Multimedia Networking Abstractions with Quality of Service Guarantees

Multimedia Networking Abstractions with Quality

of Service Guarantees

Aurel A. Lazar*, Lek Heng Ngoh** and Anupam Sahai**

*Department of Electrical Engineering and Center for Telecommunications Research,

Columbia University, New York, NY 10027-6699, e-mail: aurel@ctr.columbia.edu.

** Institute of Systems Science, National University of Singapore

Republic of Singapore 0511

Abstract

The concept of schedulable region previously introduced to broadband networks with quality of service guarantees is extended

to multimedia devices such as audio/video processing and disk storage units. The resulting multimedia capacity region charac-

terizes the amount of resources a physical device is able to provide under quality of service constraints. The modeling method-

ology supports a straightforward association of resources with logical objects and, thereby, the mapping of logical objects onto

physical objects with quality of service guarantees. Examples showing the size and shape of the multimedia capacity region of

various physical devices are given.

Keywords: Multimedia Capacity Region, high-speed networking, quality of service, abstraction, multimedia, operating sys-

tems, experimentation, performance guarantees, scheduling, resources.

1.Introduction

Multimedia networks are enabled by two basic technologies: networking and multimedia computing. Object-oriented lan-

guages provide the main high level modeling tool for both. Mapping objects onto physical resources withguaranteed quality

of service (QOS) is a key requirement.

For broadband networks the object-oriented methodology has been instrumental in modeling the network entities and in

describing the mechanisms composing the network architecture. A general model for characterizing the capacity of key net-

work abstractions with QOS guarantees was put forth in [14]. Within this model, the mapping of logical resources onto physi-

cal resources is a straightforward task.

In order to characterize the capacity region of a multiplexer in broadband networks with QOS guarantees, Hyman et al. [8]

have introduced the concept of schedulable region. The schedulable region represents themultidimensionalcapacity of the

multiplexer; its dimensionality depends on the number of traffic classes and represents the stability region of the multiplexer

under QOS constraints.

The schedulable region is a resource abstraction that allows a separation of time scales: the time scale of cells and the time

scale of call arrivals and departures. In [9] it is shown how the separation of time scales is the appropriate tool for resolving the

admission control problem. Based on a calculus of schedulable regions, the QOS in the network can be guaranteed [10].

Can the concept of schedulable region be extended to multimedia computing [11]? Is such an extension needed? Multimedia

computing platforms, such as those implemented based upon the Multimedia Systems Services Architecture [7] (see also [6],

[17]), provide a framework of middleware, e.g., system components lying in the region between the generic operating system

and specific applications. This middleware is based upon high level operating systems abstractions. These abstractions, how-

ever, exhibit only a nominal modeling of QOS constraints.Proceedings of the IEE/SPIE Multimedia Computing and Networking Conference, Feb 1995.For example, most existing real-time operating systems do not support abstractions that provide real-time QOS guarantees for

multimedia traffic. At most they support a fixed priority [16], or a dynamic priority based scheduling scheme [4]. To realize

QOS guarantees, the mapping of task requirements onto a set of priorities becomes fairly complex and low level. Higher level

abstractions are needed on which admission control decisions can be made. The situation for video on demand (VOD) systems

is very similar [18], [19], [20]. While scheduling and admission control algorithms have been proposed in the literature, appro-

priate abstractions are not available. How to map logical objects onto physical resources with guaranteed quality of service has

not been specified.

In this paper we extend the methodology for characterizing resources based on the schedulable region concept to multimedia

devices. Here the novel concepts of multimedia capacity region, an extension of the schedulable region to different media

devices with QOS guarantees, will be introduced. Using the multimedia capacity region, the problem of scheduling multime-

dia becomes identical to the one in [9], i.e., a real-time packing exercise very similar to the Tetris game.

User requirements are modeled through service class specifications with QOS constraints. The service class specification is in