Bitcoin Optech 142: LN Path Selection

News

• Paper on probabilistic path selection: René Pickhardt posted to the Lightning-Dev mailing list a paper he co-authored with Sergei Tikhomirov, Alex Biryukov, and Mariusz Nowostawski. The paper models a network of channels having a uniform distribution of balances within their respective channel capacity. E.g., for a channel with the capacity of 100 million satoshis between Alice and Bob, the paper assumes all of the following states are equally as likely for that channel, and that the same holds true for every other channel on the network:

• Making this assumption allows the authors to draw conclusions about the probability that a payment will succeed based on its amount and how many hops (channels) it needs to traverse. This allows the authors to prove the benefit of several known heuristics—such as keeping paths short and using multipath payments to break larger payments into smaller payments (under certain other assumptions). They also use the model to evaluate new proposals, such as allowing Just-In-Time (JIT) rebalancing via bolts #780.
  The paper uses its conclusions to provide a routing algorithm that it claims can reduce payment retry attempts by 20% compared to their simplification of existing routing algorithms. The new algorithm prefers routes with a higher computed probability of success, whereas existing algorithms use a heuristic approach. Combined with JIT rebalancing, they estimate a 48% improvement. Given that each retry usually requires several seconds, and could take much longer in some cases, this could provide an improved user experience. The algorithm was tested against several example networks, including one drawn from a snapshot of almost 1,000 live channels.
  The paper deliberately does not take routing fees into consideration, and most responses on the mailing list focused on how to use the results while still ensuring users don’t pay an excessive amount of fees.
• Updated article about payment batching: Optech has published an article about payment batching, updated from our original announcement of it in Newsletter #37. Payment batching is a technique that can help spenders save up to 80% on transaction fees.

Selected Q&A from Bitcoin StackExchange

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