If needed, you can start a pcap trace on the N870/N670 direct from your PC.
The trace can be made on the:
Enable SSH access
First you need to enable SSH access to the system.
Open the web-interface and go to: SETTINGS - System - Web configurator.
Enter the Password for the SSH access.
The trace can be started direct from your PC.
Download this zip file that contains all tools and a batch file you can start direct from your laptop and opens a stream from the N870 to wireshark that is installed on your PC.
The device that has the role DECT Manager + Integrator + Base will send the SIP traffic and RTP if the handset is connected to this device. Always remember that the DECT base where the call is started is sending the RTP to the outside world.