Why do calls suddenly stop ringing when I have set up a parallel call to a mobile phone?
Many mobile providers do not use “Early Media”. This means that if the mobile connection is not available, the respective provider accepts the incoming call and switches the band announcement via RTP. This means that the parallel call is also accepted and no longer displayed on other devices, even though these may be “free”.
If, however, Early Media were used, we would be able to see from the SIP feedback that the call was not accepted. This would ensure that the incoming call would continue to be signalled on the registered device.
Another problem caused by the lack of Early Media: The call accepted by the recorded message is charged to you.
The following mobile operators do not use Early Media: All mobile operators using the Vodafone network.