3CX Session Border Controller (SBC)

What Is the 3CX SBC?

The 3CX Session Border Controller (SBC) is a lightweight software service that acts as a local gateway between your IP phones and your 3CX phone system — whether that system is cloud-hosted or located at a remote site. Rather than each phone individually punching through your firewall to reach 3CX, all SIP signaling and RTP media traffic is consolidated through the SBC. This eliminates common connectivity issues caused by NAT, firewalls, and network address translation.

The result is more reliable call quality, fewer registration drops, and a simpler network configuration — especially important for multi-site businesses across Northern Ontario where network conditions vary.

When Do You Need an SBC?

An SBC is most valuable when:

• You have a branch office or remote site connecting to a central cloud-hosted 3CX system.
• You are experiencing phone registration drops, one-way audio, or intermittent call failures at a specific location.
• Your network uses strict firewall rules that interfere with SIP traffic.
• You have 10 or more IP phones at a site and want to reduce the number of external connections to your PBX.

If your site has fewer than 10 phones, SBC-capable IP phones (sometimes called router phones) may be a simpler alternative — they handle the SBC function themselves without requiring a separate device or server.

Supported Platforms

The 3CX SBC can be installed on:

• Windows — download and run the Windows installer
• Debian Linux — recommended for server deployments
• Raspberry Pi — suitable for small offices where a full server is not practical

Regardless of platform, the SBC host must have a static IP address to ensure phones can reliably locate and register through it.

Installation Overview

1. Choose a device at your site to host the SBC — a small server, PC, or Raspberry Pi with a static local IP. Ensure it will remain powered on continuously.
2. Download the appropriate SBC installer for your platform from the 3CX admin console or the 3CX website.
3. Run the installer and follow the setup prompts. You will be asked to enter a provisioning key that links the SBC to your specific 3CX system.
4. Once installed, the SBC registers with your 3CX system. You will see it appear in the 3CX admin panel under SBC.
5. Provision your IP phones to point to the SBC's local IP address rather than directly to the 3CX server. The SBC handles routing from there.

DVGVoIP handles SBC installation and configuration as part of deployment. If you are setting up a new branch or experiencing connection issues at an existing site, contact us and we will assess whether an SBC is the right solution.

High Availability (HA) Cluster

For businesses where phone uptime is critical — healthcare, dispatch, customer service — the SBC can be configured in a High Availability (HA) cluster. This eliminates the SBC itself as a single point of failure.

An HA SBC cluster consists of:

• Primary node — handles all traffic under normal operation
• Secondary node — identical hardware configuration, monitors the primary and takes over automatically if it fails
• Floating IP address — a shared IP that moves between nodes on failover, so phones always connect to the same address regardless of which node is active

Both nodes require static IP addresses and identical hardware or VM configurations. HA setup is more involved and is typically handled by DVGVoIP during a managed deployment.

Troubleshooting Common SBC Issues

Most SBC problems fall into one of these categories:

• SBC not appearing in 3CX admin — check that the provisioning key was entered correctly during setup and that the SBC host can reach the 3CX server over the internet.
• Phones registering through SBC but calls fail — verify that UDP ports required by 3CX are not blocked by the local firewall on the SBC host.
• SBC drops and reconnects intermittently — usually caused by an unstable internet connection at the branch site, or the SBC host losing its static IP (e.g. DHCP lease expired).
• One-way audio after SBC installation — confirm RTP media ports are being correctly forwarded through the SBC and not bypassing it.

If you are experiencing any of these issues, email support with the SBC hostname and approximate time the issue started — this helps us pull the right logs quickly.