ftp code to upload to my server

Hi,

hope someone can help in what may be a basic problem. I'm trying to get my site to allow users to automatically upload images to my server, however every time i run it the following error occurs: Fatal error: Call to undefined function: ftp_connect() in /myweb/post.php on line 231.

Am I missing something very basic here? The code I have in place is

$ftp_server="myweb.com";
$ftp_servername="myweb.com";
$port="21";
$ftp_user_name="myusername";
$ftp_user_pass="mypassword";

$conn_id=0;
$conn_id = ftp_connect($ftp_server, $port);

$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass);

Any suggestions greatly appreciated