PHP curl bandwidth

I have a php script that uses curl to download a remote file.

Let's say I have two servers: a and b. And the script file name is curl_download.php on the开发者_高级运维 a server.

When I access curl_download.php?filename=something, it promtes browser's download window.

Am I using bandwith on server a or b? or both?

I assume both, but I am not sure.

If the action of curl_download.php is to request a file from server b and send it back to the user's browser, you are using 1 file size unit of upload bandwidth on server b (to get the file to server a), and 2 file size units of bandwidth on server a (half download to get the file from server b, and half upload to send it to the user.) That, plus the small overhead of the request parameters (headers).