3

After the SSCP establishes a session with the device-type LU, that LU might attempt to initiate a session with a VTAM® application program LU. Action by the device-type LU to start such a session is usually initiated when a terminal operator communicates with the LU and indicates that he or she wants to work with an application program in the host processor. The LU either uses the logon information entered by the terminal operator to create an Initiate request to be sent to the SSCP, or the LU passes the logon information from the terminal operator to the SSCP in the form in which it is received from the operator. The SSCP immediately translates the logon form of the request into an Initiate request format.

In a similar manner, after its SSCP-LU session is established, a VTAM application program (replacing the device-type LU in Figure 1) can request that a session be initiated between itself and another LU (for example, another VTAM application program). It does this by issuing a VTAM macroinstruction that causes an Initiate request (containing logon information) to be sent to the SSCP.