# Setting or retrieving the nonlinear processing state

Nonlinear processing (NLP) removes residual echo by attenuating the return path when there is no far-end speech. Natural-sound, adaptive-threshold, NLP technology provides excellent voice quality while avoiding signal clipping. The NLP control allows you to enable or disable the NLP feature for a trunk port. NLP is enabled by default.

Use swiConfigLocalTimeslot to enable or disable NLP and swiGetLocalTimeslotInfo to retrieve the current setting. Set the arguments for these functions as follows:

Argument | Field | Value
swihd |  | Handle returned by swiOpenSwitch.
args | localstream | Identifies the target trunk on the local bus. Specify the number of either the transmit or receive voice stream. Refer to CG 6565 switch models for more information.
localtimeslot | Identifies the target timeslot on the trunk. Specify the timeslot number of the target trunk port on the local bus. Refer to CG 6565 switch models for more information.
deviceid | Device type on the local bus. The deviceid is MVIP95_T1_TRUNK_DEVICE or MVIP95_E1_TRUNK_DEVICE. For information about the deviceid, refer to the Dialogic® NaturalAccess™ Point-to-Point Switching API Developer's Manual.
parameterid | Data item to configure or query. Set to NMS_ECHO_CHANNEL_NLP (0x80000020).
buffer |  | Points to the NMS_ECHO_CHANNEL_NLP_PARMS structure. Valid values are: 0 = NMS_ECHO_DISABLE_NLP 1 = NMS_ECHO_ENABLE_NLP
size |  | Size of buffer, in bytes.

The NMS_ECHO_CHANNEL_NLP_PARMS structure is:

typedef struct
{
DWORD enable_NLP; // 0=no NLP, 1=NLP enabled
} NMS_ECHO_CHANNEL_NLP_PARMS;

For swiGetLocalTimeslotInfo, the value returned from the NMS_ECHO_CHANNEL_NLP_PARMS structure indicates whether the echo cancellation nonlinear processing is enabled or disabled for the specified device.

For more information about swiConfigLocalTimeslot or swiGetLocalTimeslotInfo, refer to the Dialogic® NaturalAccess™ Point-to-Point Switching API Developer's Manual.

## Setting the NLP state example

The following example shows how to enable or disable NLP:

#include "swidef.h" /* Switching service */
#include "mvip95.h" /* MVIP-95 definitions */
#include "nmshw.h" /* Hardware-specific definitions */
DWORD mySetNLP(SWIHD swihd, SWI_TERMINUS terminus, int bNLPEnabled)
{
SWI_LOCALTIMESLOT_ARGS args;
NMS_ECHO_CHANNEL_NLP_PARMS parms;
args.localstream = terminus.stream; /* from board switch model */
args.localtimeslot = terminus.timeslot; /* from board switch model */
args.deviceid = MVIP95_T1_TRUNK_DEVICE; /* mvip95.h */
args.parameterid = NMS_ECHO_CHANNEL_NLP; /* nmshw.h */
if (bNLPEnabled)
parms.enable_NLP = NMS_ECHO_ENABLE_NLP; /* nmshw.h */
else
parms.enable_NLP = NMS_ECHO_ENABLE_NLP; /* nmshw.h */
return swiConfigLocalTimeslot (
swihd, /* switch handle */
& args, /* target device and config item */
(void*) & parms, /* buffer (defined by parameterid) */
sizeof(parms)); /* buffer size in bytes */
}

## Retrieving the NLP state example

The following example shows how to retrieve the echo canceler NLP setting:

#include "swidef.h" /* Switching service */
#include "mvip95.h" /* MVIP-95 definitions */
#include "nmshw.h" /* Hardware-specific definitions */
DWORD myGetNLP(SWIHD swihd, SWI_TERMINUS terminus, int* pbNLPEnabled)
{
SWI_LOCALTIMESLOT_ARGS args;
NMS_ECHO_CHANNEL_NLP_PARMS parms;
DWORD swi = SWI_SUCCESS;
args.localstream = terminus.stream; /* from board switch model */
args.localtimeslot = terminus.timeslot; /* from board switch model */
args.deviceid = MVIP95_T1_TRUNK_DEVICE; /* mvip95.h */
args.parameterid = NMS_ECHO_CHANNEL_NLP; /* nmshw.h */
swi = swiGetLocalTimeslotInfo (
swihd, /* switch handle */
& args, /* target device and config item */
(void*) & parms, /* buffer (defined by parameterid) */
sizeof(parms)); /* buffer size in bytes */
if (parms.enable_NLP == NMS_ECHO_ENABLE_NLP) /* nmshw.h */
*pbNLPEnabled = 1; // true
else
*pbNLPEnabled = 0; // false
return swi;
}