A new kind of IPTV, different from the infrastructure-based scheme introduced previously, is
P2P IPTV, in which each IPTV user is potentially a server, multicasting received content to
other IPTV users [8]. In a P2P IPTV system,
users serve as peers and participate in video data
sharing. A popular P2P IPTV system such as
PPLive supports 100,000 users simultaneously
with proprietary signaling and video delivery
protocols [8]. PPLive has more than 400 channels with an average channel data rate of 325
kb/s. PPLive does not own video content but
limited information about its video content distribution mechanism, and is mostly fed from TV
channels in Mandarin, encoded with windows
media video (WMV) or real video (RMVB) [8].
A user must download and install the PPLive
software to use PPLive P2P IPTV. When the
PPLive software is running, the user becomes a
PPLive peer node, sending out a query message
to a PPLive channel server for an updated channel list. When the user selects one channel, the
software requests an online peer list (including
IP addresses and port numbers) for this channel
and sends probes to peers to find active peers
that may provide more peers. The software
downloads video chunks from peers, streams
them into a local media player using two buffers
(to smooth video variation and to efficiently distribute video content among peers), uploads the
cached video chunks to other peers, and launches a media player when the streaming file length
reaches a predefined threshold.
TECHNICAL CHALLENGES
In this section, we first describe the QoS guarantee and traffic management for IPTV services.
Since admission control mechanisms are essential for IPTV services, we then present multicast
admission control, admission controls for Ethernet, congestion control, WLAN (wireless IPTV),
and DSL. Finally, we briefly mention security
and standardization aspects, as well as communications among admission control schemes.