Antonis Litke, ICCS/NTUA
July 13 2020
With the recent introduction of blockchains as an enabling technology for distributed and peer-to-peer systems, it comes as a challenge to check whether modern edge computing approaches are suitable for being coupled with emerging decentralised applications built on blockchains.
A distributed trust technology, ensuring scalability, privacy, and reliability, is a cornerstone for the growth of IoT and edge computing environments. In recent years, the blockchain technology has matured significantly and is seen as a promising solution in achieving a set of goals that have to do with trust due to its capabilities, such as immutability, transparency, auditability, data encryption and operational resilience. Data integrity in distributed applications based on edge servers is a significant challenge as the data streams aggregated from widely dispersed sensors can be utilised in making timely decisions. Thus, it is essential to protect data integrity of the system and make sure that no malicious data will be injected affecting decision-making. Although blockchain offers attractive security features for distributed data processing and storage, some security issues emerge when blockchain is used with edge computing, especially in the case of private blockchains. For example, one possible implementation can be the small-scale “white-listed” IoT networks where all network nodes trust each other, and a Proof-of-Work consensus mechanism is not required. In this case, attacks can happen when transaction data is transferred from mobile or IoT devices to edge computing servers. A secure and trusted network between the devices and servers is required. For this reason, a discussion on whether using public, permissionless blockchains over private, permissioned blockchains will be always relevant as it is the case with the Pledger project itself.
With the emergence of Machine Economy, whereby the sensors are capable of participating in data marketplaces and end-to-end autonomous systems, creating trust between participating entities is a significant challenge. The situation gets even more complex when the trust among the edge nodes has to be orchestrated in larger value chains of interacting services. IoT applications on edge servers face a considerable number of additional challenges that have to do mainly with the dynamicity of the examined applications and their workloads, the volatility of infrastructures and the need for server consolidation in order to minimise costs while maintaining the guaranteed Service Level Agreements (SLAs). Moreover, edge computing has emerged as an effective offloading strategy for constrained devices. It enables low-capability devices to leverage nearby resources for assistance with computationally-intensive tasks. The long-term vision of future IoT devices is that they will be able to autonomously transact with other more powerful devices to request such offloading services. For this reason, there is a need to engineer new mechanisms and middleware approaches that will couple blockchain-based trust mechanisms with workflow management and orchestration services that are needed to achieve this.
Xiong et al. consider an edge computing enabled mobile blockchain network where IoT devices or mobile users can access and utilise resources or computing services from an edge computing service provider to support their blockchain applications. They present overviews of blockchain and edge computing architectures and propose a prototype of an edge computing system for mobile blockchain along with pricing schemes for the edge computing services for blockchain.
Papadodimas et al. propose a decentralised application (DApp) based on blockchain technology for sharing IoT sensors’ data, and demonstrate various challenges addressed during the development process. The application combines blockchain technology with IoT and operates through smart contracts that are executed on the Ethereum blockchain. The application is a platform for sharing (buying and selling) measurements of IoT weather sensors and operates on the Ethereum blockchain, acting as a marketplace for IoT sensor data. This application applies the Sensing-as-a-Service business model combined with blockchain.
Pledger will extend the work that has already been performed in implementation of Smart Contracts for blockchain based IoT applications to cover edge computing architectures so as to support the implementation of decentralised applications on the edge. The consortium will build a reference multi-layer architecture comprising of different peer networks hierarchies based on the edge capabilities and their capacity to deliver specific Quality of Service applications. Moreover, Pledger will study and implement smart contracts that will collaborate with the SLA specific contractual terms in order to let the edge resources negotiate the level of service to be delivered to the edge resource user, while at the same time the specific contractual terms will be bound to a smart contract that is deployed and executed on the Pledger blockchain.
As edge computing services have limited capacity, which may not be sufficient to support demand from all users, additional strategies for resource management and allocation will be studied in the frame of the project. The various users have different valuation of the edge computing services and this valuation depends on certain factors such as reward and number of transactions included in a block of the blockchain among others. These factors influence the computing resource demand of the users. Pledger will investigate also the use of blockchain based tokens which will act as a currency between the edge nodes when they interact with each other in service value chains, enabling thus a new paradigm of resource management and utilization.
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 Xiong, Z., Zhang, Y., Niyato, D., Wang, P., & Han, Z. (2018). “When Mobile Blockchain Meets Edge Computing”. IEEE Communications Magazine, 56, 33-39
 G. Papadodimas, G. Palaiokrassas, A. Litke, T. A. Varvarigou, “Implementation of smart contracts for blockchain based IoT applications”. 9th International Conference on the Network of the Future, NOF 2018, Poznan, Poland, November 19-21, 2018. IEEE 2018, ISBN 978-1-5386-8503-7 pages : 60-67