Skip to main content
With the custom SIP connection, customers with the SIP feature enabled can connect their existing telephony infrastructure to Placetel AI. Incoming calls are forwarded from your own SIP provider to Placetel AI, and your own phone numbers can be assigned to a voice agent. SIP setup in the phone numbers area
This feature is primarily intended for standalone customers who use their own SIP provider or SIP trunk. Placetel customers can also request and have the feature enabled if needed. Managed phone numbers from the Placetel inventory remain in the Phone numbers area.

​
Overview

The SIP setup consists of three parts:
  • Custom SIP trunk: the inbound SIP address to which your SIP provider forwards calls.
  • Custom phone numbers: phone numbers or SIP identifiers that come in via your own trunk and are assigned to a voice agent.
  • Outbound connection: optional SIP credentials for outbound calls and warm transfers via your own provider.
If only the inbound trunk is active, inbound BYOS calls can be processed. If only the outbound trunk is active, outbound calls and warm transfers can run via your own provider. Both directions can be set up independently of each other.

​
SIP address

Every enabled account receives its own SIP address. This address is shown in the SIP area and can be copied directly.
Enter this SIP address at your SIP provider as the destination for incoming calls. With providers like Twilio, this typically corresponds to the Origination URI of the SIP trunk.
Use the SIP address only for the associated account. The address contains an account-specific token and should not be shared between customers or tenants.

​
Activating the inbound SIP trunk

Open Phone numbers → SIP and select the inbound connection in the SIP connections area. Inbound SIP settings Optionally, you can enter fixed source IP addresses of your SIP provider under Allowed Source IPs / CIDRs. If this field is set, Placetel AI only accepts inbound SIP calls from these IP addresses. Examples:
Leave the field empty if your provider does not offer fixed source IP addresses.

​
Adding a custom phone number

A custom phone number describes which called number or SIP identifier is routed via your own trunk to which voice agent. Adding a custom phone number
  1. Open Phone numbers → SIP.
  2. Click Add phone number.
  3. Enter the phone number in international format, for example +491234567890.
  4. Optionally, assign a label.
  5. Select the voice agent that should answer calls on this number.
  6. Save the phone number.
You can also save custom phone numbers without immediately assigning them to a voice agent. Without an assignment, the phone number is not actively routed to an agent.

​
Setting up the outbound connection

For outbound BYOS calls and warm transfers, Placetel AI needs the SIP credentials of your provider. Outbound SIP settings The most important fields are:
  • Termination URL: your provider’s SIP domain, for example example.pstn.sip-provider.com.
  • Username: SIP username for authentication.
  • Password: SIP password for authentication.
The inbound SIP address and the outbound termination URL are different things. The inbound SIP address points to Placetel AI. The termination URL points to your SIP provider.

​
Outbound calls with your own phone number

If you want to start outbound calls via your own SIP provider, first set up the outbound connection and then add the phone number that should be shown to the person being called.
  1. Activate the outbound SIP connection.
  2. Enter the SIP credentials from your provider.
  3. Add the phone number under Custom phone numbers.
  4. Assign this phone number to the voice agent that should handle the outbound calls.
  5. Start the call under Outbound Calls with that exact voice agent.
For outbound BYOS calls, the voice agent uses the custom phone number assigned to it under Custom phone numbers. In this case, you do not need to enter a separate caller number.

​
Understanding the status

  • Inbound active: inbound calls via your own SIP address can be processed.
  • Inbound inactive or not set up: custom phone numbers remain saved, but inbound BYOS calls are not processed via your own SIP address. Existing Placetel phone numbers and standard telephony paths are not affected.
  • Outbound active: outbound calls and warm transfers can run via your own SIP provider.
  • Outbound not set up: outbound BYOS calls are not active. Existing Placetel phone numbers and standard telephony paths are not affected.

​
Example: Twilio Elastic SIP Trunk

Twilio Elastic SIP Trunking is a supported BYOS provider. The following steps show the typical flow in the Twilio Console.
The names of individual menu items in Twilio may differ slightly depending on region or Console version. What matters: Origination URI for inbound calls, Termination SIP URI and Credential List for outbound calls.

​
1. Create a SIP trunk

In the Twilio Console, open Develop → Elastic SIP Trunking → Manage → Trunks and create a new SIP trunk. Choose a unique name, for example voice-agent. Creating a Twilio SIP trunk

​
2. Assign a Twilio phone number to the trunk

In the trunk, open the Numbers area. Via Add a number → Add an Existing Number, you can connect an existing Twilio phone number to the trunk. Adding a Twilio phone number to the trunk Once the phone number is connected to the trunk, Twilio can forward inbound calls on this number to Placetel AI via the Origination URI. Twilio phone number assigned to the trunk

​
3. Set the Origination URI

In the trunk, open the Origination area and enter the Placetel AI SIP address as the Origination URI:
Save the origination setting. After that, Twilio sends inbound calls on the connected phone number to Placetel AI. Setting the Twilio Origination URI

​
4. Set up termination and SIP credentials

For outbound BYOS calls and warm transfers, open the Termination area in Twilio.
  1. Set a Termination SIP URI, for example my-company.pstn.twilio.com.
  2. Create or select a Credential List.
  3. Store a SIP username and a SIP password there.
  4. Then enter these values in Placetel AI under Set up SIP connection → Outbound.
Setting the Twilio Termination SIP URI Creating a Twilio Credential List The mapping is:
  • Twilio Termination SIP URI → Placetel AI Termination URL
  • Twilio Credential List Username → Placetel AI Username
  • Twilio Credential List Password → Placetel AI Password

​
5. Enable SIP REFER for transfers

For transfers via SIP REFER, SIP REFER must be enabled in the Twilio trunk. In the trunk, open the General area and set the feature settings as follows:
  • Call Transfer (SIP REFER): enabled
  • Enable PSTN Transfer: enabled if calls should be transferred to external PSTN numbers
  • Caller ID for Transfer Target: to match your use case, often Set caller ID as Transferee
Save the changes in Twilio. Enabling SIP REFER in Twilio

​
6. Make a test call

Call the Twilio phone number connected to the trunk. The call should arrive in Placetel AI on the assigned voice agent. If the call does not arrive, check first:
  • Is the Twilio phone number connected to the correct trunk?
  • Is the Origination URI exactly the SIP address from Placetel AI?
  • Is the inbound SIP trunk active in Placetel AI?
  • Is the called phone number created under Custom phone numbers and assigned to a voice agent?

​
Example: 3CX

3CX is a supported BYOS setup. The following steps show how to route calls from a 3CX phone system to Placetel AI. Inbound calls travel from your provider through 3CX to Placetel AI, where a voice agent answers.
These steps use an example phone number +499999999999, an internal 3CX prefix 999, and the resulting dial string 999+499999999999. Replace them with your own values. You need administrator access to the 3CX Admin Console, plus the inbound SIP trunk and a custom phone number already set up in Placetel AI (see above).

​
1. Create a SIP trunk

In the 3CX Admin console, open Trunks & Chat, click + Trunk, and choose Generic SIP Trunk (IP Based). Creating a generic SIP trunk in 3CX

​
2. Enter the trunk data

  • Main trunk number: your phone number from Placetel AI, for example +499999999999.
  • Authentication type: None – IP based.
  • Registrar/Server: the Placetel AI SIP address from above, without the sip: prefix:
Do not include the sip: prefix in the Registrar/Server field. Otherwise Placetel AI responds with 400 Bad Request.

​
3. Allow calls back to 3CX

In the trunk configuration:
  • Enable Inbound calls and Outbound calls.
  • Enable PBX delivers audio.
  • Enable Allow carrier-side forwarding (SIP REFER) if you use transfers.
Enabling inbound, outbound and SIP REFER on the 3CX trunk

​
4. Create an outbound rule

Create an outbound rule that sends the internal prefix to the Placetel AI trunk:
  1. Set the prefix to 999.
  2. Set Route 1 to the Placetel AI trunk.
  3. Under Strip digits, remove the first 3 digits.
Creating the outbound rule in 3CX

​
5. Forward the inbound number to Placetel AI

Open the existing 3CX trunk that receives your real phone number.
  1. Set the default route to Forward to external number.
  2. Set the external number to 999+499999999999 — the internal prefix followed by your number.
Forwarding the inbound number via the internal prefix

​
6. Make a test call

Call the phone number that arrives via 3CX. The call should reach Placetel AI on the assigned voice agent. If it does not, check first:
  • Does the outbound rule use prefix 999, strip 3 digits, and Route 1 to the Placetel AI trunk?
  • Does the Registrar/Server field contain the SIP address without the sip: prefix? A sip: prefix causes 400 Bad Request.
  • Is the default route of the existing 3CX trunk set to forward to 999+499999999999? Otherwise the call may land in the 3CX mailbox.
  • If 3CX reports “Call forbidden by administrator”, allow the country code under Admin → Advanced → Allowed Country Codes.
  • If Allowed Source IPs / CIDRs is set in Placetel AI, allow the public IP address of your 3CX system.
  • For transfers to colleagues, use a 3CX extension or ring group as the target first.