CUCM Deployed version 8.6.2(22025) JTAPI and CTI Bug fixed in 8.6.2(22044). Inter Opearbale with QM version 8.6.2 ES5
This is woud be first upgrade I would do to fix the bug what all things should I consdier before upgrading cucm. It is 2 cluster with 2 subs in 1st cluster and 1 sub in 2nd cluster.
and how much downtime can be quoted for all the 5 servers considering 1 at a time.