Yealink SIP-T48G - Manual (Page 159)

Troubleshooting
149
4. Select the desired value (Optional or Compulsory) from the pull-down list of RTP
Encryption (SRTP).
5. Click Confirm to accept the change.
Note
How to reboot the phone?
To reboot the phone via web user interface:
1. Click on Settings->Upgrade.
2. Click Reboot to reboot the IP phone.
SRTP is not available on all servers. Contact your system administrator for more
information.
SRTP is configurable via web user interface only.