arXiv subjects

Reinhard German

Publications and source records attributed to Reinhard German.

12 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.

cs.NI↗

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.

cs.NI↗

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.

cs.NI↗

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.

cs.NI↗

arXiv2025

Adaptive Self-Improvement for Smarter Energy Systems using Agentic Policy Search

Controlling energy systems usually involves manually designed policies for decision-making, which can be complex and time-consuming to develop. This process requires interdisciplinary collaboration among multiple domain experts, resulting in slow and inflexible adaptation to rapidly changing environments. Large Language Models (LLMs) offer a promising paradigm shift by integrating extensive contextual knowledge with the capability to generate structured, executable code. We present Agentic Policy Search (APS) -- a novel hierarchical optimization framework in which LLMs act as autonomous agents that propose complete control logics, translate them into executable code, and iteratively improve them through direct system feedback. We apply APS to a residential energy system with PV, battery, demand, and dynamic electricity prices. Within just seven simulated days, the method yields a net profit of up to 6.20 EUR compared to the no-battery reference scenario (-10.70 EUR), nearly matching the global optimum of a perfectly informed linear program. By combining LLM-driven policy search with the generation of human-interpretable control logic, APS effectively bridges adaptability and traceability in energy management -- while also offering a transferable framework for agentic optimization in other domains.

eess.SY↗

arXiv2024

On the Effect of TSN Forwarding Mechanisms on Best-Effort Traffic

Time-Sensitive Networking (TSN) enables the transmission of multiple traffic types within a single network. While the performance of high-priority traffic has been extensively studied in recent years, the performance of low-priority traffic varies significantly between different TSN forwarding algorithms. This paper provides an overview of existing TSN forwarding algorithms and discusses their impact on best-effort traffic. The effects are quantified through simulations of synthetic and realistic networks. The considered forwarding mechanisms are Strict Priority (SP), Asynchronous Traffic Shaper (ATS), Credit-Based Shaper (CBS), Enhanced Transmission Selection (ETS), and Time-Aware Shaper (TAS). The findings indicate that ATS, CBS, and ETS can significantly reduce queuing delays and queue lengths for best-effort traffic when compared to SP and TAS. This effect is enhanced when the reserved bandwidth for high priority queues - using CBS, ATS, or ETS - is reduced to the lowest possible value, within the reserved rate and latency requirements. Specifically, the simulations demonstrate that the choice of forwarding algorithm can improve the performance of low-priority traffic by up to twenty times compared to the least effective algorithm. This study not only provides a comprehensive understanding of the various TSN forwarding algorithms but can also serve as guidance at networks' design time to improve the performance for all types of traffic.

cs.NI↗

arXiv2023

On the Validity of Credit-Based Shaper Delay Guarantees in Decentralized Reservation Protocols

Resource reservation is a fundamental mechanism for ensuring quality of service in time-sensitive networks, which can be decentralized by using reservation protocols. In the Ethernet technology Time-Sensitive Networking, this has been proposed in conjunction with the Credit-Based Shaper. For the reservation, the standards assume a maximum worst-case latency bound at each hop. However, we will show through formal analysis and simulation that these worst-case latency bounds are not safe. To face this, we propose an extension to the current standards to allow the reservation of time-sensitive traffic with reliable latency guarantees. The effectiveness of our approach is demonstrated through simulations of both synthetic and industrial networks. Finally, by providing additional information about neighboring devices, we could further increase the maximum reservable traffic by up to 20% in our test cases.

cs.NI↗

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.

cs.NI↗

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.

cs.NI↗

arXiv2016

A Taxonomy for Tools, Processes and Languages in Automotive Software Engineering

Within the growing domain of software engineering in the automotive sector, the number of used tools, processes, methods and languages has increased distinctly in the past years. To be able to choose proper methods for particular development use cases, factors like the intended use, key-features and possible limitations have to be evaluated. This requires a taxonomy that aids the decision making. An analysis of the main existing taxonomies revealed two major deficiencies: the lack of the automotive focus and the limitation to particular engineering method types. To face this, a graphical taxonomy is proposed based on two well-established engineering approaches and enriched with additional classification information. It provides a self-evident and -explanatory overview and comparison technique for engineering methods in the automotive domain. The taxonomy is applied to common automotive engineering methods. The resulting diagram classifies each method and enables the reader to select appropriate solutions for given project requirements.

cs.SE↗

arXiv2015

A Holistic Approach for Modeling and Synthesis of Image Processing Applications for Heterogeneous Computing Architectures

Image processing applications are common in every field of our daily life. However, most of them are very complex and contain several tasks with different complexities which result in varying requirements for computing architectures. Nevertheless, a general processing scheme in every image processing application has a similar structure, called image processing pipeline: (1) capturing an image, (2) pre-processing using local operators, (3) processing with global operators and (4) post-processing using complex operations. Therefore, application-specialized hardware solutions based on heterogeneous architectures are used for image processing. Unfortunately the development of applications for heterogeneous hardware architectures is challenging due to the distribution of computational tasks among processors and programmable logic units. Nowadays, image processing systems are started from scratch which is time-consuming, error-prone and inflexible. A new methodology for modeling and implementing is needed in order to reduce the development time of heterogenous image processing systems. This paper introduces a new holistic top down approach for image processing systems. Two challenges have to be investigated. First, designers ought to be able to model their complete image processing pipeline on an abstract layer using UML. Second, we want to close the gap between the abstract system and the system architecture.

cs.CV↗

arXiv2014

Evaluating the Electrification of Vehicle Fleets Using the Veins Framework

The case study discussed in this paper involves a company maintaining a vehicle fleet of one hundred vehicles. In this article we will discuss how we extend and deploy the Veins framework, which couples OMNeT++ and SUMO, to help in the process of electrifying this vehicle fleet, i.e., replacing combustion engine cars with electric vehicles to save money and lower CO$_2$ emissions.

cs.OH↗