System identifiers (SYSIDs)

MSC uses system identifiers (SYSIDs), two-byte numbers between 1 - 2036, to identify the IMS systems in an MSC network.

Each IMS system in an MSC network is assigned one or more SYSIDs. The SYSIDs are local to the IMS system that they are assigned to and remote to the other IMS systems in the MSC network.

The local SYSIDs must be unique within an MSC network. If an MSC network connects to an IMSplex with shared queues, the IMS systems in the shared queues group can share local SYSIDs.

A local SYSID and a remote SYSID are paired to define a logical link path. A logical link path is assigned to a logical link between the two IMS systems that the local and remote SYSIDs represent. The term MSNAME is often used as a synonym for the term logical link path.

As messages travel through an MSC network, the local SYSID identifies the point of origin of the message and the remote SYSIDs identify the destination of the message. Generally, the IMS system identified by the remote SYSID is where a transaction message is processed and the local SYSID is where the response to the transaction must be returned. However, a remote SYSID can also represent an intermediate IMS system that doesn't process the transaction, but instead passes it to another IMS system in the network.

Local SYSIDs can be assigned to an IMS system in the following ways:
  • MSNAME stage-1 system definition macro.
  • MSC section of the DFSDFxxx member of the IMS PROCLIB data set.
  • IMS type-2 command CREATE MSNAME.

You can change SYSIDs online by using the IMS type-2 command UPDATE MSNAME NAME(msname) SET(SIDL|SIDR).

In the following figure, IMS B has local SYSIDs 1, 2 and 3. IMS A has local SYSID 4. IMS C has local SYSID 5. IMS D has local SYSIDs 6 and 7. IMS B has local SYSIDs 1, 2, and 3 because of the three MSNAME macros with local SYSIDs of 1, 2, and 3.

In the figure, IMS B has three paths to remote SYSIDs 6 (IMS D), 7 (IMS D), and 5 (IMS C). IMS D and IMS B cannot route messages to IMS A, because they do not have paths to SYSID 4 (IMS A). IMS A does, however, have a path to SYSID 7 (IMS D) and SYSID 2 (IMS B). IMS A cannot send messages that originate in IMS A to SYSID 7 or SYSID 2, because the source SYSID (SYSID 4) is not recognized by IMS B or IMS D. In this configuration, IMS A can only function as an intermediate system for IMS B and IMS D. Another path (MSNAME) must be defined for IMS B to communicate with IMS A and IMS D.

Figure 1. System identifiers (SYSIDs)
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