# Configure Call Transfers

Transfer inbound calls to a new destination (PSTN number or SIP URI) using either a **30x Redirect** SIP response or an
in-dialog **SIP REFER** request. This enables call routing decisions to be made dynamically during call handling rather
than being fixed in advance.

Transfers are typically triggered by a SIP system such as a PBX, IVR, AI agent, or custom application when a call needs
to be forwarded, escalated, or handed off to another destination. In this case, the system sends a **30x** response or a
**REFER** request, and a new outbound call is initiated to the target destination using the configured [Outbound
Trunk](../../outbound-trunks/how-to-guides/create-outbound-trunk.html#outbound-trunk-create-trunk).

To use call transfers, both **Inbound** and **Outbound** SIP trunks must be configured, and the platform must be capable
of generating valid SIP signaling for the selected transfer method.

Note

For protocol-level details, examples, and diagrams, see [Inbound Call Redirection
Methods](redirecting-calls.html#user-panel-call-redirection-outbound).

**1. Create Outbound SIP Trunk**

Create the outbound trunk DIDWW will use to place the redirected or transferred call.

[1. Create Outbound SIP Trunk](#call-transfers-outbound-trunk)

**2. Create Inbound SIP Trunk**

Create the inbound trunk, enable the required transfer method, and link it to the outbound trunk using the same
credentials.

[2. Create Inbound SIP Trunk](#call-transfers-inbound-trunk)

**3. Configure Your SIP Platform**

Configure your platform to transfer calls using SIP 30x Redirect or SIP REFER.

[3. Configure Your SIP Platform](#call-transfers-platform)

---

## 1. Create Outbound SIP Trunk

To enable call transfers, the outbound SIP trunk must be configured to accept signaling from **DIDWW Inbound SIP IPs**.
This allows a new outbound call to be initiated to the transfer destination when a **30x Redirect** or **SIP REFER**
request is received.

The outbound trunk must use **Credentials & IP-Based** authentication, and the same credentials are reused by the
inbound trunk to authorize transfer-related signaling.

### Before You Begin

Access to DIDWW outbound trunks is required. See [Get Access to DIDWW Outbound
Termination](../../outbound-trunks/get-access.html#user-panel-voice-out-get-access).

### Step 1: Open Outbound Trunks and Start Creation

1. In the [DIDWW User Panel](https://my.didww.com/#/trunks), go to **Voice > Outbound Trunks**.
2. Click **Create New**.

[![Opening Outbound Trunks and starting outbound trunk creation](../../../_images/outbound13.png)](../../../_images/outbound13.png)


**Fig. 1.** Opening Outbound Trunks and starting outbound trunk creation

### Step 2: Configure and Create the Outbound SIP Trunk

1. Enter a descriptive **Name** (for example, `Call Transfers`).
2. Keep **Credentials & IP-Based** authentication selected.
3. In **Allowed SIP IP addresses**, allow:

   - Your SIP platform's **outbound SIP signaling IPs**, if your system uses fixed IP addresses
   - The [DIDWW inbound SIP IPs](sip.html#service-did-sip), required for call redirection and transfers

   Copy the full DIDWW inbound SIP IP list below, based on your IP version:

IPv4

```
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
```


IPv6

```
2a01:ad00:1:14::14 2a01:ad00:2:14::14 2a01:ad00:4:14::14 2a01:ad00:5:14::14 2a01:ad00:6:14::14 2a01:ad00:7:14::14 2a01:ad00:8:14::14
```

4. Click **Create** to save the trunk.

Warning

- You can allow all traffic by adding `0.0.0.0/0`, which removes all IP restrictions. Although SIP Digest Authentication will still verify requests using valid credentials, this configuration is **not recommended**. Always restrict access to known signaling IPs whenever possible.
- For advanced outbound SIP trunk configuration, see [Outbound SIP Trunk Guide](../../outbound-trunks/how-to-guides/index.html#outbound-trunk-create).

[![Configuring and creating the outbound SIP trunk for call transfers](../../../_images/outbound22.png)](../../../_images/outbound22.png)


**Fig. 2.** Configuring and creating the outbound SIP trunk for call transfers

### Step 3: View Outbound Trunk Credentials

When the outbound trunk is created, you can view its credentials by selecting the key icon in the Credentials column on
the Outbound Trunks page.

1. Go to **Voice > Outbound Trunks**.
2. Locate your outbound trunk and click the **key icon** in the **Credentials** column.
3. The trunk credentials will appear, showing the **Username** and **Password**
   (click the **eye icon** to reveal the password).

Note

- These credentials will be reused in the [Authorization](#call-transfers-inbound-auth) tab of the inbound SIP trunk to authorize call redirection and transfers via the outbound trunk.
- The same credentials must also be used by your SIP platform for outbound SIP authentication.

[![Viewing outbound trunk credentials for reuse on the inbound trunk](../../../_images/outbound33.png)](../../../_images/outbound33.png)


**Fig. 3.** Viewing outbound trunk credentials for reuse on the inbound trunk



---

## 2. Create Inbound SIP Trunk

To process call transfer requests, the inbound SIP trunk must be configured to authorize **30x Redirect** responses or
**SIP REFER** requests generated during call handling. This ensures that transfer signaling is accepted and validated
before a new outbound call is initiated.

The inbound trunk must use the same **IP version** (IPv4 or IPv6) as the outbound trunk, have **Authorization** enabled,
and reuse the **same credentials** configured on the outbound SIP trunk. The required transfer method (**30x Redirect**
or **SIP REFER**) must also be enabled.

### Before You Begin

- At least one DID number is required to receive inbound calls.
- You need the outbound trunk **Username** and **Password** from [Step 3](#call-transfers-outbound-copy-credentials).

### Step 1: Open Inbound Trunks and Start Creation

1. In the [DIDWW User Panel](https://my.didww.com/#/trunks), go to **Voice > Inbound Trunks**.
2. Click **Create New > SIP Trunk**.

[![Opening Inbound Trunks and starting inbound SIP trunk creation](../../../_images/inbound13.png)](../../../_images/inbound13.png)


**Fig. 4.** Opening Inbound Trunks and starting inbound SIP trunk creation

### Step 2: Configure General Settings

1. In the **General** tab, enter a descriptive **Name** (for example, `Call Transfers`).
2. Select **Static Endpoint**.
3. Configure your platform destination (**Host**), **Transport**, and **Port** as required by your platform.
4. In **Network Protocol**, select the IP version that matches the outbound trunk configuration.

Important

The **Network Protocol** on the inbound trunk must **match** the IP addresses allowed on the outbound trunk.

- If the outbound trunk allows **IPv4** addresses, set the inbound trunk to **IPv4 only**
- If the outbound trunk allows **IPv6** addresses, set the inbound trunk to **IPv6 only**

A mismatch between IP versions will prevent call transfers from completing successfully.

[![Configuring inbound trunk general settings and network protocol](../../../_images/inbound22.png)](../../../_images/inbound22.png)


**Fig. 5.** Configuring inbound trunk general settings and network protocol

### Step 3: Enable and Configure Authorization

To authorize redirect/transfer requests, inbound trunk authorization must be enabled using the **same credentials** as
the outbound trunk.

1. Open the **Authorization** tab.
2. Turn on **Enable Authorization**.
3. Paste the **Auth User** and **Auth Password** values copied from the outbound trunk credentials
   (see [View Outbound Trunk Credentials](#call-transfers-outbound-copy-credentials)).

Note

DIDWW uses these credentials to authenticate the outbound leg initiated after a redirect or transfer request.

[![Enabling authorization and pasting outbound trunk credentials on the inbound trunk](../../../_images/inbound32.png)](../../../_images/inbound32.png)


**Fig. 6.** Enabling authorization and pasting outbound trunk credentials on the inbound trunk

### Step 4: Enable Call Transfer Method

Configure signaling limits based on the transfer method you plan to use.

SIP REFER

Enable support for in-dialog SIP REFER transfers.

1. Open the **Signalling** tab.
2. Set **Max Transfers** to **1** or higher.

Important

If **Max Transfers** is set to `0`, SIP REFER requests will be rejected.

[![Enabling Max Transfers for SIP REFER on the inbound SIP trunk](../../../_images/inbound4_refer.png)](../../../_images/inbound4_refer.png)


**Fig. 7.** Enabling Max Transfers for SIP REFER on the inbound SIP trunk


30x Redirect

Enable support for SIP 3xx redirect responses.

1. Open the **Signalling** tab.
2. Set **Max 30x Redirects** to **1** or higher.

Important

If **Max 30x Redirects** is set to `0`, SIP redirect responses will be rejected.

[![Enabling Max 30x Redirects on the inbound SIP trunk](../../../_images/inbound4_30x.png)](../../../_images/inbound4_30x.png)


**Fig. 8.** Enabling Max 30x Redirects on the inbound SIP trunk

### Step 5: Create the Trunk

Click **Create** to save the inbound SIP trunk.

[![Creating the inbound SIP trunk for call transfers](../../../_images/inbound51.png)](../../../_images/inbound51.png)


**Fig. 9.** Creating the inbound SIP trunk for call transfers

### Step 6: Assign the Inbound SIP Trunk to Your DID Numbers

Inbound calls can be redirected/transferred only after the DID number is routed to the inbound trunk.

1. In the DIDWW User Panel, go to **Phone Numbers > My Numbers**.
2. Select the DID number(s) you want to assign to the inbound SIP trunk.
3. At the bottom of the page, click **Batch Actions > Update Trunks**.

[![Assigning a SIP trunk to DID numbers](../../../_images/inbound61.png)](../../../_images/inbound61.png)


Fig. 10. Selecting **Update Trunks** from the Batch Actions menu

4. From the dropdown menu, choose the **Call Transfers** trunk you created earlier.
5. Click **Confirm** to apply the changes.

[![Assigning a SIP trunk to DID numbers](../../../_images/inbound71.png)](../../../_images/inbound71.png)


Fig. 11. Assigning the newly created SIP trunk to the selected DID(s)



---

## 3. Configure Your SIP Platform

Configure your SIP platform (PBX, IVR, AI agent, or custom SIP application) to instruct DIDWW to redirect or transfer
inbound calls.

### Before You Begin

- Identify the appropriate DIDWW outbound signaling endpoint to use (e.g., `fra.eu.out.didww.com`). See [Signaling Endpoints](../../outbound-trunks/outbound-sip-information.html#voice-out-signaling-endpoints).
- Ensure your SIP platform supports generating **SIP 30x responses** or **in-dialog SIP REFER requests**.

### Step 1: Build the Destination SIP URI

Your SIP platform must construct the transfer destination as a SIP URI in the following format:

```
sip:NEW_PSTN_NUMBER@<outbound_endpoint>
```

Where:

- `NEW_PSTN_NUMBER` is the destination number in E.164 format
- `<outbound_endpoint>` is a DIDWW outbound signaling endpoint (for example, `fra.eu.out.didww.com`)

Note

This SIP URI must be included in the **Contact** header for SIP 30x redirects,
or in the **Refer-To** header for SIP REFER transfers.

### Step 2: Configure Call Transfers

During inbound call handling, your SIP platform must trigger the transfer by sending the appropriate SIP signaling
request or response to DIDWW.

SIP REFER

Use this method when the call must be **answered first** before performing the call transfer.

1. Answer the inbound call to establish a SIP dialog.
2. Send an in-dialog SIP **REFER** request to DIDWW.
3. Include the destination SIP URI in the **Refer-To** header:

   ```
   Refer-To: <sip:1234567890@fra.eu.out.didww.com>
   ```
4. Wait for DIDWW to respond with `200 OK` or `202 Accepted`.

DIDWW then initiates a new outbound call using your **Outbound SIP Trunk**.

For protocol details and examples, see [REFER Transfer Method](redirecting-calls.html#call-redirection-refer).


30x Redirect

Use this method when the transfer destination can be determined **before answering the call**.

1. Receive the inbound SIP `INVITE` from DIDWW.
2. Do **not** answer the call.
3. Respond with a SIP **3xx** response (for example, `302 Moved Temporarily`).
4. Include the destination SIP URI in the **Contact** header:

   ```
   Contact: <sip:1234567890@fra.eu.out.didww.com>
   ```
5. DIDWW validates the redirect and initiates a new outbound call using your **Outbound SIP Trunk**.

For protocol details and examples, see [30x Redirect Method](redirecting-calls.html#call-redirection-302).

### Step 3: Make a Test Call and Verify Call Transfer

Verify that call transfers work as expected based on the method used.

SIP REFER

1. Place a call to your DIDWW number routed to your SIP platform.
2. Ensure the call is answered to establish a SIP dialog.
3. Trigger a SIP **REFER** transfer from your platform.
4. Confirm the original call leg ends and a new outbound call is established.


30x Redirect

1. Place a call to your DIDWW number routed to your SIP platform.
2. Ensure the call is **not answered** by your platform.
3. Confirm a SIP **3xx** response is sent.
4. Verify the call is redirected and two-way audio is established with the destination.

Note

Review the [Inbound](../../../logs-analytics/call-logs/inbound-logs.html#inbound-cdr-logs) and
[Outbound](../../../logs-analytics/call-logs/outbound-logs.html#outbound-cdr-logs) **CDR Logs** to verify call flow
details and confirm that the outbound leg was initiated successfully.
If you encounter issues during testing, contact **DIDWW Support** at [support@didww.com](mailto:support%40didww.com).

On this page