Editor's Note: While it may have gotten a bad wrap from an intellectual-property point of view, peer-to-peer video is a legitimate business with many commercial applications. This feature by Jonah Probell, an expert in the technology and business of digital video, semiconductors and consumer electronics, outlines many of those business models, while also pointing to some technology pain points that may present opportunities for some innovative engineering. Enjoy!
Peer-to-peer (P2P) file sharing systems allow users to download files from each other without a centralized server. BitTorrent added the ability to download different portions of files from different peers simultaneously, enabling a user to download entire files much faster than the connection speed with any single peer. After downloading, P2P software shares its files with others. All popular and many niche books, music, television shows, movies, and software are available as torrents and they are accessed worldwide. However, because of their size, movies and television shows represent a large majority of BitTorrent traffic. Though much P2P file-sharing traffic is of misappropriated copyrighted intellectual property (IP), the technology is nonetheless used widely for legitimate commercial purposes.
P2P sharing offers certain advantages to video and television content producers and distributors. To run servers with sufficient storage and bandwidth capacity to serve mass market video is expensive, prohibitively so for smaller players when the video is at high quality and high definition. With P2P sharing users might download parts of their video from distant reaches of the Internet from which transfer speed will be slow. However, most portions of the video will be downloaded from sources that are topologically closer and faster. In this way, P2P sharing naturally distributes network traffic in proportion to bandwidth availability and keeps more communication local. This is ideal in a world where bandwidth costs money but storage is essentially free.
Fig. 1: P2P naturally distributes network traffic in proportion to bandwidth availability and keeps more communication local.
As a video distribution method, P2P presents some new challenges. Downloads from multiple sources simultaneously requires that portions of video files be downloaded non-consecutively. This means that the video can not be played until the full file, or at least a significant portion, is downloaded. That could frustrate an eager viewer. While popular movies and TV shows can be downloaded over broadband in minutes, sparsely shared esoteric videos might take days or weeks.
A future enhancement to alleviate this problem might be P2P software that is content aware. When a TV show or movie is downloaded, ten or 100 similar shows begin downloading in the background, giving a good probability of ensuring that the viewer’s next movie choice is immediately available. The ability to anticipate the viewer’s next request is limited only by available storage capacity. Today’s hard disks can hold hundreds of HD movies or thousands of television shows.
P2P sharing, in the case of live video, is a particular challenge. Latency variation between peers causes lag equal to that of the most delayed source. The TCP/IP protocol guarantees no maximum latency. These limitations can be overcome. As VoIP telephony shows, latency is sufficiently reasonable in practice to allow a real-time conversation. For live television passed from peer to peer, it is possible to broadcast without much more delay than the several seconds that is introduced through existing cable and satellite distribution networks. The European MyP2P service makes sports matches available, live, over a P2P network.
For viewers whose Internet service provider (ISP) charges per bit, P2P sharing is costly because as much video data as is received is again sent. One way to address the double traffic cost to subscribers would be for ISPs to cover their bandwidth costs not through a per-bit charge but on a bandwidth-limiting basis. Different bandwidth levels can be sold at different prices. This model is particularly appealing to ISPs that are also content providers, such as Comcast, which now offers bandwidth-varying pricing levels.