arXiv subjects

Kai-Steffen Hielscher

Publications and source records attributed to Kai-Steffen Hielscher.

6 recordsLinked to original sources

arXiv2025

Trace-driven Path Emulation of Satellite Networks using Hypatia

The increasing prevalence LEO satellite mega-constellations for global Internet coverage requires new approaches to evaluate the behavior of existing Internet protocols and applications. Traditional discrete event simulators like Hypatia allow for modeling these environments but fall short in evaluating real applications. This paper builds upon our previous work, in which we proposed a system design for trace-driven emulation of such satellite networks, bridging the gab between simulations and real-time testbeds. By extending the Hypatia framework, we record network path characteristics, e.g., delay and bandwidth, between two endpoints in the network during non-real-time simulations. Path characteristics are exported to Trace Files, which are replayed in real-time emulation environments on real systems, enabling evaluations with real software and human interaction. An advantage of our approach is its easy adaptability to existing simulation models. Our extensive evaluation involves multiple scenarios with different satellite constellations, illustrating the approach's accuracy in reproducing the behavior of satellite networks. Between full simulation, which serves as a baseline for our evaluation, and emulation runs, we observe high correlation metrics of up to 0.96, validating the approach's effectiveness. Challenges such as the lack of emulation-to-simulation feedback and synchronization issues are discussed.

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arXiv2025

TheaterQ: A Qdisc for Dynamic Network Emulation

TheaterQ is a Linux qdisc designed for dynamic network emulation, addressing the limitations of static parameters in traditional tools like NetEm. By utilizing Trace Files containing timelines with network characteristics, TheaterQ achieves high-accuracy emulation of dynamic networks without involving the userspace and allows for resolutions of characteristic updates of up to 1 microsecond. Features include synchronization across mutliple qdisc instances and handling of delays, bandwidth, packet loss, duplication, and reordering. Evaluations show TheaterQ's accuracy and its comparable performance to existing tools, offering a flexible solution for modern communication protocol development. TheaterQ is available as open-source software under the GPLv2 license.

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arXiv2025

Combining Static and Dynamic Traffic with Delay Guarantees in Time-Sensitive Networking

To support reliable and low-latency communication, Time-Sensitive Networking introduced protocols and interfaces for resource allocation in Ethernet. However, the implementation of these allocation algorithms has not yet been covered by the standards. Our work focuses on deadline-guaranteeing resource allocation for networks with static and dynamic traffic. To achieve this, we combine offline network optimization heuristics with online admission control and, thus, allow for new flow registrations while the network is running. We demonstrate our solution on Credit-Based Shaper networks by using the delay analysis framework Network Calculus. We compare our approach with an intuitive and a brute-force algorithm, where we can achieve significant improvements, both, in terms of quality and runtime. Thereby, our results show that we can guarantee maximum end-to-end delays and also increase the flexibility of the network while requiring only minimal user input.

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arXiv2025

Network Calculus Results for TSN: An Introduction

Time-Sensitive Networking (TSN) is a set of standards that enables the industry to provide real-time guarantees for time-critical communications with Ethernet hardware. TSN supports various queuing and scheduling mechanisms and allows the integration of multiple traffic types in a single network. Network Calculus (NC) can be used to calculate upper bounds for latencies and buffer sizes within these networks, for example, for safety or real-time traffic. We explain the relevance of NC for TSN-based computer communications and potential areas of application. Different NC analysis approaches have been published to examine different parts of TSN and this paper provides a survey of these publications and presents their main results, dependencies, and differences. We present a consistent presentation of the most important results and suggest an improvement to model the output of sending end-devices. To ease access to the current research status, we introduce a common notation to show how all results depend on each other and also identify common assumptions. Thus, we offer a comprehensive overview of NC for industrial networks and identify possible areas for future work.

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arXiv2023

Ensuring Reliable and Predictable Behavior of IEEE 802.1CB Frame Replication and Elimination

Ultra-reliable and low-latency communication has received significant research attention. A key part of this evolution are the Time-Sensitive Networking (TSN) standards, which extend Ethernet with real-time mechanisms. To guarantee high reliability, the standard IEEE 802.1CB-2017 Frame Replication and Elimination for Reliability enables redundant communication over disjoint paths. While this mechanism is essential for time-critical applications, the standard contains some fundamental limitations that can compromise safety. Although some of these limitations have been addressed, none of the previous works provide solutions to these problems. This paper presents solutions to four main limitations of the IEEE 802.1CB-2017 standard. These are 1) choosing match versus vector recovery algorithm, 2) defining the length of the sequence history, 3) setting a timer to reset the sequence history, and 4) dimensioning the burst size in case of link failures. We show how these challenges can be solved by using best- and worst-case path delays of the network. We have performed simulations to illustrate the impact of the limitations and prove the correctness of our solutions. Thereby, we demonstrate how our solutions can improve reliability in TSN networks and propose these methods as guidance for users of the IEEE 802.1CB standard.

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arXiv2022

Performance of QUIC Implementations Over Geostationary Satellite Links

QUIC was recently standardized as RFC 9000, but the performance of QUIC over geostationary satellite links is problematic due to the non-applicability of Performance Enhancing Proxies. As of today, there are more than a dozen of different QUIC implementations. So far performance evaluations of QUIC over satellite links were limited to specific QUIC implementations. By deploying a modified version of the IETF QUIC-Interop-Runner, this paper evaluates the performance of multiple QUIC implementations over multiple geostationary satellite links. This includes two emulated ones (with and without packet loss) and two real ones. The results show that the goodput achieved with QUIC over geostationary satellite links is very poor in general, and especially poor when there is packet loss. Some implementations fail completely and the performance of the other implementations varies greatly. The performance depends on both client and server implementation.

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