Abstract: Method and apparatus for altering a round trip delay measurement in a multiple subscriber carrier pair gain system to accurately position echo cancellation where the overall delay is measured by the near end modem and when this measurement is made, it is detected to alter local delays by bypassing filters and buffers to momentarily shorten the overall delay until the measurement is completed. Alternatively, the return signal is interrupted and the round trip delay response is simulated when a round trip delay measurement is being made. In this manner, the simulated signal is received at the originating end and used for delay measurement resulting in a shorter delay being measured.

Abstract: Method and system for implementing digital filters in the data path of a Pulse Code Modulated (PCM) modem to allow efficient transition of a second analog to digital conversion process in a communication system including monitoring the upstream data path of the communication system to decode the V.34 portion of the data transmission which occurs during the handshake phase of the modem call, where the information contained in the upstream data channel during the handshake phase allows the communication system to determine the manner in which the PCM modem is training and transmitting data to the client modem.

Abstract: Method and system for implementing digital filters in the data path of a Pulse Code Modulated (PCM) modem to allow efficient transition of a second analog to digital conversion process in a communication system including monitoring the upstream data path of the communication system to decode the V.34 portion of the data transmission which occurs during the handshake phase of the modem call, where the information contained in the upstream data channel during the handshake phase allows the communication system to determine the manner in which the PCM modem is training and transmitting data to the client modem.

Abstract: An improved circuit for generating phase and amplitude modulated signals in a modem. A first circuit (161) generates a first signal (163) using a 1200 Hz carrier (160) and an input data stream (162). This signal (163) is generated at the rate of 7200 samples per second. The first signal (163) is then sampled by a sampler (164) at a 3600 Hz rate (165). The sampled signal (166) contains both a 1200 Hz signal and a 2400 Hz signal. A bandpass filter (43) selects a 1200 Hz or a 2400 Hz center frequency. The resulting output (44) is a selectable 1200 Hz or 2400 Hz signal which is generated using only the data sampling points necessary to generate the first, 1200 Hz signal (163).

Abstract: An improved V.22 bis 2400 bits per second (bps) handshake sequence detector. An incoming phase keyed (PSK) handshake sequence is autocorrelated using a frequency shift keyed (FSK) receiver (101). The autocorrelated signal is then filtered by a low pass filter (106). The autocorrelated, low pass filtered signal is then alternately fed, at a 1200 Hz rate, to two detectors (114,116). Each of the detectors (114,116) looks for one half of the handshake sequence. The output of each detector (114,116) is provided to an OR-gate (122). The 2400 bps handshake sequence is declared to be detected when either one or both of the detectors (114,116) detects its corresponding portion of the sequence.