I'm testing out the Google Chrome Speed Tracer on a few common web pages and taking a look through the results. One thing I'm not sure I understand is what the "Request Timing" and "Response Timing" properties of resources are actually measuring.

Initially I thought Request Timing must measure the time from a request for a resource being sent and when that request arrived at the server. However, I then wondered how the Speed Tracer would actually have any way of measuring this. Furthermore, the Response Timing that I'm getting for resources tends to be far less than the Request Timing (e.g. 500ms request, 1ms response), which is a little bit suss.

So is anyone able to explain exactly what Request Timing and Response Timing are measuring?