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

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

Improved Non-Real-Time Communication in FDDI Networks with Real-Time Traffic

The Fiber Distributed Data Interface (FDDI) is suitable for real-time communication because of the high speed and the performance guarantees it provides. However, these guarantees are achieved at the expense of non-real-time traffic because the real-time messages are given higher priority over non-real-time messages, resulting in excessive delays for non-real-time messages. In this paper, we propose a scheme for reducing the response time of non-real-time messages while still providing the same quality of service to real-time messages. In the proposed approach, non-real-time messages are transmitted ahead of real-time messages unless it is absolutely necessary to transmit real-time messages first in order to meet their deadlines. Simulation results show that a substantial reduction in the mean response time of non-real-time messages is achieved when using the proposed approach. Index Terms: Real-time communication, non-realtime communication, timed token protocol, FDDI. 1 Introduction..

Deferring Real-Time Traffic for Improved Non-Real-Time Communication in Fddi Networks

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