Transmission of Multimedia Data Over Lossy Networks (Thesis)

TitleTransmission of Multimedia Data Over Lossy Networks (Thesis)
Publication TypeTechnical Report
Year of Publication1996
AuthorsIsenburg, M.
Other Numbers1057

This thesis addressed quality orientated improvements for multimedia connections over packet switched and lossy networks. The problems involved in establishing real-time communication over networks such as the Internet have been investigated and the definite network characteristics that cause these problems have been clearly marked out. The quality of audio communication essentially depends on the number of packets lost and on the variation in packet arrival times. Efficient mechanism to minimize the impact of delay jitter have already been proposed in literature, whereas dealing with packet loss remains an active research area. The measurements about the packet loss rate for audio streams over the Internet showed that the number of consecutive lost packet usually is small. This rigorously proved that open loop mechanisms that add redundancy on the sending side are suited to cope with the loss of information. We presented two transmission concepts that overcome these network limitations using forward error correction schemes. The 'piggyback protected transmission' was introduced - a resilient scheme that has already showed its usefulness in improving full duplex audio communication. The 'priority encoded transmission', which had never been applied to audio streams before, was examined for its capability in protecting the transmission of audio data over lossy networks. We showed that for time critical point-to-point communication the comparatively simple 'pick a-back protected transmission' is a better choice than 'priority encoded transmission. In a broadcast scenario on the other hand where large delays are acceptable the PET approach will yield in better results because of its robustness against long packet loss periods and its capacity to transmit to receivers with widely different network bandwidth. In order to apply the 'priority encoded transmission' towards audio streams, it was necessary to develop a layered audio encoding scheme. A major part of thesis is concerned with discussing and analyzing different transformations of an audio signal in respect to time and frequency. Finally we are able to present an audio codec that we have developed from scratch and that yields into a compressed and layered representation of the audio signal. In contrast to common standard codecs this encoding scheme is well suited to work together with PET. Furthermore we demonstrated how our new encoding scheme improves the performance of the 'piggyback protected transmission'. Through diminishing the redundancy in the redundant information a better audio quality can be achieved in case of isolated packet losses.

Bibliographic Notes

ICSI Technical Report TR-96-048

Abbreviated Authors

M. Isenburg

ICSI Publication Type

Technical Report