User`s guide

2: BSC Protocol Summary
DC 900-1340I 35
2.1.4 Messages and Transmission Blocks
The client computer sends data to the BSC software as complete messages. A message
consists of one or more buffers of text or binary data. The BSC control characters are
not included in the message. The control characters are inserted by the Freeway server
before transmitting the data. Once in memory, the messages may be transmitted in
smaller blocks, called transmission blocks, to provide more accurate and efficient error
control. BSC begins each transmission block with a start-of-text (STX) control charac-
ter and ends each with an end-of-transmission-block (ETB) control character, except
for the last block of the message which ends with an end-of-text (ETX) character. All
data blocking and deblocking is transparent to the user; however, the ICP message
buffer size (Section 3.4.1.3 on page 58) and transmission block size (Section 4.8 on
page 92) must be defined by the user before a communication link is placed in opera-
tion.
2.1.5 BSC 3270 Product Features
The Protogate BSC software has the following features:
• Text blocking and deblocking
• Safe store of received messages
• Automatic polling of control units
• Adjustable poll and reply delays
2.2 BSC 3270 Access Modes
Each BSC 3270 session on a link can be set to one of the following access modes:
Manager, Read or Control. Only one session of each access mode may be active on any
one link. The access mode is defined in the DLI configuration file (Chapter 7) using the
client-related “
mode” parameter (described in the Freeway Data Link Interface Reference
Guide).