downloads manager system

INSERT INTO tres_downloads_serv (dl_start_time, dl_update_time, dl_remaining_time, dl_id, dl_link, dl_cat_folder, dl_title, dl_size, user_id, user_uname, user_email, user_status, max_connect, speed_multiplier, dl_status, serv_id, user_ip) VALUES ('".time()."', '".time()."', '".round($file_size/($speed_multiplier*1024))."', '$dl_id', '$dl_link', '$dl_cat_folder', '$dl_title', '$file_size', '$user_id', '$user_uname', '$user_email', '$user_status', '$max_connect', '$speed_multiplier', '2', '$id', '$_SERVER[REMOTE_ADDR]')

	header("Pragma: public");
	header("Expires: 0");
	header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
	header("Content-Type: $ctype");

	$user_agent = strtolower ($_SERVER["HTTP_USER_AGENT"]);
	if ((is_integer (strpos($user_agent, "msie"))) && (is_integer (strpos($user_agent, "win")))) {
		header( "Content-Disposition: filename=".basename($filename).";" );
		} else {
		header( "Content-Disposition: attachment; filename=".basename($filename).";" );
		}
	header("Content-Transfer-Encoding: binary");
	header("Content-Length: $serv[dl_size]");

	$start_time = time();
	$sessid = $start_time+30;

	$sql = mysql_query("UPDATE tres_downloads_serv SET
						dl_update_time    = '".time()."',
						dl_remaining_time = '".($serv[dl_size] / ($serv[speed_multiplier]*1000))."',
						user_ip           = '$_SERVER[REMOTE_ADDR]:$_SERVER[REMOTE_PORT]'
						WHERE serv_id = '$id'");

	$fp = fopen($filename, 'r');

	$speed=($serv[speed_multiplier] * 1024);
	while (!feof($fp)) { 
		echo(fread($fp, $speed)); 
		flush();

		sleep(1);
		if(time() > $sessid) {
			$sessid = $sessid+30;
			$currenty = ftell($fp);
			$elapsed = time() - $start_time;
			$time_left = ($serv[dl_size]/($currenty/$elapsed)) - $elapsed;

			$netstat = eregi("$_SERVER[REMOTE_ADDR]:$_SERVER[REMOTE_PORT]", shell_exec("netstat -n |grep ".$_SERVER[REMOTE_ADDR].":".$_SERVER[REMOTE_PORT].".*EST"));
			if(empty($netstat)) {
				$sql = mysql_query("DELETE FROM tres_downloads_serv WHERE serv_id = '$id' AND user_ip = '$_SERVER[REMOTE_ADDR]:$_SERVER[REMOTE_PORT]'");
				die;
				}

			$sql = mysql_query("UPDATE tres_downloads_serv SET
								dl_update_time    = '".time()."',
								dl_remaining_time = '$time_left'
								WHERE serv_id = '$id'");
			}
		}
	fclose ($fp);

	$sql = mysql_query("DELETE FROM tres_downloads_serv WHERE serv_id = '$id'");

	die;