Panoramisk / The VoIP druid 

One of the interests of IP telephony is the fact the Internet can become a network to carry telephony for some usages. We cannot consider today this network is offering a high grade quality but its ubiquity is incredible and no telco can nowadays be compared on this topic. It becomes relatively easy to imagine using a foreign ToIP operator in order to access specific prices in this country on one hand and be able to accept calls with a local number on the other hand.

Since Internet can be used in order to transport any IP traffic and telephony over IP is a good example, we can use IP Centrex based in any country and buy from these services allowing incoming calls with a geographically based number. In order to expand a company service from a regional standpoint, telephony over Internet allows proposing local users or customers a regional number. Any call arriving on that number will be routed through SIP or any voice over IP protocol to your office, like any local call. Thus you just need an Internet access and find the appropriate Centrex in the target country.

This concept of having incoming calls on a specific extension visible from the public side is not new, the first services were available from telcos back in the sixties. We generally named this service DID¹ and all telcos in the traditional telephony business are able to propose it. But, there is a geographical limit to this service proposed by a telco: a public number could only be proposed at specific presence points and not outside of the telco network. This means a PBX could easily get calls routed to a number localized in its area, but it is more difficult to get a number in another region or country.

If the telephony network runs on IP and interconnection between IP operators exist, we can imagine new services. Further more if we talk about the Internet network which by definition is available an many country and connectivity from any point to any point is available. Hopefully new service providers have imagined this and propose international DID over the Internet network and they are using VoIP standard protocols.

The main signaling protocol proposed by them is SIP, which allows easy interconnection with any standard IP PBX today. Some are proposing also IAX, the inter PBX protocol proposed around the Asterisk solution. But most operators are targeting the enterprise market more than the SOHO market, thus the product proposed is generally based on proposing a set of numbers in one area (like 10 or 30 contiguous numbers). But we can find some other proposing a single DID number localized in a specific country and at a low price.

For our lab we have tested the CALLCentric² solution and are reachable through an Ottawa local number for a low fixed price per month. This solution is really good when starting a service in a new location without the hassle of have a local line and redirect the calls to the central office.

With Asterisk, we just need to register the extension and be able to treat the call in the standard dial plan. In our sip.conf we have simply added:

register => 17772435589:password@callcentric.com

[callcentric]
type=friend
context=from-callcentric
host=callcentric.com
username=17772435589
secret=password
fromuser=17772435589
fromdomain=callcentric.com
insecure=very

This registers our account (which is not our number) at the CALLCentric registrar and allows any call to be routed towards the from-callcentric context.

In the extensions.conf file, we just added the specific context and treat the incoming call for our Canadian users to be directed to one of our phones.

Combining the telephony over IP and an Internet connection allows having access to services that were not available in the traditional telephony market, at least for SOHO and at home. But keep in mind the Internet network is not targeting quality nor availability, you will have to validate the network with the Centrex you find out prior opening the service to your client or remote users.

1. Direct Inward Dialing [↩]
2. http://www.callcentric.com [↩]