6100 BSC Programming Manual

6100 BSC Link and Station Management
DISCONNECTED State
A station is in DISCONNECTED state if the LIU has been downloaded
but a connection has not been established. Perhaps an earlier
connection was lost, or there is temporarily no caller on a
dialup line. BSC may be waiting for the application to request a
connection, or it may be trying to make a connection--waiting
for DSR to appear after raising DTR.
TRANSITIONS TO DISCONNECTED STATE. The station begins operation
in DISCONNECTED state. The following events cause transitions to
DISCONNECTED state from other states:
• The application makes a CONTROL request to disconnect the
line. If the line is switched, BSC immediately drops DTR;
the state changes to DISCONNECTED when DSR drops. If the
line is leased, BSC doesn't drop DTR; the state changes to
DISCONNECTED, even if DSR is on.
• The remote station sends a disconnect sequence (DLE EOT).
If the line is switched, BSC immediately drops DTR; the state
changes to DISCONNECTED when DSR drops. If the line is
leased, BSC doesn't drop DTR; the state changes to
DISCONNECTED, even if DSR is on.
• A modem malfunction causes DSR to drop, or the application
makes a STOP request. The state changes to DISCONNECTED;
BSC reports an error to the application.
TRANSITIONS FROM DISCONNECTED STATE. The following events cause
transitions from DISCONNECTED state to other states:
• The application makes a CONTROL request to connect the line.
If the line is switched, BSC asserts DTR and waits for DSR.
When DSR appears, the state changes to CIRCUIT ASSURANCE if
ID exchange is defined for the line; if ID exchange is not
defined, the state changes to CONTROL. If the line is leased,
the request does not change DTR, because that signal is
asserted even in DISCONNECTED state. The request changes the
state to CONTROL.
• The application makes its first request to read or write from
the line, without first making a CONTROL request. BSC first
makes the connection, as though a CONTROL request had been
issued. It then performs the requested function, which may
cause another transition. For example, the same request
can achieve connection and ID exchange, which would change
the state from DISCONNECTED to CIRCUIT ASSURANCE to CONTROL.
On a line without ID exchange, a single request can connect
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