You do not provide this environment variable. BIS sets the environment variable when a service program is started and creates
the file when
B_ReadRequest is called.
A separate file is created for each service program, and the same file is used by
B_ReadRequest to receive requests from BIS.
B_WriteResponse to transmit responses to BIS.
While the filename is already known when the service engine is started, the file itself is not created until
B_ReadRequest is called for the first time by the service program.