Cisco IP phone firmware downgrade - CME

[jagan guptha]

Im working on a LAB environment where i need to switch the phones from CUCM 8 , CUCM11 and CME 8.x

And i have all the supported firmware's for the CISCO IP Phones

But when it comes to CME and if the Phone firmware version is higher than which it supports the phone is not getting registered.

what is the best practice to downgrade a phone firmware when using CME and also CUCM

[tanios191]

Did you find any resolution for this problem

I have 7821 phones with missed call notification not appearing so I am downgrading the phone and it is giving error

[HARIS_HUSSAIN]

Make sure the IP Phone is able to contact TFTP Port of CUCM & Option 150 is configured in DHCP Pool

[tanios191]

I have a cisco CME ISR 4K not a CUCM please advise