Originally posted by David Dong: Do you mean opening a connection to another webpage? or Do you mean Tunneling ?
I believe Eric means that having each client keep an open TCP connection to your web server is what's hard on the server. It's not "hard" as in the server will crash, but there is a limit to how many physical TCP connections a given server can keep up. Similarly, each of those TCP connections might have a live server-side thread (or process even!) generating some response content which means that you're further limited by the number of simultaneous threads your server can support.