6100 ADCCP Programming Manual

Station States and Transitions
ADCCP Link and Station Management
2–8 069225 Tandem Computers Incorporated
Note Although the ADCCP protocol module never explicitly reports the state to an application, you can often
determine the state. For example, if you send a SNRM frame to a station and have not received the
completion, the local station is in the Mode Setting state (unless some error has occurred or is occurring,
or the UA just arrived and you have not discovered it yet).
Logically Disconnected
State (LDS)
The logically disconnected state (LDS) applies from the time the line is started with
CMI until an application makes a MODE SET request to establish the link. A station
can also enter this state as a result of one of the following conditions:
Modem failure
Serious line error
MODEM CONTROL request that disconnects the line.
MODE SET request that disconnects the station
protocol error (for example, a FRMR from a remote station)
A station in the LDS can be in either DEAD or DISC mode. If the station is in DEAD
mode, the ADCCP protocol module discards any frames that arrive for that station. If
the station is in DISC mode, the protocol module accepts unnumbered commands that
arrive for the station, but rejects all other frames. (The response to a mode-setting
frame is UA; the response to other frames is DM.)
A secondary station normally leaves the LDS when it receives a mode-setting frame
(like a SIM or SNRM) from the line. To receive a mode-setting frame, the station must
be in DISC mode rather than DEAD mode. To change the mode from DEAD to DISC,
the application makes a MODE SET request as shown in Figure 2-5. If the secondary
station requires a SIM from the primary station, the application specifies SIM rather
than DISC in its MODE SET request. The secondary then responds with a RIM to
every frame until it receives a SIM on the line. When a mode-setting frame arrives on
the line, the station moves into the Mode Setting state. After sending the UA response,
the station can move into one of two states:
Initialization State (IS) if the frame was a SIM
Information Transfer State (ITS) if the frame was a SNRM, SNRME, SARM,
SARME, SABM, or SABME
Normally, a primary station leaves the LDS when an application in the primary station
issues a MODE SET request to initiate a mode-setting sequence (like SIM or SNRM)
on the line.