Seeing Through the Fog: Empowering Mobile Devices to Expose and Mitigate RAN Buffer Effects on Delay-Sensitive Protocols

TL;DR

This paper introduces CellNinjia and Gandalf, systems that expose and mitigate RAN buffer delays in cellular networks, enabling delay-sensitive protocols to perform effectively despite RAN-induced delays.

Contribution

The paper presents novel software systems that provide real-time RAN visibility and compensate for RAN buffer delays, improving delay-based protocol performance in cellular networks.

Findings

Gandalf improves Copa performance by up to 7.49x.

Gandalf enhances PCC Vivace by up to 9.53x.

Real-world evaluation in 4G LTE and 5G networks demonstrates significant performance gains.

Abstract

Delay-based protocols rely on end-to-end delay measurements to detect network congestion. However, in cellular networks, Radio Access Network (RAN) buffers introduce significant delays unrelated to congestion, fundamentally challenging these protocols' assumptions. We identify two major types of RAN buffers - retransmission buffers and uplink scheduling buffers - that can introduce delays comparable to congestion-induced delays, severely degrading protocol performance. We present CellNinjia, a software-based system providing real-time visibility into RAN operations, and Gandalf, which leverages this visibility to systematically handle RAN-induced delays. Unlike existing approaches that treat these delays as random noise, Gandalf identifies specific RAN operations and compensates for their effects. Our evaluation in commercial 4G LTE and 5G networks shows that Gandalf enables substantial performance improvements - up to 7.49x for Copa and 9.53x for PCC Vivace - without modifying the protocols' core algorithms, demonstrating that delay-based protocols can realize their full potential in cellular networks.