Often you find devices that come with only RS 232 serial ports and there is no way to connect them to your computer that only has USB ports. Modems often are supplied only with ports of this type. The only way you could connect such a device to your laptop or the desk top is to use a Trendnet TU S9 cable which will have a USB connector in one end and a RS 232 connector at the other end. However, you need the driver to run it. In case you need Trendnet TU-S9 Driver you could download it here.