P2P Applications - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 26

is the synchronization of data transmission and rendering. While on-demand
video streaming needs to handle only one dimension—time, 3-D streaming
requires handling simultaneously four dimensions—3-D space plus time.
2.7 Case Study: PPLive
PPLive [PPLive, 2009, Vu et al., 2010] is a highly popular P2P IPTV
application. It is heavily used, in particular, in China. It has been reported [Vu
et al., 2010] that the daily average user population is close to 1 million. Among
PPLive's available channels are more than 100 Chinese TV stations, about
300 live channels, and over 20,000 video-on-demand programs (i.e., moviews).
The PPLive client program is free but a closed source. As discussed earlier,
the PPLive system divides the video data (live or stored) into chunks. Each
channel (or movie) is shared by one distinct overlay. At the user interface
level, each user can join one overlay at a time (i.e., view one channel at a
time). However, at the system level, each peer machine can be participating in
multiple overlays (i.e., downloading/uploading contents for channels that are
not being viewed). Each PPLive client program opens a pair of TCP and UDP
ports for each channel in order to communicate with the PPLive infrastructure
servers (i.e., the channel management servers, the group management servers,
etc.) and other peers. Currently, PPLive supports a large variety of client
platforms including mobile gadgets such as Android phones, iPads, etc.
2.8 Summary
In this chapter, we first delineate the system components and performance
metrics. We then walk through brief surveys of P2P applications in the ar-
eas of distributed processing, file sharing, voice-over-IP services, and video
streaming. While there is a proliferation of P2P applications, there are still
much more exciting developments to come because many P2P applications are
still far from perfect (e.g., many server machines are still needed to support
their operations) and some important applications (e.g., 3-D streaming) are
still not implemented in a P2P manner.