TIA TIA-889-A

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INTRODUCTION

Persons with hearing impairments or speech impediments are ableto communicate over the telephone using TTY/TDD (teletype/texttelephone devices for the deaf), hereafter referred to as TTYdevices. these devices typically have a keyboard and a 2-linedisplay, allowing a TTY user to type messages over the phone linesto another TTY user. TTY devices transmit the characters at either45.45 bps or 50 bps using the Baudot code, a binary frequency shiftkeyed scheme that is carrierless, half duplex, and without errorprotection.

In June 1996, the FCC adopted Section 20.18(c) of theCommission’s Rules. It requires that, as of October 1, 1997, allcovered wireless carriers must be capable of transmitting 911 callsfrom individuals with speech or hearing disabilities through meansother than mobile radio handsets, e.g., through the use of TTYdevices. The pre-existing digital wireless networks have renderedTTY conversations unintelligible. The frame and bit errors thatoccur over the air, as well as the variable rate speech coding,character error rates.

The purpose of this standard is to establish minimum performancerequirements and a test procedure for verifying solutions fortransporting the Baudot code over IS-2000/IS-95 wireless networksusing IS-733 13K Vocoder, IS-127 EVRC, and IS-893 SMV. Anelectronic package containing tools and test vectors for thepurpose of performing these minimum performance tests accompaniesthis standard.

For the remainder of this document, the term test vocoder refersto the speech coder with TTY extension for which compliance withthis document is being verified. The term reference vocoder refersto the C simulation of the vocoder with the most recent TTYextension, which is provided in the accompanying electronicpackage.

This specification uses the following verbal forms: “Shall” and”shall not” identify requirements to be followed strictly toconform to the standard and from which no deviation is permitted.”Should” and “should not” indicate that one of severalpossibilities is recommended as particularly suitable, withoutmentioning or excluding others; that a certain course of action ispreferred but not necessarily required; or that (in the negativeform) a certain possibility or course of action is discouraged butnot prohibited. “May” and “need not” indicate a course of actionpermissible within the limits of the standard. “Can” and “cannot”are used for statements of possibility and capability, whethermaterial, physical, or causal.

Edition:

A

Published:

12/01/2003

Number of Pages:

24

File Size:

1 file , 220 KB