TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

4.4 Conclusion
We proposed in this chapter, an extension to the MPEG-4 System architecture with a new
“Media QoS Classification Layer” to provide automatic and accurate mapping between the MPEG-
4 Application-Level QoS metrics and the underlying transport and network QoS mechanisms such
as IP Diffserv. This “Media QoS Classification Layer” makes use of a neural network classification
model to group audiovisual objects of a scene with same QoS requirement to create elementary
video streams that are subsequently mapped to IP Diffserv PHB (Per Hop Behaviors). These
MPEG-4 Audio Visual Objects (AVOs) are classified based on Application-level QoS criteria and /
or AVOs semantic descriptors according to MPEG-7 framework. Thus, MPEG-4 AVOs requiring
same QoS from the network are automatically classified and multiplexed within one of the IP
Diffserv PHB. Object data-packets within the same class are then transmitted over the selected
transport layer with the corresponding bearer capability and priority score. The performance
evaluation shows better protection of relevant video objects of a scene during transmission and
network congestion.
There are a number of RTP packetization schemes for MPEG-4 data. It is clear that many
packetization schemes can be implemented together in one terminal. Each packetization scheme is
basically adapted to a particular media stream. Thus, we proposed, a new RTP payload scheme for
MPEG-4 video and audio that addresses multiplexing and avoids packet error propagation. The
MPEG-4 streams are better recovered against errors when using this payload. The amount of
recovered data is related to audio-visual objects priority score in the MPEG-4 scene. The more the
object is important, the more the recovered data is valuable and better. Our scheme is beneficial for
transmitting MPEG-4 content over Internet.
To enhance the transport mechanism, we have proposed an adaptation mechanism for
MPEG-4 video streams that uses a TCP-Friendly Rate Control. Our mechanism adds and drops
MPEG-4 Audio-Visual Objects to perform rate adaptation and congestion control. We have
evaluated the proposed mechanism through simulations using ns2. The MPEG-4 server
implemented in ns2 uses the TFRC module as an equation-based congestion control mechanism.
We coupled end-to-end congestion control with a Diffserv network that guarantees objects
prioritization within the network. The simulation results show that important multimedia entities
are maintained by the router in case of network congestion. Combining these mechanisms into a
coherent architecture demonstrates clearly the gains obtained.
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