void callback(char *topic, byte *payload, unsigned int length) {
  int i;
  String requestCmdMsg;
  for (i = 0; i < length; i++) {
    requestCmdMsg += String((char)payload[i]);
  }
  Serial.print("requestCmdMsg="); Serial.println(requestCmdMsg);
  parseCmdRequestMsg(requestCmdMsg);
  if (cmdRequestMsg.command.equals(CMD_GET_SENSOR_ID)) {
    handleGetSensId();
  } else if (cmdRequestMsg.command.equals(CMD_BATT)) {
    handleGetBattery();
  } else if (cmdRequestMsg.command.equals(CMD_SET_MODE)) {
    handleSetMode();
  }
}