6100 BSC Programming Manual

6100 BSC Concepts and Context
BIDDING FOR THE LINE. If a station wishes to transmit data to
the other station, it must first bid to gain access to the line.
Figure 1-9 illustrates the bidding sequence.
S5066-009
Transmitting Station:
Receiving Station:
PAD SYN...SYN ENQ PAD
PAD SYN...SYN ACK0 PAD
BSC-Supplied (see text)
Figure 1-9. Bidding for the Line
As the figure shows, the station that wishes to send data first
transmits the following:
SYN SYN ... SYN ENQ PAD
To accept the bid, the other station replies:
SYN SYN ... SYN ACK 0 PAD
The application makes a WRITE or WRITEREAD request to initiate a
line bid; the application makes a READ request to accept a line
bid. The application does not put either of the above sequences
in its buffer. (See Section 3 for more information.)
Once the bid has been accepted, data transfer can begin. The
station that owns the line can transmit any number of messages or
blocks; the other station acknowledges or replies to each
transmission. For the ownership of the line to change, the
owning station must relinquish the line, as described in
"Relinquishing the Line," below.
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