6100 ADCCP Programming Manual

Link States and Transitions
ADCCP/X21 Protocol Module
069225 Tandem Computers Incorporated 3–9
Link States for
Circuit-Switched Lines
The X.21 interface uses a special set of link states that allow the DTE to establish
circuit-switched connections with remote hosts. There are five main ADCCP/X21
interface states:
Stopped
Quiescent
Call establishment
Connected
Clearing
In addition to these five states, the ADCCP/X21 interface also has the capability to
receive call charges. Figure 3-3 shows ADCCP/X21 interface states and state
transitions on a circuit-switched connection.
Figure 3-3. X.21 Circuit-Switched Link States
015
Connected
Clear
STOP
OPERATION
Request
Line Downloaded
Call
Establishment
Stopped
Quiescent
Connection Established
Request for Outgoing Call
or Incoming Call Accepted
STOP
OPERATION
Request
START
OPERATION
Request
Clear
Clearing