Design/facilities
restrictions and the potential need to replace links or components. Finally, there is no guidance on qualification procedures for large installations or future MAC work (moves, adds and changes)
Scale of the problem This category 6 alert is likely to concern a large number of data centre sites that have already adopted this standard of cabling. It has been widely sold for many years and is ubiquitous in every sector. In order to appreciate how strong the demand for 10GBASE- T migration may currently be, we would point out that Industry market research firm IDC recently reported that one million 10 Gigabit Ethernet ports were shipped during the second quarter of 2010. A high proportion of these switches are likely to have been deployed in the data centre, evidence of significant demand for 10GBASE-T migration.
No applications under development Compounding our concern regarding category 6 cabling in the data centre, is the fact that there are no applications under development for this standard. Both ISO and TIA state that the cabling systems specified in their standards are intended to have a useful life in excess of 10 years. Since the category 6 and class E cabling standards were published in 2002, these systems are already beyond the halfway point of their targeted lifecycle. Furthermore, application development groups such as IEEE 802.3 or ATM are not investigating the development of new Ethernet or other data transmission solutions for deployment over category 6 cabling.
Cannot, cannot, cannot Adding to the justification for the
category 6 data centre warning, as category 6 UTP or 26AWG cables cannot support a full 100 meter 10GBASE-T channel, design flexibility is severely limited.
Shortening
channels to use category 6 for 10GBASE-T may restrict equipment placement and require the addition of patching zones or switches, resulting in added connectivity, equipment and power cost.
Category 6 cabling cannot support power-saving short reach mode (data centre mode). According to the IEEE 10GBASE-T standard, short reach mode can reduce power consumption by approximately 1W per port when using shorter (30m or less) category 6A or higher cabling channels. Category 6 cannot take advantage of this power saving mode, therefore making it a higher cost and less environmentally responsible as a cabling choice. Finally, category 6 cables, having reduced diameter conductors, cannot dissipate heat as well as category 6A or higher systems. Data centre temperatures are increasing; ASHRAE recommendations are up to 27oC. Cable insertion loss increases as cabling temperature increases. In data centres, the majority of cabling is at the rear of server cabinets, where the heat is greatest.
The increased
current levels of PoE+ applications also generate more heat, further compounding these temperature issues. ISO and TIA specify a temperature dependent de- rating factor
used in determining horizontal cable length temperatures above 20oC. Horizontal cables having reduced diameter conductors will be further limited in distance due to a higher temperature de-rating factor, compared to category 6A and especially compared to shielded category 6A and higher standard cabling.
Finally
Clearly category 6 cabling will
already have be installed in a great many data centre environments and where that’s the case, expert help will be required to conduct alien crosstalk field tests on every channel if seeking to deploy 10GBASE-T.
Not a great
prospect but if that’s the legacy system in place, then comprehensive testing is the only route forward to establish likelihood of 10Gb/s performance. Following that testing, re-cabling work is likely to be needed on failing channels. For those considering future cabling installations, the message is clear; category 6A or higher standards compliant cabling should be specified. As the working draft of ANSI/TIA-942- A2 explicitly states, category 6A is the recommended grade of horizontal and backbone cabling to install in new data centres.
February/March 2011
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