Which communications protocol standard is most commonly used for TDD?

The most commonly used communications protocol standard for TDD (Telecommunications Device for the Deaf) is Baudot. This protocol is specifically designed for communication over telecommunication devices that were developed to assist individuals with hearing impairments.

Baudot is a code in which each character is represented by a fixed number of bits, allowing efficient transmission of information over limited bandwidth. The use of Baudot facilitates the sending and receiving of text messages in real-time, which is essential for effective communication in TDD applications. Its origins date back to early telegraph and typewriter technologies but have been adapted and widely utilized in teletypewriter communications.

In contrast, ASCII (American Standard Code for Information Interchange) is a character encoding standard but is not specifically tailored for TDD applications. Pulse Code Modulation (PCM) is a method used to digitally represent analog signals and is not a protocol specifically designated for text-based communication. ITU-T Recommendations, while encompassing various communication standards, do not focus solely on TDD protocols. Thus, Baudot stands out as the most fitting choice for TDD communications.