Overview
This topic is not overly technical, but it does take a bit of time to get your head around it all. I have therefore set up this overview page to set the scene and take you through this one step at a time. I will cover off the following topics and build on the concepts so you can see how they link together:
- Free calls to the same VSP
- Free calls between VSPs
- Non-participating VSPs
- PSTN Calls to VSPs for the cost of a local call
- ENUM routing
- IP Dialing
Once you have read this section, you should have a basic understanding of SIP Broker, e164.org and IP Dialing. You can then read up in more detail about these things by clicking the links in the navigation panel on the left.
Free VSP Calls
VSPs can offer cheap untimed calls to any PSTN number in Australia because they use the Internet for the long haul between PSTN phone numbers (as can be seen in this image).
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Now the only variable cost that at VSP incurs to connect a call from your ATA to the PSTN network is the cost to connect to the PSTN network at the other end. (ie all costs are fixed other than the fee the VSP pays Telstra to connect back into the PSTN network. This is because the VSP uses the Internet to send the call – which is free.)
Now if you are calling a user that uses the same VSP as you, then the VSP does not incur any variable cost at all. It just connects the call directly to the other user’s ATA without going through the PSTN network. If the ISP doesn’t incur any variable costs, then it has the choice to provide you free calls to other users on the same network (ie Pennytel to Pennytel).
The VSP does this because
- it assumes it will make enough money from the other services it sells
- it wants to encourage you to get your friends to sign up
- it is a competitive environment and other VSPs offer this
service.
Free Calls Between VSPs
Now technically your VSP can allow you to call another VoIP user on any other VSP network without incurring any variable costs itself. Most actually do allow you to do this – but some explicitly prevent it. Those that prevent you doing this include Engin, Myfone, Internode, and iinetphone.
SIP Broker is a free service that helps you take advantage of inter-VSP free dialing for those VSPs that allow it. Using SIP Broker you can call your friends that use other VSPs for free. What SIP Broker does is allocate every VSP a unique code to identify the VSP. Hence you can configure your ATA to allow you to dial your friend on another VSP via SIP Broker, bypass the PSTN network all together, and hence get the call for free.
The format of the unique code that SIP Broker allocates to your VSP is in the form *xxx (asterisk followed by a 3 digit number). Faktortel is assigned the code *208, Pennytel *234 etc etc. A full list of codes is available at http://www.sipbroker.com/sipbroker/action/providerWhitePages.
Details on how to use free calls between VSPs is covered on the SIP Broker page.
Non Participating VSPs
Now as mentioned above, some VSPs will not allow incoming calls to be connected to their customers unless the call first goes through the PSTN network. If you look at the White Pages link above, you will notice that some providers have a 
icon down the left hand side. These VSPs are the ones that prevent incoming calls from other VSPs.
Those wascally wabbits!
If your VSP prevents incoming calls, and if you have an ATA like the SPA-3000, you can get around this problem by setting up your ATA to accept direct incoming IP dialing. What this effectively does is allow other people to call your ATA direct, bypassing your ISP all together. Details on how to do this are covered on the IP Dialling page. Not all ATAs can be configured for IP Dialling, and setting up IP Dialling can be a bit of a challenge.
PSTN Calls to VSPs for the cost of a Local Call
Now some very nice companies all around the world have set up PSTN numbers that connect directly to SIP Broker. They have done this in return for advertising on the SIP Broker website. What is really nice about this is that if you are visiting a city that has one of these PSTN numbers, you can dial the PSTN number for the cost of a local call, enter the *xxx SIP Broker code and then the phone number of your friend (or your home). The call be connected for free other than the the cost of your local phone call. Full details of how this works is covered off on the SIP Broker page.
ENUM
Now the more people that get VoIP, the more people that you can technically call for free. The only trouble is that you may not know they have VoIP, and you almost definitely wont know which VSP they are using. As covered in the section above, you need to know which VSP they are using to be able to know what SIP Broker *xxx code to use to be able to call them for free.
Now wouldn’t it be great if there was a way to tell the world that you have VoIP, and to set up a way for anyone with VoIP to be able to call you for free – even without them knowing which VSP you are using. Well the good news is – YOU CAN! This is called ENUM (Electronic NUMber Mapping).
It takes 2 steps to achieve this:
- Your friend has to register their number(s) with an ENUM service. (You should do this too!)
- You have to set up your VoIP service to first ‘check’ if there is a free way to connect to the number before it is sent to your normal VSP. (Your friend should do this too too!)
Step 1: Your friend should register their DID phone number or/and their PSTN phone number with an ENUM database like e164.org. When they register the phone numbers, they tell e164.org that there is a free way for others to call you (provided the caller has VoIP). Your friend ‘registers’ the free connection method to their diallable DID and PSTN numbers. Anyone with VoIP that tries to call the DID or PSTN number, and first checks the numbers for ENUM will find that there is a free way to make contact with your friend. They will automatically be routed via the free path rather than going through the PSTN network.
To set up your numbers for ENUM, refer to the detailed instructions on
the e164.org page.
Step 2: You set up your ATA so that before it sends a call to your VSP (ie you are about to pay them to connect your call across the PSTN network), you first ‘check’ to see if there is a free way of connecting to your friend. This can be done a number of ways including first sending the call to SIP Broker and asking these providers to check for you. What SIP Broker does for you is check the ENUM database to find if there is a free way to connect the call to your friend. If there is a free path, your call is connected for free. If there is no free path, your call is routed through your preferred VSP and you pay the standard fee (as you would if you didn’t have ENUM checking).
To take advantage of this, you need to set up your ATA dial plan to cater for ENUM lookup. This is covered off in detail on the SIP Broker page.
IP Dialing
Now technically speaking, you do not need a VSP at all to make a call, as long as you have an advanced ATA like the SPA-3000. The ATA can initiate a call, and can also receive a call from another ATA without going via a VSP. To do this, you have to set your ATA up to accept inbound IP calls and make sure that you can tell your friends ‘where’ your ATA is located on the Internet. The trouble is that Internet addresses (IP addresses) can (and do) change over time. Given that ISPs tend to change individual IP addresses for users over time, you need a way to keep your ATA address constant despite your IP address changing. How to do this is covered off in detail on the IP Daling page.
Next Steps
OK, now that you have read all this, you should read up on each of these concepts in more detail. I suggest you read the following pages in the following order:
