Bitcoin is the first decentralized cryptocurrency ever created, and due to the transaction limit of the blockchain it is not scalable. To overcome the scalability problem, payment channel networks have been developed. Payment channel networks reduce the number of transactions loaded on the blockchain, allowing unbounded off-chain payments in almost instant time. Lightning Network is the most prominent payment channel network built for Bitcoin. With its time-based smart contract called HTLC, it allows off-chain payments across channels without trusting other participants, with small fees to route payments. Payments are routed with a few hops from peers across the network. Topological studies show that since channel creation takes funds from the blockchain nodes tend to create few channels by connecting to central nodes in the network rather than creating ad hoc ones.