Information Technology Reference
In-Depth Information
1.1 Introduction
For more than a decade, content providers have been trying to deliver
multimedia content to end users via the Internet. Before the introduction of
streaming technology, users needed to first download complete multimedia
content from the Internet down to their own storage before being able to play
back the content. Owing to the development of streaming technology, users
can playback content while downloading.
In an earlier age, multimedia content was only delivered via client/server
architecture. One of the reasons is that at that time the computing power of
a regular PC was insufficient to be a server. A server needs to serve requests
from many users and requires much computing power. Most end users could
not afford to buy computers with such server capabilities. As users' demand
for multimedia content grew and the power of their machines increased,
Internet Service Providers (ISP) and Internet Content Providers (ICP) figured
that there will always be scalability and cost problems from only deploying
client/server architectures. Subsequently, Peer-to-Peer (P2P) technologies
started to receive the spotlight.
The idea of P2P networks is in contrast to client/server architectures. In
a client/server architecture, dedicated servers are deployed to serve cli-
ents. However, as common PCs have increasingly more computing power,
a lot more processing load can be distributed to the client side. Therefore,
the roles of clients and servers have changed. In P2P networks, there are
not clear roles for servers and clients; instead, peers share duties with
both. At times, peers act as servers, and at times, as clients. By using
P2P technologies, the load and cost of the servers are distributed to and
shared by peers. Especially after the impact of Skype and BitTorrent on
telephony and file sharing, ISPs and ICPs are more and more interested in
P2P technologies.
1.1.1 Peer-to-Peer Streaming Systems
P2P streaming systems have been recently garnering more and more atten-
tion, because most people believe that IPTV is the next killer application and
that P2P technologies will be the key to solve the scalability and cost prob-
lem. Basically, there are two ways of applying P2P technologies to reduce the
cost and load on the server side. First, the media content can be distributed
into peer networks, rather than being stored in centralized repositories. In
such cases, peers are used as shared storage and requests for the content are
directed to the peers that keep the content. Second, the media content can be
relayed by peers instead of servers.
Typical modules within P2P streaming systems are shown in Figure 1.1. The
content lookup substrate
is in charge of content lookup or content discovery.
The
streaming control module
is in charge of peer management and multicast
