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Understanding the Architecture of VoIP

Updated on December 13, 2012
VoIP Integration with the PSTN System
VoIP Integration with the PSTN System

How VoIP Works

There are many ways by which one can use VoIP. As a new technology, it is facing the same teething problems that many others have gone through. Everyone wants to implement their own version of the VoIP protocol and unless the major players in the market standardize and coalesce around a single one, or at least cooperate with each other, customers using one service will not be able to communicate with those using another.

However there is a common architecture that is used by almost every VoIP service provider, barring a few like Skype that uses a complex system of interconnected P2P nodes instead. If we think of the traditional PSTN phone system as the Postal Service and if we compare VoIP to e-mail, we can have an interesting analogy as to the inner workings of this technology.

To be eligible to receive a letter by snail mail, you have to have a postal address. This is very much like having a telephone number. Like the postal address, the telephone number is also tied down to geographical location. Recently a few policies have been put in place to allow a certain amount of mobile number portability. But such portability is not guaranteed and is certainly not absolute. VoIP users also have telephone numbers – but these numbers are given to them by their VoIP service provider who in turn leases them from the telephone companies. As such, they have no relation to the physical location of any given VoIP customer.

When you sign up for VoIP, it's like signing up with an e-mail provider. As long as you are sending and receiving messages to another e-mail user, everything is fine. But how do you communicate with someone using traditional snail mail? This is the main problem of VoIP – how do we use communications on one network (the Internet) to reach a person on an entirely different one (the PSTN system)?

VoIP providers solve this problem by using gateways. It's as if someone sends you a letter by snail mail to the postal address given to you by your e-mail provider (as a placeholder – just like VoIP customers get a telephone number). When that letter reaches your VoIP provider, they repackage it and send it to you as an e-mail. This process is reversed if you want to initiate conversation with someone using the regular postal service. So when you receive a VoIP call, it's actually going to the SIP server which then contacts you via the Internet and pipes the call through.

This is more or less the basic structure by which VoIP is able to integrate with the traditional PSTN phone system. It is another matter that most VoIP service providers are unable to talk to each other. For that, we all have to standardize a single protocol and agree upon a single addressing convention. Contact a VoIP San Francisco phone service to learn about alternative VoIP solutions in your area.


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