Pieter J. L. Cuijpers

Analysis of ethernet-switch traffic shapers for in-vehicle networking applications

Switched Ethernet has been proposed as network technology for automotive and industrial applications. IEEE AVB is a collection of standards that specifies (among other elements) a set of network traffic shaping mechanisms (i.e., rules to regulate the traffic flow) to have guaranteed Quality of Service for Audio/Video traffic. However, in-vehicle control applications like advanced driver-assistance systems require much lower latencies than provided by this standard. Within the context of IEEE TSN (Time Sensitive Networking), three new traffic shaping mechanisms are considered, named Burst Limiting, Time Aware and Peristaltic shaper respectively. In this paper we explain and compare these shapers, we examine their worst case end-to-end latencies analytically and we investigate their behavior through a simulation of a particular setup. We show that the shapers hardly satisfy the requirements for 100Mbps Ethernet, but can come close under further restrictions. We also show the impact the shapers have on AVB traffic.

Constitutive Hybrid Processes: a Process-Algebraic Semantics for Hybrid Bond Graphs

Models of physical systems have to be based on physical principles such as conservation of energy and continuity of power. These principles are inherently enforced by the bond graph modeling formalism. Often, however, physical components may be best modeled as piecewise continuous with discrete mode changes, which leads to a violation of continuity principles. To support such hybrid models, bond graphs can be extended by facilitating a dynamic model structure, resulting in hybrid bond graphs. Behavior generation then requires computing continuous-time evolution, detecting the occurrence of events, executing the discrete state changes and re-initializing the continuous-time state. This paper presents a comprehensive representation of these different aspects of behavior using hybrid process algebra. The behavior of a hybrid bond graph can then be studied using a uniform representation while a direct correspondence with the elements of the bond graph is maintained. Additionally, non-determinism can be included in hybrid bond graph semantics which may alleviate the modeling task without being detrimental to the required analyses.

Model-based Engineering of Embedded Systems Using the Hybrid Process Algebra Chi

Hybrid Chi is a process algebra for the modeling and analysis of hybrid systems. It enables modular specification of hybrid systems by means of a large set of atomic statements and operators for combining these. For the efficient implementation of simulators and the verification of properties of hybrid systems it is convenient to have a model that uses a more restricted part of the syntax of hybrid Chi. To that purpose the linearization of a reasonably expressive, relevant subset of the Chi language is discussed. A linearization algorithm that transforms any specification from this subset into a so-called normal form is presented. The algorithm is applied to a bottle-filling line example to demonstrate tool-based verification of Chi models.

Reconciling urgency and variable abstraction in a hybrid compositional setting

The extension of timed formalisms to a hybrid setting with urgency, has been carried out in a rather straightforward manner, seemingly without difficulty. However, in this paper, we show that the combination of urgency with abstraction from continuous variables leads to undesired behavior. Abstraction from continuous variables ultimately leads to a timed system again, but with a much richer set of possible branching behaviors than a timed system that comprises only clocks. As it turns out, the formal definition of urgency, as defined for timed systems with clocks, does not fit our intuition of urgency anymore when applied to a timed system that is an abstraction of a hybrid system. Therefore, we propose to extend the formal semantics of timed and hybrid systems with guard trajectories. In this way, the continuous branching behavior introduced by hybrid systems remains visible even after abstraction from continuous variables. The practical applicability of the introduction of guard trajectories is illustrated by our revision of the structured operational semantics of the CIF language. The interplay between urgency and abstraction now adheres to our intuition, while compositionality with respect to urgency, variable abstraction, and parallel composition, is retained. In the future, symbolic elimination of urgency can be used to ensure that guard trajectories do not need to be actually calculated.

On bicontinuous bisimulation and the preservation of stability

Since Pappas et all. transferred the notion of bisimulation from computer science to control theory, it has attracted quite some attention in the hybrid systems community[1]. Notably, bisimulation relations are used to reduce the complexity of dynamic systems, while preserving reachability notions [1]. In [2], we argued that bisimulation needs to be strengthened with continuity conditions, in order to preserve other control science notions as well. This idea was independently explored in [3,4,5] where modal and temporal logics are extended with topological operators, to be able to reason about robustness of a control strategy for embedded systems.

Hierarchical states in the Compositional Interchange Format

CIF is a language designed for two purposes, namely as a specification language for hybrid systems and as an interchange format for allowing model transformations between other languages for hybrid systems. To facilitate the top-down development of a hybrid system and also to be able to express models more succinctly in the CIF formalism, we need a mechanism for stepwise refinement. In this paper, we add the notion of hierarchy to a subset of the CIF language, which we call hCIF? . The semantic domain of the CIF formalism is a hybrid transition system, constructed using structural operational semantics. The goal of this paper is to present a semantics for hierarchy in such a way that only the SOS rules for atomic entities in hCIF? are redesigned in comparison to CIF . Furthermore, to be able to reuse existing tools like simulators of the CIF language, a procedure to eliminate hierarchy from an automaton is given.

Proxy support for service discovery using mDNS/DNS-SD in low power networks

We present a solution for service discovery of resource constrained devices based on mDNS/DNS-SD. We extend the mDNS/DNS-SD service discovery protocol with support for proxy servers. Proxy servers temporarily store information about services offered on resource constrained devices and respond on their behalf while they are not available. We analyze two protocols for the delegation mechanism between a service provider and a proxy server: an active proxy protocol, as used in the mDNS/DNS-SD implementation by Apple, and a new, passive proxy protocol. We implement and simulate both approaches. Based on the delay and energy usage, we show that the second approach converges faster, thus saving more energy by allowing the resource constrained device to be turned off earlier.

The categorical limit of a sequence of dynamical systems

Modeling a sequence of design steps, or a sequence of parameter settings, yields a sequence of dynamical systems. In many cases, such a sequence is intended to approximate a certain limit case. However, formally defining that limit turns out to be subject to ambiguity. Depending on the interpretation of the sequence, i.e. depending on how the behaviors of the systems in the sequence are related, it may vary what the limit should be. Topologies, and in particular metrics, define limits uniquely, if they exist. Thus they select one interpretation implicitly and leave no room for other interpretations. In this paper, we define limits using category theory, and use the mentioned relations between system behaviors explicitly. This resolves the problem of ambiguity in a more controlled way. We introduce a category of prefix orders on executions and partial history preserving maps between them to describe both discrete and continuous branching time dynamics. We prove that in this category all projective limits exist, and illustrate how ambiguity in the definition of limits is resolved using an example. Moreover, we show how various problems with known topological approaches are now resolved, and how the construction of projective limits enables us to approximate continuous time dynamics as a sequence of discrete time systems.

Modeling an impact control strategy using HyPA

Abstract We analyze a control strategy for the pick-and-place module of a component mounting device. We use a combination of techniques from bondgraph-theory, systems theory process algebra and differential algebra to achieve this, and we show how the hybrid process algebra HyPA aides us in combining these techniques and in using them on a common hybrid model of the device.

Independent WCRT analysis for individual priority classes in Ethernet AVB

In the high-tech and automotive industry, bandwidth considerations and widely accepted standardization are two important reasons why Ethernet is currently being considered as an alternative solution for real-time communication (compared to traditional fieldbusses). Although Ethernet was originally not intended for this purpose, the development of the Ethernet AVB standard enables its use for transporting high-volume data (e.g. from cameras and entertainment applications) with low-latency guarantees. In complex industrial systems, the network is shared by many applications, developed by different parties. To face this complexity, the development of these applications must be kept as independent as possible. In particular, from a network point of view, progress of all communication streams must be guaranteed, and the performance for individual streams should be predictable using only information regarding the stream under study and the general parameters of the communication standard used by the network. Initial methods to guarantee latency for Ethernet AVB networks rely on the traditional busy-period analysis. Typically, these methods are based on knowledge of the inter-arrival patterns of both the stream under study and the interfering streams that also traverse the network. The desired independence is therefore not achieved. In this paper, we present an independent real-time analysis based on so-called eligible intervals, which does not rely on any assumptions on interfering priority classes other than those enforced in the Ethernet AVB standard. We prove this analysis is tight in case there is only a single higher-priority stream, and no additional information on interference is known. In case there are multiple higher-priority streams, we give conditions under which the analysis is still tight. Furthermore, we compare the results of our approach to the two most recent busy-period analyses, point out sources of pessimism in these earlier works, and argue that assuming more information on the sources of interference (e.g. a minimal inter-arrival time between interfering frames) has only limited advantages.