When a door phone (for example, R29) calls an indoor monitor (for example, C313) using the IP address (Speed Dial), the indoor monitor can display the live camera preview before the call is answered. This is because the device can directly access the camera stream through the local network.
However, when the call is made using a SIP account through a third-party SIP server, the indoor monitor will only display the video after the call is answered. This happens because the video preview depends on the RTSP URL, which must be configured manually when using SIP registration.