Why do I need to know about ENUM?
ENUM will allow you to make calls from your VoIP ATA to other VoIP users for free. You don’t need to know they have VoIP; you don’t need to know which VSP they are using; you don’t need to know anything about them other than their standard every day phone number that you can find in any white pages telephone book. Once everything is registered and set up correctly, all you need to do is dial their normal phone number from your VoIP service. If there is a free way to connect the call, then the call will be diverted away from the PSTN network and will travel via the internet instead (VoIP to VoIP). This is even though you dialled a PSTN number in the first place. You will get a free VoIP to VoIP instead- it’s that simple.
What is e164.org and ENUM?
e164.org is a public database of telephone numbers for use with VoIP. Anyone that has a normal dialable phone number (either a PSTN phone number or a DID) can register their phone number in this database. What you are actually doing when you register is you are telling the world that there is another way to contact you other than your dialable number via the PSTN network – a free way using VoIP. This free path is called a SIP URI and, the process of looking up the database is called Telephone Electronic NUMber Mapping or (ENUM).
Anyone that configures their VoIP service correctly can use this database to make free out going telephone calls without even knowing it.
Now e164.org actually does more than just map SIP URIs to to phone numbers. It can map any valid URI to any phone number. eg mailto:firstname.lastname@example.org, www.example.com, https://www.example.com, ftp://www.example.com
How ENUM Works
To get ENUM to work is a 3 step process.
1. Determine if there is a free method to connect to your VoIP service
2. Register your dialable telephone numbers with e164.org so that others can ‘find’ the free path to call you.
Now that’s all great and dandy for your friends – now they can call you for free, but how do you get free calls? Well assuming your friends also go through steps 1 and 2, then you need to set up your ATA to ‘check’ for a free calling path.
3. You therefore need to set up your ATA to use an ENUM service provider so the provider will first check the the number you are dialling to see if it has a ‘free connection path’. To make it easier to understand, I will cover off each of these starting from the last one and work backwards.
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3. Using ENUM
Lets assume that you want to dial your friend, and that your friend has ENUM set up correctly (ie as in points 1 and 2 above – has a free connection method and has registered with e164.org – we will come back to these 2 steps later).
Before you can take advantage of ENUM, you have to configure your ATA to use an ENUM service provider. The ENUM service provider will take all the outbound calls that you make and check the ENUM database managed by e164.org before the call is sent to your VSP. This all happens in a split second and doesn’t lengthen the dialling experience at all. If your ENUM service provider finds that the phone number you are calling is in the e164.org ENUM database, it queries the database to find out ‘how’ to send the call for free. The call is then routed via the free connection path rather than via the PSTN network and hence the call is free of normal call charges. If an ENUM entry is not found, then the call is routed to your VSP as if your ENUM service provider had never been
Illustration of how ENUM works
It is important to stress that ENUM routing works just as well for PSTN numbers (as in the example above). In this example your friend has a Sydney PSTN phone number 02 9817 5555 and also has a VoIP ATA with a free connection path. Your friend has registered the PSTN 02 9817 5555 number at e164.org and mapped it to the VoIP free connection path. Any VoIP user (ie you) that phones the PSTN number 02 9817 5555 and has their VoIP service set up to check for ENUM (say by using SIP Broker), will get the call for free. The caller (you) doesn’t even need to know that your friend has VoIP or a free connection path – it all happens seamlessly – and that’s why it’s so cool.
Calls that don’t match
There is one ENUM service provider covered on this website – SIP Broker. If the number is not found by Sipbroker, the call is actually sent back via the internet to your ATA. Your ATA then routes the call to your VSP as if SIP Broker had never been involved. How it does this is a little complex but believe me it actually does return the call to your ATA for resending and it does work.
1. Find a Free Calling Path
Most VSPs allow you to call another customer on the same VSP network for free. They can do this because these calls never enter the PSTN network and are completely handled over the internet. The VSP therefore does not incur any variable costs to make the call (ie the internet is free) and they pass the savings on to you in the form of a free call. Now technically your VSP can connect to any other VSP via the internet without entering the PSTN network too. So if they wanted to, they could allow you to connect to other users with other VSPs for free. In fact most VSPs actually do allow you to do this – but some explicitly prevent it. Those that prevent you doing this include Engin, Myfone, Internode, and iinetphone.
A full list of VSPs and their participation status is available at
When you have a look at this link you will see a list of VSPs like this
|icon down the left hand side. These VSPs are the ones that prevent incoming calls from other VSPs.Each VSP has a SIP proxy listed in the middle column. As you can see FactorTel has a SIP Proxy sip.faktortel.com.au and Freecall has a SIP Proxy proxy.freecall.net.au Now your free connection path for other VoIP callers is called your SIP Uniform Resource Identifier (SIP URI), and it takes the form YourVSPTelephoneNumber@yourVSPsipProxy. ie if your VoIP phone number with FaktorTel is 0282093333, the your full SIP URI will be email@example.comThis SIP URI is the free connection path for others to call you using ENUM. But how will they know where to find this free path? That is covered in the next step.Now if your VSP is in the list and is not Back to TopStep 3
You will be taken to this page. Wait until the phone rings, then enter the PIN number read out to you over the phone into the box, then click submit.
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