8.3.  Modes of Operation

• 8.3.1.  Standard Voice Processing Mode (SVP)
• 8.3.2.  Echo Cancellation Resource Mode (ECR)

When the ECR feature is enabled via the Dialogic Configuration Manager (DCM) on a supported board, there are two possible modes of operation: SVP and ECR.

Until ECR mode is activated, the board operates in the Standard Voice Processing (SVP) mode, which offers default echo cancellation. The ECR mode, which provides high performance echo cancellation, can be dynamically activated or deactivated on any voice channel of the enabled board.

8.3.1.  Standard Voice Processing Mode (SVP)

All voice channels are initially in the SVP mode with the default echo cancellation for ECR feature enabled boards. The SVP mode utilizes a 48 tap (6 ms) echo canceller.

In SVP mode, all Dialogic voice functions operate as usual, with one exception. If a channel in SVP mode is playing a file and listening (via a dx_listen( ) function), then playback transmits data on both the standard voice-transmit time slot and the echo cancellation-transmit time slot. The standard voice-transmit time slot carries the play signal. The echo cancellation time slot carries an echo-cancelled version of the signal from the receive time slot. This echo-cancelled signal is derived from the original play signal (the echo reference) and the signal from the receive time slot specified in the dx_listen( ) function (the echo carrying signal).

8.3.2.  Echo Cancellation Resource Mode (ECR)

Any voice channel can be placed into ECR mode via the dx_listenecr( ) or dx_listenecrex( ) function on an ECR feature enabled board. When a voice channel is placed in ECR mode, the echo reference SCbus time slot is specified and the high performance echo canceller is activated. The ECR mode supplies 128 tap (16 ms) echo cancellation.

When an echo carrying signal is provided as an input to the ECR by an associated dx_listen( ) function, an echo-cancelled version of that signal is produced on the echo cancellation SCbus time slot. If no echo carrying signal is defined, the contents of the echo cancellation transmit time slot are undefined and unpredictable. Other characteristics of the echo canceller can be set if the ECR mode is activated using the dx_listenecrex( ) function.

NOTE:

dx_listen( ) may precede or follow the dx_listenecr( ) or dx_listenecrex( ) function. If multiple dx_listen( ) and dx_listenecr( ) or dx_listenecrex( ) function calls are issued against a single channel, the echo cancellation operates on the last two issued. Successive dx_listenecr( ) or dx_listenecrex( ) functions can be issued without requiring any dx_unlistenecr( ) between them.

While a channel is in ECR mode, a number of standard voice operations are not available. The unavailable operations include the following:

Table 14.  Unavailable Voice Operations in ECR Mode

Unavailable Voice Operations in ECR Mode	Comment
Play	-
Record	8 KHz PCM record is the only supported record when a channel is in the ECR mode. Any such 8 KHz PCM record is a recording of the echo-cancelled signal.
Dial	-
Tone generation	-
R2MF	-
Transaction record	-

If a channel is actively performing any of the above operations, a dx_listenecr( ) or dx_listenecrex( ) function is not performed, and the function returns an error to the application. Conversely, if a channel is in ECR mode, a request for any of the these operations is not honored, except for the record noted. A channel may be returned to SVP mode dynamically via the dx_unlistenecr( ) function.

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