Copyright Goodheart-Willcox Co., Inc. 64 Networking Fundamentals Category 3 Category 3 cable has a maximum frequency rating of 16 MHz. It consists of four twist- ed pairs and three twists per foot. Th is cable is rarely encountered today in network applications but may be found in many existing telephone installations. Category 4 Category 4 cable has a maximum frequency rating of 20 MHz. It consists of four twist- ed pairs. Th is cable has a data rate of 16 Mbps. It is only a slight improvement over Category 3 cable. Category 5 Category 5 cable has a maximum frequency rating of 100 MHz. It is capable of data rates of 100 Mbps (using two pairs) and 1000 Mbps (using four pairs). It is found com- monly in 10BaseT and 100BaseTX networks. Category 5e cable has a maximum frequency rating of 100 MHz. Category 5e is not a replacement for Category 5 cable but rather an addendum to the cable classi- fi cation. With the growing need for cable that could support higher data rates, Cate- gory 5 standards were revised to Category 5e. Category 5e can support data rates up to 1000 Mbps using all four pairs of conductors. Th e improvements to Category 5 are based on Near-End Crosstalk (NEXT) and Equal Level Far-End Crosstalk (ELFEXT). At the time of the introduction of Category 5e, any existing Category 5 cable was eligible to be reclassifi ed as Category 5e if it met the requirements of the new stan- dard. Th is would allow the use of Category 5 cable for newer network installations. Existing Category 5 cable could be tested to see if it met the Category 5e standard. If it met the standard, then it could be used. If not, it would require replacement. Some of the factors that determine the results of the tests include the AWG of the conduc- tors and the insulation. Category 6 Category 6 has a maximum frequency rating of 250 MHz and a data rate of 1 Gbps. It is similar in construction to Category 5 and 5e but does not require special shielding. Category 6 is similar to Category 5 in that it has four pairs of conductors. Th e main physical diff erence is that Category 6 has more twists per pair of conductors, and the pairs are separated by a plastic spacer in the core of the cable. Figure 2-18 compares Category 5 to Category 6 cable. Notice that Category 6 has more twist per pair than Category 5 cable. Th e tight- er twist is especially apparent when comparing the blue and blue/white pairs. Cat- egory 6 also has a plastic center cable core, which provides more space between the conductor pairs. Th e tight pair twist and the plastic center core are physical features which allow the Category 6 cable to support higher frequencies as well as higher data rates than Category 5e. Enhanced Category 6 cable known as Category 6e is not a true standard but rather a marketing term used to identify Category 6 cable that exceeds the Category 6 standard. Category 6a, on the other hand, is a TIA-recognized standard. Th e a in Category 6a stands for augmented. Category 6a is an excellent choice of network cable for noisy environments such as heavy industrial manufacturing. High-amperage industrial cables and equipment, such as welders, generate a great deal of EMI. It has a maximum frequency rating of 500 MHz and a data rate of 10 Gbps. Do not confuse Category 6e with Category 6a.