Issue 4, June 2009
FOCUS CABLING
The Institute of Electrical and Electronics Engineers formed the IEEE 802.3ba task group in January of 2008 to address and develop guidance for 40 and 100 GbE data rates. The project authorisation request (PAR) objectives included a minimum 100 m distance for laser-optimised 50/125 μm multimode (OM3) fi bre. OM3 fi bre is the only multimode fi bre included in the PAR.
At the IEEE meeting in May, several baseline proposals were adopted to establish a foundation for generating the initial draft of the 40 and 100 GbE standard. Parallel optics transmission was adopted as a baseline proposal for 40 and 100 GbE over OM3 fi bre. This proposal defi nes 40 and 100 GbE interfaces as 4x10 GbE channels on four fi bres per direction, and 10x10 GbE channels on 10 fi bres per direction, respectively.
Fibre bandwidth, skew and total connector insertion loss must also be considered to ensure the cabling infrastructure meets the future requirements of 40 and 100 GbE. By taking these factors into account, the system is assured of meeting the proposed operational distance of 100 m over OM3 fi bre.
OM3 fi bre is the only multimode fi bre being considered for 40 and 100 GbE systems. The fi bre is optimised for 850 nm transmission and has a minimum 2,000 MHz km effective modal bandwidth. Minimum effective modal bandwidth calculated (minEMBc) is a measurement of system bandwidth for OM3 fi bre that offers the most desirable and precise measurement, compared to the differential modal delay (DMD) technique. With minEMBc, a true, scalable bandwidth value is calculated that reliably predicts system performance. Optical skew is defi ned as the time of fl ight difference between light signals travelling on different fi bres, and it is
Parallel optics, 100-GbE
an important consideration for parallel optics systems. Excessive skew, or delay, across the various channels can cause bit errors. Cabling skew requirements are still under consideration for 40 and 100 GbE. Deployment of a low- skew cabling infrastructure will ensure compliance across a variety of applications. For example, Infi niBand, a protocol using parallel optics transmission, has a cabling skew criteria of 0.75 ns.
Enterprise Data Center Topology
Insertion loss within a system channel impacts the ability of a system to operate over the maximum supportable distance for a given data rate. As total connector loss increases, the supportable distance at that data rate decreases. The currently adopted baseline proposal for multimode 40 and 100 GbE transmissions states a total connector loss of 1.5 dB for an operating distance up to 100 m. Because of this, you should evaluate the insertion loss specifi cations of connectivity components when designing data center cabling infrastructures. Low- loss connectivity components allow for maximum fl exibility by enabling the option to introduce multiple connector matings into the system link.
A well-designed cabling architecture,
implemented
in accordance with TIA-942 and incorporating a modular cabling design, provides the reliability,
manageability,
scalability and fl exibility needed within the data center. By design, the use of low-loss, high-quality products ensures your data center will not only meet the requirements of today, but requirements well into the future.
WRITTEN BY
David Hessong, private networks market support manager, and Daryll Kerns, private networks systems engineer, Corning Cable Systems
Parallel optics, 40-GbE Drawing
www.datacenterdynamics.com 31
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