After some configurations are modified on the eSpace U1930 (serving as a SIP server), the eSpace U1930 must be restarted. During the eSpace U1930 restart, all IP phones register with the SIP server using the session boarder controller (SBC). After the eSpace U1930 restart, the IP phones do not work. They can be used only after being powered-cycled.
Change the interval for the IP phone to update its registration with the SIP server to 120s.
The default interval for the IP phone to update its registration with the SIP server is 3600s, which is relatively long. After the eSpace U1930 is restarted, this interval has not expired. The IP phones are still registered with the SIP server with the old configurations.