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Ground Start Signaling
November 2009 296
FXS Ground Start
To configure a Brooktrout module for FXS ground start signaling,
the host must issue an L4L3mENABLE_CAS with an IISDN_
ROBBED_BIT_DATA structure that contains the following settings:
in_trunk_type = IISDNtt5ESS_GDSTART
out_trunk_type = IISDNtt5ESS_GDSTART
max_incoming_digit_count = 0 (no digits collected)
timed_answer_supervision = 1 (timer expiration indicates far
end answer)
fgb_fgd_mode = 0 (not used)
The remaining settings are described in the context of incoming and
outgoing calls in the subsections that follow.
Incoming Call Processing
During an incoming call, the host receives an L3L4mPRE_SEIZE
message if send_preseize_event = 1 in the IISDN_ROBBED_BIT_
DATA structure. This message is sent when the module detects an
incoming seizure. No digits are collected in FXS ground start mode;
to answer the call, the host must issue an L4L3mCONNECT_
REQUEST message.
Figure 35 shows how a Brooktrout module processes an incoming
call received over an FXS ground start trunk.