Why Category 6 Should Not be Specified for 10Gb/s
A recent report1 by the industry market research firm IDC provided the recordbreaking news: more than one million 10 Gigabit Ethernet ports were shipped during the 2nd quarter of 2010. A likely bet is that the majority of these switches are being deployed in the data center. As 10GBASE-T network equipment becomes increasing available, data center decision makers will want to take advantage of the cost savings, convenience, and flexibility provided by deploying 10 Gb/s technology over balanced twisted-pair copper cabling. While it is true that category 6 cabling can provide limited support of 10GBASE-T in some environments, the reality is that there are some very compelling reasons to specify category 6A or higher cabling in a new 10 Gb/s-ready data center.
Standards recognize category 6A as the minimum grade of cabling for data centers
TIA, ISO/IEC, and other telecommunications Standards organizations have developed Standards that address cabling system design and installation in the data center environment. The message of these Standards is clear: the minimum grade of cabling to be deployed in the data center is category 6A. The working draft of ANSI/TIA-942-A2 states that category 6A is the recommended grade of horizontal and backbone cabling to install in new data centers. ISO/IEC247643 explicitly states that main distribution and zone distribution cabling systems supporting data centers shall be designed to provide a minimum of class EA (equivalent to TIA category 6A) channel performance.
Category 6 support of 10GBASE-T is uncertain
Several published industry guidelines (e.g. TIA TSB-155-A4 and ISO/IEC TR 247505) are available to assist in qualifying the capability of an existing category 6 cabling plant to support 10GBASE-T. These guidelines were not intended for newly-installed cabling. According to guidelines, category 6 cabling less than 37 meters (121 feet) should support the 10GBASE-T application and cabling between 37 meters and 55 meters (180 feet) should support the application depending upon the alien crosstalk environment. However, there is no 10GBASE-T application support assurance over short runs of category 6 because alien crosstalk is highly dependent on cable density.
The only way to ensure compliance to guidelines such as TSB-155-A and ISO/IEC TR 24750 is to perform complicated alien crosstalk field tests on every channel. This testing can be extremely time-consuming and may not be fully conclusive. In a majority of data center installations, alien crosstalk mitigation will likely be required. The recognized mitigation methods cannot be easily implemented due to existing pathway fill restrictions and the potential need to replace links or components. Finally, there is no guidance on qualification procedures for large installations or future MAC ("moves, adds, and changes") work. The added cost and uncertainty associated with alien crosstalk qualification testing of category 6 cabling makes category 6A systems a much more desirable solution for new 10 Gb/s-ready data centers.
Category 6 running 10Gb/s should not be used in the same pathways as category 6A UTP
Emerging industry guidance on pathway separation (e.g. TIA TSB-1906) unequivocally states that category 6 UTP cabling transmitting 10GBASE-T signals should not be placed unbundled, in adjacent bundles, or in the same bundle as category 6A UTP cabling transmitting 10GBASE-T signals. TIA TSB-190 also reaffirms TIA's position that category 6A cabling should be used for all new installations targeted for support of 10GBASE-T.
There are no applications under development for category 6
Both TIA and ISO 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, applications 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.
Category 6 UTP cannot support a full 100 meter 10GBASE-T channel, limiting design flexibility
Category 6A and 7A can support a full 100 meter channel and potentially longer. Siemon is working with Aquantia, a leading 10GBASE-T chip manufacturer to test their shielded 6A and 7A cabling systems in extended channel distances beyond 100 meters7 - instead of using category 6 UTP and shortening it. 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 UTP cannot support power-saving short reach mode (aka data center mode)
Short reach mode, per the IEEE 10GBASE-T standard can reduce power consumption by approximately 1W per port when using shorter (30m or less) category 6A or higher cabling channels. Category 6 cabling cannot take advantage of this power savings mode, therefore making it a higher cost and less environmentally friendly option.
Cables with reduced diameter conductors cannot dissipate heat as well as category 6A or higher systems
Data center temperatures are increasing. ASHRAE recommendations are up to 81F/27C°. Cable insertion loss increases as cabling temperature increases. In data centers, the majority of cabling is at the rear of server cabinets where the heat is the greatest. The increased current levels of evolving PoE+ applications also generate more heat, further compounding these temperature issues. TIA and ISO specify a temperature dependent de-rating factor used in determining horizontal cable length at temperatures above 20C° (68F). 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 cabling.
- "Worldwide Ethernet Switch and Router 2Q10 Market Share Update", Doc # 224735, IDC, August 2010
- ANSI/TIA-942-A, "Telecommunications Infrastructure Standard for Data Centers", draft 2.0, pending publication
- ISO/IEC 24764, Ed. 1.0, "Information technology - Generic cabling for data centers", April 2010
- TIA TSB-155-A, "Guidelines for the Assessment and Mitigation of Installed Category 6 Cabling to Support 10GBASE-T", March 2010
- ISO/IEC TR 24750, "Information technology - Assessment and Mitigation of Installed Category 6 Cabling to Support 10GBASE-T", July 2007
- TIA TSB-190, "Guidelines on Shared Pathways and Shared Sheaths", draft 2.0, pending publication
- Aquantia Press Release, July 2010 - http://www.aquantia.com/pdf/AQ_120m_Reach_Release_FINAL.pdf
- ASHRAE 72-74 (22-23C)