VoIP - Voice Over IP

VoIP - Voice Over IP


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.

Pros and Cons of VoIP


Accessible for all types of users - Home users, small office and large companies can all benefit from a properly implemented VoIP system. The initial overhead costs are fairly linear with no high initial startup cost, as existing computers and routers can be used.

Free VoIP>VoIP calls - Intraoffice communication costs are reduced to zero and calls to other VoIP users are completely free.

Increased Security - It isn't as easy for someone to listen into a call when you are speaking to someone digitally.

Little Training Required - Dedicated IP phones are so similar in function to standard phones that very little extra training is required before a switchover.


Variable Quality - If the network is congested or other users are consuming too much bandwidth from the same internet connection, the quality of the call can degrade. Voices can sound strange and lag times can increase in worst cases. On the flipside, a properly implemented system can have higher quality than a normal phone.

Possible reliability issues - Complete reliance at this stage could cause problems on occasions - it isn't uncommon for "the internet to go down".

Network configuration - Home users will not experience this problem, but large networks will have to assign VoIP QoS priorities to make sure VoIP is always available under heavy networking loads.


Most of these software downloads focus on home users connecting from a PC - as other options require extra hardware and capabilities. To use this software you will need a microphone and speakers as a minimum.
  • Skype is a very popular propriety VoIP system, with free calls to other Skype users (calls to conventional landlines are also possible at much lower rates). Ideal for beginners and those familiar with standard MSN/AIM interfaces.
  • Gizmo is an open source VoIP system which is similar in functionality to Skype but has a few more features, SIP compatibility and can call landlines at similar rates.
  • Vonageoffer a more dedicated system for unlimited local and national calls to landlines and other VoIP users. A free adapter converts your landline phone to plug directly into your router to provide a familiar service.
The software you choose will depend on how often you want to make VoIP calls and the type of equipment you have. If you are a heavy usage home user, then it might make sense to go with a dedicated flat free provider which allows you to use your current landline phones. However, if this will be your primary system you need to make sure you have enough bandwidth provisioned.

Light users or people trying the system for the first time may wish to use one of the free MSN/ICQ-esq applications for the PC which allows you to use your microphone/speakers or headset to make calls. This is free between other users of the same system and allows you to make calls outside the network to a PSTN user for a per minute fee.


If you are a home user with access to a fast internet connection or a small business thinking about implementing VoIP to save costs, it is worth trialling some of the freeware PC>PC/Landline software using a simple headset to test the quality and usability of the technology. VoIP is undergoing rapid adoption by large companies and telecoms networks and still has some work to be done to make it accessible to all. However, if you are willing to trial the system for a few weeks you may be able to stay ahead of the pack and reduce your calling costs. PC based IP Telephony is the cheapest and easiest way to get started before moving onto a hardware based system.

Hardware VOIP phones can be picked up for as little as £30 now, and feel more like a conventional home phone without the need to turn the PC on each time you make a call. Emergency service calls and usage during power outages aren't available, so it may not be a true PSTN replacement quite yet.

Ian Cunningham
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