In the last of these posts we discussed the HTTP Archive stats on web page size. Also relevant to webpage performance is the number of roundtrips your customers browser must make to retrieve the objects which make up the page being delivered.
HTTP archive tells us that currently, nearly 100 roundtrips are made for every webpage delivered to a browser. Most of these will be coming back to your origin servers for this content while a few will be going off to other third party domains like Google, Facebook, livechat services etc.
What is the impact on page performance of making these roundtrips?
That all depends on the network time it takes for the browser to traverse the Internet to find and download the files it is looking for.
In an earlier blog post we discussed the performance of networking with respect to CDNs and Dynamic Site Acceleration offerings. Relevant from that article is this following comment:
If the origin servers are 1000 klm away from the requesting computer, the fastest roundtrip time will be 9.67ms. We have found that roundtrip times over our sample studied averaged 171ms.
Reducing the roundtrip time for the 100 or so roundtrips required for a page should be advantageous to delivering a fast website.
The effect of reducing distance to content
Prima Facie, reducing the distance between the customers computer and the source of the files being requested by the computer (usually the origin server) should cut the roundtrip time by an equivalent factor – e.g 1000klm to 500klm should cut the time in half. However, this time is affected by the network hops and the packet loss in the networks through which the request travels.
Therefore, ideally, the customers computer should gather content from positions as close as possible to that computer in both distance and network speed. All up – least latency.
How to Bring Files Closer to the User
This is where Content Delivery Networks (CDNs) shine. They are made to distribute copies of website content to nodes closer to the user. Importantly, good CDNs generally have high quality peering relationships with major Telco providers so not only is distribution closer to the users the network hops and therefore latency overall is reduced.
There are plenty of articles written about the caching and dispersion of website content to nodes close to the user by Content Delivery Networks so I wont cover that here. See as a starter http://en.wikipedia.org/wiki/Content_delivery_network if more info is required.
Importantly, the probability of having your content delivered from CDN nodes closer to the end user will depend on the spread of the user base, the amount of traffic from your site, the depth of the pages requested and the number of CDN PoPs your CDN employs. See my recent blog post on cachability of websites on CDNs; How Many PoPs Does it Take to Cache a Website for a detailed discussion of these factors.
Bringing content closer to the end user through the implementation of a CDN is a tried and true method of improving website speed. The trick is to choose the best distribution platform for your particular website and user base.