Couse there was no example code for this function, i had alot of troubles to make it work properly. 

So, here is working example:

function rebind_on_ref ($ds, $ldap_url) {
  global $binddn;    // DN used to bind
  global $bindpw;    // password used to bind

  // required by most modern LDAP servers, use LDAPv3
  ldap_set_option($a, LDAP_OPT_PROTOCOL_VERSION, 3);

  if (!ldap_bind($a,$binddn,$bindpw)) {
        print "Cannot bind";
  }
}