The number that callers dial to access a service.
Each SDN must be unique so that when a caller dials a number, the system can determine which service is being requested.
SDNs are CDNs or phantom DNs that are configured on the switch and then defined on the server and stored in the SDN Table. When a caller dials a number to access a service, the system looks up the number in the SDN Table and activates the appropriate service.