[REF LINK] https://www.3cx.com/docs/3cx-tunnel-session-border-controller/

What is the 3CX SBC?

The 3CX Session Border Controller (SBC) is a software service that installs in your local network to allow easy connection of IP Phones to a 3CX instance in the cloud, hosted either in your private cloud or by 3CX. The 3CX SBC combines all SIP (signaling) and RTP (media) VoIP Packets from one location and delivers them to the cloud PBX, thereby overcoming common firewall and networking issues that affect reliability.

When do you need to install an SBC?

The most important usage scenario of an SBC is to connect a number of IP phones located in an office to a PBX located in the cloud. Another scenario is to connect to 3CX installations via a bridge.

What do you need for an SBC?

An SBC is a small piece of software that should be running all the time in your network. The easiest is to install it on a Raspberry PI 4 that you can buy for about $50. You can also install it on a windows machine in your network, either directly on the machine or in a VM. This machine must be running all the time!

How does the 3CX SBC help?

The 3CX SBC overcomes common firewall issues and avoids unnecessary traffic back and forth to the cloud. Internal calls between phones located on the same network will be set-up directly with each other, without going via the internet link, resulting in improved voice quality.

When is an SBC overkill?

If you have a single remote phone that you wish to connect to your 3CX in the cloud, consider using the 3CX iOS and Android Apps instead. 3CX Apps are the modern way to connect to a phone system. The user can use it anywhere in his home, or indeed even outside, and it will save configuration and maintenance.