Requesting VTAM® to transmit buffered data is called flushing the SEND buffer. Many of the APPCCMD macroinstructions instruct VTAM to flush the SEND buffer. All macroinstructions with a QUALIFY value of FLUSH or DATAFLU flush the buffer.
The APPCCMD CONTROL=SEND, QUALIFY=ERROR macroinstruction and the abnormal termination DEALLOC and DEALLOCQ APPCCMD macroinstructions also flush the buffer. The APPCCMD CONTROL=SEND, QUALIFY=ERROR macroinstruction flushes the buffer and sends the FMH-7 on full-duplex conversations.
The only macroinstruction that sends normal information but does not flush the SEND buffer is the APPCCMD CONTROL=SEND, QUALIFY=DATA macroinstruction.
The buffering of data allows the application program to issue a macroinstruction or several macroinstructions before its partner receives anything. Consequently, the conversation partner frequently is unable to detect errors or give other feedback immediately after an APPCCMD macroinstruction is used to send information. The application program can flush the buffer to ensure that the partner receives the information in a timely manner.