Loop Start Signaling

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 seize from the far end (FXS end). The module then collects dial pulse digits from the network; the maximum number of digits the module expects to receive must be specified in the max_ incoming_digit_count field. The digits are reported to the host in an L3L4mSETUP_IND message. To answer the call, the host must issue an L4L3mCONNECT_REQUEST message. Figure 39 shows how a Brooktrout module processes an incoming call received over an FXO loop start trunk.

Outgoing Call Processing

During an outgoing call, the host receives an L3L4mPROGRESS in response to the L4L3mCALL_REQUEST to start the call. The module automatically transmits a ringing pattern using the B signaling bit. When the far end goes off hook, the host receives an L3L4mCONNECT indicating the call is connected.

Figure 40 shows how the module makes an outgoing call over an FXO ground start trunk.

Call Teardown Processing

For an incoming call teardown, refer to Figure 41; for an outgoing call teardown, refer to Figure 42.

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