User guide

234 RealCT Direct API Developer Guide
Appendix A: T1 Line Protocols
Table 42 shows the pattern of bits transmitted when the station
calls the CO.
Table 42. Ground Start: Station Calls CO
In the Ground start protocol, the CO indicates idle with a 11
pattern, and the station indicates idle with a 01. The station
seizes the line by transmitting a 00, and the CO acknowledges
by transmitting 01, which it continues to transmit throughout
the call. The station then transmits 11, which it transmits
throughout the call. This handshaking in built into
RHT_SEIZE_LINE and RHT_OFF_HOOK so there is no need
for the application to be involved in the handshaking process.
The CO then provides dial tone to indicate that it is ready to
receive digits. There is no signal from the CO to indicate an
answer by the called party. The CO or station disconnects by
returning to the idle state.
If the network you are connected to accepts call transfers, the
HookFlash duration is determined by
RDG_LOCAL_FLASH_DUR.
Status CO Station Timing Parameter
Idle 11 01
Seizure: Ground on Ring 11 <-- 00
Ground on tip from CO 01 --> 00
Station removes ground 01 <-- 11
Dialtone from CO 01 11
Digits from Station 01 11
Answer 01 11
Conversation 01 11
CO disconnects 11 --> 01
HookFlash 01 <-- 11/01/11 RDG_LOCAL_FLASH_DUR
01/11/01 --> 11