User`s guide

6: BSC 2780/3780 Link Configuration Options
DC 900-1340I 173
6.17.1 Blocking Disabled
If the message blocking option is set to disable, blocking/deblocking is not performed.
For inbound data, each received transmission block is treated as a separate message
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 performs message deblocking until the entire mes-
sage buffer is transmitted. BSC never concatenates outbound messages that are smaller
than the transmission block size.
To avoid splitting outbound data when message blocking is set to disable, the transmis-
sion block size (Section 6.8) should be set larger than the client data block size.
6.17.2 Data Blocking
If the message blocking option is set to data blocking, BSC performs logical blocking 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 char-
acters 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.