SIP trunks

SIP trunking allows Link devices to make and forward calls to external mobile numbers via Twilio. You can assign multiple trunks to different groups within your project and define routing behavior per group.

Let’s go step by step — from setting up your project structure to configuring outbound call routing:

❶ Define the project structure

1. Make sure BAS-IP Link is installed and running.

2. Log in directly to your instance with administrative access and create administrator profiles manually.

3. Navigate to User management → Object groups.

4. Create the hierarchy:

   • Root group = Building;

   • Subgroups = Units, Floors, Apartments.

4. Go to Profiles, define and assign roles.

5. Add users, assign them to roles and apartment groups.

❷ Activate the Plus license

1. Make sure your self-host license includes SIP Trunk support.

2. Navigate to Licenses and verify that SIP Trunks is Enabled.

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❸ Register a Twilio account

1. Go to Twilio.

2. Register using 2FA/two-factor authentication — it keeps your account safe and lets you use real phone numbers for calling.

3. Verify your mobile number.

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4. Top up your balance with the minimum $20 USD — this upgrades the account from trial to production mode and allows calling.

❹ Buy a phone number

1. Go to Phone Numbers → Buy a number.

2. Choose a local number with Voice capability.

3. Price is usually around $1.15/month.

4. This number will be used as Caller ID for outbound calls.

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❺ Create an Elastic SIP Trunk in Twilio

1. Use the Jump to… search in the top-right corner and enter Elastic SIP Trunks. Select it from the dropdown.

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2. Click Create new SIP Trunk button, name the trunk, and click Create.

3. In the opened General tab, check the Friendly Name field and click Save at the bottom of the page.

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4. Go to the Termination tab and create any unique hostname in the Termination SIP URI field: example.pstn.twilio.com.

5. Under Authentication click the ➕ button next to IP Access Control List:

   • If your server does NOT use NAT: add your external IP address as Proxy, with a /24 mask.

   • If your server uses NAT: add your external IP as Proxy, with a /24 mask, and add your internal IP as Node, also with a /24 mask.

6. Repeat this process for both IPs: click ➕ again to add the second address.

7. Click the ➕ button next to Credential Lists.

8. Create a username and secure password — this will be used later in Link.

9. Click Save at the bottom of the page.

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10. Go to the Numbers tab, click Add a number → Add an Existing Number and attach the phone number you previously purchased.

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❻ Add the SIP Trunk in Link

1. Go to Telephony settings → SIP Trunks.

2. Click ➕ in the lower-right corner to add a new trunk.

3. Enter a display Name — this is just a label to help you identify the trunk.

4. Paste the hostname you created in Twilio in Termination URI, e.g.: example.pstn.twilio.com.

5. Paste the phone number you attached to the trunk into Outgoing number.

6. Paste your Twilio credentials into Login and Password.

7. Assign the trunk to the relevant groups, e.g.: Building #1, Unit #1.

8. Click 💾 Save icon in the lower-right corner.

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❼ Add forwarding rule with mobile number

1. Go to User management → Object groups, then open the required apartment group where the call needs to be routed.

2. Click the ••• next to the group and select Edit.

3. In the Forwarding rule tab, choose: either a mobile number, or a virtual number.

4. Click 💾 Save icon in the lower-right corner.

✽ App vs Mobile Number

Why?

When a call is initiated, the SIP server calls all routes simultaneously — the app and the mobile number at the same time.
The device shows whichever call request arrives first.

• If the app notification (push + SIP registration) reaches the phone first, the app will show the incoming call screen.

• If the mobile network call arrives first, the mobile call screen will appear.

Mobile calls often involve complex routing via external transit operators, which can cause unpredictable delays. Because of this, the app call is usually faster and will most likely pop up first.

If voicemail answers the mobile call before the user picks up via the app, the panel will treat the call as successfully answered — breaking the forwarding flow.