CenturyLink Business - SIP Trunk

CenturyLink Business offers a reliable SIP Trunk service which can consolidate voice traffic over their robust data network allowing companies to maximize on their IT budget. We tested CenturyLink Business with 3CX and below is a guide on how to setup CenturyLink to work with 3CX.

Reference Web Address: CenturyLink Business

System Preparation

Before configuring the SIP trunk it is required to go through the following checklist and make changes where necessary:

NAT (when used) created to 3CX
(https://www.3cx.com/ports-used-3cx-phone-system-v14-v15/)
Firewall Checker passed
(https://www.3cx.com/docs/troubleshooting-firewall-checker/)
Firewall SIP ALG checked and if present disabled
(https://www.3cx.com/docs/manual/firewall-router-configuration/)

Further setup information can be found in our Academy: 3CX Academy Basic course

3CX Version

Some providers gained support and compatibility with 3CX on a specific product version. It is advisable to always run the latest version of 3CX to ensure ongoing compatibility.

Minimum 3CX Version: 3CX Phone System 15.5

Provider Capabilities

Below is a short overview of the provider's capabilities and services and whether they’re supported or not:

CLNS (Clip No Screening): Yes
Catch All Routing: Yes, static SI per trunk
Fax in T38: Yes (incoming only)
CLIR (Number Suppression): Yes
DTMF via RFC 2833: Yes
Codec Order: G729, G711U
NAT Support: Yes
Other: SRTP Supported, TLS is not supported

Provider Portal

In order to use CenturyLink Business trunks with 3CX, some settings must be made within the provider's portal and some information is required to complete the configuration with 3CX.

The portal can be accessed here with the credentials given to you by CenturyLink.

Creating DIDs

Once you have logged into the portal, go to “User Administration” → “Manage Users”, then select “Create New User” and finally create your user (each user is a DID).

Once you have done this, you must associate each new user/DID you created with the main trunk. To do this, while still in the “Manage Users” section, click on the “Edit” button next to each user

Once inside the “User Administration” section, assign it to the Trunk you want, then press “Save”

Repeat this procedure for all users/DIDs you want to create.

Collecting 3CX Configuration Settings

From within the CenturyLink portal go to “Trunk Administration” → “Manage Trunks” and click on the “Edit” button next to the Trunk you want to configure to operate on your 3CX system.

The information you need to make note of is the following:

3-way Authentication Password: “Trunk Authentication” value in the portal.
Authentication Password: Press the “Show Trunk Password” button in the portal and make note of the value.
Outbound Proxy IP: Public IPv4 information
Outbound Proxy Port: Public IPv4 information
Main Trunk Number: Pilot User

Configuring the Trunk with 3CX

The general instructions outlining how to add a new SIP Trunk to your 3CX installation can be found here.

Adding the Trunk

Specifically, the information collected in section “Collecting 3CX Configuration Settings” of this guide must be configured in the following fields in the 3CX SIP Trunk settings:

Adding Additional DIDs

To associate all other DIDs/Numbers you have in your CenturyLink account with 3CX, what you need to do is go to the Management Console → SIP Trunks, double-click on your CenturyLink Trunk and go to the “DIDs” tab.

Here you should already see 1 entry that is the Main Trunk number you have set. Add all other DIDs/Number you have to the list in a 10-digit format and press OK once you have finished.

Creating Inbound Rules

Now that you have associated all your DIDs/Number with your SIP Trunk in 3CX, you can create Inbound Rules to set where calls will be routed when those number are called. Instructions on how to create Inbound Rules can be found here.

Number Format

General

When configuring CenturyLink Business SIP Trunks in 3CX, all numbers should be entered in a 10-digit format otherwise calls will be rejected.

Outbound Caller ID

CenturyLink Business SIP Trunks supports Clip No Screening which means you can present any number you want when calling outbound.

Outbound Rules

There are no special instructions regarding Outbound Rules that are required, numbers can be dialed either in 10-digit format, 11-digit format or full + e164 format (e.g. +18135791691).

More information about how to create Outbound Rules and how they work can be found here.