How to: SIP with 3CX

This document explains how to make calls:
• From 3CX to the Synthflow AI Assistant
 • From the Synthflow AI Assistant to the PSTN

You need to configure an external number and a SIP trunk with your telephony provider before integrating with Synthflow.ai.

?Synthflow.ai connects to VoIP systems via SIP. You must set up a new SIP trunk in 3CX to use it.

However, 3CX restricts connections to custom SIP trunks. You can only connect to approved SIP providers listed in the “SIP Trunk” section of the 3CX settings page. Since Synthflow is not a telephony provider, it is not included in this list. As a result, configuring the connection via a SIP trunk requires additional steps.

Step 1. Creating SIP trunk between 3CX and Synthflow. Use allowed listed providers as a pattern for Synthflow SIP trunk.

To create a SIP trunk with Synthflow.ai you need to be able to create any trunk with listed providers on “Add Trunk” section on 3CX Admin Console. We suggest to use Twilio(Auto). You will create SIP-trunk with Twilio as a template for Synthflow setup. For this step you need to have an account on Twilio.

Choose Twilio as a Provider:

Connect Twilio Account:

Go to “Edit trunk” and change Twilio’s URI to Synthflow’s URI:

Set sipin.synthflow.ai and 32681 as Server and Port

Save changes.

?Now, you can make outbound calls from 3CX to Synthflow.ai directly through this new trunk.

Step 2: Create an Outbound Rule for Calling

To make a call from 3CX to Synthflow through the new SIP trunk, you need to attach an external +E.164 PSTN number to Synthflow’s assistant to gain access to the voice AI.
 You can purchase a new number from your SIP provider and assign it to the Outbound Rule on 3CX. Later, you will attach this number on the Synthflow customer page.

Create a New Outbound Rule

In this example, we are creating a rule to route calls to the 5555 extension as an external number through our new Twilio trunk.
 You need to prepend your rule with a real +E.164 number, which you will later attach to the Synthflow assistant.

After this step, outbound calls from your IP phone on 3CX to the 5555 extension will be routed to sipin.synthflow.ai:35681 and will dial the real number +8588341688.

However, to properly route this call to Synthflow, you need to attach this real number to the AI assistant on the Synthflow customer page (we will do it later).

To perform outbound calls from Synthflow to 3CX-PBX (as opposed to the previous steps where we configured calls from 3CX to Synthflow), you need to know the IP address of the 3CX-PBX and obtain SIP credentials.
Go to your provider’s website to retrieve the necessary credentials and IP address.

We recommend using Twilio as the external provider, especially since we previously created our SIP trunk with Twilio. Using the same provider ensures a more seamless integration in this example.

Step 3: Find Twilio's IP access control lists:

Go to the 3CX access list (which was automatically created by the 3CX API in the first step of this document) and note your 3CX PBX IP address.

The next step is to set the new credentials in Twilio to use them on Synthflow for making outbound calls:

Find the Elastic Sip Trunk section:

Go to the Elastic SIP Trunk and find the Termination section. Scroll down to Authentication and add a new Credential List with a new SIP username and SIP password.

?

Look at the Termination URI. This is the SIP address of your termination point for outbound calls from Synthflow.

You can choose your 3CX PBX IP address as the termination point to receive calls from Synthflow to the PSTN. However, this approach is more complicated, and it is generally better to use your SIP provider as the terminator.
 If you have a custom 3CX setup and it is necessary to route outbound calls through your 3CX PBX, you can contact our support team to find a solution.

Please, save credentials:

Now you are ready to add your number to Synthflow.

Find the “Numbers”section on your Synthflow.ai customer page and add a new Custom Phone Number.

Please don’t forget to provide the IP address of your 3CX PBX to our support team.

After that, you can create an inband and outbound AI Assistant, set them to the V2 version, and attach the Phone Number to them.