WPT synthetic latency: Fixed or variable?

WebPageTest General Discussion
1

Hello all,

I have a question that I couldn’t find a definitive answer to in the docs.

When I set up a webpagetest and select “advanced settings” to input a custom dl/ul/latency/packet loss configuration, is the latency fixed or variable?

For instance, if I select 300 ms latency, does that mean that 300ms of latency is always applied, or is that an upper limit for a randomized value? (math.random(0,300))

I’d assume that it’s fixed for the sake of consistency, but just wanted to know if by chance it was variable (to more accurately emulate user latency which would be more of a ‘ballpark’ figure.

Any input is useful. Thanks!

2

Latency is fixed so you can get reproducible results. With custom connectivity profiles you can alter the latency to be whatever you’d like so you can test and broad range of user characteristics if you’d like. 300ms is just a reasonably representative selection.

3

Thanks @pmeenan !!