6100 ADCCP Programming Manual

Link States and Transitions
ADCCP/X21 Protocol Module
3–12 069225 Tandem Computers Incorporated
ADCCP/X21 uses circuits t and c to signal any one of three possible DTE states during
quiescence. These states are listed in Table 3-4.
Table 3-4. DTE Quiescent States
DTE State Circuit t Circuit c
DTE Ready t = 1 c = OFF
DTE Not Ready, Uncontrolled t = 0 c = OFF
DTE Not Ready, Controlled t = 0101... c = OFF
During the quiescent state, the DCE can indicate either “ready” or “not ready” on
circuits r and i. These state are listed in Table 3-5.
Table 3-5. DCE Quiescent States
DCE State Circuit r Circuit i
DCE Ready r = 1 i = 0FF
DCE Not Ready r = 0 i = OFF
Call Establishment State
The link can enter the call establishment state only from the quiescent state and only if
both the DTE and the DCE signal “ready.” Call-control procedures begin either when
ADCCP/X21 signals a call request or when the DCE signals an incoming call.
ADCCP/X21 Signals Call Request. The following call-control procedures depend on the
type of call requested when ADCCP/X21 signals a call request:
Normal call Requires ADCCP/X21 to transmit a selection-signal
sequence that includes the address of the remote station.
ADCCP/X21 will transfer either full or abbreviated
addresses, according to the CCITT recommendation.
Direct call Is used in certain X.21 networks when a predetermined
address or group of addresses has been established with the
network provider. In this case, ADCCP/X21 does not
transfer a selection-signal sequence when requesting the call.
Selective direct call Is used in certain X.21 networks. These networks store up to
seven different addresses from which ADCCP/X21 can
select when requesting a call. The DCE must provide a byte
timing signal (b) to the X.21 LIM. ADCCP/X21 sends a
selective direct call signal to the DCE instead of a normal
call-request signal. The selective direct-call signal does not
contain a selection-signal sequence.