gtps2m4e | ACF/SNA Data Communications Reference |
A TPF/CTCP is required to handle the NPSI commands and data messages that flow between NPSI and TPF on the NPSI to CTCP LU-LU sessions in the GATE environment, as shown in Figure 104.
Figure 104. TPF/NPSI Sessions Involving a CTCP
The NPSI commands, which flow between NPSI and the CTCP, control access to the services of the X.25 Packet Switched Data Network (PSDN). The data flows between NPSI, the CTCP, and the application(s) are used to exchange data messages transported through the PSDN.
A principal function of a CTCP is to handle NPSI X.25 network commands for switched virtual circuits, such as:
With the GATE option, the CTCP is the common session partner with NPSI for both data messages and commands. Therefore, a GATE CTCP can be used to provide the equivalent of Open System Interconnect (OSI) layers 4, 5, 6 and a portion of 7.
OSI layer 4 is the Transport layer and includes:
OSI layer 5 is the Session layer and includes:
OSI layer 6 is the Presentation layer and provides:
ASCII
EBCDIC
Binary
OSI layer 7 is the Application layer and provides:
The material that follows details the GATE CTCP environment by describing how you may extend the TPF communication support using PSV routines to allow communication between non-SNA terminal end points and existing or new TPF applications.