Hobbes 256850 NETmapper Network Cable Tester is a unique and versatile tool for professional network administrators to quickly verify network connectivity and get essential information from the entire network for troubleshooting. Hobbes 256850 NETmapper is both an online active network tester and an offline cable checker. It can also check for polarity and voltage of telephone lines. The NETmapper also has an analog tone generator and portfinder function for network cable and port identification.