Using the dc_clt_connect_s function, a CUP requests the server's client extended service to establish permanent connection. When the process accepts an establishment request, it passes that request to the CUP execution process. When the CUP receives an establishment acknowledgment message from the CUP execution process, permanent connection is established between the CUP and the CUP execution process.

A one-to-one correspondence is established between a CUP and a CUP execution process. One OpenTP1 node can simultaneously accept as many CUPs as the maximum number of processes for the CUP execution process (the specification of cup_parallel_count in the client service definition).

Then the succeeding messages are transferred through the permanent connection until the CUP releases it using the dc_clt_disconnect_s function. An error also releases the permanent connection. The following figure shows how permanent connection is established and released.

Figure 2-1 Establishing and releasing permanent connection