Recently we completed one successful CUCM migration from 6.1.1 to 10.5. CUCM 6.1.1 was running on MCS and the challenge was to do the migration in limited downtime. The New CUCM cluster also should have the same IP of the OLD cluster.
1. Take DRS Backup of existing CUCM Publisher 6.1.1
2. Install CUCM 6.1.1 on MCS with the same IP of existing CUCM in a staging environment.
3. Restore Backup to New CUCM 6.1.1
4. Upgrade New CUCM 6.1.1 to 6.1.3
5. Upgrade CUCM 6.1.3 to 6.1.5
6. Install PCD and Configure VM on Staging UCS Server.
7. DO PCD Migration from CUCM 6.1.5 to 10.5.1
8. Take Backup of CUCM 10.5.1
9. Install CUCM 10.5.1 on UCS ( Isolated Network )
10.Restore Backup
11. Install Subscriber
12. Either upgrade the Phone Firmwares on OLD CUCM 6.1.1 or match firmware versions to the New CUCM 10.5.1
13. Disconnect OLD CUCM from Production Network and Connect New CUCM Cluster to Production Network.