TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

• multicasting: it takes the strengths of both of these previous approaches and try to
avoid their weaknesses. This technique is between unicast and broadcast
communication. It is similar to broadcasting but the data is sent only to limited
identified receivers. There are mainly two different approaches for achieving
multicast. Application such as IP video streaming requires sending the same data to
multiple receivers. It can be achieved by using multipoint communication in the
transport layer. This technique is called simulcast. In this context, sending the same
data, using separate point-to-point unicast connections, result in wasted
communication resources as shown in Figure 3-2 (a). IP multicast is an example of
scalable multicast providing data delivery for communication group as shown in
Figure 3-2 (b).
• Anycasting: the anycasting communication paradigm is designed to support server
replications to easily select and communicate with the best server, according to some
performance or policy criteria, in a group of content-equivalent servers.
Receiver
Receiver
Sender
Receiver
Sender
Receiver
Receiver
Receiver
(a) Unicast Packet Delivery
(b) Multicast Packet Delivery
Figure 3-2: Application layer multicast vs. IP multicast
3.1.2 Live vs. Pre-Encoded Video Applications
We can find video in two forms. Video captured by camera devices and encoded in real-time
for live communication, and pre-encoded and stored video used for later viewing. There are many
applications using real-time video encoding such as videoconferencing, videophone, interactive
games, and live broadcasting. However, many applications use pre-encoded and stored video
content. The content can be accessed locally or from remote system. A common example of local
storage is a DVD-Rom. Video streaming system is also an example of remote access.
The disadvantage of real-time encoding is the time constraint. Encoding video is a time
consuming. This can leads to choose fast encoding methods while achieving low compression
efficiency. The advantage of pre-encoded video is the ability to encode the video with an efficient
codec such as multi-pass codec. However, the main disadvantage of the pre-encoded video is the
lack of flexibility. For example, it is difficult for pre-encoded video to adapt to channel condition
and clients heterogeneity since it requires real-time transcoding.
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