"dds.transport.UDPv4.builtin.send_socket_buffer_size"

On most operating systems, setsockopt() will be called to set the SENDBUF to the value of this parameter.

This value must be greater than or equal to "<TRANSPORT_PREFIX>.parent.message_size_max". The maximum value is operating system-dependent.

By default, it will be set to 131072.

If you configure this parameter to be -1, then setsockopt() (or equivalent) will not be called to size the send buffer of the socket. The transport will use the OS default.