A VTAM® application program can initiate a session in which it acts as the PLU by issuing an OPNDST OPTCD=ACQUIRE or SIMLOGON macroinstruction. This permits an application program to initiate a session and is useful, for example, if a device-type LU (such as an unattended printer) cannot itself initiate the session, or if the time when a session is needed is known only by the application program. This requires that the application program have previous knowledge of the LU's existence. An application program can also initiate a session (for example, an LU-LU session between programs) in which it acts as the SLU by issuing a REQSESS macroinstruction. (REQSESS cannot be used when the requested PLU is an independent LU.)