🔗 3CX Bridge Trunk vs Generic SIP Trunk: Key Differences
Summary: 3CX offers two primary trunk types: Bridge Trunks for connecting multiple 3CX instances, and Generic SIP Trunks for connecting to external VoIP providers. This guide explains the fundamental differences, use cases, configuration steps, and helps you choose the right trunk for your multi-site or carrier connectivity needs.
📖 Table of Contents
🔗 What is a 3CX Bridge Trunk?
A 3CX Bridge Trunk is a specialized trunk type designed exclusively for connecting two or more 3CX PBX instances together. Think of it as a "private line" between your 3CX systems, allowing them to communicate seamlessly as if they were a single unified phone system.
🔹 Key Features of a Bridge Trunk
- Extension-to-Extension Dialing: Users can dial extensions at remote sites just like local extensions.
- Presence Sharing: See whether remote extensions are available, busy, or on a call.
- Call Transfer: Transfer calls seamlessly between sites (attended and blind transfers).
- Free Internal Calls: Calls between sites are free—no per-minute charges.
- Centralized Management: Some configurations allow centralized user management from a main PBX.
💡 Use Case: A company with a headquarters in New York and a branch office in London. Both run 3CX. A Bridge Trunk connects them, allowing employees in London to call the New York office by simply dialing an extension.
📞 What is a Generic SIP Trunk?
A Generic SIP Trunk is the standard trunk type used to connect a 3CX PBX to an external VoIP provider or carrier. This is the trunk that gives your PBX access to the Public Switched Telephone Network (PSTN), enabling you to make and receive calls from the outside world.
🔹 Key Features of a Generic SIP Trunk
- PSTN Connectivity: Make and receive calls to/from any phone number globally.
- DID Support: Inbound calls are routed based on Direct Inward Dialing (DID) numbers.
- Multiple Providers: Connect to any SIP provider (e.g., Telnyx, Twilio, Flowroute, NetviaVoice).
- Authentication: Uses IP-based authentication or SIP registration (username/password).
- Codec Negotiation: Support for multiple audio codecs (G.711, G.729, etc.).
💡 Use Case: A business needs to make and receive calls from customers. They purchase a Generic SIP Trunk from a provider like NetviaVoice, assign DIDs, and route inbound calls to their sales and support teams.
📊 Side-by-Side Comparison
| Feature | 3CX Bridge Trunk | Generic SIP Trunk |
|---|---|---|
| Purpose | Connect 3CX instances together | Connect to external VoIP carriers / PSTN |
| External Provider Required | No – connects your own systems | Yes – requires a SIP provider |
| Cost Per Call | Free (internal, no per-minute charges) | Per-minute (usually billed by provider) |
| Extension Dialing | Yes – dial remote extensions directly | No – external numbers only |
| Presence Sharing | Yes | No |
| Call Transfer Between Sites | Yes – seamless | Not applicable (external calls only) |
| DID Support | No – uses extensions | Yes – incoming DID routing |
| Authentication | IP-based or username/password (between 3CX systems) | IP-based or SIP registration with provider |
| Number of Systems | 2 or more 3CX instances | 1 (or more) 3CX instances connecting to external carriers |
🎯 When to Use Each Trunk Type
✅ Use a Bridge Trunk When:
- You have multiple offices (e.g., HQ, branch offices, remote locations) each with its own 3CX PBX.
- You want seamless internal calling across sites without PSTN charges.
- You need presence sharing so employees see remote colleagues' availability.
- You want to centralize management (e.g., one PBX handles user provisioning for all sites).
- You have a stable network (VPN or direct IP connectivity) between sites.
✅ Use a Generic SIP Trunk When:
- You need to make and receive calls from the public telephone network.
- You have DID numbers assigned to your business.
- You want to choose a SIP provider based on rates, features, or geography.
- You are connecting to external services (e.g., call centers, IVR services).
- You need to route calls to mobile phones or external numbers.
🛠️ How to Configure a Bridge Trunk in 3CX
Setting up a Bridge Trunk involves configuring both the main (master) and branch (slave) PBX instances.
- 1 On the Main PBX: Go to Voice & Chat → SIP Trunks → Add SIP Trunk. Select "Bridge Trunk" as the trunk type.
- 2 Set the Role: Choose "Main" (or "Master") for the primary PBX.
- 3 Enter the remote PBX details: Provide the IP address or hostname of the branch PBX.
- 4 Configure Authentication: Set a shared secret (password) that both PBXs will use.
- 5 On the Branch PBX: Go to SIP Trunks → Add Bridge Trunk → choose "Branch" as the role.
- 6 Enter the Main PBX details: IP address of the main PBX and the same shared secret.
- 7 Configure Inbound/Outbound Rules: Create rules on both sides to route calls between extensions.
⚠️ Important: Both PBXs must be reachable over the network (VPN or public IP with proper firewall rules). Ensure SIP ports (5060/5061) and RTP ports are open between the sites.
🛠️ How to Configure a Generic SIP Trunk in 3CX
- 1 In 3CX Management Console, go to Voice & Chat → SIP Trunks.
- 2 Click "Add SIP Trunk" and select your country and provider (or "Generic VoIP Provider" if not listed).
- 3 In the "General" tab, enter the trunk name, your DID numbers, and the provider's hostname.
- 4 In the "Authentication" tab, choose either "IP Based" (if your IP is whitelisted) or "Register" (username/password).
- 5 Fill in the required credentials (if using registration) or ensure your IP is whitelisted by the provider.
- 6 Click "OK" to save. The trunk will attempt to register (if registration mode) or show as "Registered" if IP-based.
- 7 Create Inbound Rules to route incoming DIDs to extensions, and Outbound Rules to route outbound calls through the trunk.
💡 Pro Tip: Always test your Generic SIP Trunk by making a test call after configuration. Check the Activity Log for any error messages.
✅ Pros & Cons Summary
🔗 Bridge Trunk
✅ Pros:
- Free internal calls between sites
- Extension dialing across offices
- Presence and status sharing
- Seamless call transfers
- Centralized management options
❌ Cons:
- Requires multiple 3CX instances
- Network connectivity between sites required
- Setup more complex than generic trunks
- Does not provide PSTN access
📞 Generic SIP Trunk
✅ Pros:
- Connect to any SIP provider
- PSTN access for external calls
- DID support for inbound calling
- Flexible authentication options
- Widely supported
❌ Cons:
- Per-minute costs
- No internal extension dialing
- No presence sharing
- Requires provider account and credentials
🏆 Best Practices for Both Trunk Types
🔗 Bridge Trunk Best Practices
- Use a VPN for secure communication between PBXs.
- Set up firewall rules to restrict SIP traffic to specific IPs.
- Use strong shared secrets for authentication.
- Regularly test failover scenarios if one site goes offline.
- Keep extension numbering consistent across sites.
📞 Generic SIP Trunk Best Practices
- Use TLS/SIPS and SRTP for encryption.
- Set up failover with multiple trunks from different providers.
- Monitor call quality and codec usage.
- Implement call detail recording (CDR) for billing and analysis.
- Regularly review outbound rules to prevent toll fraud.
🚀 Need Expert Help with 3CX Configuration? NetviaVoice Can Assist
Our VoIP specialists can help you set up Bridge Trunks, Generic SIP Trunks, and optimize your 3CX PBX for multi-site or carrier connectivity.
Visit NetviaVoice❓ Frequently Asked Questions
A 3CX Bridge Trunk is a specialized SIP trunk that connects two or more 3CX PBX instances together, allowing them to communicate seamlessly. It extends the phone system across multiple sites, enabling features like extension dialing, presence sharing, and call transfers between offices.
A Generic SIP Trunk is used to connect a 3CX PBX to an external VoIP provider or carrier for making and receiving calls over the public telephone network (PSTN). It uses standard SIP protocols and requires credentials or IP authentication.
A Bridge Trunk connects 3CX systems internally, allowing free internal calls, presence sharing, and extension dialing between sites. A Generic SIP Trunk connects to external carriers for PSTN access. Bridge trunks are used for multi-site PBX interconnection, while Generic SIP trunks are for connecting to the outside world.
No, Bridge Trunks are specifically designed for 3CX-to-3CX connections. To connect to an external provider (e.g., Telnyx, Twilio, or a local carrier), you must use a Generic SIP Trunk. The two types are not interchangeable.
In the 3CX Management Console, go to Voice & Chat > SIP Trunks. Click 'Add SIP Trunk', select 'Bridge Trunk' as the type, and choose the role (Main or Branch). Enter the remote PBX details, IP address, and authentication information. Then configure inbound/outbound rules to route calls between the sites.
📢 Need help choosing between a Bridge Trunk and a Generic SIP Trunk? Let NetviaVoice guide you.