Echo control in VoIP

Abstract

The challenges faced in echo control in voice over the Internet Protocol (VoIP) are discussed. There are primarily two classes of echo in telephone conversation. The first class is due to the use of a 2-to-4 wire conversion using hybrid circuits. Echo control of this class is achieved by a line echo canceller (LEC). The other class is due to the use of handsfree mechanisms where there is significant acoustical feedback coupling between the receiver speaker and the receiver microphone. Echo control of this class is achieved using an acoustic echo canceller (AEC). The design of double-talk detectors is a challenge for VoIP gateway design. Another challenge seen in deploying VoIP with voice gateways to interface with PSTN is that some PSTN local loops have strange characteristics. It is highly desirable to measure echo at the end user of an IP phone with multi-vendor networks. An important impairment, that is to be measured, is echo with its echo path loss and its associated round-trip delay.