Question

Consider the figure below that shows how the time to download a file (also known as page load time (PLT)) from a webserver decreases as the bandwidth is increased. Why do you think the page load time stops decreasing after a point even though the bandwidth is increased? 3,500 3,000 2,500 2,000 2 1,500 1,000 Bandwidth 1 Mbps 2Mbps 3Mbps 4Mbps 5Mbps 6Mbps 7 Mbps 8Mbps 9Mbps 10Mbps

Answer 1

There can be a number of reasons for this behavior. I will list a few of them below:-

1) Speed of server:- For ease of understanding suppose one server is serving to one client only. Now if bandwidth at the server side is less than the client's than here server's speed is the bottleneck. Therefore once bandwidth of server < bandwidth of client Page loading time will not decrease on increasing client's bandwidth.

2) The number of Http/Https requests:- Most of the websites make multiple requests for displaying even a single page. This is because usually CSS, javascript, media files are sent separately. On each Http request following steps are executed:-

a) DNS lookup.

b) Server processing

c) Server Response

The above processes are independent of client's bandwidth after Http requests are made. Therefore after a point, there is no decrease in page load time.

3) Latency:- Increase in bandwidth doesn't mean decrease in latency. Usually, latency is of the order of milliseconds but if the webpage uses multiple connections or makes multiple Http requests than this latency reduces the benefits gain by increasing bandwidth.

4) Processing power of server:- Servers are basically computer systems present remotely. On receiving a request, a server has to process the url to locate requested resource and return a response. This process takes time which is independent of bandwidth. Once bandwidth is sufficient this processing time of server becomes dominant in page load time. Hence, PLT remains same even if bandwidth is increased.

5) Type of webpage:- if your webpage contains only HTML than it will not affect PLT but if it uses a lot of CSS and Javascript than PLT will be significantly affected. As it takes time for a browser to render CSS and Javascript which has nothing to do with bandwidth. Also, some pages usually use deferred javascript loading which increases page load time.