Abstract: Apparatus and accompanying methods for use in a long-haul echo control device to automatically measure sufficient changes in path length and compensate a long-haul echo canceller for resulting variations in echo occurring over a path. The apparatus measures a round-trip path delay interval of, e.g., a predefined signaling tone(s) sent between international switching centers while establishing an outbound call connection over the path. Once the delay is measured, the apparatus sets echo delay of a corresponding long-haul echo canceller to accommodate that delay. For a multi-channel facility (e.g., T1 or E1), path delay is separately measured for each channel on that facility, and then the apparatus changes the echo delay to the same amount for the corresponding echo canceller associated with each and every channel on that facility.

Abstract: Apparatus and accompanying methods for use in a long-haul echo control device to automatically measure sufficient changes in path length and compensate a long-haul echo canceller for resulting variations in echo occurring over those paths. Specifically, the inventive apparatus measures a round-trip path delay interval of, e.g., a predefined signalling tone(s) sent between international switching centers during the course of establishing an outbound call connection over that path. Once this delay interval is measured, the apparatus commensurately sets echo delay of a corresponding long-haul echo canceller to accommodate this path delay. For a multi-channel facility (e.g., T1 or E1), path delay is separately measured for each channel on that facility. Should the measured path delay sufficiently change for any one such channel, then the apparatus changes the echo delay to the same amount for the corresponding echo canceller associated with each and every channel on that facility.

Abstract: Apparatus for an echo canceller, and an accompanying method for use therein, for improving voice performance in handling mobile-to-mobile calls in a GSM environment, specifically with a base station controller (BSC) at each end of a call path where one BSC supports tandem free operation (TFO) and the other does not. Here, each canceller has a capability, through unique in-band messaging carried by robbed-bit signaling, to communicate information with its peer (distant) echo canceller across the call path so as to permit each canceller to coordinate its operation with the other, and particularly to enable a specific voice enhancement feature set optimal to a particular type of call, e.g., mobile-to-mobile, and without adversely affecting the TFO protocol.

Abstract: An echo suppressor (21, 22) monitors signal levels associated with the working environment of an echo canceler (16, 17) to prevent spurious transient responses from the canceler. These spurious responses typically occur before the echo canceler has had sufficient time to appropriately adapt which is also the time when a call is first established. At such times, signaling and maintenance testing are performed in a telecommunications network and the echo canceler tends to produce an output when there is no actual transmit input signal. The echo suppressor includes a comparator (26, 27) which detects the presence of this output and the absence of an actual transmit input signal and operates a switch. The switch prevents the transient echo from propagating on the transmit path.