IT Communications Limited - SIP Trunk
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About IT Communications Limited
I.T Communications is a specialist Telecommunications Provider established in 2010. I.T Communications offers SIP Trunk Services since 2011 and is an approved Ofcom Telecommunications Provider. Has own Ofcom Telephone Number Ranges so they can offer you the best possible service. No matter what your requirements are. I.T Communications will offer a solution which is fully supported and ensure you are up and running quickly.
Reference website: IT Communications Limited
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 SP1
Below is a short overview of the provider's capabilities and services and whether they’re supported or not:
- CLNS (Clip No Screening): No
- Catch All Routing: No
- Fax T.38 support: Yes
- CLIR (Number Suppression): No (see relevant section in this guide)
- DTMF via RFC 2833: Yes
- Codec Order: G711A, G711U, G722, Speex, iLBC, GSM
- NAT Support: Yes
- 302 Diversion Support : Yes
Once you have signed up with IT Communications Limited, you will also be given access to the Trunk Management portal through which you can configure some settings related to the operation of your IT Communications SIP Trunk. The portal can be accessed from this link using the credentials you have been provided with.
Collecting SIP Trunk Configuration Data
The first step towards configuring your IT Communications SIP Trunk with 3CX is logging into their portal. Once logged in, go to the “Extensions” node on the left. Here you will see all the accounts that you have been assigned by IT Communications Limited.
To start collecting the information you need to configure the Trunk on your 3CX, click on the Account you want to configure.
This will take you to the Account/Extension Setting page. Here make note of the:
that are listed as they will be used later in this guide. Additionally, remember the Number of the Extension/Account as it will be used in the next section to associate your DIDs with your account.
Also, at this point you may want to set the codecs that your IT Communications SIP Trunk will use. The common supported codecs that both 3CX and IT Communications support are mentioned in the “Provider Capabilities” section of this guide. Some general information about the audio codecs can also be found here.
Once you have made note of the information you need and applied any changes, scroll to the bottom of the page and press “Save”.
Associating Numbers/DIDs with your Extension/Account
Next, you must associate the Numbers/DIDs you have been given to the account(s) you want. To view the Numbers/DIDs, from the IT Communications LImited portal, go to the “DIDs” node.
To associate a DID with an Extension/Account, first click on the DID number you want.
This will open the DID settings page. In the “Voice” section set the “Destination” drop-down to the Extension/Account number you want calls to this DID to be routed to.
Once you have set this, scroll to the end of the page and press Save. Repeat this process for all DIDs you want to use with your Trunk and make a note of all the DIDs you associate, as this will be needed in the next section when settings up your IT Communications Limited SIP Trunk in 3CX.
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
Go to “SIP Trunks” and select “Add SIP Trunk”:
- Select Country: UK
- Select Provider: IT Communications Limited
- Main trunk number: The number associated with your IT Communications Extension/Account. You must enter the number in the international number format (e.g. 442033272020)
- Press “OK”
Under the “General” tab and in the “Authentication” section, using the the information collected in section “Collecting SIP Trunk Configuration Data”, fill in the Authentication ID and Password fields using the “Username” and “Password” values that you found in the IT Communications portal.
Once you have filled in these fields, scroll to the top of the page and press OK. At this point if you refresh the page you should see your IT Communications Limited Trunk appear as Registered.
Adding Additional DIDs
To associate all other DIDs/Numbers you have in your IT Communications Limited account with 3CX, you need to go to the Management Console → SIP Trunks, double-click on your IT Communications Limited SIP 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 in your IT Communications account as described in section “Associating Numbers/DIDs with your Extension/Account” to the list in the International Number format (e.g. 442033272020). Once you have finished, press OK.
Important: Calls to DIDs/Numbers that have not been input in the 3CX list of DIDs, or to numbers that have be written in the wrong format will not be successfully routed and will most likely be dropped.
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 IT Communications Limited SIP Trunks in 3CX, all numbers should be entered in the International number format (e.g. 442033272020), otherwise call might be rejected.
Outbound Caller ID
IT Communications Limited Trunks do not support Clip No Screening which means you cannot present any number as outbound caller ID, only numbers associated with each account can be presented.
For this to work, in any field within 3CX where the Outbound Caller ID can be set, the numbers must be input in the International number format (e.g. 442033272020).
There are no special requirements for outbound dialing when using IT Communications Limited SIP Trunks, number can be dialed in any valid dialable number format.
More information about how to create Outbound Rules and how they work can be found here.
Anonymous Dialing (CLIR)
3CX has a dial code for hiding your Caller ID when making outbound calls, which by default is *5. Although this specific dial code does not work with IT Communications Limited SIP Trunks, there is another dial code that the Provider offers that has the same result, hiding the Caller ID when making outbound calls. This dial code is *141.
In order to make use of it, you need to create an Outbound Rule in 3CX that adds this dial code to the beginning of a dialed number. If you are unfamiliar with creating Outbound Rules in 3CX, it is recommended that you first read the relevant documentation.
Specifically, choose a prefix you want the users to dial to call anonymous, e.g. 9, then additionally to the Outbound Rules you already have, create a new one that detects numbers starting with 9 and a length larger than 7 digits, then stripping that 1 digit and prepending *141.
IT Communications SIP Trunks support SRTP on inbound and outbound calls. To enable the use of SRTP, you need to first enable it through the provider portal, then also in 3CX.
To enable it in the provider portal, login, go to “Extensions” and edit the extension/account you want to enable SRTP for. Scroll down to the “Security” section and here:
- In the “Insecure” field set “Port, Invite”
- In the “RTP Encryption (SRTP)” field select “Yes”
After, scroll to the bottom of the page and press Save.
Once you have enabled SRTP in the IT Communications Limited portal, you must also do so in 3CX. To do this log into the 3CX Management Console and go to “SIP Trunks”. Edit your IT Communications SIP Trunk and in the “Options” tab, check the “SRTP” checkbox in the “Advanced” section. Then press “OK”.