The Multiple Subscriber Number (MSN) is a feature ofISDN. It is a multiple telephone number for a multi-device connection. In ISDN, up to ten arbitrary, free call numbers from the call number volume of the respective access area can be assigned for the multi-device connection. Each terminal can thus be assigned an individual call number. Several call numbers can also be assigned to one ISDN terminal or PBX. On the other hand, several terminal devices can be connected to the passive bus via a multiple call number.