Call Forward Reminder Dial Tone (Off-Hook) upon Spanish SIP Alert-Info

The device plays a special dial tone to FXS phones in off-hook state that are activated with the call forwarding service. The special dial tone is used as a result of the device receiving a SIP NOTIFY message from a third-party softswitch providing the call forwarding service with the following SIP Alert-Info header:

Alert-Info: <http://127.0.0.1/Tono-Espec-Invitacion>;lpi-aviso=Desvio-Inmediato

This special tone is a stutter dial tone (Tone Type = 15), as defined in the CPT file (see Call Progress Tones File).

The FXS phone user, connected to the device, activates the call forwarding service by dialing a special number (e.g., *21*xxxxx) and as a result, the device sends a regular SIP INVITE message to the softswitch. The softswitch later notifies of the activation of the forwarding service by sending an unsolicited NOTIFY message with the Alert-Info header, as mentioned above. When the call forwarding service is de-activated, for example, by dialing #21# and sending an INVITE with this number, the softswitch sends another SIP NOTIFY message with the following Alert-Info header:

Alert-Info: <http://127.0.0.1/ Tono-Normal-Invitacion>; Aviso = Desvió-Inmediato

From this point on, the device plays a normal dial tone to the FXS phone when it goes off-hook.