Structured cabling standards for data centers

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CENELEC (European Committee for Electrotechnical Standardization) and ISO/IEC are developing structured cabling standards for data centers. CENELEC EN 50173-5 Information Technology-Generic Cabling Systems Part 5: Data Centres is targeted for completion this year. Work on ISO/IEC 24764 Information Technology-Generic Cabling for Data Center Premises started late last year and is projected to be completed in 2007 or 2008.

These standards follow structured cabling principles similar to TIA-942 Telecommunications Infrastructure Standard for Data Centers (see “Telecom Infrastructure for Data Centers,” Lightwave, March 2005, page 12) but address only cabling. Unlike TIA-942, they don’t cover data center pathways, spaces, and data center design and do not restrict horizontal cabling distances for all media to 100 m.

Other differences are that the CENELEC and ISO/IEC documents specify Category 6 as the minimum quality UTP cable for horizontal cabling whereas TIA specifies Category 5e at minimum. TIA permits the use of 75-Ω coaxial cable for T3, E1, and E3 circuits. Coaxial cable is not specified by the CENELEC or ISO standards.

All three data center standards support singlemode and multimode optical fiber cables. Where multimode fiber is used, OM3/850-nm laser optimized 50/125-µm fiber is recommended to provide additional bandwidth and channel lengths for high-speed applications. The draft ISO/IEC and CENELEC documents specify the LC connector for singlemode and multimode optical fiber.

The draft CENELEC and ISO/IEC standards include annexes with guidelines for maximum channel lengths for high-speed applications when more than two mated pairs of connectors are added into the channel. It is common for connections to be routed through multiple crossconnects as connections are made between devices in different parts of the data center. As the number of connections increases, the maximum lengths that can be supported decrease. The decrease in channel lengths as connector pairs are added into the channel is not linear because the distances depend on both insertion loss and channel bandwidth. The applications covered in the annexes include 10-Mbit/sec, 100-Mbit/sec, 1-Gbit/sec, and 10-Gbit/sec Ethernet.Th 223363

Jonathan Jew is the US Technical Advisory Group project lead for the ISO/IEC data center standard, and president of J&M Consultants. He can be reached at jew@j-and-m.com.

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