Local Synchronous Capacity Allocation Schemes for Guaranteeing Message Deadlines with the Timed Token Protocol *

We study the problem of guaranteeing synchronous message deadlines in communication networks where the timed token medium access control protocol is em-ployed. Synchronous capacity, defined as ihe max-rmum time for which a node can transmit its syn-chronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the iransmission of synchronous messages before their deadlines, syn-chronous capacities must be properly allocated to indi-vidual nodes. In this paper, we develop and analyze a class oflo-col synchronous capacity allocation schemes. A local scheme allocates the synchronous capacity 20 a node without using information about messages on the other nodes while a global allocation scheme uses network wide information in ihe allocaiion process. Use of local schemes benefits ihe run-time mana emeni of network in the sense that the entire networi can continue its normal operation while individual nodes chan e iheir synchronous capacities in response io the cianging message parameters. We evaluaie the local allocation schemes proposed in terms of their ability to guaran-tee message deadlines. We show that one of the local allocation schemes proposed can achieve the same per-formance as that of the best global allocation scheme known to date.

Real-Time Communication in Packet-Switched Networks

Abstract The dramatically increased bandwidths and processing capabilities of future high-speed networks make possible many distributed real-time applications, such as sensor-based applications and multimedia services. Since these applications will have tra c characteristics and performance requirements that di er dramatically from those of current data-oriented applications, new communication network architectures and protocols will be required. In this paper we discuss the performance requirements and tra c characteristics of various real-time applications, survey recent developments in the areas of network architecture and protocols for supporting real-time services, and develop frameworks in which these, and future, research e orts can be considered

General schedulability bound analysis and its applications in real-time systems

Real-time system refers to the computing, communication, and information system with deadline requirements. To meet these deadline requirements, most systems use a mechanism known as the schedulability test which determines whether each of the admitted tasks can meet its deadline. A new task will not be admitted unless it passes the schedulability test. Schedulability tests can be either direct or indirect. The utilization based schedulability test is the most common schedulability test approach, in which a task can be admitted only if the total system utilization is lower than a pre-derived bound. While the utilization bound based schedulability test is simple and effective, it is often difficult to derive the bound. For its analytical complexity, utilization bound results are usually obtained on a case-by-case basis. In this dissertation, we develop a general framework that allows effective derivation of schedulability bounds for different workload patterns and schedulers. We introduce an analytical model that is capable of describing a wide range of tasks' and schedulers'ÃÂÃÂ behaviors. We propose a new definition of utilization, called workload rate. While similar to utilization, workload rate enables flexible representation of different scheduling and workload scenarios and leads to uniform proof of schedulability bounds. We introduce two types of workload constraint functions, s-shaped and r-shaped, for flexible and accurate characterization of the task workloads. We derive parameterized schedulability bounds for arbitrary static priority schedulers, weighted round robin schedulers, and timed token ring schedulers. Existing utilization bounds for these schedulers are obtained from the closed-form formula by direct assignment of proper parameters. Some of these results are applied to a cluster computing environment. The results developed in this dissertation will help future schedulability bound analysis by supplying a unified modeling framework and will ease the implementation practical real-time systems by providing a set of ready to use bound results