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fliptop [soylentnews.org] writes:

Over at ACM.org, Carlos Baquero wants to know, what happened to peer-to-peer as a technological concept [acm.org]?

Peer-to-Peer (P2P) systems became famous at the turn of the millennium, mostly due to their support for direct file sharing among users. In the 80s, the music industry had already evolved from selling analogue vinyl records to digital compact disks, but only with the introduction of lossy data-compression techniques, such as the MP3 coding format, it became feasible to upload/download music files among users' personal computers. Still, content had to be catalogued and found, and P2P systems such as Napster emerged to provide that functionality.

Some of the early systems, such as Napster and SETI@Home [berkeley.edu], exhibited a mix of P2P and classic client-server architecture. Gnutella and Freenet [freenetproject.org], the second generation of systems, provided a much larger degree of decentralization. The emergence of P2P greatly impacted the business models of the music, and later film, industries. With time, these industries evolved to offer flat rates and subscription services decreasing the incentives for, music or video, file copying and sharing.

[...] Looking at Google trends [google.com], we see that the concept almost faded from our lexicon. Nevertheless, the technology is still used; it evolved and became more specialized. A good portion of the fabric beneath modern data centers (web 2.0) and blockchain technology (web 3.0) evolved from early P2P research.

The author chronicles the rise of systems like Gnutella and Freenet, commenting on their benefits and their eventual downfall into obscurity due to routing algorithm problems that had trouble consistently delivering content from local sources, which impacted lookup times. He then continues:

The next generation of systems, in the early 2000s, solved this problem by introducing topologies that exhibited locality. The closer one came to the target, the more paths one had to the target and the routing algorithms could pinpoint the next hop with local information and a distance metric. Functionally, these systems provided the users with a Distributed Hash Table (DHT). These efficient content-addressable networks (Chord [acm.org], CAN, Pastry, Tapestry) allowed structuring N nodes in a topology that supported log(N) routing steps while only storing log(N) network contacts on each node.

[...] The paradigm shifted again in the late 2000s. In 2007, Amazon's Dynamo [acm.org] presented a pragmatic system design that built on prior research in DHTs and Eventual Consistency (leveraging filesystems research from the early 90s, Coda [ieee.org] and Ficus [ieee.org], that exhibited P2P characteristics before the term was fully established). In Dynamo the focus was high availability, and, unlike prior P2P systems, the nodes were placed under the same administrative control and inside the data centers. The number of nodes scaled down from millions to hundreds, albeit more powerful ones, allowing some simplifications on the DHTs. Availability and low response time were now the key concerns, they were good for business.

[...] The phrase "all successful systems attract parasites" is often cited in biology, and the same can be applied to P2P systems. Filesharing users terminated nodes once their ongoing downloads finished and did not further contribute to the system. Some nodes refused to forward queries from other nodes or lied about their uptimes to improve their position in the network.

Different strategies were tested to control free riders: enforcing download and upload quotas to avoid unbalanced downloads; partitioning files in blocks and sharing them in a random order, to prevent nodes from quitting when they were close to having the full file. These strategies tried to coerce users into contributing to the collective, but an important tool was still missing: a clear incentive system.

He concludes with some words about Blockchains, commenting, "We probably need to wait for another 20 years to study the legacy of blockchain systems and see which technological concepts turned out to have a lasting impact."

Original Submission