An optimal synchronous bandwidth allocation scheme for guaranteeing synchronous message deadlines with the timed-token MAC protocol

This paper investigates the inherent timing properties of the timed-token medium access control (MAC) protocol necessary to guarantee synchronous message deadlines in a timed token ring network such as, fiber distributed data interface (FDDI), where the timed-token MAC protocol is employed. As a result, an exact upper bound, tighter than previously published, on the elapse time between any number of successive token arrivals at a particular node has been derived. Based on the exact protocol timing property, an optimal synchronous bandwidth allocation (SBA) scheme named enhanced MCA (EMCA) for guaranteeing synchronous messages with deadlines equal to periods in length is proposed. Thm scheme is an enhancement on the previously publiibed MCA scheme

Guaranteeing synchronous message deadlines with the timed token medium access control protocol

We study the problem of guaranteeing synchronous message deadlines in token ring networks where the timed token medium access control protocol is employed. Synchronous capacity, 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 capacities must be properly allocated to individual nodes. We address the issue of appropriate allocation of the synchronous capacities. Several synchronous capacity allocation schemes are analyzed in terms of their ability to satisfy deadline constraints of synchronous messages. We show that an inappropriate allocation of the synchronous capacities could cause message deadlines to be missed even if the synchronous traffic is extremely low. We propose a scheme called the normalized proportional allocation scheme which can guarantee the synchronous message deadlines for synchronous traffic of up to 33 percent of available utilization. To date, no other synchronous capacity allocation scheme has been reported to achieve such substantial performance. Another major contribution of this paper is an extension to the previous work on the bounded token rotation time. We prove that the time elapsed between any consecutive visits to a particular node is bounded by upsilon TTRT, where TTRT is the target token rotation time set up at system initialization time. The previous result by Johnson and Sevcik is a special case where upsilon = 2. We use this result in the analysis of various synchronous allocation schemes. It can also be applied in other similar studies

Design and Analysis of RT-Ring: A Protocol for Supporting Real-Time Communications

Distributed applications with quality of service (QoS) requirements are more and more used in several areas (e.g., automated factory networks, embedded systems, conferencing systems). These applications produce a type of traffic with hard timing requirements, i.e., transmissions must be completed within specified deadlines. To handle these transmissions, the communication system must use real-time protocols to provide a communication service that is able to satisfy the QoS requirements of the distributed applications. In this paper, we propose a new real-time protocol, called RT-Ring, able to support transmissions of both real-time and generic traffic over a ring network. RT-Ring provides both network guarantees and high network resource utilization, while ensuring the compatibility with the emerging differentiated service architectures. Network guarantees are fully proved and high network utilization is highlighted by a comparative study with the FDDI protocol. This comparison shows that RT-Ring network capacities are greater than the corresponding FDDI capacities. In fact, by assuming the FDDI frames with a length equal to the RT-Ring slot size and by using the same traffic load we show that the capacities of FDDI are equal to the lower bound capacities of RT-Ring. Index Terms Real-time protocol, quality of service (QoS) traffic, worst case analysis

Performance analysis of Gb/s WDM FDDI network

In this paper, we propose a time-token multi-Gb/s Wavelength Division Multiplexing Fibre Distributed Data Interface (WDM/FDDI) architecture and examine its throughput efficiency and delay under heavy load for different network configuration using discrete event simulator

Static-Threshold-Limited on-Demand Guaranteed Service for Asynchronous Traffic in Timely-Token Protocol

In this paper, an improved Timely-Token protocol with enhanced best-effort service for improved capacity allocation to the asynchronous (that is, non real-time) traffic is proposed. Through analytical approach and the use of computer simulations, the improved Timely-Token protocol is compared with the existing Timely-Token protocol. In particular, if AT denotes a threshold value, then, when compared to the existing Timely-Token protocol, the improved protocol will allocate additional average of AT time units to the asynchronous traffic in every cycle

Advanced information processing system: The Army fault tolerant architecture conceptual study. Volume 1: Army fault tolerant architecture overview

Digital computing systems needed for Army programs such as the Computer-Aided Low Altitude Helicopter Flight Program and the Armored Systems Modernization (ASM) vehicles may be characterized by high computational throughput and input/output bandwidth, hard real-time response, high reliability and availability, and maintainability, testability, and producibility requirements. In addition, such a system should be affordable to produce, procure, maintain, and upgrade. To address these needs, the Army Fault Tolerant Architecture (AFTA) is being designed and constructed under a three-year program comprised of a conceptual study, detailed design and fabrication, and demonstration and validation phases. Described here are the results of the conceptual study phase of the AFTA development. Given here is an introduction to the AFTA program, its objectives, and key elements of its technical approach. A format is designed for representing mission requirements in a manner suitable for first order AFTA sizing and analysis, followed by a discussion of the current state of mission requirements acquisition for the targeted Army missions. An overview is given of AFTA's architectural theory of operation

A Control Plane For Prioritized Real-time Communications In Wireless Token Ring Networks

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Kablosuz ağlarda gerçek zaman kısıtlarını sağlamak zor bir araştırma problemidir. Jetonlu halka mimarisine sahip ağlar yanıt süreleri deterministik olduğundan ve gecikmelerin üst sınırının tahmin edilebilir olmalarından dolayı gerçek zaman kısıtlarını sağlamak için daha elverişlidir. Bu tezde kablosuz jetonlu halka ağları için katı gerçek zaman kısıtlarını sağlamak üzere MAC katmanında zamanlı jeton protokolünü içeren merkezi bir denetim düzlemi önerilmektedir. Bu denetim düzleminde üç tane fonksiyon gerçeklenmiştir. Bunlar kabul denetimi, istasyon çıkarma ve trafik ayrımı fonksiyonlarıdır. Böylece dinamik bir halka yapısı oluşturulmuş ve yüksek öncelikli trafiğin ağa girme şansı artmış ve düşük öncelikli trafik taşıyan istasyonların gerektiğinde yüksek öncelikli trafiğe yer vermeleri için ağdan çıkarılmaları sağlanmıştır. Simülasyon sonuçlarına göre önerilen denetim düzlemi sayesinde yüksek öncelikli trafiğin düşük öncelikli trafiğe göre ağda daha fazla bant genişliğine sahip olduğu ve katı gerçek zaman kısıtlarının sağlandığı görülmüştür.Providing real-time guarantees in wireless networks is a challenging research problem. Token ring networks are more suitable for real-time communications due to the fact that the response time is highly deterministic and also the upper bound of the latency in these networks is predictable. This thesis proposes a centralized control plane incorporating the timed token protocol in the MAC layer for providing hard real-time guarantees in wireless token ring networks which implements three important functions, namely the admission control procedure, the station eviction procedure and a traffic differentiation mechanism. In this approach a dynamic ring structure is built, where high priority stations have more chance of admittance and stations with low priority can be removed from the ring. Simulation results show that the proposed control plane ensures higher priority traffic more bandwidth than lower priority traffic and guarantees that deadline constraints of hard real-time traffic are satisfied.Yüksek LisansM.Sc

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