Payment Channel Networks (PCNs) have been proposed as an alternative solution to the scalability, throughput, and cost overhead problems associated with blockchain transactions. By facilitating offchain execution of transactions, PCNs significantly reduce the burden on the blockchain, leading to faster transaction processing, reduced transaction fees, and enhanced privacy. Despite these advantages, the current state-of-the-art in PCNs presents a variety of challenges that require further exploration. In this paper, we survey several fundamental aspects of PCNs, such as pathfinding and routing, virtual channels, state channels, payment channel hubs, and rebalancing protocols. We aim to provide the reader with a detailed understanding of the various aspects of PCN research, highlighting important advancements. Additionally, we highlight the various unresolved challenges in this area. Specifically, this paper seeks to answer the following crucial question: What are the various interesting and non-trivial challenges in fundamental infrastructure design leading to efficient transaction processing in PCN research that require immediate attention from the academic and research community? By addressing this question, we aim to identify the most pressing problems and future research directions, and we hope to inspire researchers and practitioners to tackle these challenges to make PCNs more secure and versatile

翻译：支付通道网络（PCNs）被提出作为解决区块链交易可扩展性、吞吐量和成本开销问题的替代方案。通过促进交易的链下执行，PCNs显著减轻了区块链的负担，从而实现更快的交易处理、更低的交易费用和更强的隐私保护。尽管存在这些优势，当前PCNs的最新技术仍面临诸多需要进一步探索的挑战。本文系统梳理了PCNs的若干基础方面，包括路径发现与路由、虚拟通道、状态通道、支付通道枢纽和再平衡协议。我们旨在让读者详细了解PCN研究的各个维度，并重点阐述重要进展。此外，本文着重指出了该领域尚未解决的多重挑战。具体而言，本文试图回答以下关键问题：在PCN研究中，哪些基础架构设计层面存在需要学术界和科研界立即关注、能导向高效交易处理的有趣且非平凡的挑战？通过探讨这一问题，我们期望明确最紧迫的难题和未来研究方向，并激励研究人员与从业者共同应对这些挑战，使PCNs变得更安全、更通用。