0x01DB Connection Mode

Use this TLV to set the connection mode. A line can be connected to receive only, transmit only, or both.
Used in:
Resource Attribute Configure message
Resource Attribute Query message

Byte | Description
0, 1 | Tag Connection Mode (0x01DB)
2, 3 | Length 0x0001
4 | Value[0] 0x00 Two-way connection 0x01 One-way listen/receive only 0x02 One-way talk/transmit only 0x03 Hold connection. No voice is transmitted or received. 0xFF (Default) You see this value only if you query the default settings of a VoIP module or when the call is not connected.

Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.
Voice over Internet Protocol. The delivery of voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public-switched telephone network (PSTN).