CUCM Upgrade from 12.5 SU4 to 12.5 SU8a

[Mahmoud Marie]

Hello

We will upgrading our CUCM from version 12.5.1.14900-63 to 12.5.1.18901-1, we have two nodes (Publisher and Subscriber)
Our upgrading action plan to moving all phones to Subscriber and upgrade the Publisher, and once the upgrade is done successfully return back the phones to Publisher and upgrade the subscriber.
Just need to make sure if that the correct way to upgrade the CUCM.

Appreciate your help 

Thanks

[Thomas G. Johannesen]

Hey

if your phones is allready using the sub as an stand-by server you dont need to move Them. The phones Will by Them self use the the sub as primary is the pub is down

[Nithin Eluvathingal]

You dont need to move the phones to subscriber if you have configured sub as your standby call control server.  CM group defines the order of CUCM to which phones will register.

Here mentioned below will the process of upgrade.

1. Upgrade your CUCM Pub,
2. then upgrade the CUCM SUb,
3. switch version pub and during this task if your subs is acting as your stand by call control phone will register with subscriber.
4. Then switch version subscriber, during this task phones will register back to CUCM pub(assuming your primary call control is publisher)