HybridNN: Supporting Network Location Service on Generalized Delay Metrics

TL;DR

HybridNN introduces a new inframetric delay model and a scalable, accurate method for distributed nearest neighbor search that works effectively with asymmetric delays in large-scale networks.

Contribution

It proposes a relaxed delay model that does not assume symmetry or triangle inequality, and develops HybridNN, a novel scalable DNNS method based on this model.

Findings

HybridNN locates nearly optimal nearest neighbors in simulations.

HybridNN achieves accurate results with modest query overhead.

Experiments on PlanetLab confirm HybridNN's effectiveness in real networks.

Abstract

Distributed Nearest Neighbor Search (DNNS) locates service nodes that have shortest interactive delay towards requesting hosts. DNNS provides an important service for large-scale latency sensitive networked applications, such as VoIP, online network games, or interactive network services on the cloud. Existing work assumes the delay to be symmetric, which does not generalize to applications that are sensitive to one-way delays, such as the multimedia video delivery from the servers to the hosts. We propose a relaxed inframetric model for the network delay space that does not assume the triangle inequality and delay symmetry to hold. We prove that the DNNS requests can be completed efficiently if the delay space exhibits modest inframetric dimensions, which we can observe empirically. Finally, we propose a DNNS method named HybridNN (\textit{Hybrid} \textit{N}earest \textit{N}eighbor search) based on the inframetric model for fast and accurate DNNS. For DNNS requests, HybridNN chooses closest neighbors accurately via the inframetric modelling, and scalably by combining delay predictions with direct probes to a pruned set of neighbors. Simulation results show that HybridNN locates nearly optimally the nearest neighbor. Experiments on PlanetLab show that HybridNN can provide accurate nearest neighbors that are close to optimal with modest query overhead and maintenance traffic.