6100 ADCCP Programming Manual

Link States and Transitions
ADCCP/X21 Protocol Module
3–10 069225 Tandem Computers Incorporated
Stopped State
ADCCP/X21 enters the stopped state after the CLIP has been downloaded or after a
STOP OPERATION request. In this state, ADCCP/X21 will not respond to any signals
from the DCE and will not accept any of the following requests:
CONNECT
DISCONNECT
SENDTEXT
RECEIVETEXT
MODE SET
The START OPERATION request causes ADCCP/X21 to enter the quiescent state.
Quiescent State
The quiescent state indicates that no connection with a remote station is currently
established or in the process of being established. In the quiescent state, both the DTE
and the DCE indicate whether or not they are ready to enter the call establishment
state. The link can move from the quiescent state to the call establishment state only
when both the DTE and the DCE signal “ready.”
The X.21 link enters the quiescent state either because the LIU has been started or
because the link has completed the clearing state. By default, ADCCP/X21 signals
“DTE not ready, uncontrolled.” You can alter this default setting by calling
WRITEREAD with a SET X.21 CONFIGURATION request.
ADCCP/X21 signals “not ready” to the DCE to indicate that it cannot accept an
incoming call. If an application issues a request to accept incoming calls, ADCCP/X21
changes the signal to “DTE ready.” ADCCP/X21 then remains in the ready state until
the DCE signals an incoming call or until an application issues a DISCONNECT
request.
If your application issues a request to initiate a call, ADCCP/X21 signals “DTE ready.”
If the DCE is also ready, ADCCP/X21 signals a call request and the link begins the call
establishment procedures.
DTE and DCE States During Quiescence
The link can begin call-establishment procedures only when both the DTE and the
DCE indicate “ready.” Figure 3-4 shows the six possible combinations of DTE and
DCE signals during the quiescent state.