direct inward system access (DISA)

Direct Inward System Access(DISA) is a service provided by PBXs.

With the DISA service, external callers can access the PBX from outside with the appropriate access rights and establish external connections to incoming calls. With the DISA service, the external subscriber receives the internal dial tone and can use it to set up calls in the same way as within the PBX.

For protection, the subscriber receives a passcode, which is terminated with the slash character (#). If the passcode is correct, the subscriber receives the dial tone and can dial his call connections.