What do content distribution network service providers do?

What is the purpose of CDN service providers?

My guess is that large scale sites like facebook,wikipedia,youtube etc use CDN service providers for some kind of outsourcing.

My understanding:

• youtube keeps its content in these CDNs and the site actually focus on algorithms such as searching of videos,suggesting related videos, keeping subscriber list/playlist of users etc.

• The youtube site only keeps meta-data,indexes?. or may be it also contains one copy of its entire content?. The user connects to youtube site, searches for a video. The site finds out the file name and sends it to the CDN hub along with IP address of the user.

• The CDN hub than perhaps locates the CDN node closest to the user and serves the content to the user.

What is the advantage of this approach?

One most important I can see is that esp for videos, it is perhaps remarkably much more faster if you are s开发者_运维百科treaming video from the same country than from across the globe. but does distance really matter that much? Any concrete numbers to get a sense of increase in speed between getting videos from across the globe than from same country?

and Google doesn't want to install its storage nodes all over the world. It would rather outsource this to CDN service providers which have already spread their nodes all over the world. and Google only focuses on algorithms part (which it mostly keeps secret)

Is my understanding of the picture correct? Any input/pointers would be highly useful.

Thanks,

I learned about the importance of CDNs in terms of website performance a couple of years back thanks to Yahoo's "Best Practices for Speeding Up Your Web Site"

This is oft-referenced in ySlow, and Yahoo estimated a 20% speed increase.

Another "benefit" is parallel downloading, which is discussed at length by one of the above authors in this blog post.

These are some resources that I ran into when looking into site optimization so I just thought I'd share. Besides that, you seem to have a good grasp on the concept.