If you’re a regular Belden data center blog follower, you’ve probably seen several blogs in the past year that cover several of the key considerations for designing, deploying and testing today’s low-loss fiber networks.

We’ve covered everything from standards, connector types and loss values, to polarity, best testing methods and optimum multi-point topologies.

The good news is that I will be bringing all of these considerations together and covering each in much greater detail in my upcoming June 10th webinar, “Cabling the Hyper Data Center: Designing, Deploying and Testing Today’s Los-Loss Fiber Networks.”

Following are some of the key highlights:

MPO-12 vs. MPO-24

Current standards require a total connector loss budget of 1.0 dB for 40 and 100 gigabit Ethernet channels and new standards on the horizon make MPO-12 connectors the better choice. Why?

More fibers in the MPO-24 increases the odds for fiber height variances and misalignment that results in higher insertion loss values. The upcoming 100GBASE-SR4 standard that uses the MPO-12 will also likely render the MPO-24 interface defunct, and there is currently no test equipment available for field testing MPO-24s.

Max vs. Typ

While many manufacturers publish maximum and typical insertion loss values, there is no way to guarantee that you’ll get typical loss 100% of the time. Some manufacturers also have a significant variance between the two values—some even more than .25 dB.

When working with loss budgets as small as 1.5 dB to 2.6 dB, using typical values when designing fiber networks presents huge risks. Only maximum insertion loss values provide the headroom you need to avoid finding out later that you’re over budget.


Perhaps one of the more confusing topics, polarity is essential to ensure that the transmit signal at one end of the channel matches the receive signal at the other. When it comes to multi-fiber solutions like cassettes and trunk cables, polarity gets even more confusing due to gender.

Belden strongly recommends that duplex patch cords carry the same standard A/B polarity and that MPO patch cords be Type B female to female to avoid potential damage to active equipment and to simplify inventory management by only needing one type of cord on hand. MPO to LC cassettes should be female while MPO trunk cables should be Type B male to male.

There are however some exceptions to the rule regarding trunk cables when using a zone distribution area (ZDA) that I will cover in more detail in the upcoming webinar.

Testing Practices

The latest encircled flux testing method uses launch controllers that launch the right distribution of light into the core of the fiber to reduce measurement uncertainty from greater than 40% to less than 10%.

The 1-jumper reference method assesses the condition of the channel end faces against a very high quality multimode connector and it includes the loss of the connections at both ends of the channel for greater accuracy.

While not usually required for certification purposes, testing the channel with patch cords is smart and doesn’t take any extra time. Fiber patch cords can have dirty end faces or they could be damaged, and even a negligible loss on the patch cord can ultimately impact channel performance.

Multi-point Topologies

Low-loss connectivity allows for the fundamental best practice of deploying multiple connection points for convenient cross-connects ZDAs.

For example, a five-point topology allows for both a cross-connect at the core and ZDAs at each equipment row, enabling low-density patching at the core and all cabling to be preinstalled from the core to the ZDAs. The core remains completely segregated and adding new equipment requires only a short cable run from the ZDA.


For more information about multi-point topologies, download my latest white paper, “Advances in Multi-Fiber Connectivity Enable Data Center Flexibility, Manageability, Scalability and Security.”

Advances in Multifiber Connectivity