METHOD FOR ADJUSTING MEDIA PARAMETERS IN AN IP COMMUNICATIONS SYSTEM (08-Jan-2009)

METHOD FOR ADJUSTING MEDIA PARAMETERS IN AN IP COMMUNICATIONS SYSTEM

By Matthew Keller, Donald Newberg

Motorola, Inc.

Government and Public Safety

ABSTRACT

This publication describes a means to adjust media parameters of active media streams in order to:

·        assure that resources are assigned to the highest priority calls

·        assure that media parameters match user’s requirements based on their use cases

·        adjust media parameters rather than shutting streams off completely

The solution described uses  weighted media parameter requirements for making media parameter adjustment tradeoffs for existing media streams.

PROBLEM

In real-time streaming communications such as audio and video, there are multiple parameters that can be changed that each contribute to the overall perceived quality of a media stream.  Some examples for video are the frame rate, the resolution, and the delay.  Example parameters for audio include the sample rate and the delay. 

In QoS control systems it is desirable to be able to adjust the resource usage by various streams in the network in order to assure that resources are assigned to the highest priority calls.  Most QoS control mechanisms utilize preemption (shutting off a media stream) in order to free up resources for other higher priority streams.  In some cases it is more desirable to adjust the media parameters described above in order to free up resources and allow the stream to continue rather than shutting it off completely.

SOLUTION

Individual media parameter settings contribute to the overall perceived quality of a media stream.  Adjusting these parameters can trade-off aspects of media quality versus resource usage.  As an example, adjustable media parameters for a video stream can include:

•     Target bit rate

•     Resolution

•     Frame rate

•     Quality

•     Delay

When a media stream is setup, the application can assign a set of required and desired media parameter values and a set of weightings to these various media parameters based on the requirements of the user at the time.  The weightings can be used to give the system flexibility when deciding which parameters to adjust (ex. the bit rate can be changed resulting in a poorer quality picture, but don’t change the frame rate because the user is just using the video to watch for presence of activity and that activity coul...