Demand-aware Channel Topologies for Off-chain Payments

Off-chain is a common approach to deal with the scalability problem of blockchain networks. It enables users to execute multiple payments without committing each of them to the blockchain by relying on predefined payment channels. A pair of users can employ a payment even without a direct channel between them, via routing the payment through off-chain channels involving other intermediate users. Users together with the off-chain channels form a graph, known as the off-chain network topology. The off-chain topology and the payment characteristics affect network performance such as the average number of intermediate users a payment is routed through, the amount of fees, or channel capacities needed to successfully route payments. In this paper, we study two basic problems in off-chain network design. First, efficiently mapping users to an off-chain topology with a known structure. Second, constructing a topology of a bounded number of channels that can serve well users with associated payments. We design algorithms for both problems and evaluate them based on real data from Raiden, the off-chain extension for Ethereum.