This parameter allows to chose either a "POINT-TO-POINT" or "MULTIPOINT" (default) topology.

If you only intend to connect a single device/application to your ISDN line, then you only need the POINT-TO-POINT configuration. With the configuration you are assigned a single phone number per ISDN line (not one for each B-channel).

If you intend to connect multiple devices/applications, then you need the MULTIPOINT. With multipoint configuration you are assigned a phone number for each device connected...

Note that MULTIPOINT topolgy is supported in TERMINAL mode only.