> ## Documentation Index > Fetch the complete documentation index at: https://docs.fonoster.com/llms.txt > Use this file to discover all available pages before exploring further. # Connect a SIP trunk > Connect any SIP carrier to Fonoster with a trunk, so its numbers ring your agents and your calls go out through it. A trunk is your connection to a carrier. Inbound, the carrier sends calls for your numbers to Fonoster. Outbound, Fonoster sends your calls to the carrier. Use a trunk to bring numbers from any carrier that speaks SIP. For a Twilio number, [Link a Twilio number](https://docs.fonoster.com/telephony/link-twilio.md) does all of this for you. ![One trunk between your carrier and Fonoster. Inbound, the carrier sends calls for your numbers to sip:acme.pstn.fonoster.com, checked by an ACL or inbound credentials. Outbound, Fonoster sends your calls to sip.acme.com:5060 over UDP with outbound credentials, trying outbound URIs by priority, then weight.](https://mintcdn.com/fonoster/GsxtawNPYOQvohG4/images/trunks/inbound-outbound-light.png?fit=max\&auto=format\&n=GsxtawNPYOQvohG4\&q=85\&s=6d73d61ed1fddb23fa3c6093269d407a) ## Before you begin Ask your carrier for: * **How they authenticate you**: by IP address, by username and password, or both. * **Where to send outbound calls**: a host name or IP, a port and a transport (UDP, TCP or TLS). * **The addresses they send calls from**, if you want to accept calls from those addresses only. * **The format of your numbers** in the calls they send, so you can add them exactly as sent. ## Find your connection details Your carrier needs to know where to send calls and which addresses to allow. The trunk form in the dashboard shows both, under **Inbound URI**: > Point your carrier at `:` (``); allowlist ``. Give your carrier the SIP address, and ask them to allowlist the listed addresses if they filter by IP. If your workspace runs in a [private region](https://docs.fonoster.com/private-regions/overview.md), the region's own addresses are under **Settings** → **Region**, in **Connection details**. ## Create the trunk **1. Add credentials (if your carrier uses them)** If your carrier gave you a username and password, save them as credentials first. Fonoster uses them to sign in when it sends calls to the carrier. **Dashboard** Go to **Credentials**, choose **Add credentials**, and enter a **Name**, the **Username** and the **Password**. Passwords are never shown again. **CLI** ```bash theme={"system"} fonoster sipnet:credentials:create ``` Usernames take lowercase letters, numbers, dots, underscores and hyphens. **2. Add an access control list (optional)** An access control list (ACL) is an allowlist of IP addresses. Attach one to the trunk so only your carrier's addresses can send calls in. Anything not listed is rejected. **Dashboard** Go to **ACLs**, choose **Add ACL**, name it (for example `Acme signaling IPs`), and add each address or range, such as `200.88.12.0/24`. **CLI** The command asks for a name and a comma-separated list of IPv4 addresses or CIDR ranges: ```bash theme={"system"} fonoster sipnet:acls:create ``` **3. Create the trunk** **Dashboard** Go to **Trunks** and choose **Add trunk**. The form has three parts. **Inbound · carrier → Fonoster** * **Name**: the carrier's name, such as `Acme`. * **Inbound URI**: a short label that identifies this trunk, such as `acme`. The form adds your install's `.pstn.`, so the URI reads `acme.pstn.fonoster.com`. Give it to your carrier: they send calls for your numbers to this host. It must be unique, so if it's taken, pick another. **Outbound · Fonoster → carrier** Add a row for each address your carrier gave you, with its **Host**, **Port** and **Transport**. Fill in **User** only if your carrier asks for one. Fonoster tries enabled URIs by **Priority**, then spreads calls by **Weight**. A trunk without outbound URIs takes calls in but can't send them out. **Security** * **Access control list**: the ACL from the previous step. * **Inbound credentials**: credentials your carrier must sign in with when it sends you calls. Use them if your carrier authenticates by password instead of IP. * **Outbound credentials**: the credentials from the first step. * **Send REGISTER**: turn on only if your carrier requires registration. Choose **Create trunk**. **SDK** This script creates a trunk with one outbound URI and the carrier's credentials: ```javascript create-trunk.js theme={"system"} const SDK = require("@fonoster/sdk"); async function main() { const client = new SDK.Client({ accessKeyId: "WO7d2kq9x4m1c8b3n6p0r5t2v9y4z7a1e3" }); await client.loginWithApiKey( process.env.FONOSTER_API_KEY, process.env.FONOSTER_API_SECRET ); const trunks = new SDK.Trunks(client); const { ref } = await trunks.createTrunk({ name: "Acme", inboundUri: "acme.pstn.fonoster.com", // one label under pstn. accessControlListRef: "8e1d4b7a-3c9f-4e2a-b6d0-7a5c1f3e9b28", outboundCredentialsRef: "2c6a9e4f-1b7d-4f3a-8e5c-0d9b3a7f1e64", sendRegister: false, uris: [ { host: "sip.acme.com", port: 5060, transport: "UDP", priority: 1, weight: 10, enabled: true } ] }); console.log(`Trunk created: ${ref}`); } main().catch(console.error); ``` `transport` is one of `UDP`, `TCP`, `TLS`, `SCTP`, `WS` or `WSS`. Hosts are an IPv4 address or a domain name. **CLI** The command asks for the name, the inbound URI (one label under `pstn.`, such as `acme.pstn.fonoster.com`) and the ACL, then whether you need an outbound URI. If you do, it asks for the outbound credentials, host, port, transport (TCP or UDP) and user: ```bash theme={"system"} fonoster sipnet:trunks:create ``` > [!WARNING] > > Trunks created with the CLI have **Send REGISTER** on. If your carrier doesn't expect > registration, turn it off on the trunk in the dashboard. **4. Add your numbers** Add each of your carrier's numbers to the trunk, in E.164 format, exactly as the carrier sends them. Point each one at an agent, a stream or a SIP agent. See [Numbers and routing](https://docs.fonoster.com/telephony/numbers.md). ## Configure your carrier In your carrier's portal, set up: * **Inbound (their origination)**: send calls for your numbers to `sip:`, such as `sip:acme.pstn.fonoster.com`, at the SIP address from the trunk form. * **Authentication**: allowlist the addresses the trunk form lists, or give them the inbound credentials you attached to the trunk. * **Outbound (their termination)**: accept calls from the addresses the trunk form lists, signed in with the outbound credentials if you set them. Use the transport your carrier prefers, and the same one on both sides. ## Check it 1. Call one of the trunk's numbers from any phone. The agent, stream or SIP agent it points at answers. 2. Place an outbound call from the number. See [Make outbound calls](https://docs.fonoster.com/telephony/outbound-calls.md). The trunk page lists the trunk's numbers under **Numbers on this trunk**. If calls don't arrive: * Check that the number in Fonoster matches what the carrier sends, `+` included. * If the trunk has an ACL, check that it lists every address the carrier sends from. * Check that the carrier sends to your inbound URI, not to a different host. ## Delete a trunk Go to **Trunks**, open the trunk and choose **Delete**, or run `fonoster sipnet:trunks:delete `. Calls to and from the carrier stop. For every command and method, see Trunks in the [CLI reference](https://docs.fonoster.com/reference/cli.md#trunks) and the [Node SDK reference](https://docs.fonoster.com/reference/sdk.md#trunks). ## Next steps > **[Numbers and routing](https://docs.fonoster.com/telephony/numbers.md)** > > Add the carrier's numbers and send their calls somewhere. > **[Make outbound calls](https://docs.fonoster.com/telephony/outbound-calls.md)** > > Call out through the trunk. > **[SIP agents](https://docs.fonoster.com/telephony/sip-agents.md)** > > Connect softphones and desk phones. > **[Transfer calls](https://docs.fonoster.com/telephony/transfers.md)** > > Send callers to an operator through the same trunk. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.