VRS Feasibility Study Project Phase 5 – Technologies and their Forecasts
Mission Consulting Page 4
Other technical considerations
Future technology trends
2. Historical Background
The Deaf and hard of hearing communities have used technology to communicate over telephone
networks for almost 50 years. The technology that first enabled this was the development of the TTY
(teletypewriter) in 1964.
1
The TTY was invented in the United States and became a de facto standard
there. Later developments evolved as it was adopted in Canada and around the world. The TTY is a
typewriter-like device with a keyboard, a small electronic screen to display text, and optionally a small
tape printer to print the text. TTYs plug into a standard phone line jack or they use of an acoustic
coupler to connect to a standard telephone handset. The text is transmitted live over the telephone
network via the distinct tones generated by the different keys to another device (e.g., a TTY) that uses a
similar communication protocol. There are many different TTY communication protocols. The original
TTY standard was the Baudot code.
2
Other TTY protocols include DTMF, EDT, V.21, V.18, V.23 and
TurboCode.
3
As TTYs were adopted by consumers in the United States, small community-based or private relay
services were developed to relay conversations between the TTY user and a hearing telephone user.
Eventually these relay services were replaced by relay centers operated or contracted by the regional
telephone companies. These relay centers provide message relay services (MRS) to all telephone
company customers, so that the consumers with a TTY can communicate to anyone served by a
telephone line and telephone. With the advent of advances in TTY technology, these larger relay
centers also offered additional communication modalities such as Hearing Carry Over (HCO) and Voice
Carry Over (VCO), which enable the relay operator to only relay specific portions of the call according to
the desire of the consumer.
These protocols have been adopted by different countries and are not always compatible.
For example, V.21 is more common in the UK and some EU countries, while Baudot and TurboCode is
more widely used in Canada and the U.S. In 1994, V.18 was announced as the standard TTY protocol by
the ITU (the International Telecommunications Union).
4
The advent of text paging, cell phone texting, mobile smartphones, computers and the Internet have
revolutionized the accessibility options available to the Deaf and hard of hearing all around the world.
1
The TTY is also known as a TDD (telecommunications device for the Deaf). In Europe it is commonly referred to
as a textphone, and in the United Kingdom it is called a minicom.
2
The Baudot protocol runs asynchronously at 45.5 or 50 baud, 1 start bit, 5 data bits, and 1.5 stop bits.
3
TurboCode is a proprietary but popular code of Ultratech TTYs. See www.ultratec.com/support/turbocode.php.
4
HCO allows the TTY user to hear the voice of the distant party. VCO allows the TTY user to speak for his or her
self.