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

2025-06-30

AI Summary

In cellular networks, RAN buffering—particularly in retransmission and uplink scheduling buffers—introduces non-congestion-related latency that severely degrades the accuracy of end-to-end latency–based congestion control protocols (e.g., Copa, PCC Vivace). This work is the first to systematically distinguish and model these two critical RAN buffering mechanisms. We propose CellNinjia+Gandalf, a lightweight software-only solution: CellNinjia enables real-time RAN state awareness, while Gandalf performs latency attribution and dynamic compensation—without modifying protocol-stack cores. Evaluated on live 4G/5G deployments, our approach improves throughput for Copa and PCC Vivace by 7.49× and 9.53×, respectively, effectively restoring the practical performance of delay-sensitive protocols in mobile environments. The work establishes a deployable attribution-and-compensation paradigm for latency-driven protocol design in wireless networks.

Technology Category

• Planning, Routing, and Scheduling: Applications
• Machine Learning: Hardware-aware ML
• Application Domains: Mobility, Driving & Flight

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

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.

Problem

• RAN buffers cause misleading delays in cellular networks
• Existing methods treat RAN delays as random noise
• Delay-based protocols underperform due to RAN buffer effects

Innovation

• CellNinjia provides real-time RAN operation visibility
• Gandalf compensates for specific RAN-induced delays
• System improves delay-based protocols in cellular networks