Voice over IP

• How does a VoIP call work?
• What is QoS?
• What hardware do I need?
• What sort of broadband do I need?
• What is a VoIP service provider?

What hardware do I need?

The Analogue Telephone Adapter

An analogue telephone adapter, or ATA (also referred to as a media terminal adapter or broadband phone adapter), allows you to enable an ordinary telephone, including your cordless, to make VoIP calls. All you need to do is plug your analogue phone into the ATA, then take your cable from the Internet port of the ATA and plug that into a spare Ethernet port on your ADSL or cable router. If you don't have a spare port you will need a switch to provide a spare Ethernet port.

You should be able to purchase an ATA device for between $100 and $200, depending on their capabilities.

An ATA may sound like a modem, but in fact there is quite a bit of difference in the hardware technology. An ATA is specifically designed to deal with the voice traffic and not data traffic. It takes the analogue human voice and converts that to an IP packet with the use of the compression codec, then sends that over the Internet.

There are several features to look out for in ATAs:

Codec: VoIP devices, including the ATA, use codecs to compress outgoing and decompress incoming voice. The codecs in an ATA receive the data and break it into small files, or packets, for sending and receiving across the IP network. There are hundreds of codecs which can be used for VoIP and as a result the quality levels differ with each one used.

The G.711 is the codec that the PSTN (Public Switched Telephone Network) uses. It is quite large for travel across the Internet, enabling 64Kbps of voice. G.729, for example, compresses voice down to 8Kbps or 20Kbps when the packet header is factored in. This packet works out to be a quarter the size, yet still maintains a high quality, and is therefore ideal for sending over an IP network. G.729 is the most commonly deployed codec in Australia.

(See table on page 5).

CPU performance: An ATA might say it supports a bunch of codecs (G.711, G.729 or G.722). But if one codec is more CPU intensive than the other, it needs more MIPS (millions of instructions per second) to run it. Therefore a more powerful ATA will provide better voice quality as it compresses and processes that codec a lot better than a modem with less power.

Connectivity: USB or Ethernet. Ethernet is best because it gives users the versatility of plugging in multiple devices. USB ATA devices need to be connected via a PC.

VoIP phones

VoIP phones look rather simular to normal analogue phones, and manufacturers have been striving to make them look appealing more recently -- particularly by using a range of colours and LCD displays. The main difference here is that they are digital, and have an inbuilt ATA. Additionally, rather than having the standard RJ-11 phone connectors, VoIP phones use an RJ-45.

A VoIP phone is ideal for businesses, where Ethernet network ports are distributed around the office space. All that is required is for the user to plug the phone straight into an Ethernet port and away they go. Alternatively, there is now a huge market for consumer VoIP devices. Many providers are parading VoIP as a way to save a significant amount on your home telephone bill. Further, there is a range of VoIP phones built and tailored specifically for Skype.