Accessibility Technology

Real-Time Conversations: From TTY to Real-Time Text (RTT)

Presenter:  Aaron Bangor, Lead Accessible Technology Architect, AT&T Corporate Accessibility Technology Office

This is the fifth presentation I attended on Wednesday, March 4 at the #CSUN15 conference.  I’m slowly getting worn down here :-/  I’m personally interested in this session because of some recent development efforts me and my development team at CSUN have had with our National Center On Deafness (NCOD).  Not exactly sure what AT&T has on tap here, I hope it’s relevant.

Where are we with making voice communications accessible to the Deaf and Hard of Hearing community?

  • Voice communications used to go through the phone network (POTS – Plain Old Telephone Service), but the underlying circuit switching really has not changes much.  Now it mostly goes through the Internet, but the need to communicate in real-time among individuals has not changed
  • In the mid-1960s, the then-old teletype machine was adapted to create the TeleTypewriter (TTY)
  • TTY’s purpose is to provide non-voice service (aka data) over a phone line.
  • Reviewed the basics of a TTY call, including some info on how TTY work over cellular networks now.
  • 1,400 Hz and 1,800Hz tones can carry text.

Benefits and Drawbacks

  • Works well for people with hearing and speech disabilities
  • Interoperable
  • Text-based
  • Real-time
  • Interactive
  • Intermixed with voice channel
  • BUT…it’s slow
  • Turn-based/half-duplex
  • Resource intensive from a network resource perspective
  • Dedicated network resource needed for wireless
  • Requires separate assistive technology not commonly used by telephone customers without disabilities

 TTY is not

  • Instant messaging
  • Email
  • Over-the-top messaging (WhatsApp, Kik, etc.)
  • Video conferencing
  • Text messaging (SMS)
  • These are all services that can – and are – being used to communicate instead of using a TTY on a voice call

 TTY Meets the Internet Protocol

  • TTY tends to work best on a wired connection with QoS, not so great when using lossy codecs
  • There are challenges to doing this (like there was going from Standard Definition to High Definition TV)
  • Packet loss, Echo Cancellation, voice-optimized compression techniques

What is Real-Time Text, Benefits and Drawbacks

  • IP/Data, not voice
  • Lightweight
  • Less sensitive to packet loss
  • Standards-based
  • Conversational, real-time
  • BUT…it has limited adoption to date (mostly Northern Europe, not directly interoperable with legacy TTYs (internetworking function needed)

RTT is where we’re headed

  • Endorsed / recommended by many areas
  • FCC Emergency Access Advisory Committee (EAAC)
  • National Emergency Number Association (NENA); next-gen 911
  • US Access Board’s information and communication technology (ICT) standards and guidelines
  • RTT is an accessible technology that does not require a 3rd party piece of hardware to work

Are we there yet?  Not Really…

  • Much work needs to be done to build a robust, accessible service that also does not leave anyone behind
  • Network changes required to support RTT
  • Interoperability between RTT implementations (standards-based)
  • Software changes for IP phones and wireless handsets
  • Changes to ensure legacy TTY internetworking; network gateways between IP and legacy networks
  • Points of connection between legacy equipment and VoIP networks

Final Thoughts

  • TTY was a great engineering solution in its day, but it was designed for a type of technology that is disappearing
  • RTT is more user-friendly
  • Takes advantage of newer network technologies
  • Builds accessibility into the service, not requiring separate equipment
  • Opens up possibilities for all users to interact over the “phone” in more creative and expressive ways because it will be built into phones, not via separate hardware
  • It is the essence of Universal Design



By Paul Schantz

CSUN Director of Web & Technology Services, Student Affairs. husband, father, gamer, part time aviator, fitness enthusiast, Apple fan, and iguana wrangler.

%d bloggers like this: