[otrs] Customers queues

Dear All, We use OTRS for our CallCenter and HelpDesk and find it great. Could anyone tell us how it is possible to limit queues access to customers. For example, we have a queue called HelDesk and different sub-queues (Windows, Apple, Security, Mail, etc...) We would like that customers using the OTRS customer interface just have access to the main queue HelpDesk and can't see the sub-queues. Is it possible and how ? Many thanks in advance for any light. Best regards, Philippe Roth - Switzerland