An X.25 packet switching data network (PSDN) can be used to connect two NCP subarea nodes. Support for an X.25 subarea connection requires the X.25 NCP Packet Switching Interface (NPSI) licensed program. Both permanent virtual circuit (PVC) and switched virtual circuit (SVC) connectivity options are supported.

When the X.25 NCP Packet Switching Interface (NPSI) receives a virtual call request for a switched connection, VTAM® enables X.25 NPSI to identify the caller using call security verification (DTE ID verification). The DTE ID carried on the incoming call request packet is checked against the DTE IDs defined on the VERID operand of the PATH definition statement in the switched major node. This verification applies to X.25 subarea node connections. For details on X.25 NPSI system generation, see X.25 Network Control Program Packet Switching Interface Planning and Installation.