User`s guide

98 DC 900-1340I
BSC Programmer’s Guide
buffer to the client. For outbound data, each message buffer is transmitted on the line
as a separate transmission block. If the ICP message buffer size is larger than the maxi-
mum transmission block size, BSC 3270 performs message deblocking until the entire
message buffer is transmitted.
4.17.2 Data Blocking
If the message blocking option is set to data blocking, BSC 3270 performs logical block-
ing of inbound data and logical deblocking of outbound data without regard to any
embedded data records. For example, assume the ICP message buffer size is 4096 bytes
and the transmission block size is 512 bytes. If the client sends a 1024-byte message,
BSC sends that message in three separate transmission blocks (512, 512, and 6). Note
that the third 6-byte block is necessary since the transmission block count includes the
control characters STX and ETX.
Caution
When you set message blocking to data blocking, the BSC software
can concatenate non-EOM message buffers from the client into
the transmission buffer if all the following are true:
1. The transmit buffer is not full.
2. The BSC software has another message buffer queued for
transmission.
3. The client is sending the data in non-transparent mode.
Concatenation depends on the timing of the message buffers the
client queues. It does not always occur.
4.17.3 3270 Command Blocking
If this option is set to 3270 commands, BSC 3270 scans all outbound messages for escape
characters (ESC) which signify the start of a 3270 display screen command. BSC 3270