Terminal Input Destination

The destination of the terminal input is dependent upon the type of input.

An input command message goes directly to the IMS command processor modules, while a message switch or a transaction is stored on the message queue. When a 3270-based message is received by IMS, the message input is first processed by IMS's Message Format Service (MFS), except when the input is from a previously cleared or unformatted screen. MFS provides an extensive format service for both input and output messages and is discussed in detail in "Message Format Service" on page 298.

When the input message is enqueued to its destination in the message queue, the input processing is completed. If more than one LTERM is defined or assigned to a physical terminal, the LTERMs are maintained in a historical chain: the oldest defined or assigned first. Any input from the physical terminal is considered to have originated at the first logical terminal of the chain. If, for some reason (such as security or a stopped LTERM), the first logical terminal is not allowed to enter the message, all logical terminals on the input chain are interrogated in a chain sequence for their ability to enter the message. The first appropriate LTERM found is used as message origin. If no LTERM can be used, the message is rejected with an error message.