3com Corporation

Ying Wu

Stanley T Naudus

Daniel L Schoo

Vijay J Nadkarni

Leland Otis Thompson

Alexandre L Leonidov

Richard J Varman

Tom Gentles

Methods and systems pertaining to estimating and compensating for a round-trip or flat delay portion of an echo channel characteristic in an echo canceller are provided. According to a particular method, a filter coefficient vector of an adaptive filter that models the echo channel characteristic is updated. An instant flat delay is estimated by analyzing the filter coefficient vector after each update, and periodic averages of the instant flat delay estimate are performed. A final flat delay estimate average is determined when the flat delay estimate average has converged. The length of the adaptive filter is adjusted in response to the final flat delay estimate average. Further, an improved echo canceller apparatus that compensates for a flat delay portion of an echo channel characteristic is provided. The improved echo canceller includes an adaptive filter, a position detector, a periodic averager, and a level detector. The adaptive filter has an initial length N. The position detector is connected to the adaptive filter and locates the position of the maximum valued filter tap. The periodic averager is connected to the position detector and provides an average of the location position. The level detector responsive to the periodic averager provides a flat delay estimate, D. The adaptive filter shortens from the initial length N to a length N&minus;D, responsively to the flat delay estimate.

Round trip delay estimator and compensator for the echo canceller

A method and apparatus for distributing protocol processing among a plurality of computing platforms. Data communications equipment such as Remote Access Devices, Communication Servers, Terminal Servers, and Dial-up Routers provide single user or large-scale multiple user communication access to various computing environments. The equipment costs and performance of such access equipment is related to the amount of CPU processing capability and memory required to support the desired number of serial communication links. It is common to use protocols that terminate in their entirely in the same processing machine. This invention encompasses methods developed to increase the cost/performance capabilities of the communication equipment that supports these serial links, primarily by means of distributing the protocol processing for higher level protocols across multiple computing platforms, including devices such as modems. Examples of such higher level protocols include PPP, SLIP and RTP.

Distributed processing of high level protocols, in a network access server

An Acoustic Echo Control (AEC) device operates to reduce acoustic echo feedback in a speakerphone. An adaptive echo canceller responds to a far-end speech signal to generate an estimated echo which is subtracted from a near-end speech signal, to generate a compensated near-end speech signal. An Echo Return Loss (ERL) estimator provides an accurate but gradually adjusted estimate of the ERL of the echo canceller. A non-linear processor responds to the ERL estimation and provides additional attenuation to maintain the overall system ERL. The AEC device also incorporates dual talking mode detectors, one for the adaptive filter and one for the non-linear processor, to detect a plurality of talking modes, which are used to control the adaptation of the adaptive filter and the attenuation provided by the non-linear processor. A convergence indicator responds to the sudden echo path changes, and quickly corrects the ERL estimation; thereby adjusting the talking mode detector and the non-linear processor accordingly to maintain the overall system ERL and stability.

Echo control device with quick response to sudden echo-path change

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Grass Valley, CA, United States of America

Ying Wu