gtps2m0t | ACF/SNA Data Communications Reference |
Data is sent to TPF via the LWRITE instruction. 3601 applications must set indicators in the write-type (SMSCWT) and write-flags (SMSCWF) fields before issuing the LWRITE instruction. The write-type field indicates whether a function management header (FMH) is included with the data. The write-flags field indicates:
Logical units must request exception response for all data sent to TPF. All other responses result in an error. See SNA Message Protocol for an explanation of the various SNA response types.
The format of input data sent to a host application is not fixed; the designers of the 3601 and host applications should establish a format suitable to the needs of the installation.
TPF output messages (those messages TPF transmits to a logical unit) are classified as: 1) application messages, or 2) system messages. These messages are further defined as recoverable or non-recoverable (See Recoverable and Non-Recoverable Messages).
Most output messages are sent in reply to an input message. Some, however, are not associated with an input message. These messages are referred to as unsolicited messages (see Unsolicited Messages). TPF prefixes all system messages with a function management header (FMH). The user defines the contents of the FMH during system initialization (SIP).
TPF output messages are sent in a single transmission. They are segmented only when: 1) the host application requests segmented output, or 2) the logical units' input buffer is too small to contain the entire message.
Data is received from TPF via the LREAD instruction. Then, the read-type field (SMSCRT) and the read-flags field (SMSCRF) are examined. A definite response is requested for single-segment recoverable messages. An exception response is requested for non-recoverable messages.
Chained messages request exception response for the first and middle messages in the chain. For recoverable chained messages, the last message in the chain requests a definite response. For non-recoverable chained messages, the last message in the chain requests an exception response.