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Wikipedia

Content delivery network

February 15, 2024

A content delivery network or content distribution network (CDN) is a geographically distributed network of proxy servers and their data centers. The goal is to provide high availability and performance by distributing the service spatially relative to end users. CDNs came into existence in the late 1990s as a means for alleviating the performance bottlenecks of the Internet[1][2] as the Internet was starting to become a mission-critical medium for people and enterprises. Since then, CDNs have grown to serve a large portion of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social media sites.[3]

(Left) Single server distribution
(Right) CDN scheme of distribution

CDNs are a layer in the internet ecosystem. Content owners such as media companies and e-commerce vendors pay CDN operators to deliver their content to their end users. In turn, a CDN pays Internet service providers (ISPs), carriers, and network operators for hosting its servers in their data centers.

CDN is an umbrella term spanning different types of content delivery services: video streaming, software downloads, web and mobile content acceleration, licensed/managed CDN, transparent caching, and services to measure CDN performance, load balancing, Multi CDN switching and analytics and cloud intelligence. CDN vendors may cross over into other industries like security, DDoS protection and web application firewalls (WAF), and WAN optimization.

Technology edit

CDN nodes are usually deployed in multiple locations, often over multiple Internet backbones. Benefits include reducing bandwidth costs, improving page load times, and increasing the global availability of content. The number of nodes and servers making up a CDN varies, depending on the architecture, some reaching thousands of nodes with tens of thousands of servers on many remote points of presence (PoPs). Others build a global network and have a small number of geographical PoPs.[4]

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 are the fewest hops, the lowest number of network seconds away from the requesting client, or the highest availability in terms of server performance (both current and historical), to optimize delivery across local networks. When optimizing for cost, locations that are the least expensive may be chosen instead. In an optimal scenario, these two goals tend to align, as edge servers that are close to the end user at the edge of the network may have an advantage in performance or cost.

Most CDN providers will provide their services over a varying, defined, set of PoPs, depending on the coverage desired, such as United States, International or Global, Asia-Pacific, etc. These sets of PoPs can be called "edges", "edge nodes", "edge servers", or "edge networks" as they would be the closest edge of CDN assets to the end user.[5]

Security and privacy edit

CDN providers profit either from direct fees paid by content providers using their network, or profit from the user analytics and tracking data collected as their scripts are being loaded onto customers' websites inside their browser origin. As such these services are being pointed out as potential privacy intrusions for the purpose of behavioral targeting[6] and solutions are being created to restore single-origin serving and caching of resources.[7]

In particular, a website using a CDN may violate the EU's General Data Protection Regulation (GDPR). For example, in 2021 a German court forbade the use of a CDN on a university website, because this caused the transmission of the user's IP address to the CDN, which violated the GDPR.[8]

CDNs serving JavaScript have also been targeted as a way to inject malicious content into pages using them. Subresource Integrity mechanism was created in response to ensure that the page loads a script whose content is known and constrained to a hash referenced by the website author.[9]

Content networking techniques edit

The Internet was designed according to the end-to-end principle.[10] 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.

Content Delivery Networks augment the end-to-end 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.[11]

Web caches store popular content on servers that have the greatest demand for the content requested. These shared network appliances reduce bandwidth requirements, reduce server load, and improve the client response times for content stored in the cache. Web caches are populated based on requests from users (pull caching) or based on preloaded content disseminated from content servers (push caching).[12]

Server-load balancing uses one or more techniques including service-based (global load balancing) or hardware-based (i.e. layer 4–7 switches, also known as a web switch, content switch, or multilayer switch) to share traffic among a number of servers or web caches. Here the switch is assigned a single virtual IP address. Traffic arriving at the switch is then directed to one of the real web servers attached to the switch. This has the advantage of balancing load, increasing total capacity, improving scalability, and providing increased reliability by redistributing the load of a failed web server and providing server health checks.

A content cluster or service node can be formed using a layer 4–7 switch to balance load across a number of servers or a number of web caches within the network.

Request routing directs client requests to the content source best able to serve the request. This may involve directing a client request to the service node that is closest to the client, or to the one with the most capacity. A variety of algorithms are used to route the request. These include Global Server Load Balancing, DNS-based request routing, Dynamic metafile generation, HTML rewriting,[13] and anycasting.[14] Proximity—choosing the closest service node—is estimated using a variety of techniques including reactive probing, proactive probing, and connection monitoring.[11]

CDNs use a variety of methods of content delivery including, but not limited to, manual asset copying, active web caches, and global hardware load balancers.

Content service protocols edit

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[15][16] to provide an open standard for connecting application servers. A more recently defined and robust solution is provided by the Open Pluggable Edge Services (OPES) protocol.[17] This architecture defines OPES service applications that can reside on the OPES processor itself or be executed remotely on a Callout Server. Edge Side Includes or ESI is a small markup language for edge-level dynamic web content assembly. It is fairly common for websites to have generated content. It could be because of changing content like catalogs or forums, or because of the personalization. This creates a problem for caching systems. To overcome this problem, a group of companies created ESI.

Peer-to-peer CDNs edit

Further information: Peer-to-peer network

In peer-to-peer (P2P) content-delivery networks, clients provide resources as well as use them. This means that, unlike client–server systems, the content-centric networks can actually perform better as more users begin to access the content (especially with protocols such as Bittorrent that require users to share). This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor.[18][19]

Private CDNs edit

If content owners are not satisfied with the options or costs of a commercial CDN service, they can create their own CDN. This is called a private CDN. A private CDN consists of PoPs (points of presence) that are only serving content for their owner. These PoPs can be caching servers,[20] reverse proxies or application delivery controllers.[21] It can be as simple as two caching servers,[20] or large enough to serve petabytes of content.[22]

Large content distribution networks may even build and set up their own private network to distribute copies of content across cache locations.[23][24] Such private networks are usually used in conjunction with public networks as a backup option in case the capacity of the private network is not enough or there is a failure which leads to capacity reduction. Since the same content has to be distributed across many locations, a variety of multicasting techniques may be used to reduce bandwidth consumption. Over private networks, it has also been proposed to select multicast trees according to network load conditions to more efficiently utilize available network capacity.[25][26]

CDN trends edit

Emergence of telco CDNs edit

The rapid growth of streaming video traffic[27] uses large capital expenditures by broadband providers[28] in order to meet this demand and retain subscribers by delivering a sufficiently good quality of experience.

To address this, telecommunications service providers have begun to launch their own content delivery networks as a means to lessen the demands on the network backbone and reduce infrastructure investments.

Telco CDN advantages edit

Because they own the networks over which video content is transmitted, telco CDNs have advantages over traditional CDNs. They own the last mile and can deliver content closer to the end-user because it can be cached deep in their networks. This deep caching minimizes the distance that video data travels over the general Internet and delivers it more quickly and reliably.

Telco CDNs also have a built-in cost advantage since traditional CDNs must lease bandwidth from them and build the operator's margin into their own cost model. In addition, by operating their own content delivery infrastructure, telco operators have better control over the utilization of their resources. Content management operations performed by CDNs are usually applied without (or with very limited) information about the network (e.g., topology, utilization etc.) of the telco-operators with which they interact or have business relationships. These pose a number of challenges for the telco-operators who have a limited sphere of action in face of the impact of these operations on the utilization of their resources.

In contrast, the deployment of telco-CDNs allows operators to implement their own content management operations,[29][30] which enables them to have a better control over the utilization of their resources and, as such, provide better quality of service and experience to their end users.

Federated CDNs and Open Caching edit

In June 2011, StreamingMedia.com reported that a group of TSPs had founded an Operator Carrier Exchange (OCX)[31] to interconnect their networks and compete more directly against large traditional CDNs like Akamai and Limelight Networks, which have extensive PoPs worldwide. This way, telcos are building a Federated CDN offering, which is more interesting for a content provider willing to deliver its content to the aggregated audience of this federation.

It is likely that in a near future, other telco CDN federations will be created. They will grow by enrollment of new telcos joining the federation and bringing network presence and their Internet subscriber bases to the existing ones.[citation needed]

The Open Caching specification by Streaming Media Alliance defines a set of APIs that allows a Content Provider to deliver its content using several CDNs in a consistent way, seeing each CDN provider the same way through these APIs.

Improving CDN performance using Extension Mechanisms for DNS edit

 
The latency (RTT) experienced by clients with non-local resolvers ("high") reduced drastically when a CDN rolled-out the EDNS0 extension in April 2014, while the latency of clients with local resolvers are unimpacted by the change ("low").[32]

Traditionally, CDNs have used the IP of the client's recursive DNS resolver to geo-locate the client. While this is a sound approach in many situations, this leads to poor client performance if the client uses a non-local recursive DNS resolver that is far away. For instance, a CDN may route requests from a client in India to its edge server in Singapore, if that client uses a public DNS resolver in Singapore, causing poor performance for that client. Indeed, a recent study[32] showed that in many countries where public DNS resolvers are in popular use, the median distance between the clients and their recursive DNS resolvers can be as high as a thousand miles. In August 2011, a global consortium of leading Internet service providers led by Google announced their official implementation of the edns-client-subnet IETF Internet Draft,[33] which is intended to accurately localize DNS resolution responses. The initiative involves a limited number of leading DNS service providers, such as Google Public DNS,[34] and CDN service providers as well. With the edns-client-subnet EDNS0 option, CDNs can now utilize the IP address of the requesting client's subnet when resolving DNS requests. This approach, called end-user mapping,[32] has been adopted by CDNs and it has been shown to drastically reduce the round-trip latencies and improve performance for clients who use public DNS or other non-local resolvers. However, the use of EDNS0 also has drawbacks as it decreases the effectiveness of caching resolutions at the recursive resolvers,[32] increases the total DNS resolution traffic,[32] and raises a privacy concern of exposing the client's subnet.

Virtual CDN (vCDN) edit

Virtualization technologies are being used to deploy virtual CDNs (vCDNs) with the goal to reduce content provider costs, and at the same time, increase elasticity and decrease service delay. With vCDNs, it is possible to avoid traditional CDN limitations, such as performance, reliability and availability since virtual caches are deployed dynamically (as virtual machines or containers) in physical servers distributed across the provider's geographical coverage. As the virtual cache placement is based on both the content type and server or end-user geographic location, the vCDNs have a significant impact on service delivery and network congestion.[35][36][37][38]

Image Optimization and Delivery (Image CDNs) edit

In 2017, Addy Osmany of Google started referring to software solutions that could integrate naturally with the Responsive Web Design paradigm (with particular reference to the <picture> element) as Image CDNs.[39] The expression referred to the ability of a web architecture to serve multiple versions of the same image through HTTP, depending on the properties of the browser requesting it, as determined by either the browser or the server-side logic. The purpose of Image CDNs was, in Google's vision, to serve high-quality images (or, better, images perceived as high-quality by the human eye) while preserving download speed, thus contributing to a great User experience (UX).[citation needed]

Arguably, the Image CDN term was originally a misnomer, as neither Cloudinary nor Imgix (the examples quoted by Google in the 2017 guide by Addy Osmany) were, at the time, a CDN in the classical sense of the term.[39] Shortly afterwards, though, several companies offered solutions that allowed developers to serve different versions of their graphical assets according to several strategies. Many of these solutions were built on top of traditional CDNs, such as Akamai, CloudFront, Fastly, Edgecast and Cloudflare. At the same time, other solutions that already provided an image multi-serving service joined the Image CDN definition by either offering CDN functionality natively (ImageEngine)[40] or integrating with one of the existing CDNs (Cloudinary/Akamai, Imgix/Fastly).

While providing a universally agreed-on definition of what an Image CDN is may not be possible, generally speaking, an Image CDN supports the following three components:[41]

  • A Content Delivery Network (CDN) for the fast serving of images.
  • Image manipulation and optimization, either on-the-fly through URL directives, in batch mode (through manual upload of images) or fully automatic (or a combination of these).
  • Device Detection (also known as Device Intelligence), i.e. the ability to determine the properties of the requesting browser and/or device through analysis of the User-Agent string, HTTP Accept headers, Client-Hints or JavaScript.[41]

The following table summarizes the current situation with the main software CDNs in this space:[42]

Main Image CDNs on the market
Name CDN Image Optimization Device Detection
Akamai ImageManager Y Batch mode based on HTTP Accept header
Cloudflare Polish Y fully-automatic based on HTTP Accept header
Cloudinary Through Akamai Batch, URL directives Accept header, Client-Hints
Fastly IO Y URL directives based on HTTP Accept header
ImageEngine Y fully-automatic WURFL, Client-Hints, Accept header
Imgix Through Fastly fully-automatic Accept header / Client-Hints
PageCDN Y URL directives based on HTTP Accept header

Notable content delivery service providers edit

Free CDNs edit

Traditional commercial CDNs edit

Telco CDNs edit

Commercial CDNs using P2P for delivery edit

Multi CDN edit

In-house CDN edit

See also edit

References edit

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  2. ^ Nygren., E.; Sitaraman R. K.; Sun, J. (2010). "The Akamai Network: A Platform for High-Performance Internet Applications" (PDF). ACM SIGOPS Operating Systems Review. 44 (3): 2–19. doi:10.1145/1842733.1842736. S2CID 207181702. (PDF) from the original on September 13, 2012. Retrieved November 19, 2012.
  3. ^ Evi, Nemeth (2018). "Chapter 19, Web hosting, Content delivery networks". UNIX and Linux system administration handbook (Fifth ed.). Boston: Pearson Education. p. 690. ISBN 9780134277554. OCLC 1005898086.
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  13. ^ RFC 3568 Barbir, A., Cain, B., Nair, R., Spatscheck, O.: "Known Content Network (CN) Request-Routing Mechanisms," July 2003
  14. ^ RFC 1546 Partridge, C., Mendez, T., Milliken, W.: "Host Anycasting Services," November 1993.
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  17. ^ RFC 3835 Barbir, A., Penno, R., Chen, R., Hofmann, M., and Orman, H.: "An Architecture for Open Pluggable Edge Services (OPES)," August 2004.
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  31. ^ . Dan Rayburn – StreamingMediaBlog.com. 2017-12-13. Archived from the original on 2011-07-20. Retrieved 2011-07-22.
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  33. ^ "Client Subnet in DNS Requests".
  34. ^ "Where are your servers currently located?". from the original on 2013-01-15.
  35. ^ Filelis-Papadopoulos, Christos K.; Giannoutakis, Konstantinos M.; Gravvanis, George A.; Endo, Patricia Takako; Tzovaras, Dimitrios; Svorobej, Sergej; Lynn, Theo (2019-04-01). "Simulating large vCDN networks: A parallel approach". Simulation Modelling Practice and Theory. 92: 100–114. doi:10.1016/j.simpat.2019.01.001. ISSN 1569-190X. S2CID 67752426.
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  37. ^ Ibn-Khedher, Hatem; Abd-Elrahman, Emad; Kamal, Ahmed E.; Afifi, Hossam (2017-06-19). "OPAC: An optimal placement algorithm for virtual CDN". Computer Networks. 120: 12–27. doi:10.1016/j.comnet.2017.04.009. ISSN 1389-1286.
  38. ^ Khedher, Hatem; Abd-Elrahman, Emad; Afifi, Hossam; Marot, Michel (October 2017). "Optimal and Cost Efficient Algorithm for Virtual CDN Orchestration". 2017 IEEE 42nd Conference on Local Computer Networks (LCN). Singapore: IEEE. pp. 61–69. doi:10.1109/LCN.2017.115. ISBN 978-1-5090-6523-3. S2CID 44243386.
  39. ^ a b Addy Osmany. "Essential Image Optimization". Retrieved May 13, 2020.
  40. ^ Jon Arne Sæterås (26 April 2017). "Let The Content Delivery Network Optimize Your Images". Retrieved May 13, 2020.
  41. ^ a b Katie Hempenius. "Use image CDNs to optimize images". Retrieved May 13, 2020.
  42. ^ Maximiliano Firtman (18 September 2019). "Faster Paint Metrics with Responsive Image Optimization CDNs". Retrieved May 13, 2020.
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  50. ^ How Netflix works: the (hugely simplified) complex stuff that happens every time you hit Play

Further reading edit

  • Buyya, R.; Pathan, M.; Vakali, A. (2008). "Content Delivery Networks: State of the Art, Insights, and Imperatives". . Lecture Notes Electrical Engineering. Vol. 9. Springer. pp. 3–32. doi:10.1007/978-3-540-77887-5_1. ISBN 9783540778868. Archived from the original on 2017-09-27. Retrieved 2008-07-07.
  • Hau, T.; Burghardt, D.; Brenner, W. (2011). "Multihoming, Content Delivery Networks, and the Market for Internet Connectivity". Telecommunications Policy. 35 (6): 532–542. doi:10.1016/j.telpol.2011.04.002.
  • Majumdar, S.; Kulkarni, D.; Ravishankar, C. (2007). "Addressing Click Fraud in Content Delivery Systems" (PDF). Infocom. IEEE. doi:10.1109/INFCOM.2007.36.
  • Nygren., E.; Sitaraman R. K.; Sun, J. (2010). "The Akamai Network: A Platform for High-Performance Internet Applications" (PDF). ACM SIGOPS Operating Systems Review. 44 (3): 2–19. doi:10.1145/1842733.1842736. S2CID 207181702. Retrieved November 19, 2012.
  • Vakali, A.; Pallis, G. (2003). "Content Delivery Networks: Status and Trends". IEEE Internet Computing. 7 (6): 68–74. doi:10.1109/MIC.2003.1250586. S2CID 2861167.

February 15, 2024
content, delivery, network, content, delivery, network, content, distribution, network, geographically, distributed, network, proxy, servers, their, data, centers, goal, provide, high, availability, performance, distributing, service, spatially, relative, user. A content delivery network or content distribution network CDN is a geographically distributed network of proxy servers and their data centers The goal is to provide high availability and performance by distributing the service spatially relative to end users CDNs came into existence in the late 1990s as a means for alleviating the performance bottlenecks of the Internet 1 2 as the Internet was starting to become a mission critical medium for people and enterprises Since then CDNs have grown to serve a large portion of the Internet content today including web objects text graphics and scripts downloadable objects media files software documents applications e commerce portals live streaming media on demand streaming media and social media sites 3 Left Single server distribution Right CDN scheme of distributionCDNs are a layer in the internet ecosystem Content owners such as media companies and e commerce vendors pay CDN operators to deliver their content to their end users In turn a CDN pays Internet service providers ISPs carriers and network operators for hosting its servers in their data centers CDN is an umbrella term spanning different types of content delivery services video streaming software downloads web and mobile content acceleration licensed managed CDN transparent caching and services to measure CDN performance load balancing Multi CDN switching and analytics and cloud intelligence CDN vendors may cross over into other industries like security DDoS protection and web application firewalls WAF and WAN optimization Contents 1 Technology 2 Security and privacy 3 Content networking techniques 3 1 Content service protocols 3 2 Peer to peer CDNs 3 3 Private CDNs 4 CDN trends 4 1 Emergence of telco CDNs 4 2 Telco CDN advantages 4 3 Federated CDNs and Open Caching 4 4 Improving CDN performance using Extension Mechanisms for DNS 4 5 Virtual CDN vCDN 4 6 Image Optimization and Delivery Image CDNs 5 Notable content delivery service providers 5 1 Free CDNs 5 2 Traditional commercial CDNs 5 3 Telco CDNs 5 4 Commercial CDNs using P2P for delivery 5 5 Multi CDN 5 6 In house CDN 6 See also 7 References 8 Further readingTechnology editCDN nodes are usually deployed in multiple locations often over multiple Internet backbones Benefits include reducing bandwidth costs improving page load times and increasing the global availability of content The number of nodes and servers making up a CDN varies depending on the architecture some reaching thousands of nodes with tens of thousands of servers on many remote points of presence PoPs Others build a global network and have a small number of geographical PoPs 4 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 are the fewest hops the lowest number of network seconds away from the requesting client or the highest availability in terms of server performance both current and historical to optimize delivery across local networks When optimizing for cost locations that are the least expensive may be chosen instead In an optimal scenario these two goals tend to align as edge servers that are close to the end user at the edge of the network may have an advantage in performance or cost Most CDN providers will provide their services over a varying defined set of PoPs depending on the coverage desired such as United States International or Global Asia Pacific etc These sets of PoPs can be called edges edge nodes edge servers or edge networks as they would be the closest edge of CDN assets to the end user 5 Security and privacy editCDN providers profit either from direct fees paid by content providers using their network or profit from the user analytics and tracking data collected as their scripts are being loaded onto customers websites inside their browser origin As such these services are being pointed out as potential privacy intrusions for the purpose of behavioral targeting 6 and solutions are being created to restore single origin serving and caching of resources 7 In particular a website using a CDN may violate the EU s General Data Protection Regulation GDPR For example in 2021 a German court forbade the use of a CDN on a university website because this caused the transmission of the user s IP address to the CDN which violated the GDPR 8 CDNs serving JavaScript have also been targeted as a way to inject malicious content into pages using them Subresource Integrity mechanism was created in response to ensure that the page loads a script whose content is known and constrained to a hash referenced by the website author 9 Content networking techniques editThe Internet was designed according to the end to end principle 10 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 Content Delivery Networks augment the end to end 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 11 Web caches store popular content on servers that have the greatest demand for the content requested These shared network appliances reduce bandwidth requirements reduce server load and improve the client response times for content stored in the cache Web caches are populated based on requests from users pull caching or based on preloaded content disseminated from content servers push caching 12 Server load balancing uses one or more techniques including service based global load balancing or hardware based i e layer 4 7 switches also known as a web switch content switch or multilayer switch to share traffic among a number of servers or web caches Here the switch is assigned a single virtual IP address Traffic arriving at the switch is then directed to one of the real web servers attached to the switch This has the advantage of balancing load increasing total capacity improving scalability and providing increased reliability by redistributing the load of a failed web server and providing server health checks A content cluster or service node can be formed using a layer 4 7 switch to balance load across a number of servers or a number of web caches within the network Request routing directs client requests to the content source best able to serve the request This may involve directing a client request to the service node that is closest to the client or to the one with the most capacity A variety of algorithms are used to route the request These include Global Server Load Balancing DNS based request routing Dynamic metafile generation HTML rewriting 13 and anycasting 14 Proximity choosing the closest service node is estimated using a variety of techniques including reactive probing proactive probing and connection monitoring 11 CDNs use a variety of methods of content delivery including but not limited to manual asset copying active web caches and global hardware load balancers Content service protocols edit 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 15 16 to provide an open standard for connecting application servers A more recently defined and robust solution is provided by the Open Pluggable Edge Services OPES protocol 17 This architecture defines OPES service applications that can reside on the OPES processor itself or be executed remotely on a Callout Server Edge Side Includes or ESI is a small markup language for edge level dynamic web content assembly It is fairly common for websites to have generated content It could be because of changing content like catalogs or forums or because of the personalization This creates a problem for caching systems To overcome this problem a group of companies created ESI Peer to peer CDNs edit Further information Peer to peer network In peer to peer P2P content delivery networks clients provide resources as well as use them This means that unlike client server systems the content centric networks can actually perform better as more users begin to access the content especially with protocols such as Bittorrent that require users to share This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor 18 19 Private CDNs edit If content owners are not satisfied with the options or costs of a commercial CDN service they can create their own CDN This is called a private CDN A private CDN consists of PoPs points of presence that are only serving content for their owner These PoPs can be caching servers 20 reverse proxies or application delivery controllers 21 It can be as simple as two caching servers 20 or large enough to serve petabytes of content 22 Large content distribution networks may even build and set up their own private network to distribute copies of content across cache locations 23 24 Such private networks are usually used in conjunction with public networks as a backup option in case the capacity of the private network is not enough or there is a failure which leads to capacity reduction Since the same content has to be distributed across many locations a variety of multicasting techniques may be used to reduce bandwidth consumption Over private networks it has also been proposed to select multicast trees according to network load conditions to more efficiently utilize available network capacity 25 26 CDN trends editEmergence of telco CDNs edit The rapid growth of streaming video traffic 27 uses large capital expenditures by broadband providers 28 in order to meet this demand and retain subscribers by delivering a sufficiently good quality of experience To address this telecommunications service providers have begun to launch their own content delivery networks as a means to lessen the demands on the network backbone and reduce infrastructure investments Telco CDN advantages edit Because they own the networks over which video content is transmitted telco CDNs have advantages over traditional CDNs They own the last mile and can deliver content closer to the end user because it can be cached deep in their networks This deep caching minimizes the distance that video data travels over the general Internet and delivers it more quickly and reliably Telco CDNs also have a built in cost advantage since traditional CDNs must lease bandwidth from them and build the operator s margin into their own cost model In addition by operating their own content delivery infrastructure telco operators have better control over the utilization of their resources Content management operations performed by CDNs are usually applied without or with very limited information about the network e g topology utilization etc of the telco operators with which they interact or have business relationships These pose a number of challenges for the telco operators who have a limited sphere of action in face of the impact of these operations on the utilization of their resources In contrast the deployment of telco CDNs allows operators to implement their own content management operations 29 30 which enables them to have a better control over the utilization of their resources and as such provide better quality of service and experience to their end users Federated CDNs and Open Caching edit This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed June 2021 Learn how and when to remove this template message In June 2011 StreamingMedia com reported that a group of TSPs had founded an Operator Carrier Exchange OCX 31 to interconnect their networks and compete more directly against large traditional CDNs like Akamai and Limelight Networks which have extensive PoPs worldwide This way telcos are building a Federated CDN offering which is more interesting for a content provider willing to deliver its content to the aggregated audience of this federation It is likely that in a near future other telco CDN federations will be created They will grow by enrollment of new telcos joining the federation and bringing network presence and their Internet subscriber bases to the existing ones citation needed The Open Caching specification by Streaming Media Alliance defines a set of APIs that allows a Content Provider to deliver its content using several CDNs in a consistent way seeing each CDN provider the same way through these APIs Improving CDN performance using Extension Mechanisms for DNS edit nbsp The latency RTT experienced by clients with non local resolvers high reduced drastically when a CDN rolled out the EDNS0 extension in April 2014 while the latency of clients with local resolvers are unimpacted by the change low 32 Traditionally CDNs have used the IP of the client s recursive DNS resolver to geo locate the client While this is a sound approach in many situations this leads to poor client performance if the client uses a non local recursive DNS resolver that is far away For instance a CDN may route requests from a client in India to its edge server in Singapore if that client uses a public DNS resolver in Singapore causing poor performance for that client Indeed a recent study 32 showed that in many countries where public DNS resolvers are in popular use the median distance between the clients and their recursive DNS resolvers can be as high as a thousand miles In August 2011 a global consortium of leading Internet service providers led by Google announced their official implementation of the edns client subnet IETF Internet Draft 33 which is intended to accurately localize DNS resolution responses The initiative involves a limited number of leading DNS service providers such as Google Public DNS 34 and CDN service providers as well With the edns client subnet EDNS0 option CDNs can now utilize the IP address of the requesting client s subnet when resolving DNS requests This approach called end user mapping 32 has been adopted by CDNs and it has been shown to drastically reduce the round trip latencies and improve performance for clients who use public DNS or other non local resolvers However the use of EDNS0 also has drawbacks as it decreases the effectiveness of caching resolutions at the recursive resolvers 32 increases the total DNS resolution traffic 32 and raises a privacy concern of exposing the client s subnet Virtual CDN vCDN edit Virtualization technologies are being used to deploy virtual CDNs vCDNs with the goal to reduce content provider costs and at the same time increase elasticity and decrease service delay With vCDNs it is possible to avoid traditional CDN limitations such as performance reliability and availability since virtual caches are deployed dynamically as virtual machines or containers in physical servers distributed across the provider s geographical coverage As the virtual cache placement is based on both the content type and server or end user geographic location the vCDNs have a significant impact on service delivery and network congestion 35 36 37 38 Image Optimization and Delivery Image CDNs edit In 2017 Addy Osmany of Google started referring to software solutions that could integrate naturally with the Responsive Web Design paradigm with particular reference to the lt picture gt element as Image CDNs 39 The expression referred to the ability of a web architecture to serve multiple versions of the same image through HTTP depending on the properties of the browser requesting it as determined by either the browser or the server side logic The purpose of Image CDNs was in Google s vision to serve high quality images or better images perceived as high quality by the human eye while preserving download speed thus contributing to a great User experience UX citation needed Arguably the Image CDN term was originally a misnomer as neither Cloudinary nor Imgix the examples quoted by Google in the 2017 guide by Addy Osmany were at the time a CDN in the classical sense of the term 39 Shortly afterwards though several companies offered solutions that allowed developers to serve different versions of their graphical assets according to several strategies Many of these solutions were built on top of traditional CDNs such as Akamai CloudFront Fastly Edgecast and Cloudflare At the same time other solutions that already provided an image multi serving service joined the Image CDN definition by either offering CDN functionality natively ImageEngine 40 or integrating with one of the existing CDNs Cloudinary Akamai Imgix Fastly While providing a universally agreed on definition of what an Image CDN is may not be possible generally speaking an Image CDN supports the following three components 41 A Content Delivery Network CDN for the fast serving of images Image manipulation and optimization either on the fly through URL directives in batch mode through manual upload of images or fully automatic or a combination of these Device Detection also known as Device Intelligence i e the ability to determine the properties of the requesting browser and or device through analysis of the User Agent string HTTP Accept headers Client Hints or JavaScript 41 The following table summarizes the current situation with the main software CDNs in this space 42 Main Image CDNs on the market Name CDN Image Optimization Device DetectionAkamai ImageManager Y Batch mode based on HTTP Accept headerCloudflare Polish Y fully automatic based on HTTP Accept headerCloudinary Through Akamai Batch URL directives Accept header Client HintsFastly IO Y URL directives based on HTTP Accept headerImageEngine Y fully automatic WURFL Client Hints Accept headerImgix Through Fastly fully automatic Accept header Client HintsPageCDN Y URL directives based on HTTP Accept headerNotable content delivery service providers editFree CDNs edit cdnjs 43 44 BootstrapCDN Cloudflare JSDelivr Traditional commercial CDNs edit Akamai Technologies 45 Amazon CloudFront 45 Aryaka Ateme CDN Azure CDN bunny net CacheFly CDN77 46 CDNetworks 45 CenterServ 45 ChinaCache Cloudflare 47 Cotendo Edgio formed through merger of EdgeCast Networks Layer0 and Limelight Networks Fastly Gcore Google Cloud CDN HP Cloud Services Incapsula Instart Internap LeaseWeb Lumen Technologies formerly Level 3 Communications MetaCDN NACEVI OnApp GoDaddy OVHcloud Rackspace Cloud Files Speedera Networks StackPath StreamZilla Wangsu Science amp Technology Yottaa Telco CDNs edit AT amp T Inc Bharti Airtel Bell Canada BT Group China Telecom Chunghwa Telecom Deutsche Telekom KT KPN Lumen Technologies formerly CenturyLink Megafon NTT Pacnet PCCW Singtel SK Broadband Spark New Zealand citation needed Tata Communications Telecom Argentina Telefonica Telenor TeliaSonera Telin Telstra Telus TIM Turk Telekom Verizon Commercial CDNs using P2P for delivery edit BitTorrent Inc Internap Pando Networks Rawflow Multi CDN edit MetaCDN Warpcache 48 49 In house CDN edit Netflix 50 See also edit nbsp Internet portalApplication software Bel Air Circuit Comparison of streaming media systems Comparison of video services Content delivery network interconnection Content delivery platform Data center Digital television Dynamic site acceleration Edge computing Internet radio Internet television InterPlanetary File System IPTV List of music streaming services List of streaming media systems Multicast NetMind Open Music Model Over the top content P2PTV Protection of Broadcasts and Broadcasting Organizations Treaty Push technology Software as a service Streaming media Webcast Web syndication Web televisionReferences edit Globally Distributed Content Delivery by J Dilley B Maggs J Parikh H Prokop R Sitaraman and B Weihl IEEE Internet Computing Volume 6 Issue 5 November 2002 PDF Archived PDF from the original on 2017 08 09 Retrieved 2019 10 25 Nygren E Sitaraman R K Sun J 2010 The Akamai Network A Platform for High Performance Internet Applications PDF ACM SIGOPS Operating Systems Review 44 3 2 19 doi 10 1145 1842733 1842736 S2CID 207181702 Archived PDF from the original on September 13 2012 Retrieved November 19 2012 Evi Nemeth 2018 Chapter 19 Web hosting Content delivery networks UNIX and Linux system administration handbook Fifth ed Boston Pearson Education p 690 ISBN 9780134277554 OCLC 1005898086 How Content Delivery Networks Work CDNetworks Archived from the original on 5 September 2015 Retrieved 22 September 2015 How Content Delivery Networks CDNs Work NCZOnline 29 November 2011 Archived from the original on 1 December 2011 Retrieved 22 September 2015 Security Help Net 2014 08 27 470 million sites exist for 24 hours 22 are malicious Help Net Security Archived from the original on 2019 07 01 Retrieved 2019 07 01 Decentraleyes Block CDN Tracking Collin M Barrett 2016 02 03 Archived from the original on 2019 07 01 Retrieved 2019 07 01 VG Wiesbaden verbietet die Nutzung von Content Delivery Networks www taylorwessing com in German 2021 12 14 Retrieved 2023 03 02 Subresource Integrity MDN Web Docs Archived from the original on 2019 06 26 Retrieved 2019 07 01 J H Saltzer D P Reed D D Clark 1 November 1984 End to end arguments in system design PDF ACM Transactions on Computer Systems 2 4 277 288 doi 10 1145 357401 357402 ISSN 0734 2071 S2CID 215746877 Wikidata Q56503280 Retrieved 2006 11 11 a b Hofmann Markus Beaumont Leland R 2005 Content Networking Architecture Protocols and Practice Morgan Kaufmann Publisher ISBN 1 55860 834 6 Bestavros Azer March 1996 Speculative Data Dissemination and Service to Reduce Server Load Network Traffic and Service Time for Distributed Information Systems PDF Proceedings of ICDE 96 The 1996 International Conference on Data Engineering 1996 180 189 Archived PDF from the original on 2010 07 03 Retrieved 2017 05 28 RFC 3568 Barbir A Cain B Nair R Spatscheck O Known Content Network CN Request Routing Mechanisms July 2003 RFC 1546 Partridge C Mendez T Milliken W Host Anycasting Services November 1993 RFC 3507 Elson J Cerpa A Internet Content Adaptation Protocol ICAP April 2003 ICAP Forum RFC 3835 Barbir A Penno R Chen R Hofmann M and Orman H An Architecture for Open Pluggable Edge Services OPES August 2004 Li Jin 2008 On peer to peer P2P content delivery PDF Peer to Peer Networking and Applications 1 1 45 63 doi 10 1007 s12083 007 0003 1 S2CID 16438304 Archived PDF from the original on 2013 10 04 Retrieved 2013 08 11 Stutzbach Daniel et al 2005 The scalability of swarming peer to peer content delivery PDF In Boutaba Raouf et al eds NETWORKING 2005 Networking Technologies Services and Protocols Performance of Computer and Communication Networks Mobile and Wireless Communications Systems Springer pp 15 26 ISBN 978 3 540 25809 4 a b How to build your own CDN using BIND GeoIP Nginx Varnish UNIXy 2010 07 18 Archived from the original on 2010 07 21 Retrieved 2014 10 15 How to Create Your Content Delivery Network With aiScaler Archived from the original on 2014 10 06 Retrieved 2014 10 15 Netflix Shifts Traffic To Its Own CDN Akamai Limelight Shrs Hit Forbes 5 June 2012 Archived from the original on 19 October 2017 Retrieved 26 August 2017 Mikel Jimenez et al May 1 2017 Building Express Backbone Facebook s new long haul network Archived from the original on October 24 2017 Retrieved October 27 2017 Inter Datacenter WAN with centralized TE using SDN and OpenFlow PDF 2012 Archived PDF from the original on October 28 2017 Retrieved October 27 2017 M Noormohammadpour et al July 10 2017 DCCast Efficient Point to Multipoint Transfers Across Datacenters USENIX Retrieved July 26 2017 M Noormohammadpour et al 2018 QuickCast Fast and Efficient Inter Datacenter Transfers using Forwarding Tree Cohorts Retrieved January 23 2018 Online Video Sees Tremendous Growth Spurs some Major Updates SiliconANGLE 2011 03 03 Archived from the original on 2011 08 30 Retrieved 2011 07 22 Overall Telecom CAPEX to Rise in 2011 Due to Video 3G LTE Investments cellular news Archived from the original on 2011 03 25 Retrieved 2011 07 22 D Tuncer M Charalambides R Landa G Pavlou More Control Over Network Resources an ISP Caching Perspective proceedings of IEEE IFIP Conference on Network and Service Management CNSM Zurich Switzerland October 2013 M Claeys D Tuncer J Famaey M Charalambides S Latre F De Turck G Pavlou Proactive Multi tenant Cache Management for Virtualized ISP Networks proceedings of IEEE IFIP Conference on Network and Service Management CNSM Rio de Janeiro Brazil November 2014 Telcos and Carriers Forming New Federated CDN Group Called OCX Operator Carrier Exchange Dan Rayburn StreamingMediaBlog com 2017 12 13 Archived from the original on 2011 07 20 Retrieved 2011 07 22 a b c d e End User Mapping Next Generation Request Routing for Content Delivery by F Chen R Sitaraman and M Torres ACM SIGCOMM conference Aug 2015 PDF Archived PDF from the original on 2017 08 12 Retrieved 2019 10 31 Client Subnet in DNS Requests Where are your servers currently located Archived from the original on 2013 01 15 Filelis Papadopoulos Christos K Giannoutakis Konstantinos M Gravvanis George A Endo Patricia Takako Tzovaras Dimitrios Svorobej Sergej Lynn Theo 2019 04 01 Simulating large vCDN networks A parallel approach Simulation Modelling Practice and Theory 92 100 114 doi 10 1016 j simpat 2019 01 001 ISSN 1569 190X S2CID 67752426 Filelis Papadopoulos Christos K Endo Patricia Takako Bendechache Malika Svorobej Sergej Giannoutakis Konstantinos M Gravvanis George A Tzovaras Dimitrios Byrne James Lynn Theo 2020 01 01 Towards simulation and optimization of cache placement on large virtual content distribution networks Journal of Computational Science 39 101052 doi 10 1016 j jocs 2019 101052 ISSN 1877 7503 Ibn Khedher Hatem Abd Elrahman Emad Kamal Ahmed E Afifi Hossam 2017 06 19 OPAC An optimal placement algorithm for virtual CDN Computer Networks 120 12 27 doi 10 1016 j comnet 2017 04 009 ISSN 1389 1286 Khedher Hatem Abd Elrahman Emad Afifi Hossam Marot Michel October 2017 Optimal and Cost Efficient Algorithm for Virtual CDN Orchestration 2017 IEEE 42nd Conference on Local Computer Networks LCN Singapore IEEE pp 61 69 doi 10 1109 LCN 2017 115 ISBN 978 1 5090 6523 3 S2CID 44243386 a b Addy Osmany Essential Image Optimization Retrieved May 13 2020 Jon Arne Saeteras 26 April 2017 Let The Content Delivery Network Optimize Your Images Retrieved May 13 2020 a b Katie Hempenius Use image CDNs to optimize images Retrieved May 13 2020 Maximiliano Firtman 18 September 2019 Faster Paint Metrics with Responsive Image Optimization CDNs Retrieved May 13 2020 Top 4 CDN services for hosting open source libraries opensource com opensource com Archived from the original on 18 April 2019 Retrieved 18 April 2019 Usage Statistics and Market Share of JavaScript Content Delivery Networks for Websites W3Techs Archived from the original on 12 April 2019 Retrieved 17 April 2019 a b c d How CDN and International Servers Networking Facilitate Globalization The Huffington Post Delarno Delvix 2016 09 06 Archived from the original on 19 September 2016 Retrieved 9 September 2016 Latest List Of CDN Vendors Selling To Broadcasters Carriers and MSOs 13 February 2017 Cloud Content Delivery Network CDN Market Investigation Report 2019 10 05 Archived from the original on 2019 10 07 Retrieved 2019 10 07 CDN Was Sie uber Content Delivery Networks wissen mussen www computerwoche de Archived from the original on 2019 03 21 Retrieved 2019 03 21 Williams 2017 08 22T18 00 09 233ZUtilities Mike 22 August 2017 Warpcache review TechRadar Archived from the original on 2019 03 21 Retrieved 2019 03 21 a href Template Cite web html title Template Cite web cite web a CS1 maint numeric names authors list link How Netflix works the hugely simplified complex stuff that happens every time you hit PlayFurther reading editBuyya R Pathan M Vakali A 2008 Content Delivery Networks State of the Art Insights and Imperatives Content Delivery Networks Lecture Notes Electrical Engineering Vol 9 Springer pp 3 32 doi 10 1007 978 3 540 77887 5 1 ISBN 9783540778868 Archived from the original on 2017 09 27 Retrieved 2008 07 07 Hau T Burghardt D Brenner W 2011 Multihoming Content Delivery Networks and the Market for Internet Connectivity Telecommunications Policy 35 6 532 542 doi 10 1016 j telpol 2011 04 002 Majumdar S Kulkarni D Ravishankar C 2007 Addressing Click Fraud in Content Delivery Systems PDF Infocom IEEE doi 10 1109 INFCOM 2007 36 Nygren E Sitaraman R K Sun J 2010 The Akamai Network A Platform for High Performance Internet Applications PDF ACM SIGOPS Operating Systems Review 44 3 2 19 doi 10 1145 1842733 1842736 S2CID 207181702 Retrieved November 19 2012 Vakali A Pallis G 2003 Content Delivery Networks Status and Trends IEEE Internet Computing 7 6 68 74 doi 10 1109 MIC 2003 1250586 S2CID 2861167 Retrieved from https en wikipedia org w index php title Content delivery network amp oldid 1207554469, wikipedia, wiki, book, books, library,

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