1. First, enter the VoIP Setup page to configure the SIP information for both FXS ports. Then click Advanced.

2. Tick the “Enable port failover function” option.

3. Now when someone makes a VoIP call to the SIP account registered to FXS1 while busy, the call will be forwarded to the FXS2 account. Likewise, when someone makes a VoIP call to the SIP account registered to the FXS2 port while busy, the call will be forwarded to the FXS1 account.