How to Upgrade to Call Manager 12.5

It can be difficult to upgrade Cisco Unified Communications Manager (CUCM), to 12.5 Although it is worth the effort, it can be time-consuming and difficult. It is important to have a step-by, easy-to-follow guide once you have made that decision.
Verifying that the licensing has been converted to FLEX (which automatically adds licenses to Smart License Manager at Cisco) or converted to CUWL licenses to Smart License Manager is the first item on this list. We recommend that you take a look at FLEX to see what it can do.
What the Upgrade Looks Like and How Long It Takes
It’s not something I will sugarcoat. This is a major upgrade that will take approximately 2.5 hours for Publisher servers and 1.5 to 2 for subscribers. First, ensure that your hardware is available for the upgrade. VMWare ESXi6.5 or higher is required for CUCM 12.5 to work. If you are using a UCS server, you might need to upgrade the firmware and upgrade VMWare before you can upgrade CUCM.
Cisco offers a website that will help you determine if your hardware is capable of this feat and what firmware you may require. You will need to enter your Server Type, Model and Processor Version, Operating System, and OS version.
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Start trainingPre-Upgrade Tasks
To prepare for the upgrade, there are some tasks you should do before upgrading. Cisco provides a pre-upgrade cop file that you can run for both CUCM or Unity Connection. This will let you know if your server is ready to upgrade. The filename is ciscocm.preUpgradeCheck-00024 and can be found in the Software Downloads section of Cisco’s website.
The cop file checks disk space and NTP. Most likely, disk space issues will occur as this upgrade takes up more space than previous ones. When that is the case, run the ciscocm.free_common_space_v1.5.cop.sgn file to free up the necessary space. Sometimes, even this doesn’t free enough space. To free up some space, you can remove specific phone firmware from certain devices.
Next, verify that each server’s virtual hardware matches the 12.5 ova templates. This is important because the switch-version at end of the upgrade checks will verify that the hardware is correct. It will fail if it doesn’t match. You should check the Hard Disk and RAM, as well as the Network adapter, to ensure that they match the ova template. To make any changes to Vmware ESXi, you will need to shut down the server.
Here are the most recent virtualization specifications for CUCM and CUC, IM&P and UCCX.

Perform the Upgrade
Finally, you can upgrade to 12.5. First, upgrade the CUCM Publisher. To save time, you can also upgrade the Unity Connection and UCCX Publishers simultaneously. The IM & P Publisher must wait until the CUCM publisher is done. It is considered a subscriber of the CUCM publisher. All subscribers can be done simultaneously once the publishers have been completed. If you have multiple subscribers to which phones are registered, and you want to reduce downtime, each subscriber should be done individually.
You have the option to either wait until all versions are finished or switch automatically after an upgrade. Unity Connection doesn’t offer this option and switches automatically. UCCX does not offer this option, but you must make it manually.
The upgrade can be done in three ways. The Prime Collaboration Deployment Server can be used to upgrade. This server is easy to deploy on the ESXi. The PCD cannot be used for all applications. It can perform the entire cluster one at a time in some cases. There is a possibility that you will encounter problems and need to restart the upgrade manually.
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