Principal and alternate facility

The functions of CICS® synchronous EXEC terminal control commands (such as SEND, RECEIVE, CONVERSE) are exercised against a principal or an alternate facility.

In CICS, the principal facility for a task is the terminal or ISC session that is made available to the application program when the task is initiated. The alternate facility is the ISC session that is allocated as needed by the application program. Commands issued against the principal facility are issued without the use of the SESSION (name) option. Commands issued against the alternate facility are issued with this option.

When CICS is the front-end subsystem, the user terminal is the principal facility. The session allocated to IMS is the alternate facility. However, when a restart transaction is attached from the ISC session, the session is the principal facility. The restart transaction does not have direct access to the user terminal.