1、First modify 【system】–>【Settings】–>【GENERAL SIP SETTINGS】
transport：Add tls, if it’s already have pther protocol，please use ‘,’ separate them.
Tips: After modify transport need click on the reload bar to take effect.
2、Download asterisk’s script “ast_tls_cert” file, use this script to generate an SSL certificate.
wget https://download3.astercc.org/ast_tls_cert
chmod +x ast_tls_cert
./ast_tls_cert -C pbx.sorry.com -O "My Computer" -d /etc/asterisk/keys
3、Edit sip.conf file add tls support.
4、yealink upload client SSL certification file ca.crt.
5、yealink SIP Phone modify transport TLS signup for asterCC system.
Tips: Please allow access TCP port 5060 on iptables.