we also present a decidability result for simple transducer networks, but this time for the first interpretation of determinism, with infinite fair computation traces. We also compare the expressivity of simple transducer networks under both interpretations.

Bursts of Node Activation and Asynchronous Communication in Temporal Networks

Development of sensor technologies and the prevalence of electronic communication services provide us with a huge amount of data on human communication behavior, including face-to-face conversations, e-mail exchanges, phone calls, message exchanges and other types of interactions in various online forums. These indirect or direct interaction form potential bridges of the virus spread. For a long time, the study of virus spread is based on the aggregate static network. However, the interaction patterns containing diverse temporal properties may affect dynamic processes as much as the network topology does. Some empirical studies show, the activation time and duration of vertices and links are highly heterogeneous, which means intense activity may be followed by longer intervals inactivity. We take heterogeneous distribution of the node inter-activation time as the research background to build an asynchronous communication model. The two sides of the communication don't have to be active at the same time. One derives the threshold of virus spreading on the communication mode and analyzes the reason the heterogeneous distribution of the vertex inter-activation time suppress the spread of virus. At last, the analysis and results from the model are verified on the BA network.

Effect of Heterogeneity of Vertex Activation on Epidemic Spreading in Temporal Networks

Development of sensor technologies and the prevalence of electronic communication services provide us with a huge amount of data on human communication behavior, including face-to-face conversations, e-mail exchanges, phone calls, message exchanges, and other types of interactions in various online forums. These indirect or direct interactions form potential bridges of the virus spread. For a long time, the study of virus spread is based on the aggregate static network. However, the interaction patterns containing diverse temporal properties may affect dynamic processes as much as the network topology does. Some empirical studies show that the activation time and duration of vertices and links are highly heterogeneous, which means intense activity may be followed by longer intervals of inactivity. We take heterogeneous distribution of the node interactivation time as the research background to build an asynchronous communication model. The two sides of the communication do not have to be active at the same time. One derives the threshold of virus spreading on the communication mode and analyzes the reason the heterogeneous distribution of the vertex interactivation time suppresses the spread of virus. At last, the analysis and results from the model are verified on the BA network.

Towards autotuning by alternating communication methods

Interconnects in emerging high performance computing systems feature hardware support for one-sided, asynchronous communication and global address space programming models in order to improve parallel efficiency and productivity by allowing communication and computation overlap and outof- order delivery. In practice though, complex interactions between the software stack and the communication hardware make it challenging to obtain optimum performance for a full application expressed with a one-sided programming paradigm. Here, we present a proof-of-concept study for an autotuning framework that instantiates hybrid kernels based on refactored codes using available communication libraries or languages on a Cray XE6 and a SGI Altix UV 1000. We validate our approach by improving performance for bandwidth- and latency-bound kernels of interest in quantum physics and astrophysics by up to 35% and 80% respectively.

Enumeration and Leader Election in Partially Anonymous and Multi-hop Broadcast Networks

We address the enumeration and the leader election problems over partially anonymous and multi-hop broadcast networks. We consider an asynchronous communication model where each process broadcasts a message and all its neighbours receive this message after arbitrary and unpredictable time. In this paper, we present necessary conditions that must be satisfied by any graph to solve these problems and we show that these conditions are sufficient by providing an enumeration algorithm on the one hand and a leader election algorithm on the other hand. For both problems, we highlight the importance of the initial knowledge. Considering the enumeration problem, each process only knows the size of the graph and, contrary to related works, the number of its neighbouring processes is unknown. Whereas for the election problem, we show that this combination of knowledge is not sufficient. Our algorithm assumes that each process initially knows a map of the network without knowing its position in this map. From the complexity viewpoint, our algorithms offer polynomial complexities memory at each process, number and size of exchanged messages.

Use of run time predictions for automatic co-allocation of multi-cluster resources for iterative parallel applications

Metaschedulers co-allocate resources by requesting a fixed number of processors and usage time for each cluster. These static requests, defined by users, limit the initial scheduling and prevent rescheduling of applications to other resource sets. It is also difficult for users to estimate application execution times, especially on heterogeneous environments. To overcome these problems, metaschedulers can use performance predictions for automatic resource selection. This paper proposes a resource co-allocation technique with rescheduling support based on performance predictions for multi-cluster iterative parallel applications. Iterative applications have been used to solve a variety of problems in science and engineering, including large-scale computations based on the asynchronous model more recently. We performed experiments using an iterative parallel application, which consists of benchmark multiobjective problems, with both synchronous and asynchronous communication models on Grid’5000. The results show run time predictions with an average error of 7% and prevention of up to 35% and 57% of run time overestimations to support rescheduling for synchronous and asynchronous models, respectively. The performance predictions require no application source code access. One of the main findings is that as the asynchronous model masks communication and computation, it requires no network information to predict execution times. By using our co-allocation technique, metaschedulers become responsible for run time predictions, process mapping, and application rescheduling; releasing the user from these burden tasks.

Ajax Technology’s Application and Research in Network Teaching Resources Library System

This paper describes the Ajax technology as well as asynchronous communication model and the traditional model’s difference, discusses the Ajax technology’s application in network teaching resources library system, implements asynchronous data transmission in the case of no page refreshing, enhances interactive of network teaching resources library system, and improves the efficiency of the network teaching resources server. At the same time, this paper also analyzes the adverse factors; this has certain guide significance for the use of Ajax technology to develop network teaching resources library.