TLS means "Transport Layer Security", it is the security protocol used for the encryption of "information" relative to Voip calls.
TLS is the evolution of SSL universally known for being used by almost all bank web sites and sites that manage sensitive information.
TLS is a standard approved by IETF as an official document RFC5246.
TLS allows to communicate on an open network like the Internet, without the risk of being intercepted. This function is universally recognized by the entire international technical community.