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. A prototype T-Hybrid Text Transcoding Gateway is one of these tools, intended for use in networks. It is in early implementation form with continuing development. One form of it is commercially available through Omnitor, and is in use in Sweden.
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 (described below) is intended for use in networks.
- The Home RTT-ATA Gateway is for home use, for those who have analog phones with a VoIP connection to the home.
Description of Gateway
The T-Hybrid Text Transcoding Gateway is a SIP-based, real-time text to PSTN text phone (TTY) transcoder. It is a software-based transcoding solution that can reside in the internet next to a standard PSTN to VoIP gateway. It can handle any calls containing real-time text that come to the server.
The T-Hybrid transcoder can also convert between any audio coded text phone (TTY) communication in a VoIP call, and text coded in a dual media text/voice call in a VoIP call with RFC 4103 text support. The gateway could also act as a primary gateway handling both the voice and text transcoding. However, this unit is designed for a more likely configuration where it acts as a satellite server to a main voice gateway.
The T-Hybrid transcoding server is based on the common Asterisk Open Source IP service architecture. A single T-Hybrid server can handle many parallel calls. The T-Hybrid server comes with two selectable text phone soft modem implementations, one for TIA 825.1 (TTY for North America), and one for V.21 (text phones for the Nordic European area). The T-Hybrid server follows the standards IETF RFC 5291 and IETF 4103.
The T-Hybrid transcoding server is currently in prototype/reference design state, but a commercial implementation has also been done and is in use in Sweden. For more information contact www.omnitor.se .
The T-Hybrid Text Transcoding 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.