Digital frequency receiver
Call progress signal monitor and method for telephone systems
Digital tone decoder and method of decoding tones using linear prediction coding
Distance measurement control of a multiple detector system
Arrangement for determining switch port status at an adjunct processor
Configurable parameter DTMF detector
Digital signal processor synchronous network
Switch adjunct integration arrangement
Dual tone multifrequency signal detection and identification methods and apparatus
Telephone signal classification and phone message delivery method and system
ApplicationNo. 169564 filed on 12/17/1993
US Classes:379/377, Using line or loop condition detection (e.g., line circuit)370/526, Digital tone detection379/282, Voice frequency receiver379/283, Dual tone multifrequency (DTMF) receiver379/386Signal receiver (e.g., tone decoder)
ExaminersPrimary: Dwyer, James L.
Assistant: Saint-Surin, Jacques M.
Attorney, Agent or Firm
International ClassH04M 001/00
AbstractA substantially-universal detector (FIG. 2) of far-end call disconnect-indicative tones detects the foreseeable forms of tone-based signalling of remote-end call disconnect that are likely to be employed anywhere in the world, without reconfiguration or reprogramming for different tones or countries. Implemented in the digital signal processor (DSP 30) of port circuits (14, 20) of switching systems (11) or adjunct processors (12), the detector determines parameters (204) of signals carried by the call to the near end and uses them, along with already-present linear predictive coding (LPC) predictor coefficients (202) and indications of energy (203) in the signals, in a multivariate classification (230) of call progress tones from other tones. When presence of any call progress tones is thus detected substantially without interruption for a predetermined minimum time in the received signals, the call is considered (240) to have been disconnected at the far end. In response, a voice messaging system (VMS) adjunct processor, (12) deletes any recording of the call progress tones from the end of the recorded message.