Hello  baechangmin, kindly note that the downgrade concept is not supported on CUCM.you can switch versions in between the active and inactive partitions.and no lower version can be uploaded to the CUCM than the current on the both partitions. Regard...

Hi @Nizam.Ahmed ,   and if we want permanent fix,   All auto registered IP phones take their settings from the auto registration template, which is configured on Cisco Unified CM Configuration Page: To edit that Auto-registration Template, go to User...

I do appreciate your kind assistance I will proceed as you recommend. Thanks!! best regards,   Haron.

Hi Tony,No, it's 11.5And in my opinion, it doesn’t affect the upgrade process, but I want to make sure Thanks!Haron