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VoIP - Voice Over IP

VoIP - Voice Over IP Article Author : Ian
Date : 8th Jul 2005
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VoIP is a term that you may not have heard of, but will become very common over the coming years. Voice over Internet Protocol (VoIP) is a technology that enables the transmission of voice over an existing IP network (such as "the Internet" or a local network). Simply put, VoIP is a way of converting the analogue signals when using a phone to a digital format (across a network) and then back into analogue at the receiver. This means you can have free calls to other VoIP users if you are both connected to the internet or an internal network.

If you use free software available for PCs to transmit and receive VoIP calls, you will likely only be able to communicate with other VoIP users. The advantage this this is that it is completely free (except for your usual internet connection), but with a limited reach of other VoIP terminals only. There are however, companies which act as a gateway between VoIP and traditional PSTN lines (the usual telephone network). This sort of company may charge you for its services for calling a normal telephone number, but it is likely to be a heavily reduced rate to normal charges.

Connection Methods

There are several methods for communicating over VoIP, ranging in ease of use and cost:
  • Personal Computer - A standard PC can act as a VoIP receiver to make free calls, as long as it is connected to the recipient computer over a network (the internet or a LAN).
  • Analogue Telephone Adapter - This adapter interfaces your standard house phone to connect to your PC/Router to make calls.
  • IP Phone - A dedicated hardware phone that connects to a network socket on your router, this can make and receive calls all in a separate unit.
The cheapest and easiest method of trying VOIP is by using your PC as the VoIP gateway, and is great for VoIP to VoIP calls - as they are usually free. All you need is a microphone and speakers, although a headset is usually preferable. There is plenty of free VoIP software around (link later in the article), and many of these allow you to call normal phone for a small charge (almost always cheaper than land line rates).

Analogue Telephone Adapters (VoIP gateways) allow you to connect your old telephone to your PC/Router for direct calling. Some ATAs require software to be installed to act as a gateway for the phone to function. This method was very popular until dedicated IP phones arrived.

IP Phones look exactly like a normal telephone, expect they plug directly into your router to communicate directly with another VoIP gateway, server or phone. No computer or software is required and it can be used completely independently as long as an internet connection exists. This is the best option for a serious user.

Dial-up users will find VoIP impractical to use, as it requires more bandwidth than can be provided. This comparison at Speex shows the various bitrates required for different VoIP codecs. Any broadband user should be able to fully utilise VoIP without any problems.

Technical Differences

Current telephone networks are used for the same purpose (voice transmission), but require complex circuit switching to route calls to their destination. As VoIP uses existing IP technology, it uses Packet switching to send information - directing only the "packets" of voice data to their destination.

As you can imagine, this requires much less infrastructure and logistics than legacy telecommunications technologies - saving a considerable amount of money for the user. If an company requires several phone connections, they must get cables routed through the building, spend money on equipment, wait days for phone numbers to be assigned etc... With VoIP, you can use existing infrastructure (a PC) with free software and communicate for free with other VoIP users. You might not even need trailing wires if you are using a wireless network.

This technology has numerous advantages over the current system, mainly in cost reduction, but also in future capacity and capabilities. It would not be difficult to combine VoIP with other existing technologies such as streaming video.

Major telecoms companies often use VoIP "in the middle" of the virtual connection of your phone call, especially in long-distance or transatlantic calls. Many users are unaware that their call is converted from PSTN (Public Switched Telephone Network) to VoIP and then back to PSTN to the receiver of the call.

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