Logical and physical terminal relationships
The following figure shows the communication flow between a terminal user, a physical terminal, a communication line, and a logical terminal in a nonswitched communications network.
IMS system definition describes the characteristics and relationship of physical terminals, communication lines, and logical terminals. On a nonswitched communication line, the relationship between a physical terminal at one end and a logical terminal within IMS at the other end is a stable relationship defined during system definition or during signon for ETO terminals.
Except for LU 6.1, terminals using VTAM® have physical-to-logical terminal (PTERM-to-LTERM) relationship as a terminal on nonswitched line.
The relationship that is established between a physical terminal and one or more logical terminals at system definition can be changed using commands or by creating a new system definition. The /ASSIGN command dynamically changes logical and physical relationships, and it is usually executable only from the master terminal.