Routing messages with the destination name and SYSIDs

Messages in an MSC network contain information that makes it possible to route the message between IMS systems.

When a remote transaction is entered from an LTERM, a transaction message is built and queued on the message queue. This message contains information that is needed to route the message to its remote destination:
  • Remote destination name (transaction code)
  • Local or source LTERM name of the LTERM that entered the transaction
  • Remote SYSID value
  • Local or source SYSID value

If the transaction is processed by the application program and secondary messages are sent to other transactions (program-to-program switches), these messages have the destination name and SYSID of the switched-to transaction. The source (origin) name and SYSID remain the same. That is, the source SYSID and name never change. This facilitates sending the response message back to the input LTERM, regardless of where the transaction is processed.

Any IMS that locally processes a message that is received from a remote system must have a local SYSID defined to it that is the same as the remote SYSID of the message. It must have a path back to the source (origin) of the message. In the following figure, if TRANA is entered from LTERMB in IMS B, it is sent across the path MSNAME=(4,2) to IMS A. The destination name and SYSID of the message are TRANA and 4. The source name and SYSID are LTERMB and 2. IMS A accepts the message and processes it. It has SYSID=4 defined as local and has a path back to IMS B with the destination SYSID=2. If TRANA in IMS A issues a program-to-program switch to TRAND in IMS D, the destination name and SYSID are TRAND and 5. The source name and SYSID remain LTERMB and 2. IMS D accepts and processes the transaction. The transaction has SYSID=5 defined locally and has a path back to IMS B with destination SYSID=2.

If TRAND in IMS D sends a response back to input LTERMB, the response message has a destination name and SYSID of LTERMB and 2, and the source name and SYSID are also LTERMB and 2.

The input LTERM, LTERMB, is never defined as remote in IMS A or IMS D, yet the response message is returned to LTERMB in IMS B. IMS carries the originating LTERM name and SYSID in the primary message and all secondary messages. IMS knows where to route the response message when the application program responds to the input LTERM.

Figure 1. Message routing
Begin figure description: This figure was described in the preceding text. End description.