Overview of the TCP/IP and PSF interface

TCP/IP must be running on the z/OS® system before any attempt is made to start PSF. PSF must establish a communication path with TCP/IP (by issuing the INITAPI macro from each printer FSA) before any communication can occur.

TCP/IP must keep state information for this interface. If a TCP/IP abend occurs, the state information is gone and TCP/IP has no knowledge of any interfaces established previously. This has several implications to PSF FSAs:

If an FSA is actively using TCP/IP at the time of the abend, a PSF abend also occurs because communication is ended with the printer. The abend is not a restartable abend because there is a severe communication error that must be fixed.
If an FSA is idle when a TCP/IP abend occurs or is stopped, the FSA remains active until a print job is acquired, at which time an FSA abend occurs if TCP/IP is still not active. If TCP/IP has been recycled and is active again, PSF gets a bad return code from TCP/IP because PSF is still using the old interface established from the previous TCP/IP session. PSF attempts to reestablish the link with TCP/IP again by issuing an INITAPI. The print job is sent after the link is established.

No TCP/IP services are run until a TCP/IP printer is started. At that time, hangs or abends in TCP/IP services could influence other FSAs (any attachment) under the same FSS as the TCP/IP FSA. For this reason, it is recommended that TCP/IP-attached printers should not be driven by the same FSS as printers with any other attachment type (SNA, parallel channel, or ESCON).