This part of IEC61156 describes cables primarily intended for the fixed part of channels as defined in ISO/IEC11801 and in ISO/IECTR11801‑9901 which is planned to be included in the next edition of ISO/IEC11801‑1 . It covers overall screened cables with screened (X/FTP) or unscreened (X/UTP) pairs, where X stands for F, S or SF, as well as pair-screened cables without overall screen (U/FTP). The transmission characteristics of these cables are specified up to a frequency of 2000MHz and at a temperature of 20°C. Two categories of cables are recognised: Category8.1 for use in Class I according to ISO/IECTR11801‑9901 ; Category8.2 for use in Class II according to ISO/IECTR11801‑9901 . These cables are intended to be used for communication channels which use at least four pairs simultaneously. The cables covered by this International Standard are intended to operate with voltages and currents normally encountered in communication systems. While these cables are not intended to be used in conjunction with low impedance sources, e.g. the electric power supplies of public utility mains, they are intended to be used to support the delivery of low voltage remote powering applications such as IEEE802.3af (Power over Ethernet) or further developments e.g. according to IEEE802.3at or IEEE802.3bt. More information on the capacity to support these applications according to the installation practices is given in IECPAS61156‑1‑4 , IECTR61156‑1‑6 and ISO/IECTR29125 .