Early detection of in-band signals in a packet voice transmitter with reduced transmission delay

• US 6,298,055 B1
• Filed: 10/26/1998
• Issued: 10/02/2001
• Est. Priority Date: 10/26/1998
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Wildfeuer, Herbert M.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): PHAM, BRENDA H
• Application Number:
  US09/179,546
• Time in Patent Office: 1,072 Days
• Field of Search: 375/217, 370/384, 370/496, 370/517, 370/522, 370/523, 370/524, 370/525, 370/526, 370/352, 370/353, 370/354, 370/373, 370/377, 379/386, 379/351, 379/93.26
• US Class Current: 370/352
• CPC Class Codes: H04L 12/6418 Hybrid transport
• CPC Class Codes: H04L 2012/6459 Multiplexing, e.g. TDMA, CDMA
• CPC Class Codes: H04L 2012/6481 Speech, voice
• CPC Class Codes: H04L 2012/6486 Signalling Protocols
• CPC Class Codes: H04M 7/1295 Details of dual tone multiple frequency signalling

Abstract

A packet voice transmitter and method of transmitting digital audio signals are disclosed that detect and alter transmission processing for in-band signals such as DTMF signals. The present invention allows a digital audio data stream to be sent without delay when in-band signals are not present by detecting the possible presence of in-band signals early, i.e., before an entire in-band signal symbol has been received. In one embodiment, a DTMF signature detector 58 operates in parallel with a voice encoder 56 on a digital audio data stream 20. If a frame from data stream 20 resembles a leading portion of a DTMF signal, DTMF signal detection manager 60 shifts encoded audio data frames from encoded audio data stream 70 into a frame delay buffer 66 while further frames are examined for DTMF signal consistency. If a complete DTMF signal is received, buffer 66 is flushed and a DTMF signal is transmitted out-of-band in a separate packet. If a potential DTMF signal turns out to be a false alarm, frames delayed in buffer 66 are supplied to packetizer 62 for transmission. As long as no potential DTMF signals are detected, encoded audio data stream 70 is allowed to proceed directly from voice encoder 56 to packetizer 62 without delay.

Claims

1. A packet voice transmitter comprising:

a frame delay buffer;

a frame-based voice encoder incorporated into first and second voice data paths through said transmitter, said first data path bypassing said frame delay buffer and said second data path including said frame delay buffer;

an in-band signal signature detector; and

an in-band signal detection manager configured to select one of said first or second data paths and control operation of said frame delay buffer in response to the output of said in-band signal signature detector.

2. The packet voice transmitter of claim 1, wherein said in-band signal signature detector is a frame-based signature detector operating on common frames with said voice encoder.

3. The packet voice transmitter of claim 1, wherein said in-band signal signature detector detects dual-tone multifrequency signals.

4. The packet voice transmitter of claim 1, further comprising a packetizer that accepts voice-encoded frames from said frame-based voice encoder and assembles packets containing said voice-encoded frames for transmission.

5. The packet voice transmitter of claim 4, wherein said frame delay buffer accepts voice-encoded frames from said frame-based voice encoder, and wherein said packetizer accepts voice-encoded frames alternately from said frame delay buffer.

6. The packet voice transmitter of claim 4, wherein said frame delay buffer accepts packets from said packetizer, and provides an alternate source of packets for transmission by said transmitter.

7. The packet voice transmitter of claim 1, wherein said frame-based voice encoder and said in-band signal detector operate in parallel on voice data.

8. The packet voice transmitter of claim 1, wherein said in-band signal detection manager controls whether said frame-based voice encoder processes each frame of voice data.

9. The packet voice transmitter of claim 8, wherein said frame delay buffer holds frames of voice data prior to encoding of said frames by said voice encoder.

10. The packet voice transmitter of claim 1, wherein said frame delay buffer holds frames of voice data prior to encoding of said frames by said voice encoder.

11. The packet voice transmitter of claim 1, wherein said frame-based voice encoder and said in-band signal signature detector are implemented on a common microprocessor.

12. A packet voice transmitter comprising:

a frame delay buffer;

a frame-based voice encoder incorporated into first and second encoded voice data paths through said transmitter, said first data path bypassing said frame delay buffer and said second data path including said delay buffer;

a packetizer incorporated into said first and second encoded voice data paths;

a frame-based dual-tone multifrequency signal signature detector; and

a dual-tone multifrequency signal detection manager configured to select one of said first or second encoded voice data paths and control operation of said frame delay buffer in response to the output of said in-band signal signature detector.

13. The packet voice transmitter of claim 12, wherein said dual-tone multifrequency signal detection manager communicates the presence of dual-tone multifrequency signals to said packetizer.

14. The packet voice transmitter of claim 13, wherein said packetizer packetizes dual-tone multifrequency signals as out-of-band signal packets.

15. A method of transmitting digital audio signals, said method comprising the steps of:

encoding a first frame of digital audio samples, thereby producing a first audio-encoded frame;

identifying a potential in-band signal when said first frame of digital audio samples is consistent with a sampled leading portion of an in-band signal;

when a potential in-band signal is identified,

holding said first audio-encoded frame, while scanning one or more additional frames of digital audio samples for consistency with a sampled second portion of said in-band signal; and

queuing said first audio-encoded frame for packet transmission when no potential in-band signal is identified.

16. The method of claim 15, wherein when said scanning one or more additional frames step finds said one or more additional frames consistent with a complete in-band signal, discarding said first audio-encoded frame and queuing instead a signal corresponding to said in-band signal.

17. The method of claim 16, further comprising the step of, once a complete in-band signal has been detected, suspending said encoding step on additional frames of digital audio samples until a frame of samples inconsistent with said in-band signal is detected.

18. The method of claim 15, wherein when said scanning one or more additional frames step finds said one or more additional frames inconsistent with a complete in-band signal, queuing said first audio-encoded frame for packet transmission.

19. A method of transmitting digital audio signals, said method comprising the steps of:

scanning a stream of digital audio samples for a sequence of samples consistent with a leading portion of an in-band signal; and

when a sequence of samples consistent with a leading portion of an in-band signal is identified,

introducing a delay in transmission of said stream of digital audio samples while verifying the presence or absence of said in-band signal.

20. A method of transmitting digital audio signals, said method comprising the steps of:

scanning an audio stream for consistency with a leading portion of an in-band signal; and

upon detection of a leading portion of an in-band signal within said incoming audio stream,

digitally delaying said audio stream while verifying the presence or absence of said in-band signal.

21. A method of transmitting digital audio signals, said method comprising the steps of:

scanning a stream of digital audio samples for consistency with a leading portion of an in-band signal;

dividing said stream of digital audio samples into a sequence of input frames of digital audio samples;

encoding each of said input frames, thereby producing a sequence of encoded audio frames; and

transmitting each of said encoded audio frames at the earliest possible transmission time, unless said scanning step has identified digital audio samples corresponding to that encoded audio frame to be consistent with a portion of an in-band signal at said earliest possible transmission time.

22. The method of claim 21, further comprising the step of skipping said encoding step for an input frame when it is known prior to said encoding step that an encoded audio frame corresponding to that input frame is not needed.