In some Middle East countries like Egypt, Bahrain, Qatar, Oman, and Pakistan (even RTP is blocked), sip protocol (UDP) is blocked by the ISP. This leads to failure in registering IP phones or linkus to LCS Pro server remotely.
Using the TLS protocol without certificates
Step 1. Enable TLS in General-> SIP->TLS on the PBX, and restart the PBX.
Step 2. Enable Register Remotely on Advanced in the extension settings and select the TLS protocol.
Step 3. Use the LCS Pro FQDN and TLS/ port 5061 to register the phone.
Step 4. Disable the 'only accept trusted certificates' option on the phone. Otherwise, it will fail to register.
1) Disabled the option of Only Accept Trusted Certificates.
2) Disabled the option of Common Name Validation.
3) Choose All Certificates as the CA Certificates.
After completing step 2 above, log back into linkus and it will register with the TLS protocol.