Dynamic real-time scheduling strategies for interactive continuous media servers

In this paper, we propose and study a dynamic approach to schedule real-time requests in a video-on-demand (VOD) server. Providing quality of service in such servers requires uninterrupted and on-time retrieval of motion video data. VOD services and multimedia applications further require access to the storage devices to be shared among multiple concurrent streams. Most of the previous VOD scheduling approaches use limited run-time,0 information and thus cannot exploit the potential capacity of the system fully. Our approach improves throughput by making use of run-time information to relax admission control. It maintains excellent quality of service under varying playout rates by observing deadlines and by reallocating resources to guarantee continuous service. It also reduces start-up latency by beginning service as soon as it is detected that deadlines of all real-time requests will be met. We establish safe conditions for greedy admission, dynamic control of disk read sizes, fast initial service, and sporadic services, We conduct thorough simulations over a wide range of buffer capacities, load settings, and over varying playout rates to demonstrate the significant improvements in quality of service, throughput and start-up latency of our approach relative to a static approach

Dynamic scheduling of real-time tasks, by assignment

To dynamically schedule realtime tasks on a NUMA architecture, the RT-SADS algorithm emphasizes appropriate processor assignment rather than task sequencing. It minimizes scheduling overhead and task deadline violations by directly controlling scheduling time and coordinating it with task execution

Efficient sequencing techniques for variable-length messages in WDM networks

Message sequencing and channel assignment are two important issues that need to be addressed when scheduling variable-length messages in a wavelength division multiplexing (WDM) network. Channel assignment addresses the problem of choosing an appropriate data channel via which a message is transmitted to a node. This problem has been addressed extensively in the literature. On the other hand, message sequencing which addresses the order in which messages are sent, has rarely been addressed. In this paper, we propose a set of scheduling techniques for single-hop WDM passive star networks, which address both the sequencing aspect and the assignment aspect of the problem, In particular, we develop two priority schemes for sequencing messages in a WDM network in order to increase the overall performance of the network. We evaluate the proposed algorithms, using analytical modeling and extensive discrete-event simulations, by comparing their performance with state-of-the-art scheduling algorithms that only address the assignment problem [9], We find that significant improvement in performance can be achieved using our scheduling algorithms where message sequencing and channel assignment are simultaneously taken into consideration. This suggests that, when scheduling messages in WDM networks, one has to consider message sequencing, as well as channel assignment. As a result, we anticipate that this research mill open new directions into the problem of on-line scheduling in WDM networks

DYNAMIC SCHEDULING TECHNIQUES FOR HETEROGENEOUS COMPUTING SYSTEMS

There has been a recent increase of interest in heterogeneous computing systems, due partly to the fact that a single parallel architecture may not be adequate for exploiting all of a program's available parallelism. In some eases, heterogeneous systems have been shown to produce higher performance for lower cost than a single large machine. However, there has been only limited work on developing techniques and frameworks for partitioning and scheduling applications across the components of a heterogeneous system. In this paper we propose a general model for describing and evaluating heterogeneous systems that considers the degree of uniformity in the processing elements and the communication channels as a measure of the heterogeneity in the system. We also propose a class of dynamic scheduling algorithms for a heterogeneous computing system interconnected with an arbitrary communication network. These algorithms execute a novel optimization technique to dynamically compute schedules based on the potentially non-uniform computation and communication costs on the processors of a heterogeneous system. A unique aspect of these algorithms is that they easily adapt to different task granularities, to dynamically varying processor and system loads, and to systems with varying degrees of heterogeneity. Our simulations are designed to facilitate the evaluation of different scheduling algorithms under varying degrees of heterogeneity. The results show improved performance for our algorithms compared to the performance resulting from existing scheduling techniques

An efficient message scheduling algorithm for WDM lightwave networks

Two important issues that need to be addressed when designing medium access control (MAC) protocols for Wavelength Division Multiplexing networks are message sequencing and channel assignment. Channel assignment addresses the problem of choosing an appropriate data channel via which a message is transmitted. This problem has been addressed extensively in the literature. On the other hand, message sequencing, which addresses the order in which messages are sent, has rarely been addressed. In this paper, we propose a new reservation-based message scheduling algorithm called RO-EATS that addresses both the channel assignment and message sequencing during its scheduling process. We formulate an analytical model and conduct extensive simulations to evaluate the performance of this algorithm. We compare the performance results of a well-known algorithm which only addresses the channel assignment issue with those of our new algorithm. The comparison shows that our new algorithm gives significant improvement over scheduling algorithms that do not consider message sequencing. As a result, we anticipate that these research results will lead to new approaches to message scheduling on WDM networks. (C) 1999 published by Elsevier Science B.V. All rights reserved

Efficient scheduling algorithms for real-time service on WDM optical networks

In this paper we study, the problem of providing real-time service to hard and soft real-time messages in wavelength division multiplexing (WDM) optical networks. We propose and evaluate a set of scheduling algorithms which schedule message transmissions in single-hop WDM passive star networks based on specific time constraints. We compare the performances of our algorithms with that of the typical WDM scheduling algorithm which does not consider the time constraint of the transmitted messages by discrete-event simulations and an analytical model. We find that the improvement on real-time performance can be attributed to our scheduling algorithms where the time constraint of messages has been taken into consideration. This study suggests that when scheduling real-time messages In WDM networks, one has to consider not only the problem of resources allocation in the network but also the problem of sequencing messages based on their rime constraints

A receiver-oriented message scheduling algorithm for WDM lightwave networks

In scheduling the transmission of messages in a WDM network, we are facing not only the channel assignment problem but also message sequencing problem. In this paper, we propose and evaluate a new reservation-based message scheduling algorithm for single-hop, WDM passive star lightwave network which addresses both the assignment aspect and the sequencing aspect of the problem. We compare the performance of the algorithm which only addresses the channel assignment issue with the performance of our new algorithm theoretically and experimentally and demonstrate that our new algorithm has significant improvement over the performance of a WDM network with a scheduling algorithm that does not consider the message sequencing problem. As a result, we anticipate that this research can open new directions into the problem of message scheduling on WDM networks

Efficient scheduling algorithms for real-time service on WDM optical networks

One of the important issues in the design of future generation high-speed networks is the provision of real-time services to different types of traffic with various time constraints. In this paper we study the problem of providing real-time service to hard and soft real-time messages in Wavelength-Division-Multiplexing (WDM) optical networks. We propose a set of scheduling algorithms which prioritize and manage message transmissions in single-hop WDM passive star networks based on specific message time constraints. In particular, we develop time-based priority schemes for scheduling message transmissions in order to increase the real-time performance of a WDM network topology. We formulated an analytical model and conducted extensive discrete-event simulations to evaluate the performance of the proposed algorithms. We compared their performances with that of the state-of-the-art WDM scheduling algorithms which typically do not consider the time constraint of the transmitted messages. This study suggests that when scheduling real-time messages in WDM networks, one has to consider not only the problem of resources allocation in the network but also the problem of sequencing messages based on their time constraints