In the field of packet communications, for example Internet Protocol (IP) telephony, it is known to communicate voice data over a communications network, for example a packet switched network, employing a suitable transport protocol. One known type of transport protocol is the Real-time Transport Protocol (RTP). Typically, voice data is arranged in frames and received by a so-called Vocoder (Voice Encoder). The vocoder employs a compression algorithm in order to reduce bandwidth of voice data transmitted over the network, the compressed voice data being provided to an RTP encoder for generating RTP-compliant packets containing the voice data as payload. When communicating over the network, it is sometimes desirable to communicate Dual Tone Multi-Frequency (DTMF) signals, particularly when a user needs to interact with an automated system, for example an automated call direction system. However, communication of a DTMF signal “in-band” via the vocoder results in degradation of the DTMF signal due to the use of the compression algorithm, the compression algorithm having been designed for compressing voice signals and not DTMF tones. In order to avoid the degradation of the DTMF signal resulting from in-band communication of the DTMF signal, the Internet Engineering Task Force (IETF) Request For Comments (RFC) 2833 provides a framework for communicating the DTMF signal “out-of-band”.
A DTMF detector is therefore employed in order to detect the DTMF signal and communicate data identifying the nature of the DTMF signal to an RFC 2833 encoder, the RFC 2833 encoder being coupled to the RTP encoder for communication of the data identifying the DTMF signal to a receiver where the DTMF signal is regenerated based upon the data identifying the DTMF signal. In order to provide uniformity in relation to DTMF signals, the Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T) Recommendation Q.24 specifies certain conditions for a DTMF signal to observe in order to qualify as a bona-fide DTMF signal. However, known DTMF detectors are prone to mis-detecting certain signals having durations less than those specified by the Q. 24 Recommendation, for example facsimile transmission tones, as bona-fide DTMF signals, resulting in DTMF tones being regenerated at the receiver in error.
Furthermore, DTMF detectors are known to suffer from so-called DTMF leakage that can effectively became appended to a given DTMF signal, thereby extending the duration of the given DTMF signal and hence reduce a so-called “pause duration” between DTMF signals. Consequently, the pause duration can reduce below a pause duration specified in the Q. 24 Recommendation and hence no longer be compliant with the Q. 24 Recommendation. The receiver, operating in accordance with the Q. 24 Recommendation and receiving consecutive DTMF signals will reject one or more received DTMF signals as non-compliant with the Q. 24 Recommendation and hence not recognised.
USPTO Backgrounds
USPTO Backgrounds