Optimal Hub Placement and Deadlock-Free Routing for Payment Channel Network Scalability

As a promising implementation model of payment channel network (PCN), payment channel hub (PCH) could achieve high throughput by providing stable off-chain transactions through powerful hubs. However, existing PCH schemes assume hubs are preplaced in advance, not considering payment requests' distribution and may affect network scalability, especially network load balancing. In addition, current source routing protocols with PCH allow each sender to make routing decision on his/her own request, which may have a bad effect on performance scalability (e.g., deadlock) for not considering other senders' requests. This paper proposes a novel multi-PCHs solution with high scalability. First, we are the first to study the PCH placement problem and propose optimal/approximation solutions with load balancing for small-scale and large-scale scenarios, by trading off communication costs among participants and turning the original NP-hard problem into a mixed-integer linear programming (MILP) problem solving by supermodular techniques. Then, on global network states and local directly connected clients' requests, a routing protocol is designed for each PCH with a dynamic adjustment strategy on request processing rates, enabling high-performance deadlock-free routing. Extensive experiments show that our work can effectively balance the network load, and improve the performance on throughput by 29.3% on average compared with state-of-the-arts.

I. Introduction

Cryptocurrencies are gaining popularity in the financial ecosystem. However, the scalability issues of their underlying blockchain technology are still challenging. Since each transaction needs to be confirmed by the consensus mechanism, this can take several minutes to hours. Instead of continually improving the design of the consensus mechanism, a leading layer-2 proposal for addressing the scalability challenge relies on off-chain payment channels [1], [2]. The core idea is to move mass transactions submitted on-chain to off-chain and execute them securely using a locking mechanism. Only the key steps (e.g., resolving disputes, opening/closing channels) are put on-chain for confirmation.