The classification of patch cables into categories 1 to 7 follows the general definition of classes A to G for connections and transmission channels in the ISO/IEC 11801 specification. The category therefore always designates a single component of a transmission channel.
In the case described here the cables, but it can also be, for example, the junction boxes or plugs and sockets, while the class designates the entire channel. Above class F, class G is still defined with subclasses I and II, and, analogously, cabling categories 8, 8.1 and 8.2 are defined. For modern cabling these are relevant from class D or Cat.5e
Cables of this category are used for class D transmission channels and are most commonly found in existing installations. They can transmit frequencies up to 100MHz and are divided into Cat.5 and Cat.5e. While Cat.5 supported fast Ethernet with 100Mbps, it was not suitable for Gigabit Ethernet and therefore holds no substantial place within the market. Cat.5e however, was a cable standard with improved NeXT and FeXT values that is used for 1000BaseT networks. This low-cost standard is therefore popular in the home and prosumer markets and is still widely used.
Category 6 cables belong to connection class E or EA and are therefore also divided into Cat.6 and Cat.6A (Cat.6 Augmented) for the transmission of frequencies up to 250 or 500MHz. Cat.6 cables are mainly used in data networks with multimedia applications and high network load. In order to meet the higher bandwidth requirements for 10 Gigabit Ethernet, Cat.6 cables are used. Cat.6A has been chosen as the category for frequencies up to 500MHz over a maximum of 100m. This means that in modern installations designed for 10GBASE-T you should always find at least Cat.6A cable.
Category 7 is divided into Cat.7 and Cat.7A for cables and according to class F and class FA. Defined for operating frequencies up to 600 or 1000 MHz, this category relies on a cable structure with 4 individually shielded pairs and one overall shield. This improved shielding means that the cables in this category are well equipped for future developments. For the first time, new Cat.7 connectors have been added to the standard, the RJ45 downward compatible Nexans GG45 and the fully shielded TERA connector from Siemon. However, both were not able to establish themselves on the market, Cat.7 cables and modern 10GBASE-T network devices continue to use RJ45.
Category 8, which has not yet been fully adopted, is currently in the starting blocks, with class G, whichn is divided into the subcategories Cat.8.1 with class I. Cat.8 features RJ45 connectors fully compatible with Cat.6A and Class EA, and Cat.8.2 and Class II, compatible and interoperable with Cat.7A and class FA with RJ45, GG45 or TERA connectors. Cat.8 is designed for a maximum operating frequency of 2000MHz. The cables in this category are suitable for use with the latest Ethernet standards, 25GBASE-T, 40GBASE-T and 100 GBASE-T. Cat.8 cables are typically found in data centres as short connections between switches and routers due to their shorter ranges.