gtps2m1gACF/SNA Data Communications Reference

System Restart

TPF restart is generally responsible for bringing the TPF system back to the state it was in at the time of a system outage. During software IPL, the CCBs and SCBs are considered critical records, and the entire CCB and SCB areas are filed to the DASD area to insure a current copy is available for the subsequent TPF restart programs.

The TPF restart programs recognize when the TPF SNA resources have been redefined across a system outage. TPF SNA resources are redefined by loading a new copy of the OSTG pilot tape, which is used to define the SNA resources as known to TPF. When this occurs, all sessions with the remote SNA resources are disrupted. When the TPF/APPC restart programs recognize that this fresh load has taken place, the conversation allocation process must begin again; no attempt is made to notify the remote transaction program of any conversation deallocation, because the underlying session required to send the notification has been unbound.

Session Considerations

If a hardware IPL occurs, TPF unbinds all LU 6.2 sessions and does not attempt to bring these sessions back. TPF does retain the session limits previously initialized so you do not have to issue another CNOS INITIALIZE request.

If a software IPL occurs, the LU 6.2 sessions remain active; however, all conversations are deallocated.

Conversation Considerations

Conversations that were active at the time of an outage are represented as a transaction program instance, identified in a TPF entry control block (ECB) by a unique TCB ID. Because all ECBs are lost across a system outage, any conversations controlled by the transaction program instance must be deallocated. The TPF restart segments activate the TPF/APPC support restart segments. TPF/APPC restart uses the keypointed copy of the CCB on the fixed file to find all conversations that were active at the time of the system outage. Then, TPF/APPC notifies the remote transaction program that the conversation was terminated by sending a DEALLOCATE request. The local TPF transaction program, represented by the ECB and associated programs, cannot be notified of the system outage implied by a TPF restart.