Extended output component protection (SLU P)
When a SLU P is defined with the NOBID option, IMS provides support similar to the screen-protection function for the IBM® 3270 Information Display System and display-screen protection for Finance components.
IMS does not transmit two consecutive output messages to an output-protected component without an appropriate intervening input message from the LU. This gives the LU an opportunity to process one message, according to user-defined procedures, before another is sent to the same component. SLU P support allows the output of all components to be protected.
- When IMS transmits a message to a component defined as PROGRAM2 on the IMS TERMINAL macro
- When IMS transmits a message (or a page of a message) formatted by MFS with a paging option defined
- An IMS transaction with an FM header
- A message switch with an FM header
- An IMS command with an FM header
- An MFS control request with an FM header indicating a specific component to be unprotected
- Any of these, either without an FM header or with an FM header indicating component zero (which resets protection on all components of a terminal)
- An RTR command
After the component's status is reset to unprotected, IMS sends any available output. If a component is defined as PROGRAM2 and is not described by a device format with paging OPTIONS=DPAGE or OPTIONS=PPAGE, output to the component is protected on a message-by-message basis. The input messages are used to reset output component protection.
If a SLU P component is defined to use MFS DPM and the device format used is defined with the paging option OPTIONS=DPAGE or OPTIONS=PPAGE, the output component is set to protected when a logical page or presentation page is sent to the component. MFS control requests or input data are used to reset output component protection and request additional logical or presentation pages from MFS.
- Input containing no message header (resets all components' protection).
- Input containing a header indicating the specific component to which MFS is currently paging. Otherwise, the session is terminated, because IMS cannot simultaneously send output to more than one component of a terminal.
If a SLU P terminal is defined with the BID option, output component protection occurs after every message. In this mode of operation, consecutive messages are not transmitted to a terminal. Input from the terminal must be received; otherwise, if additional output is queued, a BID command is sent after one transmission before the next message is sent.
If a terminal does not use MFS, screen protection is performed on a message-by-message basis. The input of any IMS transaction, message switch, or command causes the screen to be unprotected.
If the ready-to-receive (RTR) command is received and no messages are available, or if the terminal is in a status that does not allow output to be sent (output stopped or quiesced), IMS returns an exception DR1, followed by an error message indicating no output is available. If the RTR command is received during the transmission of MFS-paged output, IMS returns an exception DR1 response, followed by an error message, indicating invalid paging request because IMS cannot determine the MFS control function to be performed.
After any exception response is sent by IMS, any display component defined for the logical unit is automatically marked protected and unavailable for output.
After an exception response is received for a current IMS output message to a component defined as PROGRAM2 or for an MFS DPM-paged output message, the component to which the output was sent is left unprotected.
After any exception response is sent by IMS, all components defined as PROGRAM2 are automatically marked protected and unavailable for output.