Functions provided by VTAM in a sysplex

A sysplex is a set of MVS™ systems communicating and cooperating with each other, through certain multisystem hardware components and software services, to process customer workloads. The inclusion of a coupling facility within the sysplex allows for high performance data sharing. For more information about sysplex, see z/OS MVS Setting Up a Sysplex.

VTAM® supports the attachment of a sysplex to a network. Sessions into the sysplex can be established from either subarea nodes or APPN nodes. There are several VTAM functions that are available only in a sysplex environment. If a coupling facility and an APPN or mixed APPN and subarea environment exists in the sysplex, the user can take advantage of the following VTAM functions:

Generic resources: Allows an user to easily connect to any one of a number of duplicate application programs on different systems. The user uses a generic name and VTAM determines the actual application program for the session based on workload and other performance criteria.
Multinode persistent sessions: Allows for the restoring of an application program session during a planned or forced takeover, or after hardware, operating system, or VTAM failures.
TSO generic resources: Allows for multiple TSO/VTAM application programs to have a common name. During session establishment, VTAM determines the actual application program to be used for the session.
Dynamic definition of VTAM-to-VTAM connections: Allows for dynamic establishment of XCF connections between VTAM nodes in a sysplex when VTAM is initialized with the XCFINIT start parameter, or at a later time when the operator determines connections can be established (by activating the XCF Local SNA major node, ISTLSXCF).

VTAM also provides support for TCP/IP functions that need access to a coupling facility. If a coupling facility exists in the sysplex, the user can take advantage of the following TCP/IP functions:

Sysplexports

Enables multiple TCP/IP stacks in the sysplex to collaborate on the assignment of ephemeral port numbers for a distributed dynamic virtual IP Address (DRVIPA) that is shared by a number of applications. This function uses a structure in the coupling facility to track the ephemeral port assignments across the sysplex.

Sysplex-wide security associations

Allows for IPSec security associations (SA) and their workloads to be distributed to target TCP/IP stacks within the sysplex. It also allows the SAs to be automatically restarted on another processor in the sysplex when a dynamic routable virtual IP Address (DRVIPA) takeover occurs. This takeover capability is provided for the following cases:

Takeover occurs because the VIPA owning stack or its host went down (unplanned takeover)
Takeover or giveback occurs when the stack and its host stay up but a VIPA ownership change between hosts is required (planned takeover)