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Loop Start Signaling
November 2009 303
FXO Loop Start
To configure a Brooktrout module for FXO loop start signaling, the
host must issue an L4L3mENABLE_CAS with an IISDN_ROBBED_
BIT_DATA structure that contains the following settings:
send_glare_err_event = 0 (not used for loop start)
in_trunk_type = IISDNttFXO_LPSTART
out_trunk_type = IISDNttFXO_LPSTART
timed_answer_supervision = 0 (answer supervision required)
fgb_fgd_mode = 0 (not used)
The remaining settings are described in the context of incoming and
outgoing calls in the subsections that follow.
Note: The FXO end of a loop start connection uses the same A and B
bit values for both idle and connected states. Because of this,
the Brooktrout module cannot detect when the FXO end goes
on hook. To idle the channel, the host must detect the presence
of a busy/reorder tone coming from the FXO end and issue an
L4L3mCLEAR_REQUEST to disconnect the call. To ensure
the FXO end returns to an idle state, the host must also reset
the channel by issuing an L4L3mDISABLE_CAS immediately
followed by an L4L3mENABLE_CAS in order to make another
call.