Abstract: High-speed rail (HSR) systems potentially provide a more efficient way of door-to-door transportation than airplane. However, they also pose unprecedented challenges in delivering seamless Internet service for on-board passengers. In this paper, we conduct a large-scale active-passive measurement study of TCP performance over LTE on HSR. Our measurement targets the HSR routes in China operating at above 300 km/h. We performed extensive data collection through both controlled setting and passive monitoring, obtaining 1732.9 GB data collected over 135719 km of trips. Leveraging such a unique dataset, we measure important performance metrics such as TCP goodput, latency, loss rate, as well as key characteristics of TCP flows, application breakdown, and users' behaviors. We further quantitatively study the impact of frequent cellular handover on HSR networking performance, and conduct in-depth examination of the performance of two widely deployed transport-layer protocols: TCP CUBIC and TCP BBR. Our findings reveal the performance of today's commercial HSR networks "in the wild'', as well as identify several performance inefficiencies, which motivate us to design a simple yet effective congestion control algorithm based on BBR to further boost the throughput by up to 36.5%. They together highlight the need to develop dedicated protocol mechanisms that are friendly to extreme mobility.
Abstract: 5G claims to support mobility up to 500 km/h according to the 3GPP standard. However, its field performance under high-speed scenes remains in mystery. In this paper, we conduct the first large-scale measurement campaign on a high-speed railway route operating at the maximum speed of 350 km/h, with full coverage of LTE and 5G (NSA and SA) along the track. Our study consumed 1788.8 GiB of cellular data in six months, covering the three major carriers in China and the recent standardized QUIC protocol. Based on our dataset, we reveal the key characteristics of 5G and LTE in extreme mobility in terms of throughput, RTT, loss rate, signal quality, and physical resource utilization. We further develop a taxonomy of handovers in both LTE and 5G and carry out the link-layer latency breakdown analysis. Our study pinpoints the deficiencies in the user equipment, radio access network, and core network which hinder seamless connectivity and better utilization of 5G's high bandwidth. Our findings highlight the directions of the next step in the 5G evolution.
Dataset: We publish IP/TCP traces (in the folder L3L4/) with cellular metrics (in the folder L1L2/, including signal conditions L1L2/rsrp and L1L2/snr, resource block allocation L1L2/rb_allocation, handover events L1L2/handover, and more). Our experiments cross six months and cover two radio access technologies (LTE and 5G) and two deployment modes (SA and NSA). The corresponding information can be extracted from the path (e.g. the path 20210911/SA contains the traces of experiments conducted on September 11th, 2021 with the radio access technology 5G and the deployment mode SA). Additionally, a plaintext file co-located with the trace file denotes the experiment type (e.g. for the IP/TCP trace file 2021-09-11T13-37-43/l3.pcap.xz, if there is a plaintext file named tcp in the same folder, i.e. the file 2021-09-11T13-37-43/tcp exists, the experiment will be a full-speed TCP test). The list of possible experiment types can be found in the paper.
Abstract: Modern high-speed railway (HSR) systems offer a speed of more than 250 km/h, making on-board Internet access through track-side cellular base stations extremely challenging. We conduct extensive measurements on commercial HSR trains, and collect a massive 1.79 TB GPS-labeled TCP-LTE dataset covering a total travel distance of 28,800 km. Leveraging the new insights from the measurement, we design, implement, and evaluate POLYCORN, a first-of-its-kind networking system that can significantly boost Internet perfor- mance for HSR passengers. The core design of POLYCORN consists of a suite of composable multipath schedulerlets that intelligently determine what, when, and how to schedule user traffic over multiple highly fluctuating cellular links between HSR and track-side base stations. POLYCORN is specially designed for HSR environments through a cross-layer and data-driven proactive approach. We deploy POLYCORN on the operational LTE gateway of the popular Beijing-Shanghai HSR route at 300 km/h. Real-world experiments demonstrate that POLYCORN outperforms the state-of-the-art multipath schedulers by up to 242% in goodput, and reduces the delivery time by 45% for instant messaging applications.
Dataset: Please see README.md in the dataset file.