gtps2m2j | ACF/SNA Data Communications Reference |
When the TPF system is connected to the network as an APPN end node, special control sessions exist between the TPF system and its network node server (NNS). An NNS is a network node that provides services to an end node (the TPF system in this case). The control point (CP) in the TPF system exchanges data with the CP in the NNS using CP-CP sessions.
CP-CP sessions are used during the LU-LU session activation process to exchange data between the TPF system and the APPN network. You cannot start new LU-LU sessions if the CP-CP sessions are not active. CP-CP sessions provide services that are similar to the services that CDRM-CDRM sessions provide to a PU 5 network. One key difference is that the deactivation of the CP-CP sessions for any reason does not cause the active LU-LU sessions to be deactivated. Only the LU-LU sessions that are in the process of being activated when the CP-CP sessions fail will be cleaned up.
When the TPF system is connected to a PU 5 network, each processor in the TPF loosely coupled complex can have CDRM-CDRM sessions to many remote hosts. In an APPN network, an end node can be connected to many different network nodes but can have active CP-CP sessions to only 1 network node. If the active CP-CP sessions fail, new CP-CP sessions can be started with the same network node or a different network node. Because the TPF loosely coupled complex is 1 end node, only 1 TPF processor has CP-CP sessions.
CP-CP sessions are critical resources; therefore, the TPF system automatically attempts to activate CP-CP sessions when the network is started. If the active CP-CP sessions fail unexpectedly (for example, because of a path failure), the TPF processor that had the CP-CP sessions will attempt to activate new CP-CP sessions.
When CP-CP sessions are not active, they can be activated by a TPF operator or by a remote operator. To activate CP-CP sessions from the TPF operator console, use the ZNETW ACT command. See TPF Operations for more information about the ZNETW ACT command.
CP-CP sessions can be deactivated by a TPF operator or by a remote operator. To deactivate CP-CP sessions from the TPF operator console, use the ZNETW INACT command. See TPF Operations for more information about the ZNETW INACT command.
If an LU is defined to the TPF system as a remote CP, the only sessions it can have are CP-CP sessions. The TPF system does not support sessions between a remote CP and a regular TPF application (that is, an application that is not a local TPF control point LU). In addition to having CP-CP sessions, the LU that represents the TPF CP can be in session with remote LU 6.2 nodes that are not control point LUs.
Only 1 processor in the loosely coupled complex can have CP-CP sessions. You can use the ZNAPN STATUS command to determine if CP-CP sessions are active and, if so, on which processor.
Before a TPF processor attempts to automatically start CP-CP sessions, the UACP user exit segment is called to determine whether this TPF processor is allowed to start CP-CP sessions. UACP allows you to limit CP-CP session activation attempts to a subset of the TPF processors that reside in the loosely coupled complex. See TPF System Installation Support Reference for more information about the UACP user exit.
Cycling down the TPF processor with the CP-CP sessions to below CRAS state prevents new LU-LU sessions from being established for the entire loosely coupled complex until that host is cycled up again. Cycling down the processor with the CP-CP sessions is not recommended and will result in an attention message on the operator console. If you need to cycle down the processor with the CP-CP sessions, do the following:
See TPF Operations for more information about the ZNETW ACT and ZNETW INACT commands.
Follow the same procedure if you want to take the processor with the CP-CP sessions out of the complex. However, if the processor with the CP-CP sessions fails causing an unplanned outage, you must follow a different procedure. If the links to the failing processor have not reached their automatic network shutdown (ANS) time-out value, the links are still considered active from the point of view of the network. This means that the network considers the CP-CP sessions to still be active. Until those CP-CP sessions are deactivated, new CP-CP sessions cannot be started. This is why the TPF system does not attempt to automatically start new CP-CP sessions when the processor with the active CP-CP sessions fails.
When the processor with the CP-CP sessions fails, do the following:
See TPF Operations for more information about the ZNETW ACT and ZNETW INACT commands.
If the TPF processor with the CP-CP sessions performs either a hardware IPL or software IPL, the TPF system deactivates the CP-CP sessions and then attempts to activate new CP-CP sessions during cycle up. Only LU-LU sessions that are being activated are affected by this action, causing the session activations to fail; LU-LU sessions that are active are not affected by the deactivation and reactivation of the CP-CP sessions.
In a loosely coupled complex, LU-LU sessions on all TPF processors that are being activated will fail if an IPL is performed on the TPF processor with the CP-CP sessions. If an IPL is performed on a TPF processor that does not own the CP-CP sessions, only the LU-LU sessions that are being activated on that TPF processor will fail; LU-LU sessions being activated on the other TPF processors are not affected.