CUCM upgrade from 11.5 to12.5 - pub and sub parallel upgrade

[mnkojima]

Hello

we will upgrade our CUCM from version 11.5 to 12.5. I remember that, when publisher upgrade reaches a step where the log shows 'PRODUCT_VERSION TARGET', the subscriber upgrade could be started.

Is that valid for CUCM 11.5 too?

Thank you

Marcos

[Jaime Valencia]

Mandatory reading regardless of what upgrade path you choose, all for target version 
 
A) Upgrade and migration guide
B) Release Notes 
C) Compatibility matrix (depending on product might be a standalone doc, or within any of the other docs I mention) 
D) README from ova
E) HW/ESXi compatibility 
 
After reading all of the above, you'll have all the information to plan the upgrade. 

Upgrade guide contains the sequencing rules for the upgrade.

[Maren Mahoney · Accepted solution]

Marcos,

The documentation says that you can begin the upgrade when that message appears on the Pub, but it does not always work as advertised. You will likely get the "version does not match the active or inactive version of the publisher" if starting the subscriber upgrade when the PRODUCT_VERSION TARGET message appears. This 'divergence' between the documentation and the actual behavior of the system started (as far as I know) with v11.

That said....when *can* you start the upgrade? I don't have specific data on that as I generally don't do parallel upgrades in my lab environment.

HTH

Maren

[mnkojima]

Thank you Maren for sharing your experience.