The meaning of Blocking in Chrome console -> Network -> Timing

Question

Recently I have noticed that Chrome browser has Timing tab in the Network section.

This tab has the following elements:

For example here is a screenshot for SO: enter image description here

Also I think I know what sending, waiting and receiving means, I have no idea what Blocking means.

So what blocking means? What does it block and what makes these numbers smaller/bigger?

possible duplicate of [What does the times mean in Google Chrome's timeline in the network panel?](http://stackoverflow.com/questions/10537399/what-does-the-times-mean-in-google-chromes-timeline-in-the-network-panel) — Steffen Nieuwenhoven, Mar 03 '14 at 13:43
This is something that answers this: https://developer.chrome.com/devtools/docs/network — Sohail xIN3N, Sep 09 '14 at 07:59

score 3 · Answer 1 · edited May 23 '17 at 11:57

'Blocking' is the time difference between the HTTP request being ready to be sent and actually being sent. Formal definition here.

Why wasn't the request sent when it was ready to be sent? There could be multiple reasons for that, e.g.

The maximum number of TCP connections that the browser could open are all busy processing some other requests. E.g. Chrome opens upto 6 TCP connections per server/proxy. So this request has to wait till one of them gets free. Refer here for other browsers.
Proxy negotiation may be required for sending the request.
The machine running the browser may be slow or overloaded. So although the request is ready, it is busy doing something else.

1 Answers1