An Axiomatic Perspective on the Performance Effects of End-Host Path Selection

TL;DR

This paper provides an axiomatic analysis of how end-host path selection influences network performance, stability, and fairness, revealing fundamental trade-offs and quantifying the impact on key network metrics.

Contribution

It introduces an axiomatic framework to analyze multi-path congestion control, quantifies the effects of path selection, and identifies inherent trade-offs in protocol design.

Findings

Path selection can improve efficiency but may cause instability.

Axiomatic analysis quantifies performance impacts of path selection.

Trade-offs exist between stability, efficiency, and fairness.

Abstract

In various contexts of networking research, end-host path selection has recently regained momentum as a design principle. While such path selection has the potential to increase performance and security of networks, there is a prominent concern that it could also lead to network instability (i.e., flow-volume oscillation) if paths are selected in a greedy, load-adaptive fashion. However, the extent and the impact vectors of instability caused by path selection are rarely concretized or quantified, which is essential to discuss the merits and drawbacks of end-host path selection. In this work, we investigate the effect of end-host path selection on various metrics of networks both qualitatively and quantitatively. To achieve general and fundamental insights, we leverage the recently introduced axiomatic perspective on congestion control and adapt it to accommodate joint algorithms for path selection and congestion control, i.e., multi-path congestion-control protocols. Using this approach, we identify equilibria of the multi-path congestion-control dynamics and analytically characterize these equilibria with respect to important metrics of interest in networks (the 'axioms') such as efficiency, fairness, and loss avoidance. Moreover, we analyze how these axiomatic ratings for a general network change compared to a scenario without path selection, thereby obtaining an interpretable and quantititative formalization of the performance impact of end-host path-selection. Finally, we show that there is a fundamental trade-off in multi-path congestion-control protocol design between efficiency, stability, and loss avoidance on one side and fairness and responsiveness on the other side.