Is P2P dead?

There have been some significant setbacks for P2P in the past year or so.

1. Pirate Bay's founders are in jail in Sweden for abetting illegal file sharing on their website.
2. Joost, the much lauded P2PTV service, is no longer P2P but is instead a CDN-type streaming service.
3. Another P2P darling, Skype, seems to be adrift with Ebay wanting to get rid of it through a sale or a spinoff.
4. There is a sustained reduction in CDN costs that is making the P2P cost reduction less attractive.
5. Websites like You-tube won the video streaming battle against P2P video streaming long ago, now websites like Rapidshare are leaving P2P file sharing behind as well.
6. Mobile P2P (near-network P2P on mobile devices over Bluetooth etc.) just didn't happen. These devices are more client-serverish than wired devices because upload bandwidth needed for P2P is too pricey.
   

So the key question is whether P2P is dead.

In my opinion, the answer is No. Here are some reasons

1. P2P lacks a business model but has proven to be a remarkably resilient and cost-effective technology. The problem is getting legal content on to P2P networks. Content companies are not going to let users take control of content delivery.
2. But if one is to look at where the biggest growth in broadband usage is going to be, one looks toward China and India. The legal protection for content is significantly weaker in these countries. Moreover, there is a large amount of reasonably priced content (e.g. regional and Bollywood content in India) that will perfectly ride P2P networks.
3. P2P has proven itself for voip (Skype has 400m users). Skype is the established voip leader and it will remain that way for a long time.
4. CDNs do not scale with video quality. That is why Youtube won't do HD - they'll go broke paying for CDN (server) bandwidth. P2P on the other hand can scale up to the extent the access networks allow.

What we may see is an amalgamation of CDNs and P2P technologies. For example, using CDNs for paid content and P2P for promoting the paid content (for free). Cache every recent movie's first 10 minutes on a user's computer using P2P, and then stream the content the user selects via a CDN. Although content pricing can recover CDN distribution costs, the monetary transaction only happens after a user selects to watch. Prior marketing can be P2P.

On dear peer-to-peer

I will be presenting a paper* at the IEEE IwQoS early next month containing the analysis of a large scale peer-to-peer live video multicast streaming session on the Internet. Think of the P2P video multicast system as the Bittorrent for video streaming (instead of file-sharing). The system was sending a video stream of a baseball match to 10s of thousands of viewers on the Internet using P2P technology.

The presentation and paper are available online. Here are two results from the paper that in my opinion warrant particular notice.

Figure 1 shows the aggregate download and upload bandwidth consumed by the P2P system. Note the scale on the Y axis - Gbps! I am wondering, this is only 1 video stream. What happens to the Internet when 1000s of such streams become available online? Were networks designed for such usage?

An interesting artifact in this figure is that the aggregate download rate of all peers exceeds the aggregate upload rate of all peers. The difference was made up through "bandwidth injecting super-servers" of the content provider. Still, it is absolutely remarkable that the amount of additional bandwidth required is almost constant even as the number of peers increase (Figure 2).

Figure 1: Total bandwidth. Click to enlarge.

In Figure 2, you can see the number of concurrent peers in the P2P system over the time-period of the streamed game (hour 4 to hour 8). Look at the rate of change of peers in (peers joining, peers leaving) the P2P system. Keeping in mind that most of the bandwidth comes from these very peers, it is remarkable that this highly dynamic pool of peers is able to sustain the P2P system. Things get very exciting at the end of the baseball game (Hour 8): Everybody wants to leave. Now that is a big challenge for any P2P system.

Figure 2: Peer Dynamics. Click to Enlarge.

*Joint work with Jatinder Pal Singh (T-Labs) and Aditya Mavlankar, Pierpaolo Baccichet, and Bernd Girod (Stanford University)