TIA TIA-889-B

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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,conspired to create unacceptably high 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 cdma2000 [7] wireless networksusing 3GPP2 13K Vocoder [2], EVRC [1], SMV [8], EVRC-B, EVRC-WB,and EVRC-NW [1], corresponding to Service Options 17, 3, 56, 68,70, and 73, respectively. An electronic package containing toolsand test vectors for the purpose of performing these minimumperformance tests accompanies this 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.

Edition:

B

Published:

03/01/2012

Number of Pages:

33

File Size:

1 file , 340 KB