VoIP glossary · Transport Layer Security
What is TLS?
TLS (Transport Layer Security) encrypts SIP signalling, typically on port 5061, so phone numbers, credentials and call details cannot be read or changed in transit.
TLS explained
It is the same technology that secures websites over HTTPS. For SIP it protects the INVITEs, registrations and SDP, which matters because SDP carries the keys for SRTP. Without TLS, SRTP keys would travel in plain text.
Enabling TLS means switching the trunk transport to TLS, pointing at port 5061 and making sure the PBX trusts the provider’s certificate. Certificate errors are the most common reason TLS trunks fail to register.
Example
After switching the trunk to TLS on 5061, a FreePBX system fails to register until the provider’s CA certificate is added to its trust store.
Put it into practice
Prepaid SIP trunks and wholesale routes from $200. Ask sales for rates or the NOC for a technical answer.