The Trace Center has worked collaboratively with Omnitor AB in Sweden as part of the RERC on Telecommunications Access project to develop tools and strategies that address next-generation IP-based text communication to ensure accessibility for all – especially individuals who are deaf or hard-of-hearing. The Home RTT-ATA Gateway prototype and reference design is one of these tools, intended for use in developing home or small business gateways to connect phones or terminal devices that are analog (would work on the PSTN) with other phones or a connection to the outside world that are VoIP.
Need Addressed
As telecommunication moves to VoIP (Voice over Internet Protocol) across the world, it becomes important to have a common real-time text over IP format instead of the myriad of different TTY formats used by different countries. For the following reasons, both mainstream telephony and emergency communications are moving toward a single, international real-time text format for IP networks that can be used in any call (together with voice and/or video as needed by the user).
- This will allow, for the first time, international communication among people who are deaf. (Although theoretically possible in the past with V.18 modems that supported all the different TTY formats, market forces did not encourage V.18 enough to bring about the general application necessary for it work.)
- Individuals who are deaf and traveling need access to emergency services without having to carry different real-time text devices for each country they visit. They need something that works in different countries, allowing them to communicate in an emergency in the same way as people who can speak and hear.
- Real-time text formats used by TTYs or textphones were designed for the analog public (switched) telephone network (PSTN) and do not work reliably or consistently with the IP environment.
- A single real-time text format is needed so that companies making VoIP terminal devices do not have to address different TTY standards used in different countries. The vast majority of these devices already have displays and text generation capability, making it possible for support of real-time text without the need to add a display, keyboard, or special connector.
Continuing Need for TTY Capability
Although IP text formats are superior and necessary in IP networks, IP text formats cannot travel over analog phone lines. Many consumers continue to have analog phone lines coming to their house. Others have VoIP coming to the house, but still use analog phones within the house.
It is likely to be many years before a complete transition to VoIP. Therefore we need a mechanism for connecting people who are on an analog system (e.g., PSTN, using TTYs) with those on VoIP (using IP-based real-time text). A gateway is needed between the PSTN and VoIP worlds, supporting translation back and forth between the various forms of TTY in the PSTN and real-time text in the VoIP environment.
To demonstrate feasibility and to provide an open source basis for commercial implementation to PSTN, two VoIP gateways were developed by Omnitor and the Trace Center.
- The T-Hybrid Text Transcoding Gateway is intended for use in networks.
- The Home RTT-ATA Gateway (description below) is for home use, for those who have analog phones with a VoIP connection to the home.
Description of Gateway
The Home RTT-ATA (real-time text analog telephone adapter) Gateway is a PSTN-to-VoIP transcoder that supports real-time text (RTT). It can be used in a home or small business situation where some or all of the phones or terminal devices are analog (would work on the PSTN), while other phones or the connection to the outside world is VoIP.
The RTT-ATA Gateway can be attached between any analog phone device or network of devices and a VoIP connection or network of devices. The RTT-ATA will transcode all voice calls back and forth between the two formats (analog and VoIP) and also translate TTY real-time text (TIA 825a) to RFC 4103 real-time text for the VoIP networks.
As a result, all voice and text traffic in both the analog (PSTN) and IP (VoIP) networks can flow back and forth.
At present, the gateway prototype and reference design supports TTY text in either the TIA 825a format or V.21 format. Other formats can be also added. The gateway is based on the open source Asterisk IP soft-switch software and runs a small IP04 box similar to other home gateways.
For more information contact www.omnitor.se.
The Home RTT-ATA Gateway development project was part of the RERC on Telecommunications Access under grant H133E040013 from the National Institute on Disability and Rehabilitation Research (NIDRR), U.S. Department of Education. However, the contents of this page do not necessarily represent the policy of the Department of Education, and you should not assume endorsement by the federal government.