File talk:HTTP pipelining.svg

Diagram doesn't match the article's description
The article on HTTP Pipelining says that the client doesn't know whether the Web server is HTTP/1.1 until it gets a response, therefore it can't use pipelining on its first request. So the timeline should show one arrow from client to server, one arrow from server to client (the initial response with the HTTP/1.1 line), then two more arrows from client to server and two from server to client (pipelined requests and responses).

I didn't know that bit about identifying the server's HTTP version until I read this article; I would've made the same mistake. I still wonder if browser authors haven't found some way around this behavior, like guessing the server's HTTP version based on past responses.