Commercial Applications

Abstract

This chapter describes several distributed databases for storing structured data in the Internet. They are known under a common name of NoSQL, to separate from traditional relational database management systems (RDBMSes). NoSQL databases are often built on top of classical DHT functionality with goals of high performance put and get operations for data using a key. Databases such as Cassandra power popular services including Facebook and therefore have to scale up to billions of users.

Summary of Part IV

In this part we covered several architectures utilizing P2P concepts, as well as commercial systems using P2P algorithms. Secure lookup routing and privacy-preserving host rendezvous services are examples of advanced P2P architectures. Identifier-locator split appears as one of new fundamental trends of Future Internet, where P2P name resolution service will play a critical role. We also covered several popular content distribution and commercial key-value storage services that are of decentralized nature and use DHT algorithms internally.

Naturally, in a few chapters it is difficult to describe all versatile P2P applications in use in the Internet. For example, also such popular voice and video communication applications as Skype utilize P2P approach. Services such as Joost help users to enjoy streaming video and IP TV using P2P approach. A music listening service Spotify is also based on P2P. With ossification of Internet architecture on the IP layer, new overlay P2P applications play increasingly important role in implementing services such as peercasting for multicast delivery. Online gaming and virtual worlds is another example where players can benefit from lower latency of direct user-to-user communication.

Advanced P2P concepts such as cooperative web cashing and search, distributed scientific computation, online academic teaching all promise a bright future for P2P architectures, backup up by multi-million R & D investments in these area. In the presence of oppressive governments, citizens will have to increasingly rely on P2P technologies such as Tor to circumvent surveillance and censorship. For example, a web of trust for Pretty Good Privacy was established for P2P user email key certification and verification. In future, it is possible that centralized social networks such as Facebook are replaced by open-source, decentralized P2P services that give the users control over who and when can access their social data.