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Explore fiber optic cable types and their effects on the data center

When evaluating fiber optic cable types, network admins should carefully consider their bandwidth, compatibility and troubleshooting requirements.

Fiber optic connectivity was once reserved for special uses cases. But, it is quickly becoming the standard for...

high-speed connections, partially due to a consolidation in compute power. This leads to the need for higher-density network platforms that can handle the aggregation of many high-speed links. Other forms of connectivity -- such as copper -- are still used for things such as out-of-band networks, but, more commonly, they are used at lower link speeds. Knowledge of fiber optic cable types -- or at least their basics -- is now a requirement when working with modern data center networks.

SFP affects fiber optic speed, compatibility

Many of the appliances in today's data center look for 10 Gb for their data path interfaces.  While the move to 10 Gb facilitates the migration from copper to fiber, most data center network administrators have some experience with fiber optics at lower speeds. To cable a link longer than 330 feet -- the maximum length that copper supports -- many use fiber optic cable types with an SX-based transceiver or optic. The SX optics can support ranges closer to 700 feet and are common in the small form-factor pluggable (SFP) format.

The majority of switches have the capability to poll information and report it back to the administrator, but DDM provides critical information, such as receive light level, transmit power and transceiver temperature in real time.

The SFP format has become a standard for 1 Gigabit Ethernet (GbE) connectivity; however, an SFP module can only provide bandwidth up to 1.25 Gb. To solve this limitation, the SFP+ module allows for 10 GbE in the same form factor as the original SFP module. In many cases, a switch that supports SFP+ modules also supports SFP modules at lower speeds, making many 10 Gb-capable switches backward-compatible with the 1 Gb SFP modules.  

Today, the majority of switch platforms are based on SFP+, which means the switch can usually accept a variety of SFP and SFP+ form factor optics. At 10 Gb speeds, the SR optic is generally used for all 10 Gb applications and can support ranges of over 1,000 feet on standard multimode fiber, making it ideal for most 10 Gb applications in the data center.

While the SFP form factor is common today, the module on the switch and the optic type are independent of one another. As long as the optic type matches, the module form factor doesn't matter -- it's possible to connect different form-factor 10 Gb modules when connecting dissimilar platforms. When connecting dissimilar modules, make sure you have the correct fiber optic cable types, since different form factors will call for different fiber optic connectors. Older modules rely on SC-type connectors, while the newer modules, such as SFP and SFP+, rely on LC-type connectors. 

Fiber optic cable types evolve

To help admins troubleshoot link issues, most newer optics include Digital Diagnostic Monitoring (DDM) -- also referred to as Digital Optical Monitoring -- which feeds information about the optics into the platform it's plugged into. The majority of switches have the capability to poll information and report it back to the administrator, but DDM provides critical information, such as receive light level, transmit power and transceiver temperature in real time. All optics come with a published range of receive light levels that are typically measured in decibels. Use the information from DDM to troubleshoot optical links and ensure the transceiver and the fiber cable work as expected. Less expensive optics typically don't include DDM, so evaluate the features of transceivers before a purchase.

As fiber optics continue to increase in popularity, data center network administrators will find themselves working less often with copper-based connectivity. And as bandwidth requirements increase, so does the need for innovation among fiber optic cable types. Keep up with this innovation; knowing the available options can often save significant time and money.

Next Steps

TIA standards affect cabling in the data center

Data center cabling requires a formal plan

Considerations for a choosing a data center-class switch

This was last published in August 2016

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