Is there a good guide to interpreting the Firebug net panel?

Question

I’m using the Net panel in Firebug to evaluate the performance of web pages I’m writing.

Specifically, I’m wondering what the precise meaning is of the stages for each resource that’s downloaded (i.e. DNS lookup, Connecting, Blocking, Sending, Waiting, receiving).

But more generally, is there a Firebug guide where I can look this stuff up?

Answer 1

You can read up on HTTP headers.

And for the whole firebug net panel you can read this.

Answer 2

The various stages correspond to the various states of the connection being made for the resource. I don't know of any documents on them and a quick look around the Firebug network page doesn't show any explanations. There is some documentation in the resources area (wiki) of the Firebug site, though it looks like its subtly different than what is actually presented in the interface. They seem reasonably obvious to me, but I suppose I could be wrong, too.

1. DNS lookup - the name of the remote server is being resolved to an IP address
2. Connecting - a TCP/IP connection is being opened to the remote server
3. Blocking - the client is waiting for another request to complete (or a thread to become available) before sending the request
4. Sending - the client is sending data to the remote server
5. Waiting - the client is waiting on a response from the remote server
6. Receiving - the client is reading data from the remote server

Answer 3

Although it doesn’t include an answer to this question, Amy Hoy and Thomas Fuchs’s PDF ebook JavaScript Performance Rocks! has a lot of good information about measuring web page performance using Firebug