For interface description parsing, I have copied the whole port-descr-parser.inc.php file to custom-port-descr-parser.inc.php file, and added below lines in the new file:

cust: cust_name [speed] (a_note) {circuit_id}

Finally, added below lines in config.php file:

$config['int_transit']             = 1;  // Enable Transit Types
$config['int_peering']             = 1;  // Enable Peering Types
$config['int_core']                = 1;  // Enable Core Port Types
$config['int_customers']           = 1;  // Enable Customer Port Parsing
$config['port_descr_parser'] = "includes/custom-port-descr-parser.inc.php";

But it's not working. Need help :-(