# Configure call transfers Configure the inbound and outbound SIP trunks and your SIP platform so that DIDWW can redirect or transfer an inbound call to an external phone number. Your platform triggers the transfer with a SIP `301` or `302` response before answering the call, or with an in-dialog SIP `REFER` request after answering it. DIDWW then places a new call to the destination through your outbound trunk. For an explanation of both methods, including SIP messages, call flows, and use cases, see [Inbound call redirection](../call-handling-and-delivery/inbound-call-redirection.html). ## 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). - At least one DID number is required to receive inbound calls. - Your SIP platform, such as a PBX, IVR, AI agent, or custom SIP application, must support SIP `301` or `302` responses, in-dialog SIP `REFER` requests, or both. **1. Create the outbound SIP trunk** Create the outbound trunk that DIDWW uses to place the redirected or transferred call. [1. Create the outbound SIP trunk](#call-transfers-outbound-trunk) **2. Create the inbound SIP trunk** Enable the required method and authorize it with the outbound trunk credentials. [2. Create the inbound SIP trunk](#call-transfers-inbound-trunk) **3. Configure your SIP platform** Send a SIP 301 or 302 response or a SIP REFER request to DIDWW. [3. Configure your SIP platform](#call-transfers-platform) ## 1. Create the outbound SIP trunk The outbound trunk must use **Credentials & IP-Based** authentication and accept signaling from the DIDWW inbound SIP addresses. The inbound trunk stores the outbound trunk credentials, which DIDWW uses to authenticate the new outbound call. ### Step 1: Start trunk 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.** Starting outbound trunk creation ### Step 2: Configure and create the outbound trunk 1. Enter a descriptive **Name**, for example `Call Transfers`. 2. Keep **Credentials & IP-Based** authentication selected. 3. In **Allowed SIP IP addresses**, add: - The outbound SIP signaling IP addresses of your SIP platform, if it uses fixed IP addresses. - The [DIDWW inbound SIP signaling addresses](../sip-connectivity-reference.html#inbound-sip-connectivity-signaling). They are required for redirects and transfers. Copy the DIDWW inbound SIP address list for 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**. Warning Adding `0.0.0.0/0` removes all IP restrictions. SIP Digest authentication still verifies each request, but this configuration is not recommended. Restrict access to known signaling addresses. For all outbound trunk fields, see [Create an outbound trunk](../../../outbound-trunks/how-to-guides/create-outbound-trunk.html). [![Configuring and creating the outbound SIP trunk for call transfers](../../../../_images/outbound22.png)](../../../../_images/outbound22.png) **Fig. 2.** Configuring the outbound SIP trunk ### Step 3: Copy the outbound trunk credentials 1. Go to **Voice > Outbound Trunks**. 2. Locate the trunk and click the key icon in the **Credentials** column. 3. Copy the **Username** and **Password**. Click the eye icon to reveal the password. You will enter these credentials in the [Authorization](#call-transfers-inbound-auth) tab of the inbound SIP trunk. Your SIP platform also uses them for outbound SIP authentication. [![Viewing outbound trunk credentials for reuse on the inbound trunk](../../../../_images/outbound33.png)](../../../../_images/outbound33.png) **Fig. 3.** Viewing the outbound trunk credentials ## 2. Create the inbound SIP trunk The inbound trunk must enable the required method and have **Authorization** enabled with the outbound trunk credentials. For **Static Endpoint** routing, **Network Protocol** must match the IP version of the DIDWW inbound signaling addresses configured under **Allowed SIP IP addresses** on the outbound trunk. To use an existing inbound SIP trunk, edit it and apply the same settings. ### Step 1: Start trunk 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.** 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 the SIP routing method used by your platform. For **Static Endpoint**, configure **Host**, **Transport**, and **Port** as required by your platform. 3. If the trunk uses **Static Endpoint**, set **Network Protocol** to match the IP version of the DIDWW inbound signaling addresses you allowed on the outbound trunk: - If the outbound trunk allows IPv4 addresses, select **IPv4 only**. - If the outbound trunk allows IPv6 addresses, select **IPv6 only**. A mismatch between IP versions prevents the transfer from completing. For all routing fields, see [Create a SIP trunk](create-sip-trunk.html). [![Configuring inbound trunk general settings and network protocol](../../../../_images/inbound22.png)](../../../../_images/inbound22.png) **Fig. 5.** Configuring general settings and Network Protocol ### Step 3: Enable authorization 1. Open the **Authorization** tab. 2. Turn on **Enable Authorization**. 3. Paste the outbound trunk **Username** into **Auth User** and its **Password** into **Auth Password**. DIDWW uses these credentials to authenticate the new outbound call 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 with the outbound trunk credentials ### Step 4: Enable the transfer method Open the **Signalling** tab and enable the method your platform uses. Configure both fields when the platform uses both methods. The default value of `0` disables the corresponding method. Field definitions and supported ranges are listed under [Authorization](../sip-trunk-settings-reference.html#inbound-sip-trunks-settings-authorization) and [Signalling](../sip-trunk-settings-reference.html#inbound-sip-trunks-settings-signalling) in the SIP trunk settings reference. SIP REFER Set **Max Transfers** to a value from `1` to `8`. [![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 SIP 30x Redirect Set **Max 30x Redirects** to a value from `1` to `8`. [![Enabling Max 30x Redirects on the inbound SIP trunk](../../../../_images/inbound4_30x.png)](../../../../_images/inbound4_30x.png) **Fig. 8.** Enabling Max 30x Redirects ### Step 5: Create the trunk Click **Create** to save the inbound SIP trunk. For an existing trunk, click **Submit**. [![Creating the inbound SIP trunk for call transfers](../../../../_images/inbound51.png)](../../../../_images/inbound51.png) **Fig. 9.** Creating the inbound SIP trunk ### Step 6: Assign the trunk to DID numbers Calls can be redirected or transferred only after the DID number routes to the inbound trunk. 1. Go to **Phone Numbers > My Numbers**. 2. Select the DID numbers to assign to the inbound SIP trunk. 3. Click **Batch Actions > Update Trunks**. 4. Select the inbound SIP trunk you created. 5. Click **Confirm**. ![Selecting Update Trunks from the Batch Actions menu](../../../../_images/inbound61.png) **Fig. 10.** Selecting **Update Trunks** from **Batch Actions** ![Assigning the inbound SIP trunk to the selected DID numbers](../../../../_images/inbound71.png) **Fig. 11.** Assigning the inbound SIP trunk to the selected DID numbers ## 3. Configure your SIP platform ### Step 1: Build the destination SIP URI Construct the destination as a `sip:` URI that points to a DIDWW [outbound signaling endpoint](../../../outbound-trunks/outbound-sip-information.html#voice-out-signaling-endpoints): ``` sip:NEW_PSTN_NUMBER@ ``` `NEW_PSTN_NUMBER` is the destination phone number in E.164 format without the leading `+`. `` is a DIDWW outbound signaling endpoint. For example: ``` sip:12025550199@fra.eu.out.didww.com ``` Place this URI in the `Contact` header of a SIP 301 or 302 response, or in the `Refer-To` header of a SIP `REFER` request. ### Step 2: Trigger the transfer SIP REFER Use this method when the call must be answered before the destination is selected. 1. Answer the inbound call to establish a SIP dialog. 2. Send an in-dialog SIP `REFER` request to DIDWW. 3. Place the destination SIP URI in the `Refer-To` header: ``` Refer-To: ``` 4. Wait for DIDWW to respond with `200 OK` or `202 Accepted`. 5. Send `BYE` to close the original call leg. DIDWW validates the request against **Max Transfers** and places a new call through the outbound trunk. See [SIP REFER transfer](../call-handling-and-delivery/inbound-call-redirection.html#call-redirection-refer) for a request example and call flow. SIP 30x Redirect Use this method when the destination can be selected before the call is answered. 1. Receive the inbound SIP `INVITE` from DIDWW without answering it. 2. Respond with `301 Moved Permanently` or `302 Moved Temporarily`. 3. Place the destination SIP URI in the `Contact` header: ``` Contact: ``` DIDWW validates the response against **Max 30x Redirects** and places a new call through the outbound trunk. See [SIP 30x Redirect](../call-handling-and-delivery/inbound-call-redirection.html#call-redirection-302) for a response example and call flow. Warning Ensure that the destination does not route back to the original DID number. Otherwise, the configuration can create a call loop. ### Step 3: Test the transfer SIP REFER 1. Call a DID number assigned to the inbound SIP trunk. 2. Answer the call on your platform. 3. Trigger a SIP `REFER` transfer. 4. Confirm that the original call leg ends and the new outbound call is established. SIP 30x Redirect 1. Call a DID number assigned to the inbound SIP trunk. 2. Do not answer the call on your platform. 3. Confirm that the platform sends a SIP 301 or 302 response. 4. Confirm that the call is redirected and two-way audio is established with the destination. Review [Inbound Call Logs](../../../../logs-analytics/call-logs/inbound-logs.html#inbound-cdr-logs) and [Outbound Call Logs](../../../../logs-analytics/call-logs/outbound-logs.html#outbound-cdr-logs) to verify both call legs and their SIP responses. If the transfer does not complete, contact DIDWW Support at [support@didww.com](mailto:support%40didww.com). ## Expected result - A valid SIP 301 or 302 response redirects the unanswered inbound call to the URI in the `Contact` header. - A valid in-dialog SIP `REFER` request transfers the answered call to the URI in the `Refer-To` header. - DIDWW authenticates the new call with the outbound trunk credentials stored in the inbound trunk's **Authorization** settings. ## Related resources - [Inbound call redirection](../call-handling-and-delivery/inbound-call-redirection.html) - Understand SIP 30x Redirect and SIP REFER transfers. - [SIP trunk settings reference](../sip-trunk-settings-reference.html) - Review Authorization and Signalling fields, defaults, and limits. - [Outbound SIP information](../../../outbound-trunks/outbound-sip-information.html) - Select signaling endpoints and review outbound SIP requirements. - [SIP connectivity reference](../sip-connectivity-reference.html) - Review DIDWW signaling and media addresses. 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