After the success of the Bitcoin blockchain, came several cryptocurrencies and blockchain solutions in the last decade. Nonetheless, Blockchain-based systems still suffer from low transaction rates and high transaction processing latencies, which hinder blockchains' scalability. An entire class of solutions, called Layer-1 scalability solutions, have attempted to incrementally improve such limitations by adding/modifying fundamental blockchain attributes. Recently, a completely different class of works, called Layer-2 protocols, have emerged to tackle the blockchain scalability issues using unconventional approaches. Layer-2 protocols improve transaction processing rates, periods, and fees by minimizing the use of underlying slow and costly blockchains. In fact, the main chain acts just as an instrument for trust establishment and dispute resolution among Layer-2 participants, where only a few transactions are dispatched to the main chain. Thus, Layer-2 blockchain protocols have the potential to transform the domain. However, rapid and discrete developments have resulted in diverse branches of Layer-2 protocols. In this work, we systematically create a broad taxonomy of such protocols and implementations. We discuss each Layer-2 protocol class in detail and also elucidate their respective approaches, salient features, requirements, etc. Moreover, we outline the issues related to these protocols along with a comparative discussion. Our thorough study will help further systematize the knowledge dispersed in the domain and help the readers to better understand the field of Layer-2 protocols.
翻译:在Bitcoin链链成功之后,过去十年中出现了几套加密和连锁解决办法。尽管如此,基于链链的系统仍然受到低交易率和高交易处理拖延的影响,这阻碍了块链的伸缩性。一整类解决办法,即称为Dire-1的伸缩性解决办法,试图通过增加/修改基本块链属性来逐步改进这些限制。最近,一个完全不同的工程类别,即称为Dire-2协议,已经出现,以使用非常规方法解决块链的伸缩性问题。第二层协议通过尽可能减少使用基本的缓慢和昂贵的连锁系统来提高交易率、期限和收费。事实上,主要链只是作为建立信任和解决第二层参与者之间争端的工具,其中只有少数交易被发送到主链中。因此,Thile-2链协议有可能改变域域。然而,迅速和分散的发展导致了第2层协议的不同分支。在这项工作中,我们系统地建立这类协议和执行的广泛分类。我们通过详细讨论每一层第二层协议的分类和成本,来帮助我们更清楚地了解各自层次协议的简况。