scope:

Introduction

The following standard provides an option for extending the current TIA/EIA-136-410 EFR Speech Vocoder standard to reliably transport the TTY/TDD 45.45 bps and 50 bps Baudot code, making digital wireless technology accessible to TTY/TDD users.

The extension is separated into two major components. Section 3 describes the new interface between the encoder and the decoder for transporting the TTY information. Section 4 is a description of the TTY/TDD software simulation of this extension, and is offered only as a recommendation for implementation. In the event of ambiguous or contradictory information between the software simulation and its description in Section 4, the software simulation shall supersede the text.

Implementers may use the example solution as a bit-exact implementation of this extension. The accompanying software distribution contains fixed-point C source code for this extension as well as a suite of test vectors for verifying bit-exact implementations. Note, the sample simulation does not contain a mechanism for blocking reflected Baudot tones. (See Section 3.2.2) The software distribution shall accompany this standard, for example, on the same CDROM, from the same internet site. These TTY test vectors are in addition to the speech test vectors supplied under TIA/EIA-136-410 for verifying bit-exact implementations of the core vocoder. Non-bit exact implementations of the TTY/TDD extension shall be verified by TIA/EIA/IS-840-A Minimum Performance Specification for TDMA/TTY/TDD.

This standard uses the following verbal forms: "Shall" and "shall not" identify requirements to be followed strictly to conform to the standard and from which no deviation in permitted. "Should" and "should not" indicate that one of several possibilities is recommended as particularly suitable, without mentioning or excluding others; that a certain course of action is preferred but not necessarily required; or that (in the negative form) a certain possibility or course of action is discouraged but not prohibited. "May" and "need not" indicate a course of action permissible within the limits of the standard. "Can" and "cannot" are used for statements of possibility and capability, whether material, physical, or causal.