Hello, if you look here:https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/upgrade/11_5_1/cucm_b_upgrade-guide-cucm-115/cucm_b_upgrade-guide-cucm-115_chapter_01100.html It states that upgrade from 8.X to 11.5 can be done by OS, from 9.1 the sam...