The Peer-to-Peer Streaming Protocol (PPSP) working group develops two
signaling and control protocols for a peer-to-peer (P2P) streaming
system for transmitting live and time-shifted media content with near
real-time delivery requirements.
Two kinds of nodes exist in the targeted P2P streaming system, i.e.,
"peers" and "trackers". Peers are nodes that are actively sending and
receiving streamed media content, and include both statically connected
hosts as well as mobile devices with connectivity and IP addresses that
change over time. The set of peers that are participating in a streaming
session will dynamically change over time. Trackers are well-known nodes
with stable connectivity that maintain meta information about the
streamed content and the dynamic peer set. Trackers can be organized in
centralized or distributed ways.
The PPSP WG designs a protocol for signaling and control between
trackers and peers (the PPSP "tracker protocol") and a signaling and
control protocol for communication among the peers (the PPSP "peer
protocol"). The two protocols enable peers to receive streaming data
within the time constraints required by specific content items. The
tracker protocol handles the initial and periodic exchange of meta
information between trackers and peers, such as peer lists and content
information. The peer protocol controls the advertising and exchange of
media data availability between the peers.
It is envisioned that the tracker protocol will be modeled as a
request/response protocol between peers and trackers, and will carry
information needed for the selection of peers suitable for real-time
streaming. The peer protocol is envisioned to be modeled as a
gossip-like protocol with periodic, pairwise exchanges of neighbor and
media chunk availability information. Both protocols will be carried
over TCP (or UDP, when delivery requirements cannot be met by TCP),
likely in combination with ICE for NAT traversal support. Perfect
privacy protection is a good feature to have but not a mandatory
requirement for the peer and tracker protocols. The WG will consider to
use existing protocols as design base for the tracker and peer
Developing mechanisms for searching trackers that contain a specific
media item is out of the scope of this WG. Additionally, the WG will
work under the assumption that trackers are logically centralized
entities (e.g., a single server or a server farm performing DNS-based
local balancing). However, as far as it is possible, the WG will not
make design decisions that could preclude the use of distributed
trackers in the future (e.g., DHT-based trackers).
A peer looking for a media chunk uses the tracker and peer protocols to
locate a remote peer (or peers) that can provide it with that media
chunk. Obtaining the media chunk from the remote peer will involve some
type of signaling exchange plus the actual media transfer. The first
task for this WG will be to decide which signaling and media transfer
protocols will be used. The WG will consider existing protocols and, if
needed, identify potential extensions to these protocols. The WG will
consider the interactions between these protocols and the peer protocol
(e.g., avoiding duplicate NAT traversal procedures). Examples of
signaling protocols to be considered are SIP, RTSP, and HTTP. Examples
of media transfer protocols to be considered are RTP and HTTP.
PPSP is not chartered to work on media transmission protocols, media
encoding techniques or other components of a P2P streaming system such
as playout, scheduling and control, etc.
The work items of the PPSP WG are:
(1) A "problem statement" document that gives an overview of the
proposed P2P streaming system, motivates the desire for
standardized protocols, defines the envisioned scope of those
standardized components and discusses common terminologies and
(2) A "requirements" document that details the specific functional,
operational and performance requirements of the two PPSP
(3) An "architectural survey" document that summarizes current P2P
streaming architectures, in particular tracker-based P2P
streaming systems, and highlights best current practices.
(4) A detailed specification of the PPSP peer protocol.
(5) A detailed specification of the PPSP tracker protocol.
(6) A "usage guide" that describes how the two PPSP protocols and
existing IETF protocols, such as P2PSIP or ALTO, can be combined
to create a deployable operational P2P streaming system. This
document may also discuss variants of such a system that, for
example, use layered media encoding and related media chunk
descriptions in the peer protocol for more robust streaming.
The work items of the PPSP WG interacts with the work performed in other
IETF WGs, including P2PSIP, SIPCORE, AVT, ALTO, LEDBAT and MMUSIC.
Whenever extensions or modification to the protocols developed in other
WGs are deemed necessary, PPSP shall communicate and discuss the
requirements for such extensions with the relevant WGs. PPSP is not
chartered to design and specify such changes.