Kiejin Park

Frame Packing for Minimizing the Bandwidth Consumption of the FlexRay Static Segment

The FlexRay protocol has emerged as the de facto standard for automotive communication systems, and it offers the advantages of both the event-triggered and time-triggered paradigms. To minimize bandwidth consumption (BC) in the static segment of the FlexRay communication cycle, we propose a frame-packing algorithm called BC minimizing with various periodic signals (BCMVPS), which is formulated as generalized integer linear programming that allows the packing of signals with different periods into a message frame. We also present the lower and upper bounds of the size of a static slot, as well as present a heuristic called BC best fit decreasing for linear frame selection for reducing the computing time of the BCMVPS algorithm. We compare the performance of the proposed algorithms with existing algorithms using the Society of Automotive Engineers benchmark data and GNU linear programming kit. The experimental results show that the BC of the proposed algorithms is less than that of the existing frame-packing algorithms.

Probabilistic delay model of dynamic message frame in flexray protocol

Since the safety and multimedia-related functions of automobile are getting increased and complex, In-vehicle network has become important. Even though FlexRay has emerged as the de-facto standard for the network, the message delay analysis problem has not been solved yet. In this paper, we propose the probabilistic delay model of message transmission in the FlexRay dynamic segment considering the variable length of messages that share identical Frame Identifier (ID). Based on the model, we analyze frame delay probability and empty minislot distribution as performance metric, which can be used during the design phase of a FlexRay network, and also derive transmission probabilities for different length of frames from the empty minislot probability. Finally, through simulation experiments, we verify the models, and show that previous model only considering fixed frame length causes pessimistic delay compared to the proposed model.

A static message scheduling algorithm for reducing FlexRay network utilization

Currently, in order to meet customer requirements about safety and convenience, many electronics and software are used in automobiles. Because high amount of data from each electronics and software needs to be communicated fast and correctly, performance evaluation of in-vehicle network is necessary. FlexRay protocol that is suggested to guarantee exact operation of in-vehicle subsystem such as x-by-wire application has emerged as de-facto standard. However, there are only a few researches about response time analysis and timing performance verification. In this paper, to reduce FlexRay network utilization, a scheduling algorithm that long static message is assigned to dynamic segment is presented. We define system model for the algorithm and carry out performance evaluation using SAE benchmark data. Though the evaluation, we show that network utilization in all transmission speed is reduced, and also in lower transmission speed, it is reduced much more.

Analysis of frame delay probability in the FlexRay dynamic segment

FlexRay is a hybrid protocol that has both advantages of Event-triggered and Time-triggered paradigm, and has emerged as the de-facto standard for in-vehicle automotive communication. However, in order for FlexRay to be exploited successfully for in-vehicle network, performance and timing analysis are necessary. Even though it is widely believed that performance analysis is important, the high flexibility of FlexRay dynamic segment makes it difficult. In this paper, we propose the analysis model of FlexRay dynamic segment considering variable message length that share identical frame ID. Based on the model, we also analyze frame delay probability as performance assessment. Finally, how the change of the length of dynamic segment affects frame delay probability is shown.

A differentiated service mechanism considering SLA for heterogeneous cluster Web systems

As the Web is becoming more widely used as the preferred method for critical information exchange, it is necessary to provide differentiated service mechanisms not only at the network level but also at the Web server level. In this paper, we study performance isolation and admission control concepts of heterogeneous cluster-based Web systems and study the availability of primary-backup Web switches. Due to the types of requests of clients, the SLA (service level agreement) between the clients and the service provider is considered

Survival of the Internet applications: a cluster recovery model

Internet applications become increasingly widely used for millions of people in the world and on the other hand the accidents or disruptions of service are also dramatically increasing. Accidents or disruptions occur either because of disasters or because of malicious attacks. The disasters could not be completely prevented. Prevention is a necessary but not a sufficient component of disaster. In this case, we have to prepare thoroughly for reducing the recovery time and get the users back to work faster. In this paper, we present a cluster recovery model to increase the survivability level of Internet applications. We construct a state transition model to describe the behaviors of cluster systems. By mapping through recovery actions to this transition model with stochastic process, we capture system behaviors as well as we get mathematical steady-state solutions of that chain. We first carry out for steady-state behaviors leading to measures like steady-state availability. By transforming this model with the system states we compute a system measure, the mean time to repair (MTTR) and also compute probabilities of cluster systems failures due in face of disruptions. Our model with the recovery actions have several benefits, which include reducing the time to get the users back to work and making recovery performance insensitive to the selection of a failure treatment parameter.

Determining the Size of a Static Segment and Analyzing the Utilization of In-vehicle FlexRay Network

In order to meet customer needs (e.g. safety, convenience) in current automotive industry, lots of electronics and software are deployed into vehicles, and this has led to many researches about In-vehicle network. FlexRay is a kind of In-vehicle network protocols and it will likely become de facto standard. However, to be used in vehicles successfully, the response time analysis of a FlexRay message is needed. In this paper, based on frame format, physical transmission rule and payload length, the actual length of FlexRay message frame is calculated, and we also determine the length of static slot in a communication cycle. Finally, the equation of network utilization in static segment is derived.

A self-healing mechanism for an intrusion tolerance system

The dependability analysis of an ITS (Intrusion Tolerance System – a system that performs continuously minimal essential services even when the computer system is partially compromised because of intrusions) is essential for the design of the ITS. In this paper, we applied self-healing mechanism, the core technology of autonomic computing to analyze the dependability of the ITS. In other words, we described the state transition of the ITS composed of a primary server and a backup server utilizing two factors of self-healing mechanism (fault model and system response) and analyzed it using M/G/1 queuing technique. We also evaluated the availability of the ITS through simulation experiments.

A survivability model for cluster system

Even in an intrusion tolerant system, the resources will be fatigued if the intrusion is long lasting because of compromising iteratively or incrementally. In due course, the system will not provide even the minimum critical functionality. Thus we propose a model to increase the cluster system survivability level by maintaining the essential functionality. In this paper, we present the cluster recovery model with a software rejuvenation methodology, which is applicable in security field and also less expensive. Firstly, we perform the steady-state analysis of a cluster system and then study the 4th Generation Security Mechanism: Restore system with cold standby cluster. The basic idea is investigate the consequences for the exact responses in face of attacks and rejuvenate the running software or/and service, or/and reconfigure it. It shows that the system operates through intrusions and provides continued the critical functions, and gracefully degrades non-critical system functionality in the face of intrusions.

A survivability model for cluster system under dos attacks

Denial of service attacks (DoS) don’t necessarily damage data directly, or permanently but intentionally compromise the functionality. Even in an intrusion tolerant system, the resources will be fatigued if the intrusion is long lasting because of compromising iteratively or incrementally. In due course, the system will not provide even the minimum critical functionality. Thus we propose a model to increase the cluster system survivability level by maintaining the essential functionality. In this paper, we present the cluster recovery model with a software rejuvenation methodology, which is applicable in security field and also less expensive. The basic idea is – investigate the consequences for the exact responses in face of attacks and rejuvenate the running software/service, or/and reconfigure it. It shows that the system operates through intrusions and provides continued the critical functions, and gracefully degrades non-critical system functionality in the face of intrusions.