  Despite growing adoption of cryptocurrencies, making fast payments at scale
remains a challenge. Payment channel networks (PCNs) such as the Lightning
Network have emerged as a viable scaling solution. However, completing payments
on PCNs is challenging: payments must be routed on paths with sufficient funds.
As payments flow over a single channel (link) in the same direction, the
channel eventually becomes depleted and cannot support further payments in that
direction; hence, naive routing schemes like shortest-path routing can deplete
key payment channels and paralyze the system. Today's PCNs also route payments
atomically, worsening the problem. In this paper, we present Spider, a routing
solution that "packetizes" transactions and uses a multi-path transport
protocol to achieve high-throughput routing in PCNs. Packetization allows
Spider to complete even large transactions on low-capacity payment channels
over time, while the multi-path congestion control protocol ensures balanced
utilization of channels and fairness across flows. Extensive simulations
comparing Spider with state-of-the-art approaches shows that Spider requires
less than 25% of the funds to successfully route over 95% of transactions on
balanced traffic demands, and offloads 4x more transactions onto the PCN on
imbalanced demands.
