6100 BSC Programming Manual

6100 BSC Link and Station Management
MULTILEAVING State
A station can be in MULTILEAVING state if you did not specify
BSCPTPT as a SYSGEN parameter (see Section 1). The state is
required for HASP operation but not restricted to use with
EXCHANGE.
In MULTILEAVING state--sometimes called full conversational
mode--the application has almost complete control over the line.
It sends and receives all its own control sequences, as well as
data; BSC takes the following protocol actions:
• If the application makes a WRITEREAD request and does not
receive the response on time, BSC transmits the buffer again.
If the number of retries exhausts the count specified for the
station, BSC reports an error to the application.
• If the block check comparison doesn't succeed for an incoming
message or block, BSC sends a NAK response to the remote
station. If the number of NAK responses exhausts the retry
count specified for the station, BSC reports an error to the
application.
• If a NAK arrives from the remote station, BSC repeats the last
transmission. If the number of retries exceeds the count
specified for the station, BSC reports an error to the
application.
• If a message is one or two bytes long, BSC assumes it's a
control sequence. Thus, BSC doesn't add a block check
sequence to outgoing data, nor does it look for a block
check sequence in incoming data.
All other data and responses, except SYN characters, are
delivered to the application.
If a line is set up to permit multileaving, it goes into
MULTILEAVING state as soon as the line is connected, and it stays
in MULTILEAVING state until it is disconnected. Thus the state
of the line is always either DISCONNECTED or MULTILEAVING.
Notice that because the application controls the line, the
protocol you use need not conform to standard BSC; nor does it
have to include interleaved data streams. The state is called
MULTILEAVING not to impose a functional restriction, but to
reflect the fact that EXCHANGE uses it for HASP operation.
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