Extend PBFT Protocol with L-DAG

The linear structure of blockchain ensures data security and credibility. But at the same time, it has become the performance bottleneck of the entire system, limiting the growth of the transaction processing rate. The inherent concurrency of directed acyclic graph (DAG) technology solves these problems, but it also brings new problems: blocks total order and ledger consistency. In this paper, we propose a Layer-based DAG (L-DAG) blockchain, which avoids the complex total ordering algorithms by keeping blocks in order between and within layers during the generation process. And we introduce the proportional-integral-derivative (PID) controller to dynamically control the width of layers by using in-degree and out-degree of blocks to achieve the consistency of ledger. We extend Practical Byzantine Fault Tolerance (PBFT) protocol in parallel based on the L-DAG structure and successfully apply it to consortium blockchain scenarios. The L-DAG blockchain structure is implemented through Hyperledger Fabric. Experimental results show that as the number of consensus threads increases, the TPS of L-DAG-based PBFT can grow with near-linear efficiency.