Switching TCP/IP and VTAM physical link types

Because of the operational similarities between MSC physical links that use TCP/IP and those that use VTAM®, the VTAM- and TCP/IP-type physical links are well-suited to serve as a back-up link types for each other.

Prerequisite: In advance of any failure, you must define a redundant set of physical links that use the alternative link type and that duplicate the primary set of MSC physical links. Both TCP/IP and VTAM physical links are defined by using either the MSPLINK system definition macros or the type-2 CREATE MSPLINK command.

Any supporting components required by the backup physical link type must also be pre-configured and ready for use. For example, if TCP/IP is your backup link type, the Structured Call Interface (SCI) component of the Common Service Layer (CSL) and IMS Connect must also be configured and ready for use.

The following steps assume a scenario in which the primary physical links in use are VTAM physical links and the back up physical links are TCP/IP. However, the steps are also a general guide for switching from TCP/IP to VTAM.

The steps reassign logical links on a failed VTAM physical link between a front-end IMS system and a back-end IMS system to a backup TCP/IP physical link that was previously defined between the two systems.

In a failure scenario like this, any terminals on the front-end IMS system that were waiting for a response are likely hung and message DFS3222I has been issued to the front-end master terminal operator (MTO). On the back-end IMS system, the IMS applications have stopped receiving messages for processing and message DFS3222I has also been issued to the back-end MTO.

The operators at the front-end and back-end IMS systems must coordinate the timing of the steps to ensure that messages from the front-end IMS system do not start flowing before the backend IMS system is ready to receive them.

Procedure

  1. Optional: At the front-end IMS system, stop the remote transactions that route messages on the failed physical link. When the remote transactions are stopped, any terminal that submits requests for the remote transactions receive message DFS065.
  2. At the back-end IMS system:
    1. Confirm that a local instance of IMS Connect is active and appropriately configured to support the backup physical link from the back-end IMS system.
      For each MSC TCP/IP physical link that the IMS Connect instance supports, at least one RMTIMSCON statement must be defined and one MSC statement for each physical link must be defined in the IMS Connect configuration member in the IMS.PROCLIB data set.
    2. Confirm that a local instance of SCI is active and available for use by the back-end IMS system and IMS Connect.
    3. Reassign the logical links from the failed VTAM physical link to the TCP/IP physical link by issuing either of the following commands:
      • The IMS type-2 command UPDATE MSLINK NAME(linkname) SET(plinkname)
      • The IMS type-1 command /MSASSIGN LINK xxx to MSPLINK plnkname
  3. At the front-end IMS system:
    1. Confirm that a local instance of IMS Connect is active and appropriately configured to support the backup physical link from the front-end IMS system.
      For each MSC TCP/IP physical link that the IMS Connect instance supports, at least one RMTIMSCON statement must be defined and one MSC statement for each physical link must be defined in the IMS Connect configuration member in the IMS.PROCLIB data set.
    2. Confirm that a local instance of SCI is active and available for use by the front-end IMS system.
    3. Reassign the logical links that use the failed VTAM physical link to the TCP/IP physical link by issuing either of the following commands:
      • The IMS type-2 command UPDATE MSLINK NAME(linkname) SET(plinkname)
      • The IMS type-1 command /MSASSIGN LINK xxx to MSPLINK plnkname
    4. After the logical links have been reassigned to the same TCP/IP physical link at both the front-end and back-end IMS systems, start the logical links by issuing either of the following commands:
      • The IMS type-2 command UPDATE MSLINK NAME(linkname) START(COMM)
      • The IMS type-1 command /RSTART LINK xxx
    5. If the remote transactions were stopped, restart them.