Peer to Peer Streaming Protocol (ppsp)

Last modified: 2016-01-13


Transport Area Director

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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 protocols.

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 concepts.
  2. A "requirements" document that details the specific functional, operational and performance requirements of the two PPSP protocols.
  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.

Goals and Milestones

Done Submit PPSP tracker protocol to IESG as Proposed Standard
Done Submit PPSP peer protocol to IESG as Proposed Standard
Done Submit requirements document to IESG as Informational
Done Submit problem statement to IESG as Informational


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