Quality Adaptation in a Multisession Multimedia System: 
Model, Algorithms and Architecture


Ph.D. Dissertation Abstract
(c) Shahadat Khan, 1998
Department of ECE
University of Victoria

Flexible and adaptive quality of service (QoS) is desirable for
real-time multimedia applications. Suppose a  multimedia system is
supporting a 30 frame/second video stream which is using a network
bandwidth of 2 Mbps, and due to network congestion the network
bandwidth is reduced to 1 Mbps. It is desirable that the system
supports graceful adaptation of quality of the video stream, for
example, by reducing the frame rate to 15 frame/second. The focus of
this dissertation is to investigate the design of an adaptive
multimedia system (AMS) with multiple concurrent sessions, where the
quality of individual sessions is dynamically adapted to the
available resources and to the run-time user preferences. 


We propose the  Utility Model -- a mathematical model to
capture the issues of resource management within multisession AMSs.
In this model,  each session provides a quality profile, which is a
set of operating qualities arranged from the minimum acceptable
quality to the maximum desired quality. Any operating quality may be
mapped to the required resources using a quality-resource mapping,
and also to a session utility using a quality-utility mapping. The
main problem in a multisession AMS is to find an  operating quality
for each session such that the overall system utility (e.g. system
revenue) is maximized under the system resource constraints. This is
called the adaptive multimedia problem (AMP). The Utility Model
formulates the AMP as the multiple-choice multi-dimension 0-1
knapsack problem (MMKP). It provides a unified and computationally
feasible way to solve the admission problem for new multimedia
sessions, and the dynamic quality adaptation and integrated resource
allocation problems for existing sessions. 


We present the Padma Architecture --  a system architecture for
multisession AMSs. This architecture has two novelties: (1)
integrated and adaptive management of system resources based on the
Utility Model, and (2) the use of metaspaces to encapsulate the
machinery of quality adaptation.  The former provides improved
resource utilization and dynamic quality adaptation, and the latter
provides the application programmers freedom from the concerns of
low-level resource management issues while developing multimedia
applications. 


Finally, we present the Utility Model Demonstration Prototype (UMDP)
-- a  prototype which demonstrates the capability of the Utility
Model to handle admission control, quality adaptation and integrated
resource allocation in a unified way. We evaluate the performance of
UMDP using random sequences of events, and show that the system
utility achieved by the UMDP is significantly higher than that of a
simple reservation model prototype (SRMP). For applications such
multimedia service providers, it means that UMDP will generate more
revenue than SRMP from the same amounts of system resources
provisioned.