Hello!
I Russian, sorry for my bad English! 
My PHP-script get files, but I need speed limit to download.
For this I use sleep() function. But I have a bad effect!
When the download starts
1) Browser tab going for a long time (from 30 seconds to 1 minute)
2) Loading begins at the right speed
3) Download suited to a specific point* and stops
4) The browser reports a problem with the connection
*specific point - multiple of the value of the variable$download_rate (limiting speed). See code. If $download_rate = 100, download stoped on 10 Mb of file, if 50 - 5 Mb...
This problem is only on IIS, Apache all right! 
Withoutsleepallrighttoo!
PHP-code:
<?php$file = 'video.avi';
set_time_limit(0);
ob_end_clean();$download_rate = 100; // speed limit kb/s$fd = fopen($file, 'rb'); // Open file from read
// HTTP-headers code... (cut)
while (!feof($fd))
{
print fread($fd, $download_rate * 1024); // read block file ang out
sleep(1); // sleep 1 second
}
fclose($fd);
exit;
?>Technical information:
Web-Server: IIS 7.5
OS: Windows Server 2008 R2 x64 SP1
PHP: v5.6.9 Win32 VC11 x64
Browser: not important
Please, Help me!