arXiv subjects

Frank Dürr

Publications and source records attributed to Frank Dürr.

16 recordsLinked to original sources

arXiv2026

An (m,k)-firm Elevation Policy for Weakly Hard Real-Time in Converged 5G-TSN Networks

Ongoing standardization efforts in 5G and Time-Sensitive Networking (TSN) aim to provide safety-critical applications with real-time communication. However, 5G-TSN network schedules often rely on idealistic delay models that can jeopardize the validity of their guarantees. This paper presents an $(m,k)$-firm Elevation Policy to uphold a base level of weakly hard real-time guarantees (WHRT). It augments the primary schedule with a dynamic priority-driven scheme to elevate the priority of $m$ out of $k$ consecutive frames if they experience unexpected delays. Our evaluations demonstrate the necessity of WHRT to increase fault-tolerance against 5G delay outliers and to uphold the quality of control within a 5G-TSN networked control system. Still, only a small resource overhead is imposed during epochs where the primary schedule is valid and can serve stronger QoS guarantees. The $(m,k)$-firm Elevation Policy thereby yields a robust but light-weight fallback mechanism to serve applications with dependable guarantees during unstable network conditions.

cs.NI↗

arXiv2026

Compensating the Packet Delay Variation for 6G Integrated with IEEE Time-Sensitive Networking

6G is deemed as a key technology to support emerging applications with stringent requirements for highly dependable and timecritical communication. In this paper, we investigate 6G networks integrated with TSN and how to compensate for wireless stochastic behavior which involves a large intrinsic packet delay variation. We evaluate a 6G solution to reduce packet delay variation that is based on de-jittering. For this, we propose to use virtual timeslots for providing the required time-awareness. We discuss the benefits of the proposed solution while evaluating the impact of the timeslot size on the number of schedulable TSN streams.

cs.NI↗

arXiv2025

Multicast-partitioning in Time-triggered Stream Planning for Time-Sensitive Networks

Multicast allows sending a message to multiple recipients without having to create and send a separate message for each recipient. This preserves network bandwidth, which is particularly important in time-sensitive networks. These networks are commonly used to provide latency-bounded communication for real-time systems in domains like automotive, avionics, industrial internet of things, automated shop floors, and smart energy grids. The preserved bandwidth can be used to admit additional real-time messages with specific quality of service requirements or to reduce the end-to-end latencies for messages of any type. However, using multicast communication can complicate traffic planning, as it requires free queues or available downstream egress ports on all branches of the multicast tree. In this work, we present a novel multicast partitioning technique to split multicast trees into smaller multicast or unicast trees. This allows for a more fine-grained trade-off between bandwidth utilization and traffic scheduling difficulty. Thus, schedulability in dynamic systems can be improved, in terms the number of admitted streams and the accumulated network throughput. We evaluated the multicast partitioning on different network topologies and with three different scheduling algorithms. With the partitioning, 5-15\% fewer streams were rejected, while achieving 5-125\% more network throughput, depending on the scheduling algorithm.

cs.NI↗

arXiv2024

Efficient Conflict Graph Creation for Time-Sensitive Networks with Dynamically Changing Communication Demands

Many applications of cyber-physical systems require real-time communication: manufacturing, automotive, etc. Recent Ethernet standards for Time Sensitive Networking (TSN) offer time-triggered scheduling in order to guarantee low latency and jitter bounds. This requires precise frame transmission planning, which becomes especially hard when dealing with many streams, large networks, and dynamically changing communications. A very promising approach uses conflict graphs, modeling conflicting transmission configurations. Since the creation of conflict graphs is the bottleneck in these approaches, we provide an improvement to the conflict graph creation. We present a randomized selection process that reduces the overall size of the graph in half and three heuristics to improve the scheduling success. In our evaluations we show substantial improvements in the graph creation speed and the scheduling success compared to existing work, updating existing schedules in fractions of a second. Additionally, offline planning of 9000 streams was performed successfully within minutes.

cs.NI↗

arXiv2023

Availability Analysis of Redundant and Replicated Cloud Services with Bayesian Networks

Due to the growing complexity of modern data centers, failures are not uncommon any more. Therefore, fault tolerance mechanisms play a vital role in fulfilling the availability requirements. Multiple availability models have been proposed to assess compute systems, among which Bayesian network models have gained popularity in industry and research due to its powerful modeling formalism. In particular, this work focuses on assessing the availability of redundant and replicated cloud computing services with Bayesian networks. So far, research on availability has only focused on modeling either infrastructure or communication failures in Bayesian networks, but have not considered both simultaneously. This work addresses practical modeling challenges of assessing the availability of large-scale redundant and replicated services with Bayesian networks, including cascading and common-cause failures from the surrounding infrastructure and communication network. In order to ease the modeling task, this paper introduces a high-level modeling formalism to build such a Bayesian network automatically. Performance evaluations demonstrate the feasibility of the presented Bayesian network approach to assess the availability of large-scale redundant and replicated services. This model is not only applicable in the domain of cloud computing it can also be applied for general cases of local and geo-distributed systems.

cs.DC↗

arXiv2023

Just a Second -- Scheduling Thousands of Time-Triggered Streams in Large-Scale Networks

Deterministic real-time communication with bounded delay is an essential requirement for many safety-critical cyber-physical systems, and has received much attention from major standardization bodies such as IEEE and IETF. In particular, Ethernet technology has been extended by time-triggered scheduling mechanisms in standards like TTEthernet and Time-Sensitive Networking. Although the scheduling mechanisms have become part of standards, the traffic planning algorithms to create time-triggered schedules are still an open and challenging research question due to the problem's high complexity. In particular, so-called plug-and-produce scenarios require the ability to extend schedules on the fly within seconds. The need for scalable scheduling and routing algorithms is further supported by large-scale distributed real-time systems like smart energy grids with tight communication requirements. In this paper, we tackle this challenge by proposing two novel algorithms called Hierarchical Heuristic Scheduling (H2S) and Cost-Efficient Lazy Forwarding Scheduling (CELF) to calculate time-triggered schedules for TTEthernet. H2S and CELF are highly efficient and scalable, calculating schedules for more than 45,000 streams on random networks with 1,000 bridges as well as a realistic energy grid network within sub-seconds to seconds.

cs.NI↗

arXiv2023

Shared Network Effects in Time- versus Event-Triggered Consensus of a Single-Integrator Multi-Agent System

Event-triggered control has the potential to provide a similar performance level as time-triggered (periodic) control while triggering events less frequently. It therefore appears intuitive that it is also a viable approach for distributed systems to save scarce shared network resources used for inter-agent communication. While this motivation is commonly used also for multi-agent systems, a theoretical analysis of the impact of network effects on the performance of event- and time-triggered control for such distributed systems is currently missing. With this paper, we contrast event- and time-triggered control performance for a single-integrator consensus problem under consideration of a shared communication medium. We therefore incorporate transmission delays and packet loss in our analysis and compare the triggering scheme performance under two simple medium access control protocols. We find that network effects can degrade the performance of event-triggered control beyond the performance level of time-triggered control for the same average triggering rate if the network is used intensively. Moreover, the performance advantage of event-triggered control shrinks with an increasing number of agents and is even lost for sufficiently large networks in the considered setup.

eess.SY↗

arXiv2022

Dynamic QoS-Aware Traffic Planning for Time-Triggered Flows in the Real-time Data Plane

Many networked applications, e.g., in the domain of cyber-physical systems, require strict service guarantees, usually in the form of jitter and latency bounds, for time-triggered traffic flows. It is a notoriously hard problem to compute a network-wide traffic plan that satisfies these requirements, and dynamic changes in the flow set add even more challenges. Existing traffic-planning methods are ill-suited for dynamic scenarios because they either suffer from high computational cost, can result in low network utilization, or provide no explicit guarantees when transitioning to a new traffic plan that incorporates new flows. Therefore, we present a novel approach for dynamic traffic planning of time-triggered flows. Our conflict-graph based modeling of the traffic planning problem allows to reconfigure active flows to increase the network utilization, while also providing per-flow QoS guarantees during the transition to the new traffic plan. Additionally, we introduce a novel heuristic for computing the new traffic plans. Evaluations of our prototypical implementation show that we can efficiently compute new traffic plans in scenarios with hundreds of active flows for a wide range of scenarios.

cs.NI↗

arXiv2022

Rollout event-triggered control: reconciling event- and time-triggered control

Event-triggered control (ETC) and time-triggered control (TTC), the classical concepts to determine the transmission instants for networked control systems, each come with drawbacks: It is difficult to tune ETC such that a certain bandwidth is respected, whereas TTC cannot adapt the sampling interval to the current state of the control system. In this article, we provide an overview over rollout ETC, a method aimed at reconciling the advantages of ETC and TTC. We unite two variants of rollout ETC under a common framework and present conditions for convergence and compliance with a predefined bandwidth limit. Furthermore, we demonstrate that rollout ETC satisfies a performance bound and that it allows for a very flexible transmission scheduling similar to classical ETC. The mentioned beneficial properties are illustrated through extensive numerical simulations.

eess.SY↗

arXiv2019

Using Surrogate Models and Data Assimilation for Efficient Mobile Simulations

Numerical simulations on mobile devices are an important tool for engineers and decision makers in the field. However, providing simulation results on mobile devices is challenging due to the complexity of the simulation, requiring remote server resources and distributed mobile computation. The additional large size of multi-dimensional simulation results leads to the insufficient performance of existing approaches, especially when the bandwidth of wireless communication is scarce. In this article, we present an optimized novel approach utilizing surrogate models and data assimilation techniques to reduce the communication overhead. Evaluations show that our approach is up to $6.5$ times faster than streaming results from the server while still meeting required quality constraints.

cs.DC↗

arXiv2018

P4CEP: Towards In-Network Complex Event Processing

In-network computing using programmable networking hardware is a strong trend in networking that promises to reduce latency and consumption of server resources through offloading to network elements (programmable switches and smart NICs). In particular, the data plane programming language P4 together with powerful P4 networking hardware has spawned projects offloading services into the network, e.g., consensus services or caching services. In this paper, we present a novel case for in-network computing, namely, Complex Event Processing (CEP). CEP processes streams of basic events, e.g., stemming from networked sensors, into meaningful complex events. Traditionally, CEP processing has been performed on servers or overlay networks. However, we argue in this paper that CEP is a good candidate for in-network computing along the communication path avoiding detouring streams to distant servers to minimize communication latency while also exploiting processing capabilities of novel networking hardware. We show that it is feasible to express CEP operations in P4 and also present a tool to compile CEP operations, formulated in our P4CEP rule specification language, to P4 code. Moreover, we identify challenges and problems that we have encountered to show future research directions for implementing full-fledged in-network CEP systems.

cs.NI↗

arXiv2018

Enabling Interactive Mobile Simulations Through Distributed Reduced Models

Currently, various hardware and software companies are developing augmented reality devices, most prominently Microsoft with its Hololens. Besides gaming, such devices can be used for serious pervasive applications, like interactive mobile simulations to support engineers in the field. Interactive simulations have high demands on resources, which the mobile device alone is unable to satisfy. Therefore, we propose a framework to support mobile simulations by distributing the computation between the mobile device and a remote server based on the reduced basis method. Evaluations show that we can speed-up the numerical computation by over 131 times while using 73 times less energy.

cs.DC↗

arXiv2017

State-dependent Priority Scheduling for Networked Control Systems

Networked control systems (NCS) have attracted considerable attention in recent years. While the stabilizability and optimal control of NCS for a given communication system has already been studied extensively, the design of the communication system for NCS has recently seen an increase in more thorough investigation. In this paper, we address an optimal scheduling problem for a set of NCS sharing a dedicated communication channel, providing performance bounds and asymptotic stability. We derive a suboptimal scheduling policy with dynamic state-based priorities calculated at the sensors, which are then used for stateless priority queuing in the network, making it both scalable and efficient to implement on routers or multi-layer switches. These properties are beneficial towards leveraging existing IP networks for control, which will be a crucial factor for the proliferation of wide-area NCS applications. By allowing for an arbitrary number of concurrent transmissions, we are able to investigate the relationship between available bandwidth, transmission rate, and delay. To demonstrate the feasibility of our approach, we provide a proof-of-concept implementation of the priority scheduler using real networking hardware.

eess.SY↗

arXiv2017

Optimized Secure Position Sharing with Non-trusted Servers

Today, location-based applications and services such as friend finders and geo-social networks are very popular. However, storing private position information on third-party location servers leads to privacy problems. In our previous work, we proposed a position sharing approach for secure management of positions on non-trusted servers, which distributes position shares of limited precision among servers of several providers. In this paper, we propose two novel contributions to improve the original approach. First, we optimize the placement of shares among servers by taking their trustworthiness into account. Second, we optimize the location update protocols to minimize the number of messages between mobile device and location servers.

cs.DC↗

arXiv2016

ZeroSDN: A Message Bus for Flexible and Light-weight Network Control Distribution in SDN

Recent years have seen an evolution of SDN control plane architectures, starting from simple monolithic controllers, over modular monolithic controllers, to distributed controllers. We observe, however, that today's distributed controllers still exhibit inflexibility with respect to the distribution of control logic. Therefore, we propose a novel architecture of a distributed SDN controller in this paper, providing maximum flexibility with respect to distribution. Our architecture splits control logic into light-weight control modules, called controllets, based on a micro-kernel approach, reducing common controllet functionality to a bare minimum and factoring out all higher-level functionality. Light-weight controllets also allow for pushing control logic onto switches to minimize latency and communication overhead. Controllets are interconnected through a message bus supporting the publish/subscribe communication paradigm with specific extensions for content-based OpenFlow message filtering. Publish/subscribe allows for complete decoupling of controllets to further facilitate control plane distribution.

cs.NI↗

arXiv2016

A Flat and Scalable Data Center Network Topology Based on De Bruijn Graphs

Due to the requirement of hosting tens of thousands of hosts in today's data centers, data center networks strive for scalability and high throughput on the one hand. On the other hand, the cost for networking hardware should be minimized. Consequently, the number and complexity (e.g. TCAM size) of switches has to be minimized. These requirements led to network topologies like Clos and Leaf-Spine networks only requiring a shallow hierarchy of switches---two levels for Leaf-Spine networks. The drawback of these topologies is that switches at higher levels like Spine switches need a high port density and, thus, are expensive and limit the scalability of the network. In this paper, we propose a data center network topology based on De Bruijn graphs completely avoiding a switch hierarchy and implementing a flat network topology of top-of-rack switches instead. This topology guarantees logarithmic (short) path length. We show that the required routing logic can be implemented by standard prefix matching operations in hardware (TCAM) allowing for using commodity switches without any modification. Moreover, forwarding requires only a very small number of forwarding table entries, saving costly and energy-intensive TCAM.

cs.NI↗