Starting from firmware version 126.96.36.199 all deskphones equipped with a USB port can store PCAP traces on a mass-storage device connected via USB. In this case the trace size is limited only by the free space of the USB device.
Create the "flag file" pcap.flg into the root directory
Plug the USB device into the phone USB port. The phone should detect the storage device:
At this point the phone starts saving the pcap trace onto the USB device. Once you have reproduced the issue you can unmount and unplug the USB device. Unmounting the device before unplugging is fundamental in order to avoid data corruptions.
The USB device can be un-mounted pressing the Menu key, selecting Maintenance and then Unmount USB disk:
Now your are ready to plug the USB device into your computer and start analysing the saved PCAP trace: