Distributed ledgers provide many advantages over centralized solutions in IoT projects including but not limited to improved security, transparency and fault tolerance. However, in order to leverage them at scale, their well-known limitations, i.e., scalability and performance, should be adequately addressed. DAG-based distributed ledgers have been proposed to tackle the performance and scalability issues by design. The first among them, IOTA, has shown promising signs in terms of scalability and performability. In this thesis, we first conduct a comprehensive literature review on both distributed ledger technology applications in IoT and the performance evaluation of such decentralized systems. Then we present a detailed technical overview of IOTA, following a contractive review of different DAG-based distributed ledger technologies. Next, we propose a scalable transactive smart homes infrastructure by leveraging IOTA protocol and following the separation of concerns (SOC) design principle. Based on the proposed solution, an experiment with 40 home nodes is conducted to prove the concept at large scale in a cloud environment. The results show that our solution provides a high transaction speed and scalability, as well as good performance on micropayment which is important in IoT initiatives. We conduct an analysis and discuss how the new system breaks out the Blockchain Trilemma, which claims that it is almost impossible for a blockchain platform to simultaneously reach decentralization, scalability and security. Based on our findings on scalability and performance, we conclude that the proposed DAG-based distributed ledger is an effective solution for building an IoT infrastructure for smart communities, in which local residents can freely and securely transfer values. Finally, we rigorously study the performance of the ledger to examine its applicability for IoT projects in which a high throughput is required. More specifically, we investigate the IOTA system to answer two key research questions: 1) what is the confirmation rate in the system given the design parameters and 2) what will be the optimal waiting time for a user to resend its previously submitted but not yet confirmed transaction to the ledger? In order to answer these vital questions, we perform real experimentation, simulation and analytical modeling. Our findings reveal the impact of arrival rate of transactions, consensus algorithm, randomness of the weighted random walk for tip selection and network delay on the confirmation rate. By decomposing the transaction confirmations in each graph layer, we build an analytical layered model. Thanks to the analytical modeling, we shed some light on the distribution of confirmation process, which is leveraged to calculate the optimal time for resending the unconfirmed transaction to the distributed ledger. Our performance model can be used by IoT project designers to perform what-if analysis and capacity planning in advance of the real deployments, with high level of accuracy.
Interconnecting cyber-physical systems in networks leads to the creation of cyber-physical system-of-systems. In a cyber-physical system-of-systems (CPSoS), systems communicate by exchanging and sharing data and information, which this chapter also refers to as interoperability of information. To ensure reliable and secure interoperability of information between distributed cyber-physical systems, using blockchain technology or distributed ledging technology for distributed entities is an interesting option. Such a blockchain must, at a minimum, be fault tolerant and enable the entities involved to reach consensus on the information transactions that are to be performed. Once consensus about transactions between cyber-physicals is reached, it must be possible for these to record consistently the used data in a distributed ledger that provides a permanent shared overview of completed information transactions. The development of the new technology we call blockchain creates a new and as yet unfathomable reality of interconnected autonomous and self-organising cyber-physical systems that have the ability to make decisions about or for us as human beings.
It is difficult these days to avoid hearing about blockchain. Despite the significant potential of blockchain, it is also difficult to find a consistent description of what it really is. This article looks at the basics of blockchain: the individual components, how those components fit together, and what changes might be made to solve some of the problems with blockchain technology.
The Practical Byzantine Fault Tolerance algorithm (PBFT)has been highly applied in consortium blockchain systems, however, this kind of consensus algorithm can hardly identify and remove faulty nodes in time, and also vulnerable to many attacks against the primary node of PBFT. The equality of consortium members' discourse rights is inapplicable to some real scenarios where dominating members are likely to have a larger discourse rights in the voting process. To address these problems, this paper presents Reputation-based Byzantine Fault Tolerance (RBFT)algorithm that incorporates a reputation model to evaluate the operations of each node in the consensus process. The faulty nodes will get lower discourse rights in the voting process if any malicious behavior is detected, with their reputation decreased. Furthermore, this paper presents an innovative reputation-based primary change scheme. The node with higher reputation obtains greater opportunities to be a primary to generate new valid blocks, which reduces the security risk of the primary. The experimental results demonstrate that RBFT gains better performance and ensures system security and reliability. Compared with PBFT, it increases the average throughput by 15% and reduces delay by 10%, and the faulty node rate of the system can continue to decrease over time.
The requirement of supporting both latency sensitive and computing intensive Internet of Things (IoT) applications is consistently boosting the necessity for integrating Edge, Fog and Cloud infrastructure. Although there are a number of real-world frameworks attempt to support such integration, they have many limitations from various perspectives including platform independence, security, resource management and multi-application assistance. To address these limitations, we propose a simplified but effective framework, named FogBus for facilitating end-to-end IoT-Fog(Edge)-Cloud integration. FogBus offers a platform independent interface to IoT applications and computing instances for execution and interaction. It not only assists developers in building applications but also helps users in running multiple applications at a time and service providers to manage their resources. In addition, FogBus applies Blockchain, authentication and encryption techniques to secure operations on sensitive data. Because of its lightweight and cross platform software systems, it is easy to deploy, scalable and cost e_cient. We demonstrate the effectiveness of our framework by creating a computing environment with it that integrates finger pulse oximeter as IoT devices with Smartphone-based gateway and Raspberry Pi-based Fog nodes for Sleep Apnea analysis. We also run several experiments on this computing environment varying FogBus settings. The experimental results show that different FogBus settings can improve latency, energy, network and CPU usage of the computing infrastructure.
Permissioned Blockchain (PBC) has become a prevalent data structure to ensure that the records are immutable and secure. However, PBC still has significant challenges before it can be realized in different applications. One of such challenges is the overhead of the communication which is required to execute the Byzantine Agreement (BA) protocol that is needed for consensus building. As such, it may not be feasible to implement PBC for resource constrained environments such as Internet-of-Things (IoT). In this paper, we assess the communication overhead of running BA in an IoT environment that consists of wireless nodes (e.g., Raspberry PIs) with meshing capabilities. As the the packet loss ratio is significant and makes BA unfeasible to scale, we propose a network coding based approach that will reduce the packet overhead and minimize the consensus completion time of the BA. Specifically, various network coding approaches are designed as a replacement to TCP protocol which relies on unicasting and acknowledgements. The evaluation on a network of Raspberry PIs demonstrates that our approach can significantly improve scalability making BA feasible for medium size IoT networks.
Tyler Crain, Vincent Gramoli, Mikel Larrea, Michel Raynal
This paper introduces a new leaderless Byzantine consensus called the Democratic Byzantine Fault Tolerance (DBFT) for blockchains. While most blockchain consensus protocols rely on a correct leader or coordinator to terminate, our algorithm can terminate even when its coordinator is faulty. The key idea is to allow processes to complete asynchronous rounds as soon as they receive a threshold of messages, instead of having to wait for a message from a coordinator that may be slow. The resulting decentralization is particularly appealing for blockchains for two reasons: (i) each node plays a similar role in the execution of the consensus, hence making the decision inherently “democratic” (ii) decentralization avoids bottlenecks by balancing the load, making the solution scalable. DBFT is deterministic, assumes partial synchrony, is resilience optimal, time optimal and does not need signatures. We first present a simple safe binary Byzantine consensus algorithm, modify it to ensure termination, and finally present an optimized reduction from multivalue consensus to binary consensus whose fast path terminates in 4 message delays.
Nguyen Cong Luong, Tran The Anh, Huỳnh Thị Thanh Bình, Dusit Niyato · 6 authors
To ensure that the data aggregation, data storage, and data processing are all performed in a decentralized but trusted manner, we propose to use the blockchain with the mining pool to support IoT services based on cognitive radio networks. As such, the secondary user can send its sensing data, i.e., transactions, to the mining pools. After being verified by miners, the transactions are added to the blocks. However, under the dynamics of the primary channel and the uncertainty of the mempool state of the mining pool, it is challenging for the secondary user to determine an optimal transaction transmission policy. In this paper, we propose to use the deep reinforcement learning algorithm to derive an optimal transaction transmission policy for the secondary user. Specifically, we adopt a Double Deep-Q Network (DDQN) that allows the secondary user to learn the optimal policy. The simulation results clearly show that the proposed deep reinforcement learning algorithm outperforms the conventional Q-learning scheme in terms of reward and learning speed.
Fedor Muratov, Andrei Lebedev, Nikolai Iushkevich, Bulat Nasrulin · 5 authors
Consensus in decentralized systems that asynchronously receive events and which are subject to Byzantine faults is a common problem with many real-life applications. Advances in decentralized systems, such as distributed ledger (i.e., blockchain) technology, has only increased the importance of finding performant and secure solutions to consensus of state machine replication in decentralized systems. YAC is a practical decentralized consensus algorithm, that solves the problems of inefficient message passing and strong leaders that occur in classical Byzantine fault tolerant consensus algorithms. The algorithm is open source and currently is used to provide Byzantine fault tolerant consensus for the Hyperledger Iroha blockchain project. We provide proofs of safety and liveness, as well as empirical results showing that our algorithm can scale to dozens of validating peers.
This paper proposes Consensus-Before-Talk (CBT), a spectrum etiquette architecture leveraged by distributed ledger technology (DLT). In CBT, secondary users' spectrum access requests reach a consensus in a distributed way, thereby enabling collision-free distributed dynamic spectrum access. To achieve this consensus, the secondary users need to pay for the extra request exchanging delays. Incorporating the consensus delay, the end-to-end latency under CBT is investigated. Both the latency analysis and numerical evaluation validate that the proposed CBT achieves the lower end-to-end latency particularly under severe secondary user traffic, compared to the Listen-Before-Talk (LBT) benchmark scheme.
Consensus is one of the key problems in blockchains. There are many articles analyzing the performance of threat models for blockchains. But the network stability seems lack of attention, which in fact affects the blockchain performance. This paper studies the performance of a well adopted consensus algorithm, Raft, in networks with non-negligible packet loss rate. In particular, we propose a simple but accurate analytical model to analyze the distributed network split probability. At a given time, we explicitly present the network split probability as a function of the network size, the packet loss rate, and the election timeout period. To validate our analysis, we implement a Raft simulator and the simulation results coincide with the analytical results. With the proposed model, one can predict the network split time and probability in theory and optimize the parameters in Raft consensus algorithm.
Pietro Danzi, Anders E. Kalør, Čedomir Stefanović, Petar Popovski
The emerging blockchain protocols provide a decentralized architecture that is suitable of supporting Internet of Things (IoT) interactions. However, keeping a local copy of the blockchain ledger is infeasible for low-power and memory-constrained devices. For this reason, they are equipped with lightweight software implementations that only download the useful data structures, e.g. state of accounts, from the blockchain network, when they are updated. In this paper, we consider and analyze a novel scheme, implemented by the nodes of the blockchain network, which aggregates the blockchain data in periodic updates and further reduces the communication cost of the connected IoT devices. We show that the aggregation period should be selected based on the channel quality, the offered rate, and the statistics of updates of the useful data structures. The results, obtained for the Ethereum protocol, illustrate the benefits of the aggregation scheme in terms of a reduced duty cycle of the device, particularly for low signal-to-noise ratios, and the overall reduction of the amount of information transmitted in downlink (e.g., from the wireless base station to the IoT device). A potential application of the proposed scheme is to let the IoT device request more information than actually needed, hence increasing its privacy, while keeping the communication cost constant. In conclusion, our work is the first to provide rigorous guidelines for the design of lightweight blockchain protocols with wireless connectivity.
As an integral part of V2G networks, EVs receive electricity from not only the grid but also other EVs and may frequently feed the power back to the grid. Payment records in V2G networks are useful for extracting user behaviors and facilitating decision-making for optimized power supply, scheduling, pricing, and consumption. Sharing payment and user information, however, raises serious privacy concerns in addition to the existing challenge of secure and reliable transaction processing. In this article, we propose a blockchain-based privacy preserving payment mechanism for V2G networks, which enables data sharing while securing sensitive user information. The mechanism introduces a registration and data maintenance process that is based on a blockchain technique, which ensures the anonymity of user payment data while enabling payment auditing by privileged users. Our design is implemented based on Hyperledger to carefully evaluate its feasibility and effectiveness.
Some of the appealing characteristics of distributed ledger technology (DLT), which blockchain is a type of, include guaranteed integrity, disintermediation and distributed resilience. These characteristics give rise to the possible consequences of immutability, unclear ownership, universal accessibility and transborder storage. These consequences have the potential to contravene data protection principles of Purpose Specification, Use Limitation, Data Quality, Individual Participation and Transborder Data Flow. This paper endeavours to clarify the various types of DLTs, how they work, why they exhibit the depicted characteristics and the consequences. Using the universal privacy principles developed by the Organisation of Economic Cooperation and Development (OECD), this paper then describes how each of the consequence causes concerns for privacy protection and how attempts are being made to address them in the design and implementation of various applications of blockchain and DLT, and indicates where further research and best-practice developments lie.
Zhen Hong, Zehua Wang, Wei Cai, Victor C. M. Leung
Device-to-device (D2D) communication is becoming an increasingly important technology in future networks with the climbing demand for local services. For instance, resource sharing in the D2D network features ubiquitous availability, flexibility, low latency and low cost. However, these features also bring along challenges when building a satisfactory resource sharing system in the D2D network. Specifically, user mobility is one of the top concerns for designing a cooperative D2D computational resource sharing system since mutual communication may not be stably available due to user mobility. A previous endeavour has demonstrated and proven how connectivity can be incorporated into cooperative task scheduling among users in the D2D network to effectively lower average task execution time. There are doubts about whether this type of task scheduling scheme, though effective, presents fairness among users. In other words, it can be unfair for users who contribute many computational resources while receiving little when in need. In this paper, we propose a novel blockchain-based credit system that can be incorporated into the connectivity-aware task scheduling scheme to enforce fairness among users in the D2D network. Users’ computational task cooperation will be recorded on the public blockchain ledger in the system as transactions, and each user’s credit balance can be easily accessible from the ledger. A supernode at the base station is responsible for scheduling cooperative computational tasks based on user mobility and user credit balance. We investigated the performance of the credit system, and simulation results showed that with a minor sacrifice of average task execution time, the level of fairness can obtain a major enhancement.
Harish Sukhwani, José Manuel Martínez, Xiaolin Chang, Kishor S. Trivedi · 5 authors
While Blockchain network brings tremendous benefits, there are concerns whether their performance would match up with the mainstream IT systems. This paper aims to investigate whether the consensus process using Practical Byzantine Fault Tolerance (PBFT) could be a performance bottleneck for networks with a large number of peers. We model the PBFT consensus process using Stochastic Reward Nets (SRN) to compute the mean time to complete consensus for networks up to 100 peers. We create a blockchain network using IBM Bluemix service, running a production-grade IoT application and use the data to parameterize and validate our models. We also conduct sensitivity analysis over a variety of system parameters and examine the performance of larger networks
Existing security mechanisms for managing the Internet infrastructural resources like IP addresses, AS numbers, BGP advertisements and DNS mappings rely on a Public Key Infrastructure (PKI) that can be potentially compromised by state actors and Advanced Persistent Threats (APTs). Ideally the Internet infrastructure needs a distributed and tamper-resistant resource management framework which cannot be subverted by any single entity. A secure, distributed ledger enables such a mechanism and the blockchain is the best known example of distributed ledgers.
Ke Zhang, Yuming Mao, Supeng Leng, Ming Zeng · 7 authors
Vehicle-to-Grid (V2G) is a promising paradigm to alleviate energy supply and demand imbalance of the grid. To further improve the power transmission efficiency, in this paper, we propose a cloudlet-based Vehicle-to-Vehicle (V2V) energy exchange framework. In the framework, the Energy Switch Center (ESC) serves as a trading broker, which purchases electricity from discharging vehicles and then resells it to the charging ones without energy transmission on the grid. The energy trading process is modeled in a contract theoretic approach. We derive the optimal feasible contracts which maximize the profit of the ESC. Furthermore, we systematically study the practical scenario where both the charging demand and renewable energy supplement are random variables, and propose a practical optimal contract-based electricity purchase scheme. Simulation results show that the proposed scheme can efficiently increase the profit of the ESC than the other mechanisms.
Fault-tolerant consensus has been studied extensively in the literature, because it is one of the most important distributed primitives and has wide applications in practice. This paper surveys important results on fault-tolerant consensus in message-passing networks, and the focus is on results from the past decade. Particularly, we categorize the results into two groups: new problem formulations and practical applications. In the first part, we discuss new ways to define the consensus problem, which includes larger input domains, link fault models, different network models . . . etc, and briefly discuss the important techniques. In the second part, we focus on Crash Fault-Tolerant (CFT) systems that use Paxos or Raft, and Byzantine Fault-Tolerant (BFT) systems. We also discuss Bitcoin, which can be related to solving Byzantine consensus in anonymous systems, and compare Bitcoin with BFT systems and Byzantine consensus.
The Distributed Computing Column covers the theory of systems that are composed of a number of interacting computing elements. These include problems of communication and networking, databases, distributed shared memory, multiprocessor architectures, operating systems, verification, internet, and the web.This issue consists of the paper "Reconstructing Paxos" by Romain Boichat, Partha Dutta, Svend Frølund, and Rachid Guerraoui. Many thanks to them for contributing to this issue.The celebrated Paxos algorithm of Lamport implements a fault-tolerant deterministic service by replicating it over a distributed message-passing system. In a companion paper [2], we presented a deconstruction of the algorithm by factoring out its fundamental algorithmic principles within two abstractions: an eventual leader election and an eventual register abstractions. Using those abstractions, we show in this paper how to reconstruct, in a modular manner, powerful variants of Paxos. In particular, we show how to (1) alleviate the need for stable storage access if some processes remain up for sufficiently long, (2) augment the resilience of the algorithm against unstable processes, (3) enable single process decision with shared commodity disks, and (4) reduce the number of communication steps during stable periods of the system.The Island of Paxos used to host a great civilisation which had developed a sophisticated parttime parliament protocol. Paxons codified various aspects of their parliament protocol which enabled them to easily adapt the protocol to specific functioning modes throughout the seasons. In particular, during winter, the parliament was heated and some legislators did never leave the chamber: their guaranteed presence helped alleviate the need for the writing of decrees on ledgers. This was easy to obtain precisely because the subprotocol used to "store and lock" decrees was precisely codified. In spring, and with the blooming days coming, some legislators could not stop leaving and entering the parliament. Their indiscipline prevented progress in the protocol. However, as the election subprotocol used to choose the parliament president was also precisely codified, the protocol could easily be adapted to cope with indisciplined legislators. During summer, very few legislators were in the parliament and it was hardly possible to pass any decree because of the lack of the necessary majority. Fortunately, it was easy to modify the subprotocol used to store and lock decrees and devise a powerful technique where a single legislator could pass decrees by directly accessing the ledgers of other legislators. Fall was a protest season and citizens wanted a faster procedure to pass decrees. Paxons noticed that, in most periods, messengers did not loose messages and legislators replied in time. They could devise a variant of the protocol that reduced the number of communication steps needed to pass decrees during those periods. Again, this optimisation was obtained through a simple refinement of the subprotocol used to propose new decrees.