The Screening function checks E.164 numbers (calling party number or connected party number) according to a predefined pattern. AMO SCREN defines the screening pattern. In case of a wrong or missing number, a default number is transmitted to the network, if required. Screening modifies only the calling and the called numbers (display) and not the dialed station numbers. Screening can be assigned to any node using the NPI (numbering plan identifier) E.164. If used as a trunk interface in a Carrier network, the OpenScape 4000 must carried out the screening procedure, as is required of an EWSD trunk interface.

The network depicted in Figure 69, which contains a OpenScape 4000 and an ISDN PBX, shows the relation between the network side (N) and the user side (U) for DSS1 and trunk interface networking.

The interface from the OpenScape 4000 (in the example: node 1-1-100) to another PBX (in the example: node 1-1-400) serves as a gateway either to an individual PBX or to an "external" network.