From Cisco’s internal release notes (paraphrased):
Authentication Error: If the phone displays an authentication error during the upgrade, ensure that the ITL (Identity Trust List) file on the phone is current. You may need to manually delete the ITL file from the phone's security settings to allow it to download the new firmware. cmterm7975sip942sr4zip 2021
: This release was a "Service Release" (SR), which typically focuses on bug fixes and security vulnerabilities rather than new features. In 2021, these updates were vital for keeping older 7900-series phones compatible with newer versions of Cisco Unified Communications Manager (CUCM) End-of-Life Tracking In 2021, these updates were vital for keeping
The file is a firmware upgrade package for Cisco Unified IP Phone Go to product viewer dialog for this item. cmterm7975sip942sr4zip 2021
: You must create a SEP .cnf.xml file that directs the phone to use the SIP942SR4 image.