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DIDWW SIP integration

Connect DIDWW SIP trunks to Vapi so your assistants can receive calls, place outbound calls, and transfer active calls with SIP REFER.

Before you begin

1. Route incoming calls to Vapi

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

1

Create an inbound SIP trunk

In the DIDWW User Panel, go to Voice → Inbound Trunks and select Create New → SIP Trunk.

2

Configure the required trunk fields

In the General tab, configure every field below:

FieldValue
NameA descriptive name, such as Vapi
Endpoint typeStatic Endpoint
Hostsip.vapi.ai for US organizations or sip.eu.vapi.ai for EU organizations
TransportUDP, TCP, or TLS
Port5060 for UDP/TCP or 5061 for TLS
Network ProtocolMatch the IP version allowed on the DIDWW outbound trunk; use Prefer IPv4 over IPv6 or IPv4 only when allowlisting IPv4 addresses
DIDWW inbound SIP trunk General tab with host, endpoint type, transport, and port fields configured for Vapi
Required DIDWW inbound SIP trunk settings for Vapi.
3

Enable call transfer signaling

In the Signalling tab, set Max transfers to 1 or higher. This permits the in-dialog SIP REFER requests used for call transfers.

DIDWW inbound trunk Signalling tab with Max transfers set to 1
Allow at least one SIP transfer on the inbound trunk.
4

Save the inbound trunk

Click Create. For additional DIDWW options, see the inbound SIP trunk guide.

2. Enable outbound calling through DIDWW

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

1

Create an outbound voice trunk

In the DIDWW User Panel, go to Voice → Outbound Trunks and click Create New.

2

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:

RegionVapi signaling IPs
US44.229.228.186/32, 44.238.177.138/32
EU63.182.83.170/32

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

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
DIDWW outbound trunk Allowed SIP IP addresses list containing the Vapi and DIDWW signaling addresses
Allow Vapi and DIDWW signaling addresses on the outbound trunk.

Do not use 0.0.0.0/0 in production. Restrict the trunk to the current Vapi signaling IPs and DIDWW SIP servers.

3

Save the outbound trunk

Click Create to save it.

4

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.

DIDWW outbound trunk credentials dialog showing the username and password fields
Open and copy the DIDWW outbound trunk credentials.
5

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.

DIDWW inbound trunk Authorization tab with Enable Authorization turned on and the Auth User and Auth Password fields filled
Reuse the outbound credentials for authenticated SIP REFER transfers.

For more detail, see Add outbound credentials to the inbound trunk.

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

In the Vapi dashboard, 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, 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.
Vapi SIP trunk configuration with the DIDWW outbound endpoint, transport, port, and outbound calls enabled
Configure the DIDWW gateway for outbound calls.
  1. Under Authentication, enter the DIDWW outbound username and password. Leave SIP registration off and save the trunk.
Vapi SIP trunk Authentication section with the DIDWW outbound username and password entered
Add the DIDWW outbound trunk credentials.

Step 2: Create the inbound trunk

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.
Vapi SIP trunk with one inbound gateway per DIDWW signaling IP address
Create one inbound gateway for each DIDWW signaling IP.
  1. Under Authentication, enter the DIDWW outbound username and password, then save the trunk.
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
Vapi inbound SIP trunk Authentication section with the DIDWW credentials entered
Add the DIDWW credentials to the Vapi inbound trunk.

Step 3: Create a call transfer tool

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.
Vapi Transfer Call tool with a SIP destination whose URI points to a DIDWW outbound endpoint
Configure the DIDWW SIP transfer destination.

Step 4: Add the transfer tool to your assistant

Open the assistant, go to Tools → Add tool, and select the transfer tool. Click Publish, then confirm the publication.

Vapi assistant Tools section with the DIDWW transfer tool added
Add the transfer tool to the Vapi assistant.

Next step

Import a number from DIDWW: Purchase or select a DIDWW number, assign the inbound trunk, and import the number into Vapi.