MSC initialization

To start Multiple Systems Coupling (MSC) communications between two IMS systems, issue either the IMS type-1 command /RSTART LINK or the IMS type-2 command UPDATE MSLINK NAME(linkname) START(COMM).

If the physical link type is either a channel-to-channel connection or a main-storage to main-storage connection (MTM), you must issue the command in both IMS systems at each end of the link.

If the physical link type is either TCP/IP or VTAM®, you need to issue the command in only one IMS system. The normal procedure is for the operator to issue this command when a system has started. Communication is allowed only if the characteristics of the specified links are compatible. If a required link is not successfully started, messages wait until the links are reassigned.

The SYSID of each IMS system running in a shared queues group can either be cloned across all systems, or not. If the SYSIDs are not cloned, initialize all IMS systems in the shared queues group before starting regions to process the transactions on the shared queue to avoid occurrences of pseudoabend U0830.

After all IMS systems have been initialized, transaction processing can begin, and individual IMS systems can be brought down and later restarted as needed. Initialization allows all IMS systems to exchange MSC SYSIDs and MSNAMEs, and creates a SYSID table that contains all of the SYSIDs for that shared queues group. If the SYSIDs for all IMS systems in a shared queues group are cloned, then you do not need to perform this initialization.

Attention: If you cold start a non-shared queues system that has messages queued, the queued messages are lost. Because the messages that were lost can be from or to terminals and programs in other systems, the impact of a cold start is not limited to the cold-started system.

In a shared-queues environment, IMS systems in the IMSplex exchange SYSIDs and MSNAMEs at initialization. During this SYSID exchange, each IMS system creates dynamic MSNAMEs for any MSNAMEs that are defined in other IMS systems that it does not define itself. The dynamic MSNAMEs result in paths to all of the IMS systems in the IMSplex. The SYSIDs are merged to create a common SYSID routing table. The table is the same in each IMS. Therefore, any local SYSIDs are local in all IMS systems and override any remote or undefined SYSIDs. Remote SYSIDs override only undefined SYSIDs.