DFM enables authorized users and applications on DDM source systems to access z/OS® data remotely. Applications executing on DDM source systems can access z/OS data by exploiting the DFM target support.

DFM participates in APPC LU 6.2 conversations with DDM source implementations. The conversations are exchanges of DDM source commands and DDM target responses. APPC/MVS works with VTAM® to provide the logical connection on z/OS for network conversations with source systems. VTAM manages the local logical unit (LU) that forms an LU 6.2 to LU 6.2 link with a partner LU on a remote system.

RACF®, or an equivalent product, provides authorization services for controlling access to DFM. Once a conversation is established, RACF also provides authorization services for controlling access to the z/OS data.

DFM provides access to z/OS data to DDM source implementations as follows (see Figure 1):

1. An LU 6.2 to LU 6.2 network link is established between a DDM source and VTAM and APPC/MVS on the DDM target z/OS system.
2. The DDM source sends an LU 6.2 allocate request to initiate a conversation with DFM.
3. The RACF authorizes the DDM source access to DFM.
4. The APPC/MVS scheduler (ASCH), running in an APPC conversation address space, initiates and schedules the DFM started procedure address space.
5. DFM, running in the DFM central address space, processes the allocate request from the DDM source. It begins a network conversation with the DDM source exchanging DDM commands and messages.

Figure 1. Distributed FileManager Processing Environment