Yealink SIP-T54S Administrator's Manual page 973

Select TLS from the pull-down list of Transport.
3.
Click Confirm to accept the change.
4.
To configure the trusted certificates via web user interface:
Click on Security->Trusted Certificates.
1.
Select the desired values from the pull-down lists of Only Accept Trusted Certificates,
2.
Common Name Validation and CA Certificates.
Click Confirm to accept the change.
3.
A dialog box pops up to prompt that the settings will take effect after a reboot.
Click OK to reboot the phone.
4.
To upload a trusted certificate via web user interface:
Click on Security->Trusted Certificates.
1.
Configuring Security Features
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