page 1  (11 pages)
2to next section


Andrew Campbell, Alexandros Eleftheriadis and Cristina Aurrecoechea

Center for Telecommunications Research,
Columbia University
New York, NY 10027-6699.
{campbell, elef, cris}


Distributed audio and video applications need to adapt to fluctuations in delivered quality of service (QoS). By trading off temporal and spatial quality to available bandwidth, or manipulating the playout time of continuous media in response to variation in delay, audio and video flows can be made to adapt to fluctuating QoS with minimal perceptual distortion. In this paper we introduce dynamic QoS management (DQM) for the control and management of multi-layer coded flows operating in heterogeneous multimedia networking environments. Two key techniques are proposed: i) an end-to-end dynamic rate shaping scheme which adapts the rate of MPEG-coded [1] flows to the available network resources while minimising the distortion observed at the receiver; and ii) an adaptive network service, which offers ?hard? guarantees to the base layer of multi-layer coded flows, and ?fairness? guarantees to the enhancement layers based on a bandwidth allocation technique called weighted fair sharing. We also discuss a number of types of media scaling object1 which are used to manage and control end-to-end QoS. These include QoS filters which manipulate multi-layer coded flows [2] as they progress through the communications system, QoS adaptors which scale flows at end-systems based on the flow's measured performance and user supplied QoS scaling policy, and QoS groups which provide baseline QoS for multicast flows.


In this section, we introduce a set of media scaling objects used to manipulate flows as they progress through the communications system. These comprise QoS adaptors, QoS filters and QoS groups:

Media Scaling Objects

QoS adaptors are used in conjunction with flow monitoring [8] function to ensure that the user and provider QoS specified in the service contract are actually maintained. In this role QoS adaptors are seen as quality of service arbiters between the user and network. QoS adaptors scale flows at the end-systems based on a user supplied QoS scaling policy (see QoS specification API section) and the measured performance of on-going flows.

QoS filters manipulate multi-layer coded flows [4] [5] [6] at the end-systems and as they

1 Media scaling is a general term, first proposed by [3], we use to refer to the dynamic manipulation of media flows as they pass through a communications channel.