Patent Number: 6,298,055

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

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.

Inventors: Wildfeuer; Herbert M. (Santa Barbara, CA)

Assignee: Cisco Technology, Inc.

International Classification: H04L 12/64 (20060101); H04M 7/00 (20060101); H04L 012/66 (); H04L 012/50 ()

Expiration Date: 10/02/2018