The user plane information can be can be media QoS parameters, such as media QoS parameters of VoLTE/ViLTE/VoNR/Web RTC calls. These are the media streams transported in RTP packets and the RTCP packets. This user information can be obtained from the UPF 114. The control plane information can be information relating to signalling procedures, such as VoLTE/ViLTE/VoNR call-related SIP signalling procedures, particularly call termination-related cause codes and cause texts.

Those skilled in the art will be aware of various techniques for correlating user plane information and control plane information for a particular session to determine some insight into that session. For example the correlation logic described in WO 2017/037598 (PCT/IB2016/055120) can be used to collect the user plane information and the control plane information for individual sessions, and to correlate that information. Records of the correlated data provide information from both domains, and also their temporal relationship, enabling the monitoring system to detect the time difference between events on the user plane and control plane.