Perigee: Efficient Peer-to-Peer Network Design for Blockchains

TL;DR

Perigee is a decentralized algorithm that optimizes peer-to-peer network topology in blockchains, reducing message propagation latency by 33% through adaptive learning based on network heterogeneities.

Contribution

It introduces a novel, lightweight, and adversary-resistant P2P protocol that learns optimal network connections using multi-armed bandit principles, improving blockchain message propagation.

Findings

Reduces broadcast latency by 33%

Learns efficient topology based on network heterogeneities

Compatible with blockchain peers' selfish interests

Abstract

A key performance metric in blockchains is the latency between when a transaction is broadcast and when it is confirmed (the so-called, confirmation latency). While improvements in consensus techniques can lead to lower confirmation latency, a fundamental lower bound on confirmation latency is the propagation latency of messages through the underlying peer-to-peer (p2p) network (inBitcoin, the propagation latency is several tens of seconds). The de facto p2p protocol used by Bitcoin and other blockchains is based on random connectivity: each node connects to a random subset of nodes. The induced p2p network topology can be highly suboptimal since it neglects geographical distance, differences in bandwidth, hash-power and computational abilities across peers. We present Perigee, a decentralized algorithm that automatically learns an efficient p2p topology tuned to the aforementioned network heterogeneities, purely based on peers' interactions with their neighbors. Motivated by the literature on the multi-armed bandit problem, Perigee optimally balances the tradeoff between retaining connections to known well-connected neighbors, and exploring new connections to previously-unseen neighbors. Experimental evaluations show that Perigee reduces the latency to broadcast by $33\%$. Lastly Perigee is simple, computationally lightweight, adversary-resistant, and compatible with the selfish interests of peers, making it an attractive p2p protocol for blockchains.