# Overview of channel structures

When creating MSPP channels with mspCreateChannel, you must specify channel configuration information in two structures:

- MSPP channel address structure

- MSPP channel parameters structure

## Channel address structure

When applications create MSPP channels with mspCreateChannel, they specify the following parameters in the MSP_CHANNEL_ADDR structure:

typedef struct tag_MSP_CHANNEL_ADDR
{
DWORD size;
DWORD nBoard;
MSP_CHANNEL_TYPE channelType;
DWORD FilterAttribs;
} MSP_CHANNEL_ADDR;

### MSP_CHANNEL_ADDR

#### Dependent function: mspCreateChannel

Field | Type | Default | Units | Description
size | DWORD | N/A | N/A | Size of the address structure.
nBoard | DWORD | N/A | N/A | Channel location (board number).
channelType | MSP_CHANNEL_TYPE | N/A | N/A | Type of MSPP channel. Can be one of the following values: G711FullDuplex G723FullDuplex G726FullDuplex G729FullDuplex FaxRelayFullDuplex G711EncodeSimplex G711DecodeSimplex G723EncodeSimplex G723DecodeSimplex G726EncodeSimplex G726DecodeSimplex G729EncodeSimplex G729DecodeSimplex RTPSwitching
FilterAttribs | WORD | Null | N/A | Enables or disables functionality in the channels. The following value is defined: MSP_FCN_ATTRIB_RFC2833: Enables inband DTMF carriage capability for the channel.

## Channel parameter structures

Depending on the type of channel specified with the MSP_CHANNEL_TYPE parameter in the MSPP endpoint channel parameter structure, you must specify parameters in the following structures:

Channel type | Structure
Voice encode/decode (G.723.1, G.729A, G.726 simplex or duplex) or record channel | MSP_VOICE_CHANNEL_PARMS
T.38 fax | MSP_FAX_CHANNEL_PARMS
RTP switching | None. Only address parameters are required for switch channels.

This section discusses the Voice channel parameter structure and the T.38 fax relay channel parameter structure.