On what parameter will UE send the PDN connectivity request for IMS?

Hello Experts.

On what parameter will UE send the PDN connectivity request for IMS?

Will it happen by default or will UE check any flag to send the request?

Admin note: this post was updated with image below.

If IMS APN is not set as default APN, MME will inform UE about IMS support.

Thanks.

In which message and what’s the flag?

If VoLTE flag is enable at UE side, it will initiate registration for IMS PDN.

And if it doesn’t get IMS preferred over s1 from MME?

In such will it initiate?