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SSCP takeover z/OS Communications Server: SNA Network Implementation Guide SC27-3672-01 |
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In a combined APPN and subarea network, VTAM® provides full takeover capability. A connection that is established as an APPN or LEN connection remains such until it is deactivated. However, an SSCP taking over an APPN connection views it as an LEN connection if the takeover SSCP has not implemented APPN. No CP-CP sessions can be established over the connection until the original SSCP regains control. For example, in Figure 1, if HOSTA fails and HOSTB takes over, the connection from the NCP to the adjacent CP is viewed by HOSTB as an LEN connection if HOSTB has not implemented APPN. No CP-CP sessions can be established over the connection until HOSTA regains control. Figure 1. SSCP takeover when adjacent
CP does not support CP name change
If the takeover SSCP has implemented APPN, a connection is still
treated as an LEN connection if both of the following are true:
For example, in Figure 1, if HOSTA fails and HOSTB takes over, the CP name (from the perspective of the adjacent CP) changes from HOSTA to HOSTB. If the adjacent CP does not support the changing of CP names, HOSTB treats the connection to the adjacent CP as an LEN connection (even if HOSTB has implemented APPN) and no CP-CP sessions can be established over the connection until HOSTA regains control. If the adjacent CP does support the changing of CP names, CP-CP sessions can be established when HOSTB takes over. If the adjacent CP is located over a subnetwork boundary, the following
conditions must also be met to allow a new CP-CP session with the
takeover SSCP:
If the adjacent control point is another composite network node as shown in Figure 2, SSCP takeover with APPN connectivity occurs if the takeover SSCP has implemented APPN. For example, in Figure 2, if HOSTB has implemented APPN and HOSTA fails, HOSTB can take over, and a CP-CP session between the composite network nodes (HOSTC/NCP2 and HOSTB/NCP1) is established. The APPN connection between the NCPs is viewed as an LEN connection by the adjacent control point after takeover if the takeover SSCP has not implemented APPN. Figure 2. SSCP takeover when adjacent
CP is another composite network node
Notes:
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Copyright IBM Corporation 1990, 2014
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