User`s guide

64 DC 900-1340I
BSC Programmer’s Guide
3.4.1.8 Safe Store Acknowledge Command
Use the dlWrite function with the pOptArgs.usProtCommand field set to
DLI_PROT_SAFE_STORE_ACK to acknowledge a stored message. When the safe store option
is enabled, this command must be sent to the BSC software after each end-of-message
data block (
pOptArgs.usProtCommand field set to DLI_PROT_SEND_NORM_DATA_EOM or
DLI_PROT_SEND_TRANS_DATA_EOM) is received by the client.
Safe store provides the ability to acknowledge a received data message after it has been
examined by the client application program or stored on disk. Safe store is often used
by financial institutions where a line acknowledge constitutes acceptance of a sale or
trade.
Normally, the BSC software automatically acknowledges each received data block. With
the safe store option enabled, the BSC software continues to acknowledge received
intermediate blocks (ETB); however, when the last block (ETX) is received, the BSC
software does not send an automatic acknowledgment on the line. Instead, the BSC
software waits for the client to either accept the message by issuing a Safe Store
Acknowledge command or reject the message by issuing a Send EOT command
(Section 3.4.1.11).
The Safe Store Acknowledge command causes the BSC software to transmit a positive
acknowledgment (ACK0 or ACK1) in response to the last block (ETX) received from
the remote station. This is in contrast to the Send EOT command which causes the BSC
software to reject the message by sending an EOT sequence instead of ACK. In this case,
the remote station either records the data transmission as unsuccessful or attempts to
retransmit the entire message.
If the client sends a Safe Store Acknowledge command while the line is still “active”
(i.e., before an EOT sequence is received on the line), the client receives a Safe Store
Acknowledge response back from BSC signifying that the safe store operation was suc-
cessful.