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1. Automated, Cross-Layer Root Cause Analysis of 5G Video-Conferencing Quality Degradation

   Yi, Fan; Wan, Haoran; Jamieson, Kyle; Michel, Oliver (October 2025, ACM Internet Measurement Conference (IMC))

   5G wireless networks leverage complex scheduling, retransmission, and adaptation mechanisms to maximize their efficiency. These mechanisms interact to produce significant fluctuations in uplink and downlink capacity and latency, markedly impacting the the performance of real-time communication and multimedia applications, such as video conferencing. These applications are particularly sensitive to such fluctuations, resulting in lag, stuttering, distorted audio, and low video quality. In this paper, we present a cross-layer view of 5G networks and their impact on and interaction with video-conferencing applications. We conduct novel, detailed measurements of both private CBRS and commercial carrier cellular network dynamics, capturing physical- and link-layer events and correlating them with their effects at the network and transport layers, and the video-conferencing application itself. Our two datasets comprise days of low-rate campus-wide Zoom telemetry data, and hours of high-rate, correlated WebRTC-network-5G telemetry data. Based on these data, we trace performance anomalies back to root causes, identifying 24 previously unknown causal event chains that degrade 5G video conferencing. Armed with this knowledge, we build Domino, a tool that automates this process and is user-extensible to future wireless networks and interactive applications. 

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2. A Measurement-Derived Functional Model for the Interaction Between Congestion Control and QoE in Video Conferencing

   He, Jia; Ammar, Mostafa; Zegura, Ellen (March 2023, Springer)

   Video Conferencing Applications (VCAs) that support remote work and education have increased in use over the last two years, contributing to Internet bandwidth usage. VCA clients transmit video and audio to each other in peer-to-peer mode or through a bridge known as a Selective Forwarding Unit (SFU). Popular VCAs implement congestion control in the application layer over UDP and accomplish rate adjustment through video rate control, ultimately affecting end user Quality of Experience(QoE). Researchers have reported on the throughput and video metric performance of specific VCAs using structuredexperiments. Yet prior work rarely examines the interaction between congestion control mechanisms and rate adjustment techniques that produces the observed throughput and QoE metrics. Understanding this interaction at a functional level paves the way to explain observed performance, to pinpoint commonalities and key functional differences across VCAs, and to contemplate opportunities for innovation. To that end, we first design and conduct detailed measurements of three VCAs(WebRTC/Jitsi, Zoom, Blue Jeans) to develop understanding of their congestion and video rate control mechanisms. We then use the measurement results to derive our functional models for the VCA client and SFU. Our models reveal the complexity of these systems and demonstrate how, despite some uniformity in function deployment, there is significant variability among the VCAs in the implementation of these functions. 

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3. Sidekick: In-Network Assistance for Secure End-to-End Transport Protocols

   Yuan, Gina; Sotoudeh, Matthew; Zhang, David K; Welzl, Michael; Mazières, David; Winstein, Keith (April 2024, USENIX Association)

   Vanbever, Laurent; Zhang, Irene (Ed.)

   In response to concerns about protocol ossification and privacy, post-TCP transport protocols such as QUIC and WebRTC include end-to-end encryption and authentication at the transport layer. This makes their packets opaque to middleboxes, freeing the transport protocol to evolve but preventing some in-network innovations and performance improvements. This paper describes sidekick protocols: an approach to in-network assistance for opaque transport protocols where in-network intermediaries help endpoints by sending information adjacent to the underlying connection, which remains opaque and unmodified on the wire. A key technical challenge is how the sidekick connection can efficiently refer to ranges of packets of the underlying connection without the ability to observe cleartext sequence numbers. We present a mathematical tool called a quACK that concisely represents a selective acknowledgment of opaque packets, without access to cleartext sequence numbers. In real-world and emulation-based evaluations, the sidekick improved performance in several scenarios: early retransmission over lossy Wi-Fi paths, proxy acknowledgments to save energy, and a path-aware congestion-control mechanism we call PACUBIC that emulates a “split” connection. 

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4. Octopus: In-Network Content Adaptation to Control Congestion on 5G Links

   Chen, Yongzhou; Tahir, Ammar; Yan, Francis; Mittal, Radhika (February 2024, ACM/IEEE)

   It is challenging to meet the bandwidth and latency requirements of interactive real-time applications (e.g., virtual reality, cloud gam- ing, etc.) on time-varying 5G cellular links. Today’s feedback-based congestion controllers try to match the sending rate at the endhost with the estimated network capacity. However, such controllers can- not precisely estimate the cellular link capacity that changes at timescales smaller than the feedback delay. We instead propose a different approach for controlling congestion on 5G links. We send real-time data streams using an imprecise controller (that errs on the side of overestimating network capacity) to ensure high through- put, and then adapt the transmitted content by dropping appropriate packets in the cellular base stations to match the actual capacity and minimize delay. We build a system called Octopus to realize this ap- proach. Octopus provides parameterized primitives that applications at the endhost can configure differently to express different content adaptation policies. Octopus transport encodes the corresponding app-specified parameters in packet header fields, which the base- station logic can parse to execute the desired dropping behavior. Our evaluation shows how real-time applications involving standard and volumetric videos can be designed to exploit Octopus, and achieve 1.5–18× better performance than state-of-the-art schemes. 

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5. Joint Caching and Routing in Congestible Networks of Arbitrary Topology

   Liu, B.; Poularakis, K.; Tassiulas, L.; Jiang, T. (August 2019, IEEE internet of things journal)

   In-network caching constitutes a promising approach to reduce traffic loads and alleviate congestion in both wired and wireless networks. In this paper, we study the joint caching and routing problem in congestible networks of arbitrary topology (JoCRAT) as a generalization of previous efforts in this particular field. We show that JoCRAT extends many previous problems in the caching literature that are intractable even with specific topologies and/or assumed unlimited bandwidth of communications. To handle this significant but challenging problem, we develop a novel approximation algorithm with guaranteed performance bound based on a randomized rounding technique. Evaluation results demonstrate that our proposed algorithm achieves nearoptimal performance over a broad array of synthetic and real networks, while significantly outperforming the state-of-the-art methods. 

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