A wireless local area network (WLAN) or a cell with quality-of-service (QoS) guarantees for various types of traffic is considered. A centralized (i.e., star) network topology is adopted as the topology of a cell which consists of a base station and a number of mobile clients. Dynamic Time Division Duplexed (TDD) transmission is used, and hence, the same frequency channel is timeshared for downlink and uplink transmissions under the dynamic control of the base station. We divide traffic into two classes: class I (real-time) and II (nonreal -time). Whenever there is no eligible class-I traffic, class-II traffic is transmitted, while uplink transmissions are controlled with a reservation scheme. ClassI traffic is handled with the framing strategy [1] combined with the admission test for adding new class-I connections. Finally, we present the performance (average delay and throughput) evaluation of the reservation scheme for class-II traffic using both analytical calculations and simulati...

CONTENTS Acknowledgements : : : : : : : : : : : : : : : : : : : : : : : : : : : : : iii List of Figures : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : viii Chapter 1. INTRODUCTION : : : : : : : : : : : : : : : : : : : : : : : : : : 1 2. BACKGROUND : : : : : : : : : : : : : : : : : : : : : : : : : : : 5 2.1 Real-Time Systems and Classification : : : : : : : : : : : : : 5 2.2 Characteristics of Real-Time Systems : : : : : : : : : : : : : 6 2.3 Scheduling : : : : : : : : : : : : : : : : : : : : : : : : : : : : 8 2.3.1 Rate-Monotonic (RM) Algorithm : : : : : : : : : : : : 9 2.3.2 Earliest Deadline First (EDF) Algorithm : : : : : : : : 10 2.4 Task Allocation : : : : : : : : : : : : : : : : : : : : : : : : : 10 2.5 Fault Tolerance : : : : : : : : : : : : : : : : : : : : :

There is increasing use of distributed computer systems to support real-time applications. The key to successfully developing such systems is to have a communication network which supports the timely delivery of inter-task messages. The main focus of this research is to address some important issues related to guarantees of message deadlines in a communication network. Our effort has concentrated on the timed token ring networks, such as FDDI, where the timed token medium access control (MAC) protocol is employed. Specifically, we studied the problem of guaranteeing synchronous message deadlines by appropriate allocation of the synchronous bandwidths. Synchronous bandwidth, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous bandwidths must be properly allocated to i...

. In this paper, we present an Ethernet-based protocol called RTCC that provides a good basis for distributed hard real-time applications without requiring any modifications to existing Ethernet hardware. Two novel mechanisms, the command / response multiplex transmission and a bus table, are introduced in RTCC in order to schedule the channels. Performance measurements from experiments on a 10 Mbps Ethernet indicate that RTCC has a satisfactory determinism. 1 Introduction A real-time system is one in which the correctness of the system depends not only on the logical results, but also on the time at which the results are produced. In hard real-time systems, results must be produced within an ordained timing constraint, otherwise, the results will lose their usability.For safety-critical systems, incorrect operations can lead to the loss of life or other catastrophes. With the increasing use of distributed hard real-time systems (such as command and control systems, image proce...

We report our ongoing research in real-time communication with FDDI-based reconfigurable networks. The original FDDI architecture was enhanced in order to improve its fault-tolerance capability while a scheduling methodology, including message assignment, bandwidth allocation, and bandwidth management is developed to support real-time communication. As a result, message deadlines are guaranteed even in the event of network faults.

We report our work on FDDI based networks for multimedia applications. It lifts previous research limitations and shows a systematic way for bounding message delays at the application level. The synchronous server is designed to control application admissions and properly multiplex messages from multiple applications on one node. We consider an integrated system including both the sender and receiver hosts, and the network. A set of constraints are proposed for controlling application admissions and guaranteeing the normal operation of the integrated system so that the total message delays can be bounded. 1 INTRODUCTION The development of high-speed networks makes multimedia communication services possible [14, 16, 21]. Such services include teleconferencing, video telephony, video-on-demand, distant learning, telemedicine, etc. For these applications, the bandwidth requirement is much higher than the bandwidth provided by many traditional local area networks. In addition, timely tran...

Abstract The problem of real-time communication over a multiple access network has been well studied in the recent past. But, there has been no prior work addressing realtime communication over a Switched Local Area Network (SLAN), where several LAN segments are connected through a switch. In this paper, we propose real-time protocols for the SLAN. The proposed protocols are based on CSMA/CD with deterministic collision resolution and belong to the dynamic planning based category, where an admission test is performed for guaranteeing message transmission. This test is based on the worst case channel access time that can elapse before a particular node can transmit its message. We also compute the worst case buffer requirement at the switch and nodes. We study the effectiveness of the proposed protocols through extensive simulation studies.Keywords:

In the area of distributed control systems (DCS) a systematic design of a modular control system and reliable communication support are of major importance. This paper presents a field level of automation systems and its real time factors. A DCS is supposed to be real time capable if both application and communication as two qualitatively different sub-systems meet the real time requirements. The real time capability of the communication part of automation components is determined by the fieldbus protocol specification and its implementation. Therefore training in this type of know-how should be regarded as an integration process of several related areas. Since this knowledge has an applied character, the best effect can be achieved when the training process is closely connected with direct practical experience. A multi-national effort to create a RTS teaching/learning program brings new perspectives to a foundation of competence centers equipped with necessary technologies. 1 Introdu...