Unable to establish secure connection with CUCM

[Georgi]

Hello community,

I am trying to deploy W56 phone with CUCM using TLS/SSL between them.
Disabling SSL the phone registers and works just fine. But when I enable secure communication I can't get the phone to register. TLS handshake can't be established.
I've done a packet capture and what I see is that we have the client and server Hello and the server requests certificate. Then the phone sends its own certificate, but the CUCM server rejects it with "Unknown CA" error.

My question is how to get the phone certificate and upload it in CUCM so I can make CUCM trust the phone? Or am I doing something wrong here? Is there someone who has this kind of setup? I would appreciate any help!

Regards!