Background

For a number of years, the telecommunication infrastructure has been moving slowly from switched telephone architecture to an IP or other digital format. As these digital techniques were introduced, the conditions for text telephone traffic became worse. Transmission approaches and quality, which was sufficient for voice, was simply insufficient for transmission of modem signals without an inappropriate and unacceptable level of error. When sending audio over IP, packet loss is a concern. With voice transmission, the loss of packets can be smoothed over by using techniques that provide a transition from the last good packet to the next good packet, bridging the gap from the missing data. When sending digital data, such as text telephone tones, this type of smoothing can actually cause bit errors resulting in inaccurate characters or worse.

In order to address the problem, a number of standards groups are proposing competing solution strategies. Some propose to take the analog text telephone tones and change them into ITU-T T.140 (an IP text standard), and transmit the in a digital fashion with built in error correction. At the receiver's end, the T.140 characters can then be displayed on an IP telephone or be changed back into the text telephone tones of the native country. This approach would allow computer users to send and receive in T.140 digital format and have it translated into tones if the call is transferred to the public switched telephone network and have to proceed over analog lines.

The T-hybrid Strategy

The Telecom PERC has proposed a hybrid approach, which has been dubbed the T-hybrid strategy. This approach makes use of special servers, which could provide translation services between different protocols. This approach has a number of unique advantages, among others:

• Allows different components in the telecommunication system to implement different strategies, and allow them all to work together
• Allows individuals with computers or other digital text communication devices to interact with individuals using analog text telephone technologies
• Allows individuals with different incompatible text telephone technologies from different countries to be able to interact successfully
• Allows individuals using a wide range of text chat technologies to be able to use these technologies transparently to communicate with individuals using other text chat technologies as well as traditional analog text telephones

T-hybrid provides a natural path for connecting analog with digital. It would allow anyone to continue using text telephones, and still communicate freely with friends who have moved to digital technologies. Finally, T-hybrid would allow different companies or industry segments freedom in implementing different strategies as long as they provide the equivalent translation capabilities.

Functionality:

Recommendations and standards supported:

Requirements for an IP device calling through T-hybrid: