TLS (Transport Layer Security) and SIP
TLS is a common security protocol used for private, and secure communications over the Internet.  When enabled, TLS encrypts the signaling of VoIP calls. 

Why Use TLS?

TLS is often used for security purposes and is typically employed to accommodate a customer’s needs for, or policies around encryption.  

However, TLS can be used under some circumstances to effectively mitigate issues on the customer’s LAN. 

For example, TLS can allow you to bypass ALGs (Application layer Gateways), which inspect SIP messages, and avoid Network Address Translations (NAT) processes. These features are common on routers and gateways and can negatively impact the customer’s experience, resulting in problems like one way audio issues, dropped calls, temporary loss of audio and many other issues.  

With TLS enabled, SIP packets become unreadable to the router or gateway and so packets are unaltered by the ALG and NAT features. 

How To Enable TLS 

TLS is enabled at the device level. When adding or modifying a device for TLS, go to the phones tab in the PBX. You will see a tab for advanced phone configurations as shown below. On this tab, you will see choices for UDP, TCP, and TLS. Select TLS and save.