Content Delivery Network (CDN) – An Insight

Posted by at 5 March, at 12 : 20 PM Print

Content Delivery Network popularly known as CDN are one of the fastest emerging technologies supporting cost-efficiency and something that caters to a variety of content to numerous end points. These end-points maybe anything from web browsers, mobile devices or gaming consoles. The information delivered to you below would help you understand about CDN’s and how it’d be used for your businesses.

A CDN can be categorised into : (a) CDNs that cater general content but isn’t restricted to video only; (b) CDNs delivering on-demand video and (c) CDNs delivering Live Video or what we usually call it as Live Streaming.

Some of these technologies have gained greater popularity than others. Some work on the methods of complete/progressive download /streaming or HTTP delivery.

Lets take a closer look at the features of these technologies.

General Purpose CDNs

It might have so happened that unknowingly you’d have used services based on a general purpose CDN, a very good example is the iTunes Store.

The general purpose Content Delivery Networks carries out a function known as web acceleration. To use such a CDN technology you are essentially required to have multiple servers located at different geo-locations. To increase it efficiency, one must ensure that the servers are hosted in a close vicinity of large connection points between Internet service providers (ISPs) or even within the same data centers as a popular website or gaming/application provider. The Content Delivery Network cache’s content, and serves to the user requests from the stored copy of content.

This technology of web acceleration has evolved from the past to a state of a complex form due to the very fact that the internet connectivity offered by ISPs have much restrictions and fail to cover larger areas. In order to achieve an efficient CDN delivery with web acceleration, it is necessary that the content is cached at multiple locations, resulting in the necessity of a nation-wide branching of multiple servers hosted at maximum number of data-centers and ISP headends / POPs.

On-Demand Video CDNs

You’d attimes find that the general purpose CND services also deliver an on-demand video content. Such content usually consists of large files such as a game, large downloadable application hence pointing to a fact that isn’t too different than other content.

Until recently it was essential for a video delivery to be served from special high config streaming servers. These servers could deliver the content at the time of a request, but had a drawback, it’d just deliver the bits requested instead of the complete video file. This usually happened due to the hesitance of CDN services to invert in costly steaming servers and the software required to run the network. Therefore the service wasn’t necessarily serving well to the expectations. This led to a choice of direct downloads, wherein full video clip had to be downloaded to a local computer of the requester inorder for it to be viewed. This is exactly what was required for downloading large files, but in this patience used to be tested and the requester couldn’t wait that long until the process could complete.

This formed the base reason for the discovery of progressive download, which is something we see at YouTube. In this type of delivery system, the CDN’s could deliver the download, and the requester could view it within few seconds (ofcourse the Internet speed played an important role) and download process would continue in the background. In this the waiting time could be greatly reduced and the content could be downloaded much faster and before the viewer could reach half way to viewing the video.

It was later observed that, if the requester abandoned viewing the video mid-way, the owner of the content was still changed for the entire download. Such a problem was managed by a streaming server wherein it’d enhance content delivery (curtail the speed at which content was downloaded to a level just a bit faster than content would be viewed) while still avoiding the use of a specialized streaming server for on-demand content.

It is just recently that the Industry got to use an even advanced technology of HTTP streaming that had a rigid adaptive bitrate (ABR) encoding and delivery.

As the name suggests, an HTTP streaming technology makes use of generic HTTP servers (usually an Apache or Windows Server) to service the on-demand video files similar to ways the requests of website content is served. Enhanced speeds of delivery was inherent in HTTP system, its just that it was also capable of serving on-demand video clip delivery.

Further, the adaptive bitrate (ABR) was added to the CDN, that gave a capability of converting a video stream into fragments, often 2-10 seconds in length. It created discrete streams at various bitrates and then uses feedback from the Internet user’s video player to dynamically detect the optimum network speed for delivery of the video clip.

Based on the network conditions, the stream that had the best appropriate bitrate is served for a particular data fragment and time. This eased the pain of the content owner as the bitrate could be limited and also limiting the need for large numbers of special streaming servers. This technological advancements and advantages offered by ABR gave an opportunity to the big players in the Industry to offer it as a solution.

Live Video Delivery CDNs

A Live video delivery CDN can be said to be still in an immature state. Despite the advancements as stated above, we can expect more advancements in the Live Video Delivery CDN’s. One of the factors that awaits improvements is the caching of live video’s similar to textual content.

Expense is still one of the most concerning factors to run and manage a live streaming infrastructure. With every addition of viewer the cost of bandwidth increases as well. Though there’s a partial solution that the providers have discovered viz. broadcasting. Service providers broadcast part of their digital frequency spectrum to be viewable on mobile devices and gadgets. This has also offered an opportunity to reach out to a greater geo-location.

Though issues still persist with live event streaming as an indepth planning and infrastructure setup needs to be made months before the D-day. Sufficient sizing up of resources is required based on the assumptions of simultaneous viewers at peak periods of time. The Cloud Hosting technology is rightfully being considered for the smooth live delivery of video.

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