5.13. EURO-ISDN Exchange Interface 
The OpenScape 4000 can be connected as an NT2 unit at the V reference
point (TO basic access and T2 primary rate access) of the European EURO-ISDN
network.
Figure 19. Reference model
The supplementary services supported on the exchange interface onward
are as follows:
- Direct Dialing In (DDI) An exchange subscriber can dial straight through to a OpenScape 4000 user. In this case the OpenScape 4000 user receives a different type of call signalling (trunk call) from that used for inside calls.
- Calling Line Identification Presentation (CLIP) The number of the calling party appears on the display at the called terminal. The number is displayed during the ringing phase.
- Calling Line Identification Restriction (CLIR) The calling party can suppress the call number display by pressing a key at the start of an outpoing call.
- Connected Line Identification Presentation (COLP) The number of the user who has actually been accessed is indicated on the display of the calling terminal. The number is displayed when the connection is switched through.
- Connected Line Identification Restriction (COLR) Display of the user who has been accessed is suppressed by the called terminal.
- User-to-User Signaling (UUS) Communication between terminals.
- Subaddressing (SUB) The ISDN subaddress is used for the more precise addressing of subcomponents within the user equipment selected with the ISDN number.
The following figure illustrates the structure of the ISDN addres:
Figure 20. Structure of the ISDN address
