8.1. Echo Cancellation Resource Overview
This chapter describes the Echo Cancellation Resource feature, how it works, its modes of operation, as well as sample application models and sample code.
The Echo Cancellation Resource (ECR) feature is a functional component of a voice channel. In ECR mode, a voice channel can dynamically perform echo cancellation on any external SCbus time slot signal.
Prior to the implementation of the ECR feature in the Dialogic Voice Library, each voice channel device had a single transmit (TX) SCbus time slot assigned to it for data communication across the SCbus. To connect one device to another across the SCbus, an application would call xx_listen( ) on one voice or network device to connect to a second device's transmit channel. Any signal transmitted by the second device on its transmit channel (TX channel) would be received by the first device's receive channel (RX channel). For a full duplex connection, the second device would then call xx_listen( ) to connect its receive channel to the first device's transmit channel.
The Dialogic ECR feature provides the ability to utilize echo cancellation on signals external to the voice channel. The echo cancellation capability becomes a system-wide resource that may be applied to any SCbus PCM stream. The addition of the ECR feature allows the application to dynamically configure a voice channel as either an echo cancellation device (ECR mode) or as a standard voice processing channel (SVP mode). In ECR mode, a portion of the standard voice functionality remains available while another portion of it becomes unavailable. See section 8.2. How Echo Cancellation Resource Works for details.
For technical information on ECR functions such as parameters, see the Voice Software Reference Volume 2 (Programmer's Guide).
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