TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

multitude of streams. It can switch from one stream to another very easy. Here, the client is a
simple single layer decoder.
3.2.1.6 Real-Time Single Stage Encoding
Real-time coding means to encode the video stream right before the transmission process. The
client connects to the servers and specifies the encoding parameters. This result in a high
complexity at the server and rate adaptation in the network is not possible.
3.2.1.7 Transcoding
One of the methods to modify the media bit stream is the transcoding. The transcoding aims
to transform of one media format to another media format. For example transcoding from MPEG-
2 format to H.264 format. This allows bit rate reduction, frame rate reduction, and temporal and
special downsampling [64]. The transcoding is applied by decoding the video to raw format
(uncompressed video) and then re-encode the video to the target format. There are mainly two
drawbacks when using this approach. First, the quality of the result format is generally lower than
the original format. Second, media transcoding generally requires extensive computation and large
storage spaces, which makes this approach very expensive. The advantage in transcoding is that it
allows media adaptation both at the server and in the network. However, it can be efficient using a
dedicated media gateway [65] [66].
3.2.1.8 Streaming over TCP
The Transmission Control Protocol (TCP) is the most widely used protocol in the current IP
networks. It can be used for packet video streaming. However, it has been noted that TCP is not
adapted for real time traffic for theses reasons. First, TCP guarantees delivery via retransmissions,
but because of the retransmissions its delay is unbounded and not suitable for real-time traffic.
Second, TCP provides flow control and congestion control that make packet video streaming
unpractical. Finally, TCP requires a back channel for packets acknowledgements. All theses reasons,
led us to choose UDP for media streaming applications
3.2.1.9 Streaming over UDP
The User Datagram Protocol (UDP) is simply a user interface to IP. It is therefore unreliable
and connectionless. UDP does not guarantee delivery of packet video applications, but for those
delivered packets their delay is more predictable. UDP does not provide any flow control or
congestion control. If the video application needs theses techniques, it should implement its own
one like TCP-Friendly congestion control.
3.2.1.10 Streaming over Rate Controlled UDP: TCP-Friendly
In order to avoid network congestion, in which the transmitted traffic exceeds the designed
limit, it is necessary to implement functions that perform congestion control such as rate control.
The congestion is a phenomenon that has symptoms on packet losses, transmission delay, and
delay jitter. As we have discussed in Section 3.1.6, such symptoms represent significant challenges
for media streaming systems. The congestion control can be performed at many levels, by the
network (e.g. edge router policy, source quench, DEC-bit, RED) or by the end-hosts. In
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