The number of HTTP requests need to be made for downing a webpage?

Are all assets (html files, js files, css files, images) in one webpage transmitted through a single HTTP reques开发者_运维问答t/response, or through multiple HTTP requests/responses, one for each asset? Assumed no XHR in that webpage.

All the digital assets on a web document are transmitted on separate HTTP requests. However modern web servers and browsers are able to use the same TCP connection with HTTP keep-alive.

Conceptually, each asset is a separate request. In practise, most servers allow the browser to re-use the same physical socket connection for multiple requests (but they are still issued one after the other) and this can significantly improve performance (because you need extra round-trips to establish a connection, and subsequent requests can piggy-back on the ACKs for the previous request: you cut down on a lot of round-trips).

But yes, there is always one request/response per asset on the page.

On connections with high latency (e.g. Australia -> U.S.) the number of round-trips can be a significant bottleneck, and that's why things like CSS sprites are widely used.

It's one request per asset, but you can use multiple TCP connections to send multiple HTTP requests in parallel. In fact all browser do exactly that.

I'd recommend downloading Firebug for Firefox, then watching its 'Net' tab while you browser some sites. It would answer this question and so many more.