in the RIDBuff. The higher level application can then take data
off on the CODBuff, incrementing SOD as it does so.
STARTING UP AND FINISHING OFF COMMUNICATIONS
The problem is that the SLIP's on either side need to know (and
keep knowing) the sequence number of the other SLIP. The easiest
way to solve most of these problems is to have the SLIP check the
Request to Send and Clear to Send Lines to see if the other SLIP
is active. On startup, or if it has reason to believe the other
side has died, the SLIP assumes: all connections are closed, no
data from any connection has been sent, and both its SEQ and the
SEQ of the other SLIP are zero. To start up a connection, the
instigating SLIP sends a SSNM with its starting sequence number in
it. The receiving SLIP acknowledges this SSNM and replies with
its starting sequence number (combined into one message). Then
the sending SLIP acknowledges the receiving SLIP's starting
sequence number and the transmission commences. This is the three
way handshake taken from TCP, After which data transmission can
begin.