User`s guide

B: BSC 2780/3780 Control Procedures
DC 900-1340I 217
B.1.5 Normal Data Transmission
In Figure B–7, the client program sends a two-block message to the BSC 2780/3780
software to be transmitted on the line. The BSC 2780/3780 software segments the data
into transmission blocks, sends the ETB/ETX blocks, sends the two acknowledgments
to the client program, then turns the line around.
Note
The STX and ETX control characters are included in the transmis-
sion block size. For example, a 256-byte transmission block can
transmit only 254 bytes of actual data.
Figure B–7: Normal Data Transmission Sequence
C
l
ient Freeway
Remote Station
608 Bytes Normal Data
ACK0
ENQ
EOT
Block 1 (ETB)
254 bytes data
Block 2 (ETB)
254 bytes data
ACK1
ACK0
Block 3 (ETB)
254 bytes data
ACK1
508 Bytes Normal Data
Data Acknowledge
ACK1
Block 4 (ETB)
254 bytes data
ACK0
Block 5 (ETX)
100 bytes data
Data Acknowledge
dlWrite
(
DLI_PROT_SEND_NORM_DATA)
dlWrite
(
DLI_PROT_SEND_NORM_DATA_EOM)
dlRead
(
DLI_PROT_RESP_LOCAL_ACK)
dlRead
(
DLI_PROT_RESP_LOCAL_ACK)