Aastra 53i Release Note page 36

IP Phone Release Notes 2.1
Security Features
Parameter –
sips trusted certificates
Trusted Certificates
(in Web UI)
Description
Format
Default Value
Range
Example
30
Aastra Web UI
Configuration Files
Allows you to specify the Trusted Certificate files to use when the phone
uses the TLS transport protocol to setup a call.
The Trusted Certificate files define a list of trusted certificates. The phone's
trusted list must contain the CA root certificates for all the servers it is
connecting to. For example, if the phone is connecting to server A which
has a certificate signed by CA1, and server B which has a certificate
signed by CA2, the phone must have CA1 root certificate and CA2 root
certificate in its Trusted Certificate file.
This parameter is required when configuring TLS or Persistent TLS.
Note: The certificate files must use the format ".pem". To create custom
certificate files to use on your IP phone, contact Aastra Technical Support.
<file name>.pem
N/A
N/A
sips trusted certificates: trustedCert.pem
Advanced Settings->TLS Support
aastra.cfg, <mac>.cfg
RN-001029-00, Rev 03, Release 2.1