How to setup VoIP destinations

Forwarding your calls over the Internet (or using VoIP) can be beneficial in connecting multiple call management systems together. The following information gives clear instructions on how to set-up VoIP destinations for your incoming calls.

A guide to set up Call Fowarding to a VoIP User can be found here

VoIP Destinations

A VoIP destination is an address on the Internet which can receive telephone calls using a VoIP protocol (for instance; SIP, IAX or H.323). The calls will travel over the Internet rather than the Public Switched Telephone Network (PSTN). Many companies who use in-house PBX or Call Management systems may wish to receive calls by VoIP as their system has Internet connectivity.

Like Telephone Numbers, VoIP destinations are provided and managed by service providers. Unlike Telephone Numbers, anyone with the equipment and know-how can build a VoIP system to receive calls over the Internet. Because of this there are hundreds of VoIP providers all offering a variety of different services in the market. Depending on what you are trying to achieve will depend on which kind of VoIP provider to use.

VoIP is generally the cheapest Call Forwarding option available (free in some cases), however if you want to receive calls on your landline or mobile it is unlikely that VoIP will help you. You may be able to forward you calls from a TTNC number to a VoIP provider for free, but they will charge you to get the call to your landline or mobile. This is because there is an inherent cost to call any telephone number (except for Freephone numbers). You may as well just forward to your landline or mobile directly using TTNC, as this will mean less people in the chain, and a higher reliability of service.

Some companies will describe telephone numbers, or telephone lines as VoIP numbers, or VoIP lines. They usually do this to describe the nature of their internal network, or how the calls are delivered to your home or business. If they provide you with a UK telephone number in order to receive calls, then this is not a VoIP destination, and will have a charge associated with calling it.


In order to set up VoIP Termination using myTTNC you'll need to type in a SIP or IAX URI. These look a little like email addresses. Please see the examples below:

Please specify the following for IAX or SIP:

These are only examples to demonstrate URI formatting and will not work if set up in myTTNC.

Your SIP provider may not give you your SIP destination in the form of a URI, but you can create one from your SIP credentials;

  • Username – this may be called your account number/name or your 'inbound route' name.
  • Password – you will probably have a couple of passwords from your VoIP provider to distinguish these. They may call this the 'secret'.
  • VoipHostDomain – this may be called the 'Domain', 'Host' or could be the inbound IP they provide.

Originating IP Addresses

Sometimes you may wish to protect your end equipment by placing it behind a firewall. Please can you ensure that at a minimum you allow incoming traffic from us on the following IP addresses on all ports:


In addition, RTP traffic may originate from any of the IP addresses contained in the following subnets:

If you firewall UDP traffic on your network you must ensure the above subnets are permitted.


We support RFC2833 DTMF and inband DTMF.


We support G711a (PCMA).

Further reading....