After an IP phone makes an outgoing call through the AT0 trunk, the ringback tone is heard after about 8s. Why

If the trunk function is not used, change the dialup timer value of the AT0 trunk to 0. The AR does not need to spend 5s on detecting the ringback tone. A user needs to wait for only 3s to hear the ringback tone.

Run the pbx number-parameter 40 0 command in the voice view to set parameter 40 to 0.
The modification may cause failures of calls transferred through trunks. The pbx number-parameter 40 0 command can be used only when POTS or SIP phones make outgoing calls through AT0 trunks.

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