Abstract
This chapter provides an overview on the recent advances and perspectives on Content Delivery Networks. The first section, the introduction, sets the context. The second section identifies the different types of current CDNs and also insights on their evolution. The third section deals with CDN interconnection, reporting work status such as IETF and ETSI. The fourth section, on CDN and virtualization, describes the related initiatives in this area, in standardization bodies as well as in experimental deployments and evaluations. The fifth section focuses on the convergence of CDNs and clouds, presenting new business opportunities for the market players, as well as technical challenges. The sixth section addresses another trend, which is the extension of CDNs to home networking and terminal devices. The last section discusses content delivery for mobile, introducing solutions that operators can to optimize their networks and avoid being overwhelmed by ever growing traffic.
TopIntroduction
A Content Delivery Network (CDN) is a set of servers specifically designed and deployed over one or several networks for optimizing the storage and delivery of content (e.g., web objects, audiovisual live or on-demand content, large files, etc.). From a high-level and functional perspective the main components of a CDN include request routing server(s) that handle and redirect content requests towards cache node servers, cache node servers that deliver the requested content, content ingestion server(s) that ingest content in the CDN, analytics and accounting server(s), and management server(s), as shown on Figure 1.
Today a large part of the Internet traffic is distributed via CDNs. As an illustration, the CDN market leader Akamai estimates that its infrastructure handles 20 percent of the world's total Web traffic (Akamai, 2014). The outstanding development of the CDNs since the late 90s has been driven by their intrinsic strengths: improved service latency thereby leading to a better quality of experience for end users, and better network resource utilization leading to a reduction of congestion risks and costs.
From a business perspective there is an increasing trend for “commoditization” in the CDN industry, with strong market competition and price decline. In this challenging context CDNs must evolve to meet the requirements of the supported applications. Among them, it is worth focusing on new promising areas such as CDN interconnection, network virtualization, convergence of CDNs and clouds, CDN extension in the home network, and content delivery for mobile users.
This chapter aims to provide an overview on these recent advances and perspectives on CDNs.
Given its strategic importance, the CDN market has attracted many new entrants these last years. Section 2 identifies the different types of current CDNs which have been deployed to address different CDN market segments, such as Internet Protocol Television (IPTV) service offers provided by Telecom operators (Telcos) and Over The Top (OTT) applications.
Section 3 deals with CDN interconnection, by presenting a status of the corresponding standardization effort. CDN interconnection techniques allow CDN service providers and Telcos to federate CDNs deployed in different countries, to scale up their CDN capacity and their CDN service portfolio.
Section 4 focuses on CDN and virtualization. Network Function Virtualization (NFV) is a major trend that emerged recently. The goals of NFV are to improve network capital and operational expenditures, flexibility, rapidity of service deployment and energy efficiency as compared to dedicated hardware implementations. Section4 describes the current initiatives in this area, in standardization bodies as well as in the field of experimental deployments and evaluations.
Sections 5 and 6 emphasize respectively on Cloud and CDN convergence, and on CDN extension in the home network and terminal devices. The converging and competitive landscape of online content delivery presents new business opportunities for the market players, as well as technical challenges these sections introduce.
The last section deals with CDN and mobile. Content distribution services are blooming on mobile networks and they are expected to be responsible for the majority of future mobile Internet traffic. This section introduces different solutions that operators may envision in the short and longer terms to optimize their networks.
TopCdn Market Ecosystem
This section introduces the CDN positioning within a service delivery ecosystem. Then it provides an overview of the current CDN market. Finally, it presents an insight into the evolution trend.
Key Terms in this Chapter
Caching: Caching is a special form of memory deployed in networks (on specific servers) as well as on computer architectures and web browsers. When the same object is requested several times, caching aims at avoiding this object to be accessed as many times from its origin location so as to minimize resource utilization and latency.
HTTP2.0: Network Protocol developed by the IETF Hypertext Transfer Protocol Bis (httpbis) Working Group as the next version of HTTP.
Over-The-Top: Designate a market player, application or service that does not rely upon telecom operators or Internet Service Providers, except for just getting connected to the end users via the Internet.
Home Network: The private local network inside the end user’s premises, including all the terminal devices connected to it. The home network is connected to the Internet via a Home Gateway.
Cloud: Set of servers accessed remotely to manage, manipulate and store data.
Content Delivery Network Interconnection: A relationship between CDNs that enables one CDN to provide content delivery services on behalf of other CDNs.
vCDN: Virtualization of the different components of the Content Delivery Network appliance.
HTTP Adaptive Streaming: Content delivery scheme based on HTTP. Content is segmented into small objects called chunks encoded at multiple bitrates. The client accesses the content by requesting one after the other the chunks that best fit the terminal and network conditions.
Home Gateway: Equipment connecting the local area network of the home to a wide area network. It is essentially a modem (FTTH, ADSL, Cable, etc.) embedded in a box that provides routing and switching features.
Transparent Caching: Transparent caching is a special form of network caching, transparent for both the requesting and requested entities. The transparent caching node intercepts transparently the content request and delivers the requested content if its cache has a copy of it.
Content Delivery Network: Set of servers specifically designed and deployed over one or several networks in order to optimize the storage and delivery of content objects (web objects, audiovisual live or on-demand content, large files, etc.).