Terminal-response mode

Terminal-response mode is a mode of operation that can be defined for transactions, users, and terminals attached to IMS.

When a SLU P station is operating in terminal-response mode, all operations are stopped between the workstation and IMS from the time IMS receives a transaction until IMS receives acknowledgment that the reply message has been received by the workstation. For normal IMS output messages, this acknowledgment is the receipt of the DR2 response requested for recoverable transaction output. For Fast Path output messages, this acknowledgment is the receipt of the next input message or an RTR command. For MFS-paged output messages, this acknowledgment is the receipt of the next input message, MFS NEXTMSG or NEXTMSGP control commands, or a requested DR2 response (if not Fast Path output) on the last page of the message. Output caused by a nonrecoverable transaction requests an exception DR2 response and does not require a response from the workstation. Terminal-response mode can reduce the processing required by the controller application program.

Terminal-response mode can be selected by an installation during IMS system definition or with an ETO user descriptor. Your system can be defined as forced, negated, or transaction-dependent:
  • If it is defined as forced, every input transaction is in terminal-response mode.
  • If it is defined as negated, no input transaction is in terminal-response mode.
  • If it is defined as transaction-dependent, terminal response mode is determined on a transaction-by-transaction basis. The use of transaction-dependent terminal-response mode can make the controller application programs more complex, because they must handle communication protocols resulting from both forced and negated terminal-response mode environments.

Terminal-response mode can only be invoked by valid transactions, not by message switches, IMS commands, VTAM® commands and indicators, or MFS control requests. Transactions that are unacceptable (for example, because of a security violation or an invalid transaction code) cannot invoke terminal-response mode.

When a workstation is operating in terminal-response mode, the following processing occurs after the workstation has established a session with IMS:

  1. The workstation sends an input transaction.
  2. IMS places the workstation in terminal-response mode.
  3. IMS passes the transaction to a message processing program (MPP).
  4. The MPP processes the transaction.
  5. The MPP returns a reply, using either the I/O PCB or an response alternate PCB.
  6. IMS returns a DRx response, if one is requested.
  7. IMS sends the reply to the workstation.
  8. The workstation returns a DR2 response, if one is requested.
  9. IMS removes the workstation from terminal-response mode.

While a workstation is in terminal-response mode, IMS accepts no input from it, and sends no output to it other than the reply from the MPP. If the MPP abends while processing the input transaction, IMS might send an exception response and the associated IMS error message. Any output that is not in reply to the transaction that initiated terminal-response mode is held in IMS's output queue. After IMS removes the workstation from terminal-response mode, it sends the unsolicited output.

When Fast Path is used, the following processing occurs:

  1. The workstation sends an input transaction.
  2. IMS places the workstation in terminal-response mode.
  3. IMS passes the transaction to a Fast Path message processing program (IFP).
  4. The IFP processes the transaction.
  5. The IFP returns a reply, using either the I/O PCB or a response alternate PCB.
  6. IMS returns DRx, if one is requested.
  7. IMS sends the reply to the workstation.
  8. An exception DR2 response is required on output; therefore, the workstation sends the next input message or RTR command. If IMS has output for the workstation on the message queue, a definite response is required. The workstation sends DR2.
  9. IMS removes the workstation from terminal-response mode.

The master terminal operator can reset a workstation in Fast Path terminal-response mode before the response is returned by issuing the /STOP NODE and /START NODE commands in sequence from the master terminal.