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docs: add DIDWW SIP trunking and phone number integration guides #1115

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docs: add DIDWW SIP trunking and phone number integration guides
tadasj-didww Jul 23, 2026
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docs: edit pass on DIDWW guides for style-guide conformance
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309 changes: 309 additions & 0 deletions fern/advanced/sip/sip-didww.mdx
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---
title: DIDWW SIP integration
subtitle: Connect DIDWW SIP trunks to Vapi so your assistants can receive calls, place outbound calls, and transfer active calls with SIP REFER.
description: Set up DIDWW SIP trunking with Vapi. Create inbound and outbound trunks, allowlist signaling IPs, and configure authenticated SIP REFER call transfers.
slug: advanced/sip/didww
---

## Before you begin

- An active DIDWW account is required. [Sign in](https://my.didww.com/users/sign_in) or [create an account](https://my.didww.com/users/sign_up#/users/sign_up).
- Access to [DIDWW Outbound Trunks](https://doc.didww.com/voice/outbound-trunks/get-access.html) is required.
- A Vapi account and assistant is required.

## 1. Route incoming calls to Vapi

Create a DIDWW inbound SIP trunk that sends calls from your DIDWW numbers to Vapi.

<Steps>
<Step title="Create an inbound SIP trunk">
In the [DIDWW User Panel](https://my.didww.com/#/trunks), go to **Voice → Inbound Trunks** and select **Create New → SIP Trunk**.
</Step>

<Step title="Configure the required trunk fields">
In the **General** tab, configure every field below:

| Field | Value |
| --- | --- |
| **Name** | A descriptive name, such as `Vapi` |
| **Endpoint type** | **Static Endpoint** |
| **Host** | `sip.vapi.ai` for US organizations or `sip.eu.vapi.ai` for EU organizations |
| **Transport** | **UDP**, **TCP**, or **TLS** |
| **Port** | `5060` for UDP/TCP or `5061` for TLS |
| **Network Protocol** | Match the IP version allowed on the DIDWW outbound trunk; use **Prefer IPv4 over IPv6** or **IPv4 only** when allowlisting IPv4 addresses |

<Frame caption="Required DIDWW inbound SIP trunk settings for Vapi.">
<img src="../../static/images/sip/sip-didww-inbound-general.png" alt="DIDWW inbound SIP trunk General tab with host, endpoint type, transport, and port fields configured for Vapi" />
</Frame>
</Step>

<Step title="Enable call transfer signaling">
{/* "Signalling" (double-l) intentionally matches DIDWW's on-screen tab label shown in the screenshot; do not change it. Use single-l "signaling" for our own prose everywhere else. */}
In the **Signalling** tab, set **Max transfers** to `1` or higher. This permits the in-dialog SIP REFER requests used for call transfers.

<Frame caption="Allow at least one SIP transfer on the inbound trunk.">
<img src="../../static/images/sip/sip-didww-inbound-transfer-signaling.png" alt="DIDWW inbound trunk Signalling tab with Max transfers set to 1" />
</Frame>
</Step>

<Step title="Save the inbound trunk">
Click **Create**. For additional DIDWW options, see the [inbound SIP trunk guide](https://doc.didww.com/voice/inbound-trunks/creating-a-new-sip-trunk.html).
</Step>
</Steps>

## 2. Enable outbound calling through DIDWW

Create a DIDWW outbound trunk for Vapi calls and for authenticated SIP REFER transfers.

<Steps>
<Step title="Create an outbound voice trunk">
In the DIDWW User Panel, go to **Voice → Outbound Trunks** and click **Create New**.
</Step>

<Step title="Configure authentication and allowed IPs">
Set a **Friendly Name**, such as `Vapi`, and keep **Credentials & IP-based** authentication selected.

Under **Allowed SIP IP addresses**, add the signaling addresses for your Vapi region:

| Region | Vapi signaling IPs |
| --- | --- |
| US | `44.229.228.186/32`, `44.238.177.138/32` |
| EU | `63.182.83.170/32` |

To support call transfers, also add all DIDWW inbound signaling addresses:

```text
46.19.209.14
46.19.210.14
46.19.212.14
46.19.213.14
46.19.214.14
46.19.215.14
185.238.173.14
```

<Frame caption="Allow Vapi and DIDWW signaling addresses on the outbound trunk.">
<img src="../../static/images/sip/sip-didww-outbound-allowlist.png" alt="DIDWW outbound trunk Allowed SIP IP addresses list containing the Vapi and DIDWW signaling addresses" />
</Frame>

{/* The #sip-signalling anchor is intentionally double-l to match the current sip-networking heading; switch to #sip-signaling when that page is standardized to single-l (tracked as a separate issue). */}
<Warning>
Do not use `0.0.0.0/0` in production. Restrict the trunk to the current [Vapi signaling IPs](/advanced/sip/sip-networking#sip-signalling) and [DIDWW SIP servers](https://doc.didww.com/voice/inbound-trunks/technical-data/sip.html#service-did-sip).
</Warning>
</Step>

<Step title="Save the outbound trunk">
Click **Create** to save it.
</Step>

<Step title="Copy the outbound credentials">
On **Voice → Outbound Trunks**, click the key icon in the trunk's **Credentials** column. Copy the **Username** and **Password**; you will use both in DIDWW and Vapi.

<Frame caption="Open and copy the DIDWW outbound trunk credentials.">
<img src="../../static/images/sip/sip-didww-outbound-credentials.png" alt="DIDWW outbound trunk credentials dialog showing the username and password fields" />
</Frame>
</Step>

<Step title="Authorize transfers on the inbound trunk">
Edit the Vapi inbound trunk and open **Authorization**. Turn on **Enable Authorization**, paste the outbound trunk **Username** and **Password** into **Auth User** and **Auth Password**, then click **Submit**.

<Frame caption="Reuse the outbound credentials for authenticated SIP REFER transfers.">
<img src="../../static/images/sip/sip-didww-inbound-authorization.png" alt="DIDWW inbound trunk Authorization tab with Enable Authorization turned on and the Auth User and Auth Password fields filled" />
</Frame>

For more detail, see [Add outbound credentials to the inbound trunk](https://doc.didww.com/integrations/vapi/index.html#step-5-add-outbound-credentials-to-the-inbound-trunk).
</Step>
</Steps>

## 3. Connect the SIP trunks in Vapi

Use the same transport and port on both sides. In API examples, use `https://api.vapi.ai` for US organizations or replace it with `https://api.eu.vapi.ai` for EU organizations.

### Step 1: Create the outbound trunk

<Tabs>
<Tab title="Dashboard">
In the [Vapi dashboard](https://dashboard.vapi.ai), select your organization name in the top left, then click **Settings**. Under organization settings, go to **Integrations → SIP Trunk** and click **Configure New SIP Trunk**.

1. Set **Name** to `DIDWW Outbound Trunk`.
2. Set **IP Address / Domain** to a [DIDWW outbound endpoint](https://doc.didww.com/voice/outbound-trunks/technical-data/sip-details.html#voice-out-signaling-endpoints), such as `fra.eu.out.didww.com`.
3. Select the transport and port: `5060` for UDP/TCP or `5061` for TLS.
4. Turn off **Allow inbound calls** and leave **Allow outbound calls** on.

<Frame caption="Configure the DIDWW gateway for outbound calls.">
<img src="../../static/images/sip/sip-didww-outbound-gateway.png" alt="Vapi SIP trunk configuration with the DIDWW outbound endpoint, transport, port, and outbound calls enabled" />
</Frame>

5. Under **Authentication**, enter the DIDWW outbound username and password. Leave SIP registration off and save the trunk.

<Frame caption="Add the DIDWW outbound trunk credentials.">
<img src="../../static/images/sip/sip-didww-authentication.png" alt="Vapi SIP trunk Authentication section with the DIDWW outbound username and password entered" />
</Frame>
</Tab>

<Tab title="cURL">
```bash
curl -X POST https://api.vapi.ai/credential \
-H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
-H "Content-Type: application/json" \
-d '{
"provider": "byo-sip-trunk",
"name": "DIDWW Outbound Trunk",
"gateways": [
{
"ip": "YOUR_DIDWW_OUTBOUND_ENDPOINT",
"port": 5060,
"inboundEnabled": false,
"outboundEnabled": true,
"outboundProtocol": "udp"
}
],
"outboundAuthenticationPlan": {
"authUsername": "YOUR_DIDWW_TRUNK_USERNAME",
"authPassword": "YOUR_DIDWW_TRUNK_PASSWORD"
}
}'
```

Replace the endpoint with the DIDWW signaling endpoint selected for your deployment.
</Tab>
</Tabs>

### Step 2: Create the inbound trunk

<Tabs>
<Tab title="Dashboard">
Create another Vapi SIP trunk named `DIDWW Inbound Trunk`.

1. Add one gateway for each DIDWW IP below, using netmask `32` and the same port as the DIDWW inbound trunk.
2. For every gateway, turn on **Allow inbound calls** and turn off **Allow outbound calls**.

<Frame caption="Create one inbound gateway for each DIDWW signaling IP.">
<img src="../../static/images/sip/sip-didww-vapi-inbound-gateways.png" alt="Vapi SIP trunk with one inbound gateway per DIDWW signaling IP address" />
</Frame>

3. Under **Authentication**, enter the DIDWW outbound username and password, then save the trunk.

```text
46.19.209.14
46.19.210.14
46.19.212.14
46.19.213.14
46.19.214.14
46.19.215.14
185.238.173.14
```

<Frame caption="Add the DIDWW credentials to the Vapi inbound trunk.">
<img src="../../static/images/sip/sip-didww-vapi-inbound-authentication.png" alt="Vapi inbound SIP trunk Authentication section with the DIDWW credentials entered" />
</Frame>
</Tab>

<Tab title="cURL">
```bash
curl -X POST https://api.vapi.ai/credential \
-H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
-H "Content-Type: application/json" \
-d '{
"provider": "byo-sip-trunk",
"name": "DIDWW Inbound Trunk",
"gateways": [
{ "ip": "46.19.209.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false },
{ "ip": "46.19.210.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false },
{ "ip": "46.19.212.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false },
{ "ip": "46.19.213.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false },
{ "ip": "46.19.214.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false },
{ "ip": "46.19.215.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false },
{ "ip": "185.238.173.14", "port": 5060, "netmask": 32, "inboundEnabled": true, "outboundEnabled": false }
],
"outboundAuthenticationPlan": {
"authUsername": "YOUR_DIDWW_TRUNK_USERNAME",
"authPassword": "YOUR_DIDWW_TRUNK_PASSWORD"
}
}'
```

Save the returned credential `id`; it is required when you [import the DIDWW number](/phone-numbers/didww).
</Tab>
</Tabs>

### Step 3: Create a call transfer tool

<Tabs>
<Tab title="Dashboard">
In Vapi, go to **Tools → Create Tool → Transfer Call**.

1. Enter a tool name and describe when the assistant should transfer the caller.
2. Add a **SIP** destination.
3. Set **SIP URI** to `sip:+E164_NUMBER@OUTBOUND_ENDPOINT`, for example `sip:+447700900123@fra.eu.out.didww.com`.
4. Add the customer message and destination description, keep **Blind Transfer**, and save.

<Frame caption="Configure the DIDWW SIP transfer destination.">
<img src="../../static/images/sip/sip-didww-transfer-destination.png" alt="Vapi Transfer Call tool with a SIP destination whose URI points to a DIDWW outbound endpoint" />
</Frame>
</Tab>

<Tab title="cURL">
```bash
curl -X POST https://api.vapi.ai/tool \
-H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
-H "Content-Type: application/json" \
-d '{
"type": "transferCall",
"destinations": [
{
"type": "sip",
"sipUri": "sip:+447700900123@YOUR_DIDWW_OUTBOUND_ENDPOINT",
"message": "Please wait while I transfer your call.",
"description": "Use when the caller asks to speak with a live person.",
"transferPlan": {
"mode": "blind-transfer",
"sipVerb": "refer"
}
}
]
}'
```

Save the returned tool `id` for the next step.
</Tab>
</Tabs>

### Step 4: Add the transfer tool to your assistant

<Tabs>
<Tab title="Dashboard">
Open the assistant, go to **Tools → Add tool**, and select the transfer tool. Click **Publish**, then confirm the publication.

<Frame caption="Add the transfer tool to the Vapi assistant.">
<img src="../../static/images/sip/sip-didww-assistant-tool.png" alt="Vapi assistant Tools section with the DIDWW transfer tool added" />
</Frame>
</Tab>

<Tab title="cURL">
Retrieve the assistant, add the transfer tool ID to `model.toolIds`, and PATCH the complete model back. The example uses `jq` to preserve the existing model configuration and tool IDs.

```bash
VAPI_API_BASE="https://api.vapi.ai"
ASSISTANT_ID="YOUR_ASSISTANT_ID"
TRANSFER_TOOL_ID="YOUR_TRANSFER_TOOL_ID"

CURRENT_MODEL=$(curl -s "$VAPI_API_BASE/assistant/$ASSISTANT_ID" \
-H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" | jq '.model')

UPDATED_MODEL=$(printf '%s' "$CURRENT_MODEL" | jq \
--arg toolId "$TRANSFER_TOOL_ID" \
'.toolIds = (((.toolIds // []) + [$toolId]) | unique)')

jq -n --argjson model "$UPDATED_MODEL" '{model: $model}' | \
curl -X PATCH "$VAPI_API_BASE/assistant/$ASSISTANT_ID" \
-H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
-H "Content-Type: application/json" \
--data-binary @-
```
</Tab>
</Tabs>

## Next step

**[Import a number from DIDWW](/phone-numbers/didww):** Purchase or select a DIDWW number, assign the inbound trunk, and import the number into Vapi.
4 changes: 4 additions & 0 deletions fern/docs.yml
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Expand Up @@ -317,6 +317,8 @@ navigation:
path: phone-numbers/import-twilio.mdx
- page: Telnyx
path: phone-numbers/telnyx.mdx
- page: DIDWW
path: phone-numbers/didww.mdx
- section: SIP integration
icon: fa-light fa-sitemap
contents:
Expand All @@ -332,6 +334,8 @@ navigation:
path: advanced/sip/sip-twilio.mdx
- page: Telnyx
path: advanced/sip/sip-telnyx.mdx
- page: DIDWW
path: advanced/sip/sip-didww.mdx
- page: Zadarma
path: advanced/sip/sip-zadarma.mdx
- page: Plivo
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