# PnV: An Efficient Parallel Consensus Protocol Integrating Proof and Voting
###### Abstract  
Consensus protocols, as crucial components of blockchain technology, play a vital role in ensuring data consistency among distributed nodes. However, the existing voting-based and proof-based consensus protocols encounter scalability issues within the blockchain system. Moreover, most consensus protocols are serialized, which further limits their scalability potential. To address this limitation, parallelization methods have been employed in both types of consensus protocols. Surprisingly, however, novel fusion consensus protocols demonstrate superior scalability compared with these two types but lack the utilization of parallelization techniques. In this paper, we present PnV, an efficient parallel fusion protocol integrating proof-based and voting-based consensus features. It enhances the data structure, consensus process, transaction allocation, and timeout handling mechanisms to enable concurrent block generation by multiple nodes within a consensus round. Experimental results demonstrate that PnV exhibits superior efficiency, excellent scalability, and acceptable delay compared with Proof of Vote (PoV) and BFT-SMART. Moreover, at the system level, the performance of the PnV-based blockchain system optimally surpasses that of the FISCO BCOS platform. Our proposed protocol contributes to advancing blockchain technology by providing a more efficient and practical solution for achieving decentralized consensus in distributed systems. osmotium blockchain; consensus protocol; parallelization +
Footnote †: journal:  
0000-0001-4000-0001-4000][PERSON]. [PERSON]  
0000-0001-4000-0001-4000-0001-4000-0001-4000-000 As mentioned earlier, the performance bottlenecks of consensus protocols based on voting and proof are primarily attributed to the limitations in communication resources and computational capabilities of nodes, respectively. Consequently, each consensus type possesses its own merits regarding support for node numbers and efficiency. This drives the emergence of integrating both consensus types to leverage their respective advantages and achieve extensive scalability. A notable example is Proof of Vote (PoV) [12; 13], which is a robust consensus protocol with high efficiency and strong security features. By combining voting-based and proof-based characteristics through a delegated mechanism, PoV establishes committee members as the central cluster responsible for monitoring and verifying block production via voting. Independence is ensured by an elected bookkeeper team responsible for block packaging. Only bookkeeper candidates recommended by committee members and who meet minimum participation and performance standards are eligible. These standards include depositing funds and subjecting their work to ongoing supervision and evaluation. This approach aims to select bookkeepers who demonstrate honesty and reliability over multiple election cycles, thereby guaranteeing the safety and reliability of team work. In addition, by leveraging implicit two-phase commit, PoV significantly reduces communication complexity while ensuring fairness within the committee. Other fusion consensus protocols include HotStuff [14] and Votes-as-a-Proof (VaaP) [15]. The proposal of fusion protocols effectively overcomes performance bottlenecks related to communication resources and computing power. However, the maintenance of a single-chain structure presents an additional challenge to blockchain scalability, as it necessitates the serialization of all concurrent blocks. To alleviate this limitation, an intuitive approach involves parallelization methods instead of solely relying on a single chain for achieving superior concurrency [16]. This idea has been implemented in various proof-based consensus protocols, including parallel-chain structures [17; 18] and Directed Acyclic Graph (DAG)-based structures [19; 20]. Additionally, DAG-based consensus protocols such as DAG-Rider [21], Tusk [22], and Bull-Shark [23] have been proposed as viable scalable voting-based solutions.