3CX Version 20 SIP Trunk Configuration

Overview

This guide walks you through configuring a Simtex SIP trunk on 3CX Version 20 using the web-based management console. 3CX v20 introduced a redesigned admin interface with streamlined SIP trunk configuration — if you're coming from v16 or v18, the workflow is similar but the UI has changed significantly.

Simtex uses registration-based SIP trunks, where your 3CX system authenticates with our servers using your account credentials.

What you'll need

• Your Simtex account number (e.g. 214XXXXXXX)
• Your Simtex SIP password
• Your allocated DIDs (phone numbers)
• 3CX Version 20 installed with admin console access

Step 1 — Add a SIP Trunk

1. Click the Admin cog on the bottom left-hand side of the console
2. Select Voice & Chat
3. Click Add Trunk

A pop-up will appear prompting you to select your country and provider.

Step 2 — Select Provider & Basic Settings

In the Add Trunk pop-up, configure the following:

Country:   Australia
Provider:  Generic VOIP Provider (Registration)

Then set the trunk basics:

Trunk Name:      Simtex SIP
Default Route:   (select your main ring group or receptionist extension)

Check the box Create an outbound rule for this SIP Trunk — this saves you from manually creating outbound rules later (you can customise them afterwards).

Step 3 — Account Details

Under the Account Details section, configure your Simtex credentials:

Main Trunk Number:       (your primary DID, e.g. 61894883344)
Authentication ID:       214XXXXXXX
Authentication Password:  XXXXXXXX
Type of Authentication:  Register/Account Based

The Main Trunk Number is used as the default outbound caller ID when no extension-level override is configured.

Step 4 — Server Details

Under the Server Details section, configure the connection to Simtex:

Registrar/Server:  siptcp.simtex.com.au
Port:              0
Auto Discovery:    Checked

Check the Auto Discovery checkbox — this greys out the port field and sets it to 0, allowing 3CX to use NAPTR/SRV DNS records to automatically discover the optimal connection endpoint and port.

Step 5 — Save & Verify Registration

Click Save to create the trunk. 3CX will attempt to register with Simtex immediately.

1. Navigate back to Voice & Chat → SIP Trunks
2. Your new trunk should show a green status indicator, meaning it has successfully registered
3. If the status is red, see the troubleshooting section below

Step 6 — Codec Configuration

Edit the trunk you just created and navigate to the Codecs section. Configure the codec priority order for Australian deployments:

Priority 1:  G.711 A-Law  (alaw)
Priority 2:  G.711 U-Law  (ulaw)
Priority 3:  G.729        (optional, if licensed)

Drag the codecs to reorder them. Remove any codecs you don't intend to use — a cleaner codec list speeds up call setup.

Step 7 — Caller ID & Advanced Settings

In the trunk's advanced or options section, configure caller ID passthrough:

Send Remote-Party-ID (RPID):    Yes
Send P-Asserted-Identity (PAI):  Yes
Trust Inbound RPID/PAI:          Yes
Caller ID From:                  RPID/PAI Header

These settings ensure your outbound caller ID is correctly transmitted and any per-extension overrides work as expected.

Step 8 — Add Your DIDs

Navigate to the DIDs tab on the trunk configuration and add your allocated phone numbers:

1. Click Add DID
2. Enter your DID number in E.164 format without the plus sign (e.g. 61894883344)
3. Assign a destination for each DID — extension, ring group, IVR, or queue
4. Repeat for all your allocated numbers

Step 9 — Outbound Rules

If you checked Create an outbound rule for this SIP Trunk in Step 2, a basic outbound rule was created automatically. You can customise it or add additional rules.

Navigate to Outbound Rules in the admin console. For each rule, specify a Rule Name, select the Simtex SIP trunk as the route, and configure the dial pattern.

Step 10 — Security Hardening

After configuring your trunk, take these essential security steps:

Limit concurrent calls

Set the Number of SIM Calls to the number of concurrent calls you actually need. This acts as a hard limit — if your system is compromised, attackers can't exceed this call count.

Set strong extension passwords

3CX auto-generates extension passwords — do not simplify them. Weak extension credentials are the #1 cause of toll fraud.

Enable the 3CX anti-fraud module

• Go to Security → Anti-Fraud in the admin console
• Set daily call limits and international call restrictions
• Enable email alerts for suspicious activity

Keep 3CX updated

3CX v20 receives regular security patches — enable automatic updates or check regularly.

Testing Your Trunk

Once configured, verify everything works:

1. Check trunk status — the trunk should show as Registered (green) in the SIP Trunks list
2. Make an outbound call — dial an external number from an extension and confirm audio in both directions
3. Receive an inbound call — call one of your DIDs from a mobile and confirm it routes to the correct destination
4. Check caller ID — verify your outbound caller ID displays correctly on the receiving end

Extension-Level Caller ID

By default, all outbound calls use the Main Trunk Number as the caller ID. To override this per extension:

1. Navigate to Users in the admin console
2. Select the extension you want to modify
3. Under Outbound Caller ID, enter the DID you want that extension to present
4. The DID must be allocated to your Simtex account — you cannot present arbitrary numbers

Need Help?

If you run into any issues configuring your 3CX trunk, our support team can verify your trunk registration status from our side and assist with troubleshooting.

Contact Simtex Support