What it is Voice over IP – VoIP

VoIP allows you to have a phone call for FREE!! want to know how is that? Let me explain you.


If your not a Geek (Information Technology expert) this articule is for you.

Up to these days almost everybody already used an Instant Messenger for Desktop/Laptop like Jabber, Skype, YahooMessenger or even Facebook, these programs has the main ability to Chat between peers, where Chat means to establish a text conversation with a friend in real time. On the first launch only text was allowed to exchange between members. Then the option to Share files was allowed and Skype was the first to incorporate Voice and make possible a life conversation just like have a Phone Call but with the relevance that is Free of Charge!! How could it be possible? Because of using the Voice over IP.

Thanks to the Internet expansion those Instant Messengers applications could work efficiently and reach almost every user connected and be OnLine, in another Post I will explain how they works for Text Interexchange and I will asume that you already used one of those.

The Telephone Network.

Lets have a quick review of the Telephone Service, to make a phone call first both users (the Caller and the Receiver) needs 220px-Local_networkto have a Telephone equipment, both also has and Identifier meaning the Telephone Number builded by 4 segments: Country Prefix, City or Location Prefix, District Prefix and finally the User Prefix, the sequence result on a unique world wide phone number for every user. The caller dials the destination phone number where a Central Voice Switch translate the Prefix as a route to establish the connection between Voice Switches and finally rings the Receiver Telephone. When answer the call, the voice is exchange it, in the beginning the voice was transmitted in analog form now is converted to a digital signal where Codecs make their first apparition converting the electrical voice form into bits (1/0).


The IP address.

Now Internet is almost in everywhere, but how all the devices (Hosts) could be identify on a huge Network? Just like the Telephone Service, all the Host has an IP Address [for more details check our next Post] where exist two types of Directions, IPv4 and IPv6, but this address is just to identify the Device this is not the ID used to dial on a phone call, keep in mind later because this ID has the Free Trick!!, the IP address will be assigned depending on where are you located and connected, for example if you connect your PC on your home, your local Internet Service Provider (ISP) will give you one. If you connect into a Coffee Shop, their provider will give you one. By this is possible to have Mobility, meaning that you can connect to the Internet from almost any point of contact no matter what is your Name.

cisco-voipThe introduction of an IP Phone raise now, this device looks like a traditional Telephone device but you need to plug an Ethernet Cable to establish a network connection. Also one of the main functions is to convert the Voice from Analog to Digital and put it into Data IP packets with some extra features like echo cancellation (where eliminate repetitions or echo sounds) and noise reduction (capable to eliminate environmental noise and keep the voice clear).

When using an Instant Messenger like Skype on your PC, this application use the IP and PC credentials to establish the Internet Connection, no network configuration need it mostly of time. This application will be in charge to convert the Voice into Data packets as well.

The VoIP Gateway.

You already know that IP is the main transport connection on VoIP, also the Instant Messaging and IP Phone will be in charge to convert the voice into IP packets, dial and receive the phone calls, BUT if the IP address isn’t the dialed number to make a VoIP phone call, How do we do?

We still need to use a Telephone Number to reach the destination user and the use of a Voice Gateway, who will be in charge of the following:

  • Register the IP Phones and Messenger to be able on the VoIP service, meaning the responsable to receive the Login session, authenticate and assign its own User ID matching with a Telephone Number & IP Address where the device is connect to the Internet.
  • Convert the Phone Numbers into IP Address.
  • Time tracking to restore the call duration.
  • Allows phone call to the Traditional Telephone Network or PSTN (Public Switching Telephone Network)
  • And control the phone session by the use of Protocol Connection like SIP (Session Initiation Protocol) mainly.


The VoIP Magic.

Now, how it works everything?

Someone use an IP Phone to make a phone call, dial a number, the request goes to the IP Network then cross the Internet to reach the Voice Gateway how will translate the phone number into an IP Address and returns to the Dialing user the destination IP Address of the calling user. An IP connection is stablished between the IP Phones or Messenger, both terminals sense the Network and settling the better codec, and the voice conversation can flows.

voip-lab1Because the Voice Gateway is on the Internet, every time a voice device is plugged to the Internet, need to be registered and updated with the IP Address and Login credential. Now imagine that you are in New York, USA, launch Skype, in this case Skype assign you an Skype ID based on your Login User and IP Address no matter where you are connected. Then you double click a friend who is already OnLine on Skype as well but is on a trip somewhere in France, Skype use its own Voice Gateway and through the Internet is possible to connect several gateways located around the world, and establish the connection between users based on the Skype ID’s, by this all the voice conversation is converting into IP Packets and flows to the internet as Skype Interaction, your Internet Service Provider is not allowed to see the traffic and neither control it, that’s why is possible to establish a Free phone call.

A better service.

On the example, the voice conversation was established between Skype Users as Free of Charge and Best effort quality sound. For a better experience and the option to make a Phone Call to a PSTN number, her is where an Extra Fees comes up, but for just a Cents is possible to call your Grand mom with her old Telephone device.

 Hope the explanation was good and now you have a better understand how VoIP service works. Now if you want to increase your knowledge, let me suggest the following link in Cisco where a complete technical description you can find.

Beto Garcia

Telecom consultant & sales engineer, Blogger contributor @Cisco & @TiTiApps. Mobile Apps business initiator. Experienced Engineer with more than 10 years on Service Providers Networks.

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