Changing logical link assignments

You define initial logical link assignments (logical link to physical link) as part of the IMS system definition process. However, you can change logical link assignments dynamically.

To dynamically make or change a logical link assignment, use either the type-1 command /MSASSIGN or the type-2 command UPDATE MSLINK NAME(linkname) SET(MSPLINK(msplinkname)).

Recommendation: Use the /MSASSIGN command or the UPDATE MSLINK NAME(linkname) SET(MSPLINK(msplinkname)) command to create logical links only for unscheduled reassignments resulting from failing physical connections or systems.

Because a logical link must always communicate with its partner, the operators for the two systems must coordinate their assignments of corresponding physical links. You can replace any type of physical link with any other type of physical link.

Changes to logical link assignments remain in effect until you change them using an /MSASSIGN command, UPDATE MSLINK NAME(linkname) SET (MSPLINK(msplinkname)) command, or cold start IMS. The commands only alter the relationship of MSC resources in the local system.

The logical link relationships you can change and the commands you can use to change them include:

  • Logical link to physical link
    • Type-1 command /MSASSIGN.
    • Type-2 command UPDATE MSLINK NAME(linkname) SET (MSPLINK(msplinkname)).
  • Remote SYSID to logical link
    • Type-1 command /MSASSIGN.
    • Type-2 command UPDATE MSNAME NAME(linkname) SET (MSPLINK(msplinkname)) assigns an MSNAME with the desired remote SYSID to a logical link. Alternately, you can modify the remote SYSID of the MSNAME already associated with the logical link by issuing the type-2 command UPDATE MSNAME NAME(msname) SET(SIDR (remote_sysid)).
  • Logical link path to logical link:
    • Type-1 command /MSASSIGN.
    • Type-2 command UPDATE MSNAME NAME(msname) SET(MSLINK(mslinkname)).

You can also use the /MSASSIGN command to complete the following tasks:

  • Change a remote program to local
  • Change a local program to remote
  • Assign a logical path

When you modify logical link assignments:

  • Operating logical or physical links must be assigned one-to-one, except for TCP/IP and VTAM® link types, which can have parallel sessions in effect. In this case, multiple logical links can be assigned to one physical link.
  • If the link uses TCP/IP or VTAM, before you assign a logical link either to or from an MSPLINK name you must stop the physical link by executing one of the following commands:
    • The type-1 command /PSTOP MSPLINK
    • The type-2 command UPDATE MSPLINK NAME(msplinkname) STOP(LOGON)
    • In a TCP/IP generic resource group, the type-2 command UPDATE MSPLINK NAME(msplinkname) STOP(GENLOGON)
  • Before reassigning a logical link, you must stop the logical link by using either a type-1 command /PSTOP or a type-2 command UPDATE MSLINK NAME(linkname) STOP(COMM) and the logical link must be idle.
  • A destination SYSID cannot be reassigned to a logical link unless its currently assigned logical link is idle after a type-1 command /PSTOP or a type-2 command UPDATE MSLINK NAME(linkname) STOP(COMM).
  • MSC communication can occur only when logical links in two IMS systems share the same partner identification and have assignment to an operating communications facility between the systems.
  • IMS does not determine whether the requested logical link assignment is reasonable or results in a valid configuration for MSC communication. This is only done by communication with appropriate remote systems. You can accomplish this using the /MSVERIFY command after making assignment changes.