Nexmo - Elastic SIP Trunking
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Since 2010 Nexmo has been providing high quality and innovative yet affordable voice solutions to businesses working on both a national and international scale. Their SIP trunking service is a simple yet reliable solution for businesses looking to utilize their existing VoIP infrastructure.
Reference website: Nexmo
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
- Firewall Checker passed
- Firewall SIP ALG checked and if present disabled
Further setup information can be found in our Academy: 3CX Academy Basic course
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 SP2
Below is a short overview of the provider's capabilities and services and whether they’re supported or not:
- CLNS (Clip No Screening): Yes - offered as a separate service
- Catch All Routing: Yes
- Fax in T38: No
- Fax in G711: No
- CLIR (Number Suppression): Yes
- DTMF via RFC 2833: Yes
- Codec Order: G711A ,G711U, iLBC, G729, G722
- NAT Support: Yes
- Other: Only one registered account per installation
Nexmo provides the ability to create an account directly from their website and immediately create and start using SIP Trunks with your 3CX installation.
The first thing you need to do is create an account and add the necessary funds to create your SIP Trunk in the Nexmo portal and to be able to purchase the DIDs you want to use.
Once you have created your Nexmo account, the next step is to acquire DIDs. To do this go to “Numbers” → “Buy Numbers”. Here you can acquire telephone numbers that will act as your DIDs and you can choose from the various options and numbers Nexmo has to offer.
Once you have acquired the Numbers/DIDs you want, go to “Numbers” → “Your Numbers” where you should see a list of all numbers you have acquired and that are associated with this Nexmo Account.
To correctly route the numbers to your PBX you will need to then click on Edit next to each number and under “Voice” choose “Forward to SIP”. Fill in the SIP URI with your number, FQDN and port
The correct format should be sip:<number>@<FQDN>:<port>
Collecting 3CX Configuration Settings
From the Nexmo portal go to “Getting Started” which is also the first page you see once you log in. Here, make a note of:
- Authentication ID: “key” value in the portal.
- Authentication Password: “secret” value in the portal. You will have to press the “Show Password” button to reveal the password.
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
In the 3CX Management Console go to “SIP Trunks” and press the “Add SIP Trunk” button. Select the U.S. from the country drop-down and then select Nexmo. In the ”Main Trunk No” field enter one DID number that is associated with your Nexmo SIP Trunk as described in section “Acquiring DIDs”. Note that the ”Main Trunk No” must be written in the E.164 number format without the ‘+’ symboltt, e.g. if your number is 8135910130, you must write it as 18135910130. Once you have filled this in, press OK.
This will take you to the SIP Trunk settings. Using the information collected in section “Collecting 3CX Configuration Settings” of this guide, it must be entered in the the following fields in the “Authentication” section:
- “key“ → “Authentication ID”
- “secret” → “Authentication Password”
After doing this, scroll to the top of the page and press OK to create the SIP Trunk in 3CX. At this point your Nexmo Trunk should be registered.
Adding Additional DIDs
To associate all other DIDs/Numbers you have in your Nexmo account with 3CX, go to the Management Console → SIP Trunks, double-click on your Nexmo 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/Numbers you have to the list in a E.164 format, e.g. 18135910130, then press OK once you have finished.
Creating Inbound Rules
Now that you have associated all your DIDs/Numbers with your SIP Trunk in 3CX, you can create Inbound Rules to set where calls will be routed when those numbers are called. Instructions on how to create Inbound Rules can be found here.
When configuring Nexmo SIP Trunks in 3CX, all numbers should be entered in a E.164 format without though the ‘+’ symbol or international dialing prefix, e.g. 18135910130 or 442033272020, otherwise calls will be rejected.
Outbound Caller ID
Nexmo SIP Trunks do support Clip No Screening, but as a separate service. Clip No Screening means you can present any number as a Caller ID when calling outbound. For this to work correctly however, in all 3CX fields where the Outbound Caller ID can be set, the number must be entered in the International number format (e.g. 18135910130).
By default on all new accounts this feature is disabled, but can be enabled by contacting the Nexmo support team at email@example.com.
In order to perform Outbound Calls using your Nexmo SIP Trunk, all numbers must be dialed in a E.164 format without the ‘+’ symbol or international dialing prefix, e.g. 18135910130, 442033272020, etc. otherwise the calls will fail. Outbound Rules in 3CX can be created to adjust the dialed number format into the required format. More information about how to create Outbound Rules and how they work can be found here.