Also known as a network interface unit (NIU). A device that serves as the demarcation point (demarc) and interface between the public carrier network and the customer premises. An NID includes some form of protector that insulates the premises from potentially disastrous high voltage current caused by lightening strikes on outside copper cable plant. An NID also generally contains a chipset that supports remote testing of the local loop from a centralized Network Operations Center (NOC).