I have 80 T23G phones that were recently installed for a client on a 3CX system running the latest V15.5. They seem to lose their network connection at random times and the display shows it is requesting an IP address. These phone replaced some old Cisco phones that did not have this issue. The phones are on various Cisco C2960 switches running C2960X-UNIVERSALK9-M firmware. When the phones lose their IP, which I assume is because they are losing their ethernet connection, they do not lose power so just request an IP and then re-register. Client has installed new Cat5e cable on a couple, changed patch cords, set the switch to 100/full from auto as a test, upgraded the firmware on the phones, factory defaulted the phone, etc. The switches are probably running cdp but not lldp. The phones are running on trunk ports with with the voice on vlan 100 in a custom template. Any ideas of suggestions would be appreciated. I suspect it is a Cisco switch issue or protocol of some sort, but have not found it yet.