TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

If we look on PHB selection, it is obvious that for loss tolerant multimedia streams, like
compressed video or audio they will be transmitted with an AF PHB. Moreover, EF PHB will be
more expensive than AF PHB, because it guarantees additional constraints compared to AF PHB
group (minimal latency, minimal jitter, and minimal loss). Once this choice is made, it remains us to
identify the class of AF drop precedence that we use for IP packet. We recall that AF PHB group
defines currently 4 AF classes within each class 3 degrees of drop precedence according to the
importance of the packet.
Speech has a greater importance compared to the music or other background sounds in a
scene. Thus, we privilege foreground audio speech compared to other audio. Moreover, using high
quality voice coding tools, speech bit rates are between 2 and 24 Kbps. Signaling MPEG-4
information bit rates are in the same order of magnitude. Both data are essential for video quality
decoding and rendering. Consequently, i.e. low bit rate streams are given higher priority score to
raw video data (i.e. property 2).
MPEG-4 uses hierarchical coding for resolving system scalability and heterogeneity issues.
Different coding modes exist: “spatial scalability” allows the decoder to treat a subset of streams
produced by the coder to rebuild and display textures, images and objects video with a reduced
spatial resolution. For textures, a maximum of 11 levels of spatial scalability is supported, while for
the visual sequence, a maximum of 3 levels is proposed. Temporal scalability permits the decoder to
treat a subset of streams produced by the coder to rebuild and display a video with reduced
temporal resolution. A maximum of 3 levels is supported. With SNR Scalability (Signal to Noise
Ratio), the coder transmits the difference between the original image and the preceding. This allows
improving subjective quality of the final image to get maximum perceived quality (i.e. property 3).
Moreover, MPEG-4 introduces additional data control streams such as: the scene description and
media objects description, all these signaling streams are very sensitive and need to be preserved from
errors and loss during transmission (i.e. property 4). If EF PHB is not implemented, scene
description stream will be marked as an AF PHB with low drop precedence (i.e. AF31).
We also assume that audio and video are carried with two distinct AF classes. This enables
network nodes to better cope with congestion by given some routing privilege to audio compared
to video. However, a problem of media synchronization may appear which can be tackled by using
RTP Timestamps.
In order to generalize this algorithm we used our classification layer. The classification layer
can classify any MPEG-4 AVO in the scene and affect one of the given labels. The label affected
can be in our case the Diffserv PHB. Figure 5-2 gives a description of DVMA using the
classification layer.
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