This article will explain how to identify SIP registration issues using a the built in packet capture function found on most Grandstream devices.


Step 1:

Login to your device and start the packet capture (in this example we will perform a packet capture from a UCM6202):


Step 2:

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.


Step 3:

Wait a few moments (or if rebooting please wait until the phone has fully rebooted, connected to the network and attempted to register).


Step 4:

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.


Step 5:

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: is sending a Request to Register with the UCM62xx at IP Address

The UCM62xx is then returning a 401 Unauthorized message back to the IP Phone (

Multiple 401 Unauthorized requests indicate that the SIP registration password is invalid.