User`s guide

174 DC 900-1340I
BSC Programmer’s Guide
6.17.3 BSC 2780/3780 Record Handling
When message blocking is set to data blocking, the BSC 2780/3780 software performs
2780 and 3780 record handling if appropriate. The software scans the first block of all
messages for 3780 record separator (RS) or 2780 unit separator (US) characters. The
BSC 2780/3780 software performs 2780 or 3780 message blocking depending on which
type of character it encounters first. If it does not find a RS or US character in the first
data block, it blocks or deblocks the entire message regardless of embedded data
records. If the BSC 2780/3780 software receives a block of records ending in ETB, and
the last record of the block does not end with a record separator, the BSC 2780/3780
software inserts an RS or US character at the end of the block to separate the last record
of that block from the first record of the next block; otherwise, the BSC 2780/3780 soft-
ware never inserts RS or US characters into the text block.
If the BSC 2780/3780 software encounters a 2780 US character in the first block of a
non-transparent message, it then blocks and deblocks the message such that the 2780
records are not split across a transmission block or ICP message buffer boundaries.
Outgoing message records from the BSC 2780/3780 software have a BCC appended
after each US, whereas records incoming to the client have the BCCs stripped away.
Refer to Section 5.4.3.3 on page 148 for details on the format of transparent 2780
blocks.
If the BSC 2780/3780 software encounters a 3780 RS character in the first block of a
non-transparent message, it then blocks and deblocks the message such that the 3780
records are not split across transmission block or ICP message buffer boundaries. As
mentioned above, the software handles transparent 3780 data as if message blocking is
set to disable; that is, each transmission block is sent as a separate message buffer to the
client, thus enabling the client to preserve transparent record boundaries.