Essay About Application Layer Multicast And Tree Structure

Combining Alm Codecs For Improved Video Streaming
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Combining ALM and customized codecs in
improving video streaming
Abstract—Streaming media and IPTV are two
emerging technologies that promise to bring high
quality video signals to the end user. IPTV is likely
to use application layer multicast to distribute the
video to different users interested in the same content.
Though much work has been done on application layer
multicast and how the receivers organize themselves in
a tree structure, not much prior work has been done on
the interaction between video codecs and application
layer multicast trees.
In this paper we are going to study the interaction
of videocodecs with application layer multicast trees.
First, we study the effect of the codec parameters on
the quality of the video signal that the end user experiences.
Second, based on the result of the comparision,
we study how reorganization of the tree structure can
improve the end user experience. To evaluate end user
experience we use the PSNR metric.
I. INTRODUCTION
Video is a high bandwidth signal which is susceptible
to delay and packet loss. Different methods for
distributing video while accomendating these challenges
have been proposed. These methods can be divided
into three classes; Native multicast, application
layer multicast and peer to peer based distribution.
The former relies on the physical routers of the
internet to support native multicasting, which, as of
today, has unfortunetly not been widely deployed.
Peer to peer based distribution has been deployed
in some commercial video streaming applications
using technologies like Bittorrent to distribute the
video1. In the scientific community the main focus
for distributing video have been on application layer
multicast.
Though much work has been done on application
layer multicast and how the receivers organize
themselves in different topologies, not much prior
work has been done on the interaction between video
codecs, user experience and how these topologies are
created.
The focus of this paper is on how to construct
data distribution trees with properties that are well
suited for video distribution.We have chosen to focus
on the MPEG-4 video codec for encoding the test
videos. The reason for choosing MPEG-4 is that it
is widely deployed and used in the real world, which
gives us different well documented methods for comparing
video qualities. More specificly we are going
to use the PSNR2 as comparison metric between both
video streams and between tree topologies.
Data distribution trees can experience error propagation
if proper messures are not taken. That is, as
the video content is distributed down the layers of
the tree, there is a potential for propagation of errors
caused by missing packets. This may lead to some
nodes in the tree not receiving a proper video signal.
In section ?? we manipulate different parameters
of the MPEG-4 video codec to see which are best
suited for internet-like video distribution. We will
also look at decoding and encoding of the received
video content in different resolutions and with different
bit-rates before forwarding the video signal
to the lower layer nodes of the tree that have less
bandwidth capacity. In section ?? we use this result
to test the quality of different distribution trees, using
the PSNR at each end host to compare the trees. We
are constructing NICE trees having different sized
clusters and different metrics for joining hosts.
II. BACKGROUND
A. Application layer multicasting
As mentioned in section I we are going to focus on
application layer multicasting as means for distributing
the video stream. Application layer multicasting
differes from native or network layer multicasting in
where the responsibility for duplicating the stream
lies. In application layer multicasting it is the end
host, which has the responsibility, which results in