This structure describes destination information to send response. It is initialized by calling pjsip_get_response_addr().
If the response message should be sent using transport from which the request was received, then transport, addr, and addr_len fields are initialized.
The dst_host field is also initialized. It should be used when server fails to send the response using the transport from which the request was received, or when the transport is NULL, which means server must send the response to this address (this situation occurs when maddr parameter is set, or when rport param is not set in the request).