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Voice over Internet Protocol (VoIP)

VoIP's ability to converge voice, video and data into one application makes available new accessibility options not possible previously. Emerging VoIP applications are allowing blind and partially sighted people to use voice enabled applications for access to newspapers and magazines; hearing impaired people to use video telephones and text to speech applications to communicate; cognitively impaired people to use their voice to command their world and physically impaired people to use their work telephone number from home.

Other terms used include: IP telephony, internet telephony, voice over broadband (VoBB), broadband telephony and broadband telephone.

What is VoIP?

VoIP allows users to make telephone calls using a computer network, over a data network like the internet. VoIP converts the voice signal from the user's telephone into a digital signal that travels over the internet then converts it back at the other end so they can speak to anyone with a regular telephone number.

VoIP can be implemented in several ways, from a software program (softphone) on a computer used with a headset and microphone to adaptors used with regular analogue home telephones or a user can use dedicated VoIP telephones which look and act like regular telephones but have specially designed chips to improve call quality.


How does VoIP work?

Just like a modem converts digital signals from the computer into analogue (voice) traffic for transmission over a telephone line, a VoIP-enabled telephone or VoIP adaptor converts the user's voice into digital packets (using the special Session Initiation Protocol - SIP) for transmission over the internet. If the user makes a call to another VoIP telephone, the opposite process occurs at the other end and their voice emerges intact from the ether. If they make a call to a mobile or landline, their VoIP providers gateway decodes the call and sends it on as an ordinary voice call to the telephone exchange (Public Switched Telephone Network - PSTN).

The fact that VoIP transmits voice as digitised packets over the internet means that it has the potential to converge with other digital technologies, which in turn will result in new services and applications becoming available.

What is needed to make a VoIP call?

A VoIP enabled telephone

This can be an all-in-one handset, or a normal handset plugged into an adaptor, or a softphone: a computer program that uses a microphone and headphones attached to a computer to emulate a real handset. The softphone can be installed on a variety of hardware devices including wireless devices such as a Personal Digital Assistant (PDA).

An internet connection

A leased line or ADSL/cable broadband is ideal; dial-up (ISDN or ordinary telephone line) or a satellite internet connection will likely cause a reduction in sound quality. A standard 256Kb ADSL connection can accommodate 2-3 simultaneous calls; if a user expects to need more frequently, they may wish to upgrade to a higher-bandwidth package.

An account with a VoIP service provider

This gives the user a VoIP external number which is what other people dial to call them.

Mobile and PC VoIP

While the majority of VoIP services, such as Skype and Vonage, act like a normal landline, there are a range of other options for making VoIP calls over the internet.


VoIP on a mobile

VoIP is still mainly limited to use at home, but some VoIP providers are teaming up with mobile networks to offer VoIP calls on the go. Notably, Skype is now available on some mobile handsets, including a range of 3's mobiles and the Apple iPhone.

Barablu offers mobile VoIP calling on any internet-enabled mobile telephone. Users download Barablu software to their mobile and can then call other Barablu users free, or normal landlines and mobiles cheaply.

A variation on VoIP is offered by websites like Jajah. These offer free or cheap calls between normal landlines or mobiles by redirecting calls through the internet. The user will need to be near a computer with an internet connection for it to work, because to make calls they will have to type in their number and the number they are calling on Jajah's website. Many calls are free once the user is registered with the service, but they will have to pay if they exceed Jajah's fair usage limit.

VoIP using instant messaging services

Some instant messaging services also offer the ability to make VoIP calls over the internet, though typically they only offer the option to ring other computers with the same instant messaging service as the caller.

The most popular of these is Windows Live Messenger, though GoogleTalk and Yahoo Messenger also offer VoIP voice calling.

Problems encountered by disabled people and the ageing population using VoIP

Potential accessibility barriers include:

Blind and partially sighted

People with visual impairments may face problems reading from the small or hard to read displays of some VoIP hardware telephones.

They may also face problems with some VoIP softphones that are not compatible with screen readers, in particular those that use moving text methods. Also, some VoIP softphones are not compatible with screen magnifiers and high contrast screens. Graphics-rich screens of some VoIP softphones may be hard to navigate through and read.

Hearing impaired

Reduction in audio quality may reduce intelligibility for people who are hearing impaired. Also, loss of synchronisation between audio and video in IP videotelephony reduces their intelligibility during speech-reading.

Softphone use on a computer may also cause interference.

Physically impaired

Physically impaired people may not be be able to use some VoIP hardware telephones due to hard-to-use controls, including touchscreens.

Cognitively impaired

People with an intellectual impairment may have difficulties managing softphone installation and configuration may be hard to understand. Some VoIP softphones have graphics-rich screens that may also be hard to understand.

Ageing population

Some members of the ageing population may experience a range of difficulties with VoIP, such as those stated above: from not reading the display of a VoIP hardware telephone; being unable to use some VoIP hardware telephones controls and being unable to hear or understand clearly.

Checklist for VoIP


Possible recommended features include:

VoIP hardware telephone

VoIP softphones

Relevant standards

Further information



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