If you want to use VTAM® services to access a CICS® region on another MVS™ image, you must ensure that the required cross-domain services are defined to the VTAMs involved.
For example, to be able to use a VTAM APPC connection between a CICS region (applid CICSHTH1) on MVS image MVSH and a CICS region (applid CICSHAJ1) on MVS image MVSJ:
For example, you could:
CDIDHAJ1 VBUILD TYPE=CDRSC
*********************************************
* CDRSC for access to applid CICSHAJ1 on MVSJ
*********************************************
CICSHAJ1 CDRSC CDRM=IYAMCDRM MVSJ
/V NET,ACT,ID=CDIDHAJ1
CDIDHTH1 VBUILD TYPE=CDRSC
*********************************************
* CDRSC for access to applid CICSHTH1 on MVSH
*********************************************
CICSHTH1 CDRSC CDRM=IYALCDRM MVSH
/V NET,ACT,ID=CDIDHTH1
Specifying a prefix string on the LUAPFX parameter of the CICS APPL statement indicates that VTAM is to generate LUALIAS names for dynamic cross-network CDRSCs in session with the CICS region defined by the APPL statement. This enables CICS to use an LU alias for autoinstalled terminals and work stations and thus ensure unique names in a CICSplex comprising terminal-owning and application-owning regions (TORs and AORs). VTAM generates the LUALIAS names dynamically.
CICS supports both forms of the VTAM alias function--predefined and dynamic--only where shown in the following table:
CICS-to-CICS APPC connections (APPL definitions) | APPC devices (LU definitions) | Terminals | ||||||
---|---|---|---|---|---|---|---|---|
Synclevel 1 | Synclevel 2 | Synclevel 1 | Synclevel 2 | |||||
Predefined alias only | Predefined alias | Dynamic alias | Predefined alias | Dynamic alias | Predefined alias | Dynamic alias | ||
VTAM | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
CICS | Yes | No | Yes | Yes | No | No | Yes | Yes |
CICS supports the use of a dynamic LU alias for CICS terminals and workstations that are autoinstalled only. You enable dynamic LU alias support by specifying LUAPFX on the VTAM APPL definition for any CICS terminal-owning region that could receive duplicate netnames. Also, when starting VTAM, specify the following options on the VTAM START command:
VTAM generates a dynamic LU alias only if LUAPFX is specified on the CICS APPL statement and the resource comes from another network. That is, it has a different network name from the network to which the CICS region belongs.
Use dynamic LU alias where:
The CICS region receives logons from terminals and synclevel 1 connections (both parallel and single sessions) and those logons (or binds) are from cross-network resources that might have duplicate network names.
However, be aware that synclevel 1 connections could become synclevel 2 in the future. For example, if you have a connection between a TXSeries CICS and CICS TS it is synclevel 1, but if you change to using TXSeries CICS with a PPC gateway, synclevel 2 is used. CICS does not support dynamic LU aliases for synclevel 2 APPC connections.
CICS supports the use of a predefined LU alias for CICS terminals and workstations that are explicitly defined and those that are autoinstalled. You can also use a predefined LU alias for CICS regions that communicate using CICS intersystem communication (ISC). You enable predefined alias support by specifying LUALIAS=alias on any cross-domain resource (CDRSC) that needs a specific alias.
An LUALIAS option in the CDRSC is effective if the resource comes from another VTAM domain (or network). That is, it is not used if the resource comes from the same MVS image, but is used if the resource comes from another MVS image regardless of whether it is from the same sysplex, another sysplex in the same network, or from a different sysplex. If an LU alias is predefined, a dynamic LU alias is not generated.
Use predefined LU alias where:
If the following VTAM cross-network resources are to be connected to a CICS region that is defined to VTAM with LUAPFX specified on its APPL statement, they must each have a CDRSC LUALIAS=netname entry:
Like other LUTYPE 6.2 connections limited resource connections release their dynamic LU alias when CDRSCTI expires after the last session is unbound. However, these sessions are unbound whenever they are not in use, and if they rebind after the dynamic LU alias is released, CICS would install another connection, potentially with a different LU alias.
When choosing an LUAPFX value, consider the scope of this parameter within the CICSplex, and also consider its scope within the sysplex in which your CICS regions operate.
A predefined LUALIAS name is supplied to CICS for cross-domain and cross-network resources. All the CICS regions in an MVS image share the same VTAM and are in the same domain. A CICS region in a different MVS image uses a different VTAM and is thus in a different domain. Resources coming from one VTAM to another, but which share the name NETID, are cross-domain resources
A dynamic LUALIAS name is only supplied to CICS for cross-network resources. A resource is a cross-network resource if it has a different network id (NETID). VTAM ensures that all the dynamic LUALIAS names assigned in one MVS image are unique. However, CICS needs network names to be unique across MVS images so that we do not get network name clashes in AORs.
It is important that all CICS regions across all connected networks use unique APPLIDs. This is true whether or not dynamic LUALIASs are used--it just makes it more important.
To ensure that all VTAM resources in a CICSplex have unique network names, use the LUAPFX prefix as follows:
If the LUAPFX values are not the same throughout an MVS image, you risk one resource having two different network names in the CICS regions in that image.
If the LUAPFX values are not unique to each MVS image in the sysplex, you risk two resources attempting to install in a TOR with the same dynamic LUALIAS, or having two resources with the same network name in an AOR.
To ensure the uniqueness of the LU prefix in each MVS, IBM® recommends that you use model APPL definitions, and within these use an MVS system symbol (&SYSCLONE) as suggested in the z/OS V1R4.0 Communications Server: SNA Resource Definition Reference.
The following are some other factors to consider when you are planning to use VTAM LU aliases with CDRSC resources:
There is an example of such code (commented-out) in the sample autoinstall URM, which extracts the network qualified name from the CINIT and BIND. The example illustrates how to create a TERMID from the last non-blank character of the NETID and the last 3 non-blank characters of the real network name (NETNAME).
Resources for which CICS uses any VTAM LUALIAS (predefined or dynamic) and which come from a different network are catalogued if CICS is using persistent sessions. This enables CICS to restore resource terminal session information from the CICS catalog pending recovery of the session from VTAM. However, if the resource does not persist, the resource is deleted during an emergency restart.
This action is necessary because VTAM may have been restarted, which would cause dynamic LU aliases to be reissued to different sessions. CICS is unable to tell if VTAM has been restarted, and CICS cannot tell the difference between a predefined and a dynamic LU alias.