Windowed Backoff Algorithms for WiFi: Theory and Performance under Batched Arrivals

TL;DR

This paper evaluates the performance of traditional and newer backoff algorithms in WiFi under bursty traffic, revealing that newer algorithms underperform BEB due to collision costs, with implications for future algorithm design.

Contribution

It demonstrates that theoretically superior backoff algorithms may perform worse in practice under bursty traffic conditions in WiFi networks.

Findings

Newer algorithms underperform compared to BEB in bursty traffic scenarios.

Collision costs significantly impact algorithm performance beyond makespan.

Analytical insights highlight the importance of collision metrics in backoff algorithm design.

Abstract

Binary exponential backoff (BEB) is a decades-old algorithm for coordinating access to a shared channel. In modern networks, BEB plays an important role in WiFi (IEEE 802.11) and other wireless communication standards. Despite this track record, well-known theoretical results indicate that under bursty traffic BEB yields poor makespan, and superior algorithms are possible. To date, the degree to which these findings impact performance in wireless networks has not been examined. To address this issue, we investigate one of the strongest cases against BEB: a single burst batch of packets that simultaneously contend for access to a wireless channel. Using Network Simulator 3, we incorporate into IEEE 802.11g several newer algorithms that, while inspired by BEB, possess makespan guarantees that are theoretically superior. Surprisingly, we discover that these newer algorithms underperform BEB. Investigating further, we identify as the culprit a common abstraction regarding the cost of collisions. Our experimental results are complemented by analytical arguments that the number of collisions - and not solely makespan - is an important metric to optimize. We argue that these findings have implications for the design of backoff algorithms in wireless networks.