6100 ADCCP Programming Manual

Link States and Transitions
ADCCP/X21 Protocol Module
3–14 069225 Tandem Computers Incorporated
If ADCCP/X21 has no frames in the output queue, the X.21 LIM transmits an idle
sequence over the link. If an application requests a data transfer or if the ADCCP
protocol requires ADCCP/X21 to send a response frame, the link enters the frame
transfer state. When the output queue is empty, the link returns to idle. Figure 3-5
shows ADCCP state changes while ADCCP/X21 is in the connected state.
Figure 3-5. ADCCP Link States During the Connected State
Frame
Sent
Transmit
Clear
Frame
Queued
for
Output
Successful Completion of
Call-Control Phase
Idle
017
Clearing State
The DTE or the DCE can initiated clearing at any time during the call control or the
connected states. After the clearing phase is complete, the link enters the quiescent
state and ADCCP/X21 signals “not ready.”
Some of the conditions that cause ADCCP/X21 to clear a connection are the following:
An application has issued a DISCONNECT or STOP OPERATION request.
A DTE time limit has expired during connection establishment.
ADCCP/X21 has detected a DCE error.
Call Charges
ADCCP/X21 provides your application with the capability to receive call charges after
the link has been cleared. When configured to accept call charges, ADCCP/X21 sets
timer T7 after clearing has been signaled, and waits for charging information to be
transmitted from the DCE.
If the DCE delivers the requested call charges before T7 times out, ADCCP/X21
completes your DISCONNECT request and enters the quiescent state. The charging