TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI

Chapter 3
3 Related Work
Nowadays, multimedia is becoming indispensable feature on networking environments. Audio
and video content become more and more popular on the Internet. Many systems are being
designed to carry this media such as video conferencing, video on demand, IP Telephony, Internet
TV, etc.
Multimedia networking is defined by a set of hardware and software infrastructure that
support multimedia stream on network so that users can communicate in multimedia. Using IP
based network as a communication infrastructure is not a trivial task. Many problems rise for
delivering multimedia data over IP.
First, multimedia applications require a higher bandwidth compared to a traditional textual
applications. A typical uncompressed video movie of 1 minute length, with a temporal and special
resolution of 25 images per second, and 320 x 240 pixels respectively requires 330 Mega Bytes and
about 46 Mbps(Mega bit per second) bandwidth for real-time transmission. As a consequence,
audio-visual compression is vital for transporting such media on networking environments. This
compression process leads to new problems that we expose later.
Second, most multimedia applications require a real-time traffic. Audio and video data must be
played-back continuously at the rate they are sampled. If the data does not arrive at the expected
time the play-back process will stop. Buffering some parts of this data on the receiver can reduce
this problem but the latency remains a challenge. For example, with IP telephony, one can tolerate
an end-to-end transmission delay of about 250 millisecond. If the latency exceeds the limit, the
voice will sound with a poor quality and will encounters echo. In addition to high bandwidth and
low latency, network congestion has more serious effects on real-time traffic. If the network is
congested, the transfer takes longer to complete and real-time data becomes obsolete and unused if
it doesn’t arrive at the expected time.
Third, the compression process will transform the traffic characteristic of audio video data
stream from CBR (constant Bit Rate) to VBR (Variable Bit Rate). For most multimedia
applications, the receiver has a limited buffer. Smoothing the data can reduce the burstiness
problem of multimedia traffic. Sending bursty traffic may overflow or underflow the applications
buffer. When data arrives too fast, the buffer will overflow and some data will be lost, resulting in
poor quality. When data arrives too slowly, the buffer will underflow and the application will starve.
Fourth, using a large scale networking environment such as the Internet with millions of users
using the network, a fairness problem in bandwidth share arises.
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