Logical-terminal chains

When a logical terminal is assigned to a physical terminal for input, any message that is entered from the physical terminal is considered to have originated at the logical terminal. When more than one logical terminal is assigned to a physical terminal for input, a chain of input logical terminals is formed. Any input from the physical terminal is considered to have originated at the first logical terminal on the chain.

The following figure shows the relationship between physical and logical terminals for input.

Figure 1. Relationship between physical and logical terminals for input to IMS
A physical terminal sends input through two logical terminals that are assigned to that physical terminal or through one of the logical terminals.

If the first logical terminal is not allowed to transmit a message (for example if it is not authorized or it is a stopped logical terminal), all logical terminals on the input chain are interrogated in chain sequence for their ability to transmit messages. If the physical terminal is a Finance, SLU 1, SLU P, or LU 6.1, only the logical terminals associated with the input component are scanned. The first appropriate logical terminal found is considered the originator of the message. If no appropriate logical terminal is found, the message is rejected with an error message.