This article will explain how to identify SIP registration issues using a the built in packet capture function found on most Grandstream devices.
Login to your device and start the packet capture (in this example we will perform a packet capture from a UCM6202):
Initiate a registration request from an IP Phone by either rebooting the phone or; disabling the account, save and apply settings, re-enable the account, save and apply settings.
Wait a few moments (or if rebooting please wait until the phone has fully rebooted, connected to the network and attempted to register).
Stop the packet capture and download it to your computer. You will need a packet capture software such as Wireshark to view this file which can be downloaded here.
Filter the packets to only contain SIP using sip.CSeq contains "REGISTER":
As we can see in the packet capture the IP Phone (Source address: 192.168.2.100) is sending a Request to Register with the UCM62xx at IP Address 192.168.2.1.
The UCM62xx is then returning a 401 Unauthorized message back to the IP Phone (192.168.2.100).
Multiple 401 Unauthorized requests indicate that the SIP registration password is invalid.