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How to determine data center cabling requirements

With the new TIA-942 data center standard having been out for nearly a year and the new 10 gigabit standards either published or well under way, data center managers are beginning to ask what is the best infrastructure

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to put in place:

  • Should I install copper or fiber?
  • What category of copper and what type of fiber?
  • Should I go with a combination of both?
  • If I use both again what category and grade of each?
    More on data center cabling:
    TIA-942: Cookie cutter or cost cutter?

    Best practices: A guide to cable management

    The answers to these questions will depend on a variety of factors. One must first determine the length of time the data center will be in operation. Depending on that length of time, other factors will come into consideration as well, for instance, it must be determined what equipment exists and then what equipment may potentially be installed during that useful life. If new equipment is to be purchased, then careful planning will be required. The days of facilities and IT being separate departments are long gone. Budget savvy CIO's are consolidating budgets if not for the entire year, at least on a per project basis.

    Another consideration is what will be connected to the channel and overall distances. With 10GBASE-T (IEEE 802.3an), category 6 operations are limited to 55 meters, and that is only after some type of mitigation to lessen the effects of alien crosstalk. Augmented category 6, either shielded or unshielded, will provide a 100 meter channel. But little is known as to whether these channels will support another speed increase, although the shielded systems have a better potential due to the enhanced noise canceling properties. Category 7/Class F, which has been a standard since 2002, has the highest bandwidth and greatest potential to support additional speed increases. All are backward compatible with existing equipment that utilizes category 5e, but provide a bandwidth increase for the newer 10GBASE-T copper components.

    Copper systems have an additional consideration over many fiber systems due to the cost of pathways and spaces. The increased diameter for augmented category 6 systems could significantly increase cable tray, ladder rack and pathways. This may not be possible in some retrofit situations.

    For fiber channels the key component beyond channel cost is the cost of the electronics. When moving to 10 gigabit transmissions, typically 10GBASE-SR in data centers, the fiber recommended is 50 micron laser optimized (such as XGLO) or 50 micron standard multimode fiber supporting 300m and 58m respectively. Very little 62.5 micron is being installed as, the same 10GBASE-SR components, are distance limited at 28m. The 50 micron products are backwards compatible with the active electronics and provide a significant bandwidth and distance increase.

    Single mode fiber (SMF) can also be installed but again, there is another increase in electronics cost. IEEE (Institute of Electrical and Electronics Engineers)has just formed a higher speed working group to evaluate 100Gb/s over SMF. If you chose to protect future applications it may be prudent to include some strands of SMF. In order to achieve 10 gigabit over 300m of fiber with less expensive electronics, 50 micron laser optimized (or zero water peak) fiber is recommended. This fiber will also likely support future applications. More expensive electronics such as 10GBASE-LX4 that provide 10 Gb/s operations over older FDDI grade fiber may prove to be more costly than changing fiber channels due to the increased cost of electronics. 10GBASE-LRM was just released and will provide 10Gb/s up to 220 meters over legacy fiber, however, at this time the equipment has not been released.

    In all active electronics maintenance costs may also be affected by higher component prices. Many companies base the maintenance costs on the original equipment costs. So if a piece of equipment costs 3x more than another counterpart, a significant increase in day two costs may be seen due to the additional maintenance costs of the more expensive component(s). Power consumption should also be included in ownership costs.

    In part two of our series on data center cabling decisions, data center infrastructure expert Carrie Higbie offers a cost calculator for determining TCO on a cabling project: Calculating costs of data center cabling infrastructure.

    About the author: As the Global Network Applications Market at The Siemon Company, Carrie supports the end-user and electronics communities. She has won the "Communication News" Editor's Choice Award for the last two years. See Carrie's Ask The Experts page for more of her articles.

This was first published in January 2007

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