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	Another example of a federated CDN arrived in the form of infrastructure as a service provider (IaaS) OnApp's CDNify in 2013, which was touted as being able to "tap into the spare capacity of service providers around the world, with more than 150 points of presence (PoPs) theoretically being at their disposal."<ref name="MeyerCD1">{{cite web \|url=http://gigaom.com/2013/04/22/cdnify-launches-based-on-onapps-federated-cdn/ \|title=CDNify launches, based on OnApp’s federated CDN \|author=Meyer, David \|publisher=GigaOM \|date=22 April 2013 \|accessdate=22 August 2014}}</ref> However, a year later, the product was revamped, moving away from the federated CDN model due to limitations in what it could achieve.<ref name="MeyerCD2">{{cite web \|url=http://gigaom.com/2014/04/30/onapps-federated-cdn-model-has-limitations-says-departing-customer-cdnify/ \|title=OnApp’s federated CDN model has limitations, says departing customer CDNify \|author=Meyer, David \|publisher=GigaOM \|date=30 April 2014 \|accessdate=22 August 2014}}</ref>		Another example of a federated CDN arrived in the form of infrastructure as a service provider (IaaS) OnApp's CDNify in 2013, which was touted as being able to "tap into the spare capacity of service providers around the world, with more than 150 points of presence (PoPs) theoretically being at their disposal."<ref name="MeyerCD1">{{cite web \|url=http://gigaom.com/2013/04/22/cdnify-launches-based-on-onapps-federated-cdn/ \|title=CDNify launches, based on OnApp’s federated CDN \|author=Meyer, David \|publisher=GigaOM \|date=22 April 2013 \|accessdate=22 August 2014}}</ref> However, a year later, the product was revamped, moving away from the federated CDN model due to limitations in what it could achieve.<ref name="MeyerCD2">{{cite web \|url=http://gigaom.com/2014/04/30/onapps-federated-cdn-model-has-limitations-says-departing-customer-cdnify/ \|title=OnApp’s federated CDN model has limitations, says departing customer CDNify \|author=Meyer, David \|publisher=GigaOM \|date=30 April 2014 \|accessdate=22 August 2014}}</ref>

			==Notes==

			This article reuses numerous content elements from [http://en.wikipedia.org/wiki/Content_delivery_network the Wikipedia article].

	==References==		==References==

Shawndouglas: Created as needed.

2014-08-22T23:07:43Z

Created as needed.

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[[File:NCDN - CDN.png|thumb|500px|right|(Left) Single server distribution <br/>(Right) CDN scheme of distribution]]
A '''content delivery network''' or '''content distribution network''' ('''CDN''') is a large distributed system of servers deployed in multiple data centers or "nodes" across the Internet. The goal of a CDN is to serve content to end-users with the intended benefit of reducing bandwidth costs, improving page load times, and/or increasing global availability of content. This is done by hosting the content on several servers, and when a user makes a request to CDN-hosted content, the domain name server (DNS) will resolve to an optimized server based on location, availability, cost, and other metrics.<ref name="AkamaiCollab">{{cite journal |url=http://www.akamai.com/dl/technical_publications/Akamai_Tech_Pub_CDN-ISP_Collaboration.pdf |format=PDF |journal=ACM SIGCOMM Computer Communication Review |title=Pushing CDN-ISP Collaboration to the Limit |author=Frank, Benjamin; Poese, Ingmar; Lin, Yin; Smaragdakis, Georgios; Feldmann, Anja; Maggs, Bruce; Rake, Jannis; Uhlig, Steve; Weber, Rick |volume=43 |issue=3 |date=July 2013 |pages=35–44 |doi=10.1145/2500098.2500103 |accessdate=22 August 2014}}</ref>

Content providers such as media companies and e-commerce vendors pay CDN operators to deliver their content to their audience of end-users. In turn, a CDN pays Internet service providers (ISPs), carriers, and network operators for hosting its servers in their data centers. Besides better performance and availability, CDNs also offload the traffic served directly from the content provider's origin infrastructure, resulting in possible cost savings for the content provider.<ref name="AkamaiOver">{{cite journal |url=http://www.akamai.com/dl/technical_publications/network_overview_osr.pdf |format=PDF |journal=ACM SIGOPS Operating Systems Review |title=The Akamai Network: A Platform for High-Performance Internet Applications |author=Nygren, Erik; Sitaraman, Ramesh K.; Sun, Jennifer |volume=44 |issue=3 |date=July 2010 |pages=2–19 |doi=10.1145/1842733.1842736 |accessdate=22 August 2014}}</ref> In addition, CDNs provide the content provider a degree of protection from denial-of-service (DoS) attacks by using their large distributed server infrastructure to absorb the traffic.

An increasing number of ISPs have built their own CDNs to improve on-net content delivery, reduce demand on their own infrastructure, and generate revenues from content customers.<ref name="KamiyamaCDN">{{cite journal |url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5072157 |journal=INFOCOM Workshops 2009, IEEE |title=ISP-Operated CDN |author=Kamiyama, N.; Mori, T.; Kawahara, R.; Harada, S.; Hasegawa, H |pages=1–6 |date=19–25 April 2009 |doi=10.1109/INFCOMW.2009.5072157 |accessdate=22 August 2014}}</ref><ref name="AkamaiCollab" /> Additionally, some companies such as Microsoft, Amazon, and Netflix have built their own CDNs to tie in with their own products.<ref name="MicrosoftAzure">{{cite web |url=http://blogs.msdn.com/b/windowsazure/archive/2010/08/09/20-nodes-available-globally-for-the-windows-azure-cdn.aspx |archiveurl=https://web.archive.org/web/20120126040442/http://blogs.msdn.com/b/windowsazure/archive/2010/08/09/20-nodes-available-globally-for-the-windows-azure-cdn.aspx |title=UPDATED: 24 Nodes Available Globally for the Windows Azure CDN Including New Node in Doha, QT |author=Windows Azure Team |work=Windows Azure Team Blog |publisher=Microsoft Corporation |date=24 February 2011 |archivedate=26 January 2012 |accessdate=22 August 2014}}</ref><ref name="AmazonCF">{{cite web |url=http://www.zdnet.com/blog/btl/amazon-launches-cloudfront-content-delivery-network-margins-go-kaboom/10904 |title=Amazon launches CloudFront; Content delivery network margins go kaboom |author=Dignan, Larry |work=ZDNet |publisher=CBS Interactive |date=18 November 2008 |accessdate=22 August 2014}}</ref><ref name="NetflixOC">{{cite web |url=http://techcrunch.com/2012/06/04/netflix-open-connect/ |title=Netflix Rolls Out Its Own CDN: Open Connect |author=Lawler, Ryan |work=TechCrunch |publisher=AOL, Inc |date=04 June 2012 |accessdate=22 August 2014}}</ref>

CDNs serve a large fraction of the Internet content today, including web objects (text, graphics, and scripts), downloadable objects (media files, software, documents), applications (e-commerce and portals), streaming media, and social networks. IT company Cisco Systems reported in June 2014 that 36 percent of global Internet traffic was delivered via CDNs in 2013, with that number expected to reach 55 percent by 2018.<ref name="CiscoCDN">{{cite web |url=http://www.cisco.com/c/en/us/solutions/collateral/service-provider/ip-ngn-ip-next-generation-network/white_paper_c11-481360.html |title=Cisco Visual Networking Index: Forecast and Methodology, 2013–2018 |publisher=Cisco Systems, Inc |date=10 June 2014 |accessdate=22 August 2014}}</ref>

==Technology==
The Internet was designed according to the end-to-end principle.<ref name="SaltzerEnd">{{cite journal |url=http://web.mit.edu/Saltzer/www/publications/endtoend/endtoend.pdf |format=PDF |journal=ACM Transactions on Communications |title=End-to-End Arguments in System Design |author=Saltzer, J.H.; Reed, D.P.; Clark, D.D |volume=2 |issue=4 |date=November 1984 |pages=277–288 |doi=10.1145/357401.357402}}</ref> This principle keeps the core network relatively simple and moves the intelligence as much as possible to the network end-points: the hosts and clients. As a result, the core network is specialized, simplified, and optimized to only forward data packets. However, CDNs alter the transport network by distributing on it a variety of intelligent applications employing techniques designed to optimize content delivery. The resulting tightly integrated overlay uses web caching, server-load balancing, request routing, and content services to optimize the data stream.<ref name="Hofmann 2005">{{cite book |url=http://books.google.com/books?id=JSJkAZmwIFIC&pg=PA19 |title=Content Networking: Architecture, Protocols, and Practice |author=Hofmann, Markus; Beaumont, Leland R |publisher=Morgan Kaufmann Publisher |year=2005 |isbn=9780080490779 |accessdate=22 August 2014}}</ref>

Requests for content are typically algorithmically directed to nodes that are optimal in some way. When optimizing for performance, locations that are best for serving content to the user may be chosen. This may be measured by choosing locations that offer the fewest hops, the least number of network seconds away from the requesting client, or the highest availability in terms of server performance (both current and historical), so as to optimize delivery across local networks.<ref name="AkamaiOver" /> When optimizing for cost, locations that are least expensive may be chosen instead. In an optimal scenario, these two goals tend to align, as servers that are close to the end-user at the edge of the network may have an advantage in performance or cost.<ref name="AkamaiCollab" />

Most CDN providers will provide their services over a varying, defined, set of point-of-presences (PoPs) or locations, depending on the geographic coverage desired, such as United States, Asia-Pacific, international, global, etc. These sets of PoPs can be called "edges" or "edge networks" as they would be the closest edge of CDN assets to the end user. Those edge networks can later grow outward from their origin(s) through further acquisitions (via purchase, peering, or exchange) of co-location facilities, bandwidth, and servers.

===Content service protocols===
Several protocol suites are designed to provide access to a wide variety of content services distributed throughout a content network. The Internet Content Adaptation Protocol (ICAP) was developed in the late 1990s to provide an open standard for connecting application servers.<ref name="ElsonICAP">{{cite web |url=http://tools.ietf.org/html/rfc3507 |title=Internet Content Adaptation Protocol (ICAP) |author=Elson, J.; Cerpa, A |publisher=The Internet Society |date=April 2003 |accessdate=22 August 2014}}</ref>A more recently defined and robust solution is provided by the Open Pluggable Edge Services (OPES) protocol.<ref name="BarbirOPES">{{cite web |url=http://www.ietf.org/rfc/rfc3835.txt |title=An Architecture for Open Pluggable Edge Services (OPES) |author=Barbir, A.; Penno, R.; Chen, R.; Hofmann, M.; Orman, H |publisher=The Internet Society |date=August 2004 |accessdate=22 August 2014}}</ref> This architecture defines OPES service applications that can reside on the OPES processor itself or be executed remotely on a callout server.

===edns-client-subnet EDNS0===
In August 2011, a global consortium of leading Internet service providers led by Google announced their official implementation of "edns-client-subnet," which is intended to accurately localize DNS resolution responses. The initiative involves a limited number of leading DNS and CDN service providers. The general idea involves the situation where a CDN relies on the IP address of the DNS resolver, which can lead to incorrectly geo-locating a client if the client is using Google anycast addresses for their DNS resolver. This creates latency problems. With the edns-client-subnet extension mechanism for DNS (EDNS0), the recursive DNS servers of CDNs can instead utilize the IP address of the requesting client subnet when resolving DNS requests. However, not all CDN providers allow anycast for HTTP and/or support edns-client-subnet.<ref name="CDNPlanEDNS">{{cite web |url=http://www.cdnplanet.com/blog/which-cdns-support-edns-client-subnet/ |title=Which CDNs support edns-client-subnet? |author=Kayan, Sajal |publisher=CDN Planet |date=17 October 2012 |accessdate=22 August 2014}}</ref><ref name="EDNSRFC">{{cite web |url=http://tools.ietf.org/id/draft-vandergaast-edns-client-subnet-02.txt |title=Client Subnet in DNS Requests - draft-vandergaast-edns-client-subnet-02 |author=Contavalli, C.; van der Gaast, W.; Leach, S.; Lewis, E |publisher=IETF |date=04 July 2013 |accessdate=22 August 2014}}</ref>

==CDN types==

===Peer-to-peer CDNs===
While most early CDNs served content using dedicated servers owned and operated by the CDN, some began to serve content via a hybrid model that uses peer-to-peer (P2P) technology.<ref name="MalikSwoosh">{{cite web |url=http://gigaom.com/video/akamai-goes-p2p-buys-red-swoosh-2 |title=Akamai goes P2P, buys Red Swoosh |author=Malik, Om |publisher=GigaOM |date=02 April 2007 |accessdate=22 August 2014}}</ref><ref name="RoettgersP2P">{{cite web |url=http://gigaom.com/2013/03/28/peercdn-p2p-cdn/ |title=PeerCDN uses WebRTC to build a browser-based P2P CDN |author=Roettgers, Janko |publisher=GigaOM |date=28 March 2013 |accessdate=22 August 2014}}</ref> In the hybrid peer-to-peer model, content is served using both dedicated servers and other peer-user-owned computers. Unlike client-server systems, the content serving capacity of a peer-to-peer-capable CDN can actually increase as more users begin to access the content.

===Telco CDNs===
The rapid growth of streaming video traffic<ref name="DeutscherVid">{{cite web |url=http://siliconangle.com/blog/2011/03/03/online-video-sees-tremendous-growth-spurs-some-major-updates/ |title=Online Video Sees Tremendous Growth, Spurs some Major Updates |author=Deutscher, Maria |work=Silicon Angle |date=03 March 2011 |accessdate=22 August 2014}}</ref> forces broadband providers to make large capital expenditures in order to meet this demand and to retain subscribers by delivering a sufficiently good quality of experience.<ref name="CNCAPEX">{{cite web |url=http://www.cellular-news.com/story/46986.php |title=Overall Telecom CAPEX to Rise in 2011 Due to Video, 3G, LTE Investments |publisher=Cellular News |date=15 December 2010 |accessdate=22 August 2014}}</ref>

To address this, some telecommunications service providers (TSPs) have launched their own content delivery networks as a means to lessen the demands on the network backbone and to reduce infrastructure investments. As of December 2013, many of these CDNs, however, tend to be used primarily for internal use.<ref name="CDNList">{{cite web |url=http://blog.streamingmedia.com/2013/12/heres-current-cdn-landscape-looks-like-list-vendors.html |title=Here’s What The Current CDN Landscape Looks Like, With List Of Vendors |work=StreamingMediaBlog |author=Rayburn, Dan |date=10 December 2013 |accessedate=22 August 2014}}</ref>

===Federated CDNs===
In May 2011, Cisco Systems senior director Chris Osika stated "the future of CDN models is a federated structure" and would likely run under a hybrid of bilateral agreements, bilateral hierarchical, and CDN exchange service models.<ref name="CastilloCisco">{{cite web |url=http://www.streamingmedia.com/Articles/Editorial/Featured-Articles/Cisco-Federated-CDN-is-the-Future-of-Content-Delivery-75388.aspx |title=Cisco: Federated CDN is the Future of Content Delivery |author=Castillo, Jose |publisher=StreamingMedia |date=10 May 2011 |accessdate=22 August 2014}}</ref> A month later, a group of TSPs had founded the Operator Carrier Exchange (OCX) to interconnect their CDN networks and compete more directly against large traditional CDNs like Akamai and Limelight Networks, which have extensive PoPs worldwide.<ref name="RayburnFedCDN">{{cite web |url=http://blog.streamingmedia.com/2011/06/telco-and-carriers-forming-new-federated-cdn-group-called-ocx-operator-carrier-exchange.html |title=Telcos And Carriers Forming New Federated CDN Group Called OCX (Operator Carrier Exchange) |work=StreamingMediaBlog |author=Rayburn, Dan |date=27 June 2011 |accessedate=22 August 2014}}</ref>

Another example of a federated CDN arrived in the form of infrastructure as a service provider (IaaS) OnApp's CDNify in 2013, which was touted as being able to "tap into the spare capacity of service providers around the world, with more than 150 points of presence (PoPs) theoretically being at their disposal."<ref name="MeyerCD1">{{cite web |url=http://gigaom.com/2013/04/22/cdnify-launches-based-on-onapps-federated-cdn/ |title=CDNify launches, based on OnApp’s federated CDN |author=Meyer, David |publisher=GigaOM |date=22 April 2013 |accessdate=22 August 2014}}</ref> However, a year later, the product was revamped, moving away from the federated CDN model due to limitations in what it could achieve.<ref name="MeyerCD2">{{cite web |url=http://gigaom.com/2014/04/30/onapps-federated-cdn-model-has-limitations-says-departing-customer-cdnify/ |title=OnApp’s federated CDN model has limitations, says departing customer CDNify |author=Meyer, David |publisher=GigaOM |date=30 April 2014 |accessdate=22 August 2014}}</ref>

==References==
<references />


[[Category:Software and hardware terms]]

Content delivery network - Revision history

Shawndouglas: Added notes

Shawndouglas: Created as needed.