Input, destination, and intermediate systems
Depending on the message, an IMS can be either an input system, a destination system, or an intermediate system.
For example, in the following figure, the transaction message originates from LTERMB in IMS B and is routed over path BD to TRAND in IMS D. IMS B is the input system and IMS D is the destination system. This message is called a primary message. When the message is processed by the application program in IMS D and a reply is returned to the input terminal in IMS B, this reply message is called a response. For this response message, the destination and input system is IMS B. The destination of the message is LTERMB in IMS B. The input that caused this response message is also from LTERMB in IMS B, which is the primary transaction.
If a message is sent through one IMS and routed directly to another IMS for processing, the routing system is called the intermediate system. For example, if TRAND is sent from IMS B through IMS A to IMS D (path BAD), IMS A is the intermediate system and IMS D is the destination system. Similarly, IMS A and IMS D are intermediate systems for TRANC when TRANC is sent from IMS B through IMS D through IMS A to IMS C (path BDAC).
Remote destination names must be defined as remote in the input system and as local in the destination system. Intermediate systems, however, do not need to define the input, destination name, or the path back (a local SYSID) for the routed message. Only the path to the destination system needs to be defined. The path back might not even be through the intermediate system. Input and destination name checking is not performed on a message when it is routed through an intermediate system.
