Error correction method and apparatus for TTY on VoIP transmissions
View Patent ↗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.
1. A method for providing signal tones in a voice communication system, comprising:
receiving a first signal tone having a first length;
creating a first data packet encoding a first portion of said first signal tone, wherein said first portion of said first signal tone has a second length; and
creating a second data packet encoding a second portion of said first signal tone, wherein said second portion of said first signal tone has a third length, wherein said second length and said third length are each about equal to one-half said first length.
2. The method of claim 1 , wherein said first packet of data encoding said first portion of said first signal tone comprises a digital representation of said audible signal synchronized to a start of said audible tone.
3. The method of claim 1 , further comprising:
providing said first and second data packets to a communication channel.
4. The method of claim 1 , wherein said first signal tone is an audible tone, and wherein said step of creating first and second data packets encoding said first and second portions of said first signal tone comprises creating a digital representation of said audible tone.
5. The method of claim 1 , wherein said voice communication system comprises a voice over Internet protocol communication system.
6. The method of claim 3 , further comprising:
receiving a voice communication;
providing said voice communication to said communication system.
7. The method of claim 3 , further comprising:
receiving packets of data encoding a sequence of signal tones, wherein each of said tones is encoded by a first and a second packet of data;
decoding said received packets of data;
displaying a textual character corresponding to said sequence of signal tones.
8. The method of claim 3 , further comprising:
receiving packets of data encoding a sequence of signal tones, wherein a first and a second packet of data is expected in connection with each of said signal tones, and wherein only a one of said first and second packets of data is received with respect to at least one signal tone included in said sequence of signal tones;
generating a missing portion of said at least one signal tone for which only a one of said first and second packets of data is received;
displaying a textual character corresponding to said sequence of signal tones.
9. The method of claim 8 , wherein said step of generating a missing portion of said at least one signal tone for which only a one of said first and second packets of data is received comprises duplicating said data within said received packet of data.
10. The method of claim 8 , wherein said step of generating a missing portion of said at least one signal tone for which only a one of said first and second packets of data is received comprises duplicating said received packet.
11. The method of claim 1 , wherein said first signal tone is part of a sequence of tones comprising a Baudot character.
12. The method of claim 1 , further comprising:
receiving voice data;
creating a plurality of data packets encoding said voice data, wherein each of said data packets encodes a portion of said received voice data having a length about equal to one-half said first length.
13. The method of claim 1 , wherein said first length is about 22 ms, wherein said second length is about 11 ms, and wherein said third length is about 11 ms.
14. The method of claim 1 , wherein said first length is about 20 ms, wherein said second length is about 10 ms, and wherein said third length is about 10 ms.
15. A method of transmitting textual characters over a packet data voice communication network, comprising:
receiving a first data packet, wherein said first data packet contains data regarding a first portion of a first audible tone;
receiving a second data packet, wherein said second data packet contains data regarding a second portion of said first audible tone;
receiving a third data packet, wherein said third data packet contains data regarding a first portion of a second audible tone; and
generating from said data regarding a first portion of a second audible tone data corresponding to a second portion of said second audible tone.
16. The method of claim 15 , wherein said step of generating comprises copying said third data packet.
17. The method of claim 15 , wherein said step of generating comprises copying said data regarding a first portion of said second audible tone from said third data packet.
18. The method of claim 15 , further comprising:
detecting that said third data packet is unpaired.
19. The method of claim 15 , wherein said first data packet is received after at least one of said second data packet and said third data packet, said method further comprising:
reordering said packets, wherein said first packet is positioned before said second data packet and said second data packet is positioned before said third data packet.
20. The method of claim 15 , wherein said data regarding a first portion of said second audible tone comprises a first half of said second audible tone, and wherein said generated data regarding a second portion of said second audible tone comprises a second half of said second audible tone.
21. The method of claim 15 , wherein said data regarding a first portion of said second audible tone comprises a second half of said second audible tone, and wherein said generated data regarding a second portion of said second audible tone comprises a first half of said second audible tone.
22. A system for transmitting textual characters in connection with a voice over Internet protocol communication system, comprising:
textual data input means;
means for encoding said textual data as a sequence of audible tones;
means for packetizing said encoded textual data, wherein each encoded audible tone within a sequence of audible tones is distributed between at least first and second packets of data such that for each audible tone in said sequence a first half of said audible tone is encoded by said first packet and a second half of said audible tone is encoded by said second packet.
23. The system of claim 22 , further comprising:
packet data transmission means, wherein said sequence of audible tones may be transmitted from a first location to a second location.
24. The system of claim 22 , further comprising:
means for receiving data packets containing a sequence of audible tones;
means for decoding said sequence of audible tones;
means for displaying textual data.
25. The system of claim 24 , further comprising:
means for reconstructing missing data, wherein data encoded by a one of said at least first and second packets encoding an audible tone that is not received by said means for receiving within a predetermined time period is reconstructed from a received one of said at least first and second packets.
26. The system of claim 22 , further comprising: means for receiving voice data, wherein said means for packetizing creates packets of data representing received voice data.
27. A device for transmitting textual characters in connection with a voice communication system, comprising:
a tone generator for creating a sequence of audible tones representing a textual character;
an encoder for creating a digital representation of said audible signal;
a packetizer for creating packets of data comprising said digital representation of said audible signal, wherein each audible tone comprising said sequence of audible tones is provided to said communication system as at least two packets of data each containing one-half of said audible tone.
28. The device of claim 27 , wherein said tone generator creates tones for representing characters using Baudot signaling.
29. The device of claim 27 , wherein a first of said packets of data comprising an individual audible tone comprises a digital representation of said audible signal synchronized to a start of said audible tone.
30. The device of claim 27 , further comprising:
a receiver for creating an electrical representation of said audible tones representing a textual character.
31. The device of claim 27 , wherein each audible tone comprising a sequence of audible tones is provided to said communication system as a pair of packets, said device further comprising:
a depacketizer, wherein characteristics of a first packet of data of a pair of packets are copied into a second packet of data.
32. The device of claim 27 , wherein said packets of data comprise voice over Internet protocol data packets.