Total conversation

Total conversation is an ITU standard of simultaneous video, voice and text service in telecommunications. Total conversation allows people in two or more locations to: (a) see each other, (b) hear each other, and (c) conduct a text interaction (real-time text) with each other, or choose to communicate with any combination of those three modes and to do so in real-time.
The standard was defined in ITU-T recommendation F.703 of 2000 as "an audiovisual conversation service providing bidirectional symmetric real-time transfer of motion video, text and voice between users in two or more locations".
Universal design.
Total conversation is a straightforward application of universal design principles applied to telecommunication field. This standard brings communication services to the broadest range of population including deaf people, hard or hearing people but also people who have speech impairment, people with cognitive impairment, elderly people, children, and also ... regular users. It is an enhancement of call services that provides a better experience to all. Total conversation uses video, text and audio. These media can be combined or not depending on the type of profile used : many user profiles have to be taken into account. Such methodology is named Universal Design.
Implementation of the standard.
Available implementations.
A number of European companies including 4CTel, Aupix, IVèS, nWise, Omnitor, and Orange Labs produced implementations. These are mostly used to provide user-to-user calls and relay services for deaf and hard of hearing people.
REACH112.
Total conversation was piloted in a European project called REACH112, named after the 1-1-2 European emergency number, whose purpose was to carry out test deployment of total conversation in a live environment with several thousands users and for three usages:
Specifications.
Total conversation specifications describe:
Total conversation defines three basic services
Example of technical protocols used by total conversation are:
Over instant messaging.
AOL Instant Messenger supports the simultaneous use of audio, video, and real-time text via the "Real-Time IM" feature. This would be considered compliant with Total Conversation.
For other chat networks such as Google Talk, the XMPP protocol technically allow for total conversation by combining multiple XMPP Extensions, such as XEP-0266 audio, XEP-0299 video, and XEP-0301 real-time text. As of December 2011, Google Talk only supports audio/video, but not real-time text yet.
Skype has been supporting simultaneous audio, video, and real-time text.
IP multimedia subsystem.
Total conversation basically provides a multi-media call services with specific media enabled. 
The currently most common implementation environment is native SIP as described above.
Total conversation can also be implemented in other call control environments. 
One such environment is IP Multimedia Subsystem (IMS) in its IMS multimedia telephony service.
Firstly, total conversation can be defined as a pragmatic selection of existing standards related to Session Initiation Protocol with the selection of audio, video and text codecs. It is a private initiative of services provider and technology vendors seeking interoperability in the broadtest sense.
Secondly, this can apply to existing and deployed SIP platform rather than future or next generation networks.
Thirdly, IMS is much more ambitious and define a whole architecture, including all internal interfaces and billing and physical infrastructure. These standards are more suitable for large telecommunication operators and their equipment vendors. This complexity has consequences: