# Connecting TPKT endpoints

Applications use mspConnect to join TPKT endpoints with MSPP channels to create end-to-end gateway media paths. TPKT endpoints can connect with the following MSPP service channel types:

Channel type | Payload data rate | Basic frame duration | VAD support | Recommended frames/packet
G.711 | 64 kbit/s | 10 ms | N/A | 1
G.723.1 | 6.4 kbit/s or 5.33 kbit/s | 30 ms | G.723.1 Annex A | 1
G.729A | 8 kbit/s | 10 ms | G.729 Annex B | 1
G.726 | 32 kbit/s | 10 ms | N/A | 1

T.38 fax channels are not currently supported for TPKT endpoints.

When maintaining 120 channels of voice data, using a number of frames per packet lower than the minimum indicated (for the specific vocoder) in the preceding table can exceed the CG board's processing capabilities. To reduce latency, use one frame per packet for all vocoders.

For more information about connecting MSPP endpoints and channels, refer to the MSPP Service Developer's Reference Manual.

## Configuring G.723.1 vocoders for use with TPKT endpoints

MSPP endpoints vocoders use static payload IDs as defined by RFC 1890. TPKT endpoints map to different payload IDs. The following table provides a mapping of TPKT vocoders to NMS vocoders:

Vocoder Description | TPKT Mapping | NMS Vocoder | NMS Payload ID
G.723.1 at 6.4 kbit/s | 1 | G723 | 4
G.723.1 at 5.33 kbit/s | 2 | G723 | (4) 127 *

As the table shows, the default payload ID the MSPP service associates with G.723.1 vocoders (4) assumes operation at 6.4 kbit/s. Applications can dynamically change the TPKT endpoint's payload ID to a value associated with 5.33 kbit/s operation (127) by invoking the MSPP service function mspSendCommand.

TPKT endpoints distinguish between G.723.1 vocoders running at 6.4 kbit/s and G.723.1 vocoders running at 5.33 kbit/s. Standard Fusion G.723.1 vocoders, in accordance with RFC1890, do not distinguish between these vocoder types. You must change the payload ID for G.723.1 voice encoders and decoders to 127 when configuring the G.723.1 channel for 5.33 kbit/s operation.

Applications perform the following steps to configure TPKT endpoints to use G.723.1 encoders or decoders for 5.33 kbit/s operation.

Step | Action
1 | Set the coderType parameter in the TPKT endpoint msp_TPKT_ENDPOINT_CONFIG structure to kG723Low. If the application is creating the endpoint, it can specify this parameter in the endpoint's configuration parameters. If the endpoint is already created, the application must disable the endpoint first, and then send a command to the endpoint to change its coderType to kG723Low. For more information about sending commands to TPKT endpoints, refer to Sending commands to TPKT endpoints.
2 | Send a command to the voice decoder filter to change the decoder payload ID to 127.
3 | Send a command to the voice encoder filter to change encoder payload ID to 127.
4 | Send a command to the voice encoder filter to change the encoder rate to 53.

For more information about sending commands to MSPP endpoints, refer to the Dialogic® NaturalAccess™ Media Stream Protocol Processing API Developer's Manual.