The ratified standards of copper Ethernet cables dictate that they should only be used for distances of up to 100 metres. Fibre optics are used for longer distances. There are, however, products called Ethernet Extenders which use low grade copper cable (eg telephone cable) or coax CCTV cable can transmit for many km, the data rate generally decreasing with distance. These are especially useful when existing cabling is in place and high bandwidth is not required.