Ece Guran Schmidt

Message Scheduling for the FlexRay Protocol: The Dynamic Segment

The FlexRay communication protocol is expected to be the de facto standard for high-speed, in-vehicle communication. In this paper, we formally investigate the scheduling problem for the dynamic segment (DS) of FlexRay. We take the bounds on the generation times and the timing requirements of the signals into consideration to propose a reservation-based scheduling approach that preserves the flexible medium access of the DS. To obtain efficient schedules, we formulate a nonlinear integer programming problem (NIP) that minimizes the required duration of the DS. This NIP is then decomposed into two linear binary integer programming problems to facilitate the computation of feasible message schedules. An experimental study illustrates our message scheduling approach for the DS of FlexRay.

Machine learning algorithms for accurate flow-based network traffic classification: Evaluation and comparison

The task of network management and monitoring relies on an accurate characterization of network traffic generated by different applications and network protocols. We employ three supervised machine learning (ML) algorithms, Bayesian Networks, Decision Trees and Multilayer Perceptrons for the flow-based classification of six different types of Internet traffic including peer-to-peer (P2P) and content delivery (Akamai) traffic. The dependency of the traffic classification performance on the amount and composition of training data is investigated followed by experiments that show that ML algorithms such as Bayesian Networks and Decision Trees are suitable for Internet traffic flow classification at a high speed, and prove to be robust with respect to applications that dynamically change their source ports. Finally, the importance of correctly classified training instances is highlighted by an experiment that is conducted with wrongly labeled training data.

Systematic Message Schedule Construction for Time-Triggered CAN

The most widely used standard for in-vehicle communication networks that interconnect electronic control units is the controller area network (CAN). However, the event-triggered architecture of CAN introduces several issues, such as predictability, signal jitter, and reliability. Different time-triggered networks are being developed to address these issues. In this paper, we focus on time-triggered CAN (TTCAN), which achieves time-triggered behavior by implementing time-division multiple access on the existing CAN network standard. The main task is thus to construct a message schedule for a given set of messages while fulfilling certain performance criteria. To this end, we provide a formal framework for the construction of feasible message schedules in TTCAN networks by considering several performance metrics, such as bandwidth utilization and jitter, as well as the hardware constraints of the TTCAN controller specification.

Optimal Message Scheduling for the Static Segment of FlexRay

In this paper, we study the scheduling of periodic messages in the static segment of the FlexRay protocol. Our approach is based on two performance metrics. Similar to previous work, we seek to allocate a minimum number of frame IDs (FIDs) in the static segment. In addition, different from existing work, we want to minimize the message jitter, i.e., the deviation of the message transmission from the required periodicity. To this end, we first derive analytical expressions that quantify the FID allocation and the jitter, and then formulate a linear integer programming problem whose solution is the desired message schedule. An example illustrates our schedule optimization.

Schedulability Analysis and Message Schedule Computation for the Dynamic Segment of FlexRay

In this paper, we perform the schedulability analysis and schedule computation for sporadic real-time messages in the dynamic segment of the FlexRay protocol. We first formulate a linear integer programming problem that allows to determine if a given message schedule is feasible, i.e., the worst-case delay of each message is smaller than its deadline. Then, we develop a heuristic algorithm that enables the efficient computation of feasible schedules. Our results are illustrated by an experimental setup with three FlexRay nodes.

Performance evaluation of FlexRay/CAN networks interconnected by a gateway

The coexistence of both CAN and FlexRay networks in contemporary and future automobiles necessitates the use of FlexRay/CAN gateways that support the timely data exchange among the different networks. In this paper, we report on the implementation of such FlexRay/CAN gateway. Moreover, for the first time, we investigate appropriate network and gateway configurations that are beneficial for the overall network performance in the sense of small delays of gateway messages.

Distributed Real-Time Protocols for Industrial Control Systems: Framework and Examples

The automation of todays large-scale industrial systems relies on the operation of distributed controller devices that perform local computations and exchange information via communication networks. The subject of this paper is the development of a family of shared-medium industrial communication protocols that support the transmission of real-time (RT) and nonreal-time (nRT) data among distributed controller devices. Different from existing protocols, we suggest to incorporate information that is available from the control application in the protocol definition. As a result, our protocols dynamically change the bandwidth allocation on the shared medium according to the instantaneous communication requirements while ensuring hard RT guarantees. Following the recent developments in industrial automation, our protocols can be realized as software layers on top of low-cost conventional Ethernet.

A shared-medium communication architecture for distributed discrete event systems

Recently, several efficient supervisor synthesis approaches for distributed discrete event systems (DES) have been established. In this paper, the implementation of such supervisors on interacting distributed programmable logic controllers (PLCs) on a network is considered for the hierarchical and decentralized control approach elaborated in our previous work. A communication model that captures the controller behavior relevant for communication is developed, and a network architecture together with a scheduling policy that ensures correct operation of the networked controllers is proposed. In addition to the formal statements, simulation results for an example system are presented.

An accurate evaluation of machine learning algorithms for flow-based P2P traffic detection

Today, peer-to-peer (P2P) traffic consumes the largest fraction of network bandwidth. The files shared by P2P communications are mostly copyright protected, and there are issues related to Quality of Service (QoS) support and billing of P2P traffic. Hence, scalable and accurate detection of peer-to-peer (P2P) traffic is a significant problem for network service providers. Flow-based detection methods employ characteristics of data flows such as the number of packets per flow to classify P2P and non-P2P traffic. Thus, they provide solutions to problems of port-based and signature-based detection such as P2P applications with dynamic ports, updating the signature database and encrypted packets. In this paper, a comparative evaluation of several flow-based P2P traffic detection methods that employ machine learning (ML) techniques is presented. Different from previous work, the effect of network parameters is taken into consideration in our evaluation. Furthermore a new verification approach based on custom-made data is presented which can circumvent the accuracy problems of the previous verification methods that use port-based or signature-based techniques for the accuracy evaluation.

A longest-path problem for evaluating the worst-case packet delay of switched ethernet

In the recent years, the use of real-time Ethernet protocols becomes more and more relevant for time-critical networked industrial applications. In this context, this paper presents a method to compute the worst-case packet delays on switched Ethernet. Based on an evaluation of the packet delays at each switch port and the network topology, we construct a weighted directed graph that allows to find the worst-case end-to-end packet delay by solving a conventional longest-path problem.