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.
Make sure you read the upgrade guide and release notes for the version and refer to the compatibility matrix to ensure all other apps will remain compatible.
As to timing it depends on your db size and hardare you are running, but expect 2 hours for Pub, and 1.5 or so per Sub.
Also, consider that with an upgrade phone firmware are changing so there may be additional time for all of the phones to update.
thx chris for your suggestions those ill be taken care .
Great, please remember to mark questions as answered to help others.