Multiple Subscriber Number

Multiple Subscriber Number - a telephone number associated with an ETS 300 BRI line. Providers of ETS 300 often give you three MSNs with a BRI, although additional MSNs can be purchased. An ISDN terminal will "ring" (provide an alerting signal) only when calls are made to the MSN (or MSNs) entered in that terminal. If a terminal has no MSNs entered it will "ring" whenever there is a call to any of the MSNs on that BRI.