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Asterisk: The Definitive Guide, 3rd Edition by Russell Bryant, Jim Van Meggelen, Leif Madsen

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Chapter 12. Internet Call Routing

There ain’t no such thing as a free lunch (TANSTAAFL).

Robert Heinlein

One of the attractions of VoIP is the concept of avoiding the use of the PSTN altogether, and routing all calls directly between endpoints using the Internet at little or no cost. While the technology to do this has been around for some time, the reality is that most phone calls still cost money—even those that are routed across VoIP services.

From a technology standpoint, there are still many systems out there that cannot handle routing VoIP calls using anything other than a dialpad on a telephone.

From a cultural standpoint, we are still used to calling each other using a numerical string (a.k.a., a phone number). With VoIP, the concept of being able to phone somebody using name@domain (just as we do with email) makes sense, but there are a few things to consider before we can get there.

So what’s holding everything up?

DNS and SIP URIs

The Domain Name System (DNS) is designed to make it easier for humans to locate resources on the Internet. While ultimately all connections between endpoints are handled through numerical IP addresses, it can be very helpful to associate a name (such as www.google.com ...

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