Peer-to-peer caching (P2P caching) is a computer network traffic management technology used by Internet Service Providers (ISPs) to accelerate content delivered over peer-to-peer (P2P) networks while reducing related bandwidth costs.

P2P caching is similar in principle to the content caching long used by ISPs to accelerate Web (HTTP) content. P2P caching temporarily stores popular content that is flowing into an ISP?s network. If the content requested by a subscriber is available from a cache, the cache satisfies the request from its temporary storage, eliminating data transfer through expensive transit links and reducing network congestion.

P2P content responds well to caching because it has high reuse patterns. An estimated 75% of P2P content is requested multiple times.

Some P2P caching devices can also accelerate HTTP video streaming traffic from YouTube, Google, AOL Video, MySpace and other Web video-sharing sites.

How P2P caching works

P2P caching involves creating a cache ? or temporary storage space ? for P2P data, using specialized communications hardware, disk storage and associated software. This cache is placed in the ISP?s network, either co-located with the Internet transit links or placed at key aggregation points or at each cable head-end.

Once a P2P cache is established, the network will transparently redirect P2P traffic to the cache, which either serves the file directly or passes the request on to a remote P2P user and simultaneously caches that data for the next user. It is estimated that 4 of 5 files requested via P2P can be served by the cache. This ratio is significantly higher than HTTP/Web caching.

P2P caching typically works with a network traffic-mitigation technology called deep packet inspection (DPI). DPI technology is used by service providers to understand what traffic is running across their networks and to separate it and treat it for the most efficient delivery. DPI products identify and pass P2P packets to the P2P caching system so it can cache the traffic and accelerate it.

Peerapp Ltd. holds the first patent ^[1] for P2P caching technology, which was filed in 2000.

P2P caching as a tool to manage P2P

It is estimated that peer-to-peer traffic accounts for upwards of 60% of all Internet traffic. However, P2P traffic is expected to quadruple between 2006 and 2011, reaching 3 exabytes per month ? or the equivalent of 750 million DVDs each month. ^[2]

Increasing P2P traffic is creating problems for ISPs. Their networks are being flooded with P2P traffic but they don?t get any revenue from this additional traffic because they sell flat-rate packages of bandwidth. To prevent P2P traffic from degrading service for all subscribers, ISPs typically must invest in additional bandwidth and equipment. Unfortunately, increasing bandwidth often does not solve the problem, because P2P applications inherently tend to consume as much bandwidth as available.

P2P caching enables ISPs to better accommodate P2P on their networks by effectively managing the peaks and valleys associated with P2P usage. P2P caching frees up bandwidth from the network, reducing the need for ISPs to purchase more bandwidth to meet increasing demand and reducing the need to limit P2P usage through byte caps, policies or traffic shaping. Therefore, P2P caching provides an improved experience for all subscribers ? P2P users whose file sharing is improved through using the cache, and non-P2P users who experience better performance from networks un-congested from P2P traffic.

The initial adopters of P2P caching have been ISPs in Asia, the Pacific Rim, Latin America, the Caribbean and the Middle East, whose subscribers are heavy users of P2P networks and where providing the additional bandwidth to handle P2P data is very costly due to the expense of international transit links.

P2P caching is expected to become an increasingly essential technology for ISPs and MSOs (multiple system operators) worldwide, particularly with the growing popularity of P2P content among broadband subscribers and the adoption of P2P as a content-distribution strategy by mainstream content providers such as the British Broadcasting Company.

See also

• Caching
• Deep packet inspection
• Traffic-shaping

Sources

1. ↑ U.S Patent Number 7,203,741 B2 http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7,203,741.PN.&OS=PN/7,203,741&RS=PN/7,203,741/
2. ↑ http://www.cisco.com/application/pdf/en/us/guest/netsol/ns537/c654/cdccont_0900aecd806a81a7.pdf,The Exabyte Era, Cisco Systems, 2007