Visibilità variabili in funzioni

[wallrider]

ho questo file db_functions.php

<?
include './db_config.php';
function db_connect(){
    return odbc_connect($odbc_dsn,$db_utente,$db_password);
}
function db_close($idConn){
    return odbc_close($idConn);
}
function db_exec($idConn,$query){
    return odbc_exec($idConn,$query);
}
function db_fetch_row($idRs){
    return odbc_fetch_row($idRs);
}
function db_result($idRs,$numCampo){
    return odbc_result($idRs,$numCampo);
}
function db_num_fields($idRs) {
    return odbc_num_fields($idRs); 
}
?>

con db_config.php così

<?
$odbc_dsn="odbcOrdini";
$db_utente="";
$db_password="";
?>

perchè la connect mi da errore

Notice : Undefined variable: odbc_dsn in C:\symo\www\Ordini\db_functions.php on line 7