Always be Two Steps Ahead of Your Enemy

TL;DR

This paper presents a new algorithm for maintaining a highly resilient overlay network under massive churn and adversarial conditions, ensuring connectivity and efficiency with minimal message overhead.

Contribution

It introduces the Linearized DeBruijn Swarm (LDS), a novel overlay topology, and an algorithm that rebuilds the overlay every 2 rounds, independent of previous overlays.

Findings

Maintaining connectivity is impossible if the adversary has up-to-date topology information.

The join restriction is necessary for network stability.

The proposed algorithm uses only O(log^3 n) messages per node per round.

Abstract

We investigate the maintenance of overlay networks under massive churn, i.e. nodes joining and leaving the network. We assume an adversary that may churn a constant fraction $\alpha n$ of nodes over the course of $\mathcal{O}(\log n)$ rounds. In particular, the adversary has an almost up-to-date information of the network topology as it can observe an only slightly outdated topology that is at least $2$ rounds old. Other than that, we only have the provably minimal restriction that new nodes can only join the network via nodes that have taken part in the network for at least one round. Our contributions are as follows: First, we show that it is impossible to maintain a connected topology if adversary has up-to-date information about the nodes' connections. Further, we show that our restriction concerning the join is also necessary. As our main result present an algorithm that constructs a new overlay -- completely independent of all previous overlays -- every $2$ rounds. Furthermore, each node sends and receives only $\mathcal{O}(\log^3 n)$ messages each round. As part of our solution we propose the Linearized DeBruijn Swarm (LDS), a highly churn resistant overlay, which will be maintained by the algorithm. However, our approaches can be transferred to a variety of classical P2P Topologies where nodes are mapped into the $[0,1)$-interval.