Echo cancellation in voice telephony over ATM networks
Aparna Rane, Arne A. Nilsson · NCSU Libraries Repository (North Carolina State University Libraries) · 1999
Forecasts for the year 2002 estimate that close to 20% of all domestic phone trac will be carried over data lines, up from less than just 1% now.Organizations around the world want to reduce rising communications costs.The consolidation of separate voice and data networks oers an opportunity for signicant savings.However, it will take a while for a large Public Switched Telephone Network (PSTN) to migrate completely to a B-ISDN architecture.As a result, services such as voice applications (Voice and Telephony Over AT M -V T O A) require the interworking of the ATM-based B-ISDN and PSTN.One of the key issues in addressing the QoS for such a service of interworking voice connections is the echo problem, especially the talker echo.Echo becomes an issue in Voice over packet networks because the round-trip delay through the network is almost always greater than 50msec.Thus, echo cancellation techniques are always used.The echo cancellers can be located either in the subscriber line unit where echoing occurs because of the hybrid circuits or at the entrance to the ATM network.The rst method is not practical because of the numberof local switches that would require modication.The latter has economic disadvantages too.As the ATM networks expand, it will be necessary to remove previously installed entrance based ECs and install new ones at other locations.These problems could be overcome if we placed the echo canceller inside the ATM network.In this study we simulate a ATM network-based echo canceller.The echo canceller is implemented using the LMS (Least Mean Squares) algorithm.We have considered the performance of the echo canceller under various echo path delays and corresponding number of lter taps.Our results show t h a t a n e c ho canceller can be successfully implemented inside the ATM network.