DCN April 2016 - Page 21

cabling COPPER AWE The launch of Category 8.2 cable systems is set to transform data centre infrastructures as a cost effective alternative to fibre optic for 40GBase-T applications, as Lee Stokes of Draka UC Connect explains. T he amount of digital data in the universe is growing exponentially as increasing numbers of people, businesses and devices connect to the Internet. Experts predict the quantity of digital data will double every two years heaping pressure on data centres and their cable infrastructures to continue to maintain capacity without a degradation of service. In July 2012, industry representatives decided that a copper cable capable of handling 40Gbps of data was worth developing. Now, three years after that announcement, cable and systems manufacturers are now launching Category 8.2 copper cabling systems. The introduction means some leading manufacturers can now offer the choice of both 40Gbs copper and 40Gbs fibre optic data cabling. The 40GBase-T copper system is targeted primarily at data centre applications. It will be particularly useful for applications where cable installers are more familiar working with copper cabling for both endof-row (EoR) and top-of-rack (ToR) architecture. The system will also provide operators and installers with a cost effective alternative to fibre optic systems by enabling them to take advantage of the reduced cost of copper compatible switches. The preferred way of connecting servers to switches in data centres is over twisted-pair cable. It is a fact that 88 per cent of all switch-to-server links are typically less than 30m. The standards bodies have recognised this statistic; as a consequence, all three bodies – the TIA, ISO and IEEE – have deemed the maximum link length for both 25GBase-T and 40GBase-T to be 30m. At 30m, the Category 8 linklength is shorter than link-lengths for other cable categories. The shortened length is necessary, however, because above 30m attenuation results in the link’s performance dropping to an unacceptable level. For reference, the 30m maximum length is defined as an assembly of three cable sections: a 26m long installation cable and a 2m long patch cable at each end. Significant differences It is important to be aware that while the maximum length of reach is broadly similar in all 25GBase-T and 40GBase-T cable standards, there are significant differences between the standards when it comes to defining backwards compatibility. The North American standards body the TIA, for example, has broken with convention with its definition of Category 8 in that it does not require the system to be backwards compatible with Category 7A or Category 7 systems but it does have to be compatible with Category 6A, Category 6 and systems with a lower specification. 21