In a combined APPN and subarea network, VTAM® provides for shared ownership of a local or remote NCP by two VTAMs.

If two VTAMs share an NCP, they both must have a subarea connection to that NCP and thus a subarea path between them. These two VTAMs can communicate through an SSCP-SSCP session. The topology of the APPN network connected to one VTAM is not shared with the APPN network connected to the other VTAM, unless CP-CP sessions also exist between the two VTAMs. If CP-CP and SSCP-SSCP sessions exist between the two VTAMs, the decision about which control session to use for a specific LU-LU session setup depends on resource locations, start options, and tables.