On Windows 32 systems.
With Apache Server or IIS

$file = fsockopen ("10.1.1.121", 80, $errno, $errstr, 3);
Where 10.1.1.121 is an generic IP address

If the IP address is not active or there is not an service active on the port the script dead with a timeout (not of 3 seconds but of 30 seconds).

The same problem if I use this:

$file = fopen("http://10.1.1.121", "r");

If I use the @ the script dead after 30 seconds, so also the fopen example with remote url that I have read in the php4 manual dead.