Error correction method and apparatus for TTY on VoIP...

Multiplex communications – Duplex – Transmit/receive interaction control

Reexamination Certificate

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Details

C370S356000, C370S493000, C379S052000, C379S088170, C379S093180

Reexamination Certificate

active

07379431

ABSTRACT:
The present invention is directed to a system for reliably transmitting characters encoded as audible signals using voice over Internet protocol communication systems. According to an embodiment of the present invention, tones within a sequence of tones encoding a textual character are transmitted using two data packets. The first data packet includes a segment of time having a starting boundary that is synchronized with the start of the encoded tone and extending for a time period equal to about one-half the total time period of the tone. The second packet encodes the remaining half of the audible tone. At the receiving end, data packets encoding a textual character are ordered according to the position occupied by the data encoded by the packet within the sequence of tones. If any unpaired packets of data are detected at the receiving end, the characteristics of the packets that are unpaired are copied into the time slot that would have been occupied by the missing packet. Accordingly, the present invention allows for the accurate transmission of textual characters over VoIP networks, even where a packet of data encoding part of a sequence of packets encoding a character is dropped.

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“Access for 9-1-1 and Telephone Emergency Services,” Americans with Disabilities Act, U.S. Department of Justice, Civil Rights Division (Jul. 15, 1998), available at http://www.usdoj.gov/crt/ada/911ta.htm, 11 pages.
H. Schulzrinne et al., “RFC 2833—RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals,” Network Working Group Request for Comments 2833 (May 2000), available at http://www.faqs.com/rfcs/rfc2833.html, 23 pages.
G. Hellstrom et al., “RFC 2793—RTP Payload for Text Conversation,” Network Working Group Request for Comments 2793 (May 2000), available at http://www.faqs.org/rfcs/rfc2793.html, 8 pages.

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