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Real-time databases (RTDBs) are increasingly being used as an integral part of many computer systems. During normal operation, transactions in RTDBs must be executed in such a way that transaction timing and data time validity constraints can be met. RTDBs must also prepare for possible failures and provide fault tolerance capability. Principles for fault tolerance in RTDBs must take timing requirements into consideration and are distinct from those for conventional databases. We discuss these issues in this paper and describe a logging and recovery technique that is time- cognizant and is suitable for an important class of RTDB applications. The technique minimizes normal runtime overhead caused by logging and has a predictable impact on transaction timing constraints. Upon a failure, the system can recover critical data to a consistent and temporally valid state within predictable time bounds. The system can then resume its major functioning while non- critical data are being recovered in the background. As a result, the recovery time is bounded and shortened. In short, we are providing a bounded and predictable logging and recovery technique for critical transactions accessing critical variant and invariant data, while the database may consist of all kinds of data. Our performance evaluation via simulation shows that logging overhead has a small effect on missing transaction deadlines while adding recovery capability. In addition, our algorithm scales well with respect to large I/O page sizes, indicating that it can be adapted to future generations of storage devices with larger I/O page sizes. We compare our algorithm with another approach that does more frequent checkpointing for data with certain special characteristics. Simulation results disclose conditions under which each approach performs better than the other. Experiments also show that recovery using our approach is 3-6 times faster than traditional recovery. [ABSTRACT FROM AUTHOR]

Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we proposed a new multiversion concurrency control protocol that ensures that both security and real-time requirements are met. The proposed protocol is primarily based on locking. However, in order to satisfy timing constraints and security requirements, a new method, called the freezing method, is proposed. In order to show that our protocol provides a higher degree of concurrency than existing multiversion protocols, we define a new serializability for multiversion concurrency control, called FR-serializability, which is more general than traditional serializability. We present several examples to illustrate the behavior of our protocol, along with performance comparisons with other protocols. The simulation results show significant performance improvement of the new protocol. [ABSTRACT FROM AUTHOR]

In the near future, tens of millions of users will have access to distributed information systems through the wireless interface in their mobile computers. The physical characteristics of the wireless medium pose new challenging issues on data consistency of transaction processing in wireless environments. In particular, the monetarily expensive wireless bandwidth and the asymmetric communication between the mobile clients and the server bar the applicability of conventional transaction processing techniques. In this paper, we first propose a concurrency control protocol in wireless environments that is adapted from the optimistic concurrency control with forward validation protocol. The protocol offers autonomy between the mobile clients and the server such that the mobile clients can read consistent data off the air without contacting the server. To reduce the number of unnecessary transaction restarts such that the timeliness of mobile transactions can be enhanced, we propose another protocol based on timestamp ordering that can show significant performance improvement. The timestamp ordering technique enjoys a number of benefits from the separate processing and flexible adjustment of serialization order by exploiting the semantics of read-only transactions. Most of the existing applications, such as information dispersal systems for stock prices, weather information and traffic condition updates, are comprised of read-only transactions. The simulation results confirm that the proposed protocol could be an efficient and effective approach to transaction processing in real-time broadcast environments for meeting transaction deadlines. [ABSTRACT FROM PUBLISHER]

Presents a study which explored the potential benefits of incorporating priority cognizance in conflict resolution for firm real-time database systems (RTDBS). Dynamic adjustment of serialization order on which optimistic concurrency control variant called OCC-APR is based; Priority cognizant concurrent control algorithm; Simulation model for RTBS evaluation; Performance analysis and discussion.

In a distributed real-time database system (DRTDBS), a commit protocol is required to ensure transaction failure atomicity. If data conflicts occur between executing and committing transactions, the performance of the system may be greatly affected. In this paper, we propose a new protocol, called deadline-driven conflict resolution (DDCR), which integrates concurrency control and transaction commitment management for resolving executing and committing data conflicts amongst firm real-time transactions. With the DDCR, a higher degree of concurrency can be achieved, as many data conflicts of such kind can be alleviated, and executing transactions can access data items which are being held by committing transactions in conflicting modes. Also, the impact of temporary failures which occurred during the commitment of a transaction on other transactions, and the dependencies created due to sharing of data items is much reduced by reversing the dependencies between the transactions. A simulation model has been developed and extensive simulation experiments have been performed to compare the performance of the DDCR with other protocols such as the Opt [1], the Healthy-Opt [2], and the base protocol, which use priority inheritance and blocking to resolve the data conflicts. The simulation results show that the DDCR can significantly improve the system performance under different workload and workload distributions. Its performance is consistently better than the base protocol and the Opt protocols in both main-memory resident and disk-resident DRTDBS. [ABSTRACT FROM PUBLISHER]

Feature interactions in telecommunications software systems commonly refer to unanticipated interference among features of call processing software. Features, such as call forwarding and call screening, are supplementary functionality packages that provide value-added services to telephone users. A newly created feature may alter the working assumptions of other existing features, causing them to function abnormally. Similarly, a new feature may fail to anticipate the impacts of some existing features; hence it cannot work properly in conjunction with those features. The guest editorial of the October 1998 issue of the journal "IEEE Transactions on Software Engineering" introduces various articles related to the management of feature interactions in telecommunications software systems. The evolution of distributed software systems has been a subject of many interesting research efforts. With this special section the authors hope to encourage the application of their results to the feature-interaction problem.

The article presents an introduction to a special section in the October 1997 issue of the journal IEEE Transactions on Software Engineering. This special section focuses on real-time systems. These systems are defined as those for which correctness depends not only on the logical properties of the produced results, but also on the temporal properties of these results. The growing interest in real-time systems has led to a body of real-time computing research work, which permeates many areas in computer science and engineering. As real-time systems evolve, their applications become more complex, and the demand for advanced functionality and dependability continues to grow. It poses formidable intellectual and engineering challenges that must be tackled to create practical solutions to the problems faced in design and development of real-time systems. A symposium on it provides an annual forum for exchanging information on recent technological advances and practice in real-time computing.

The article reports on the study conducted by Radu Stoleru of Texas A&M University and John A. Stankovic and Sang H. Son of the University of Virginia on node localization in wireless sensor networks and the potential of localization protocol composability in the U.S. There are several wireless sensor network (WSN) systems are developed for several domains including military surveillance, environmental monitoring, habitat monitoring and structural monitoring. When researchers studied how one can effectively locate sensor nodes at low cost, they failed because despite the myriads of schemes available in the market, no robust localization system has potential to provide the solution needed. Presented are the details of the research.

Presents a protocol use for processing read-only and update mobile transactions. Detection and resolution of data conflicts by the protocol; Advantage of the protocol; Effectiveness of the protocol.

Vehicle platooning reduces the safety distance between vehicles and the travel time of vehicles so that it leads to an increase in road capacity and to saving fuel consumption. In Europe, many projects for vehicle platooning are being actively developed, but mostly focus on truck platooning on the highway with a simpler topology than that of the urban road. When an existing vehicle platoon is applied to urban roads, many challenges are more complicated to address than highways. They include complex topology, various routes, traffic signals, intersections, frequent lane change, and communication interference depending on a higher vehicle density. To address these challenges, we propose a distributed urban platooning protocol (DUPP) that enables high mobility and maximizes flexibility for driving vehicles to conduct urban platooning in a decentralized manner. DUPP has simple procedures to perform platooning maneuvers and does not require explicit conforming for the completion of platooning maneuvers. Since DUPP mainly operates on a service channel, it does not cause negative side effects on the exchange of basic safety messages on a control channel. Moreover, DUPP does not generate any data propagation delay due to contention-based channel access since it guarantees sequential data transmission opportunities for urban platooning vehicles. Finally, to address a problem of the broadcast storm while vehicles notify detected road events, DUPP performs forwarder selection using an analytic hierarchy process. The performance of the proposed DUPP is compared with that of ENSEMBLE which is the latest European platooning project in terms of the travel time of vehicles, the lifetime of an urban platoon, the success ratio of a designed maneuver, the external cost and the periodicity of the urban platooning-related transmissions, the adaptability of an urban platoon, and the forwarder selection ratio for each vehicle. The results of the performance evaluation demonstrate that the proposed DUPP is well suited to dynamic urban environments by maintaining a vehicle platoon as stable as possible after DUPP flexibly and quickly forms a vehicle platoon without the support of a centralized node. [ABSTRACT FROM AUTHOR]

While emerging technology for self-driving automation in vehicles progresses rapidly, the transition to an era of roads full of fully connected and automated vehicles (CAVs) may take longer than expected. Until then, it is inevitable that CAVs should coexist and interact with drivers of non-autonomous vehicles (NAVs) in urban roads. During this period of transition, it is critical to provide road safety with the mixed vehicular traffic and uncertainty caused by human drivers. To investigate the issues caused by the coexistence and interaction with humans, we propose to build a component-based and interactive intelligent transportation cyber-physical systems (ITCPS) framework. Our design of the interactive ITCPS framework aims to provide a standardized structure for users by defining core components. The framework is specified by behavior models and interfaces for the desired ITCPS components and is implemented as a form of human and hardware-in-the-loop system. We developed an intersection crossing assistance service and an automatic emergency braking service as an example of practical applications using the framework. To evaluate the framework, we tested its performance to show how effectively it operates while supporting real-time processing. The results indicate that it satisfies the timing requirements of vehicle-to-vehicle (V2V) communication and the limited processing time required for performing the functions of behavior models, even though the traffic volume reaches the road capacity. A case study using statistical analysis is conducted to assess the practical value of the developed experimental environment. The results of the case study validate the reliability among the specified variables for the experiments involving human drivers. It has shown that V2V communication support has positive effects on road safety, including intersection safety, braking events, and perception-reaction time (PRT) of the drivers. Furthermore, V2V communication support and PRT are identified as the important indicators affecting road safety at an un-signalized intersection. The proposed interactive framework is expected to contribute in constructing a comprehensive environment for the urban ITCPS and providing experimental support for the analysis of human behavior in the coexistence environment. [ABSTRACT FROM AUTHOR]

Under a stochastic roadway, drivers need a route guidance system incorporating travel time variability. To recommend a customized path depending on the trip purpose and the driver's risk-taking behavior, various path ranking methods have been developed. Unlike those methods, our proposed disutility method can easily incorporate a target arrival time in the ranking process by measuring how late the travel is and by penalizing it depending on the severity of lateness. In addition, the disutility-based route guidance system can properly address travel time unreliability that causes unacceptable disruptions to the driver's schedule (i.e., unexpected long delay). We compare the disutility-based path ranking method with other ranking methods, the percentile travel time, the mean excess travel time, and the on-time arrival probability. We show that the disutility has stronger discriminating power and requires less solution space to find an optimal path. The most important advantage is that it can estimate a driver's risk-taking behavior for each trip purpose by using the discrete choice analysis. We construct a simulation framework to acquire the travel time data on a hypothetical roadway. We analyze the data and show how various ranking methods recommend a customized path. Using the data, we show the advantage of the disutiltiy method over the other methods, which is generating a customized path with respect to the target arrival time by properly penalizing the travel time lateness. [ABSTRACT FROM AUTHOR]

Vehicular networks represent a research area of significant importance in improving the safety, efficiency and sustainability of transportation systems. One of the key research problems in vehicular networks is real-time data dissemination, which is crucial to the satisfactory performance of many emergent applications providing real-time information services in vehicular networks. Specifically, the two issues need to be addressed in this problem are maintenance of temporal data freshness and timely dissemination of data. Most existing works only considered periodical data update via backbone wired networks in maintaining temporal data freshness. However, many applications rely on passing vehicles to upload their collected information via wireless network, which imposes new challenges as the uplink data update will have to compete with the downlink data dissemination for the limited wireless bandwidth. With such observations, we propose a temporal information service system, in which vehicles are able to collect up-to-date temporal information and upload them to the roadside units (RSU) along their trajectories. Meanwhile, RSU can disseminate its available data items to vehicles based on their specific requests. Particularly, in this paper, we first quantitatively analyze the freshness of temporal data and propose a mathematical model to evaluate the usefulness of the temporal data. Next, we give the formulation of the proposed real-time and temporal information service (RTIS) problem, and prove the NP-hardness of this problem by constructing a polynomial-time reduction from 0–1 knapsack problem. Subsequently, we establish a probabilistic model to theoretically analyze the tradeoff between timely temporal data update and requested data dissemination sharing a common communication resource, which provides a deeper insight of the proposed RTIS. Further, a heuristic algorithm, namely adaptive update request scheduling (AURS), is designed to enhance the efficacy of RTIS by synthesizing the broadcast effect, the real-time service requirement and the service quality in making scheduling decisions. The computational complexity and scalability analysis of AURS is also discussed. Last but not least, a simulation model is implemented and a comprehensive performance evaluation has been carried out to demonstrate the superiority of ARUS against several state-of-the-art approaches in a variety of application scenarios. [ABSTRACT FROM AUTHOR]

Abstract: Traffic congestion has become a major source of fuel waste, economic burden, environmental pollution, and commuter frustration. A lot of effort has been made to alleviate these problems, but traditional countermeasures, such as expanding transportation capacity, are no longer a sustainable solution to the rapidly growing levels of congestion. Both governments and transportation planners are actively engaged in the development of traffic management strategies and policies, but their endeavors are not sufficient either. Therefore, it is imperative to further improve the efficiency of the existing road infrastructure by leveraging the latest technological advances in computing and networking. Recent studies have shown that emerging technologies in vehicular networks have made the roadway reservation system a viable option for mitigating traffic congestion and improving transportation efficiency. In this paper, we present a roadway reservation system, where the drivers make reservations in advance in order to enter a high-priority lane. The drivers who successfully make the reservation are guaranteed certain quality of service, i.e. end-to-end travel delay. We propose a token-based reservation system which monitors and controls the traffic workload in real-time. We have also designed an on-line scheduling algorithm which maintains sufficient transportation efficiency by selecting which reservation requests should be accepted. The algorithm also handles any necessary user interaction for reservation. A comprehensive performance evaluation based on our simulation model demonstrates the practicality and soundness of the proposed reservation system. [Copyright &y& Elsevier]