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Data Center

Fiber Selection Considerations for Today’s Data Centers

Fiber Selection Considerations for Today’s Data Centers

8 June 2018 | Reading Time: 4 minutes


Multimode or Singlemode: Which Fiber Type is Best in the Data Center?

Data centers and fibre-optic connectivity sit at the heart of modern business today. With the data centre driving critical business processes, and with fibre-optic connectivity as the fabric, allowing connection to link servers, storage systems and switches, they are both core to the effective continuity of daily operations and processes.

As the data center continues to evolve, it’s important to select the right fiber type for the use case, to ensure best affordability, connectivity and long-term future proofing. Today,
data center technicians largely have two high-level options when it comes to selecting fiber types: Multimode fiber, and singlemode fiber.

But which offers the advantage, and in what use case? In this post, we will examine the development, deployment and pros and cons of each fiber type.

Benefits of Multimode Fiber in the Data Center

Multimode Fiber (MMF) is still firmly the front runner in modern Enterprise Data Centers. It was first deployed in the early 1980s, with a light-carrying core diameter about six times larger than singlemode fiber. MMF provides a logical solution to the alignment challenges of getting light into and out of the cabling efficiently.

A key benefit of using multimode fiber is that it is a low cost way to transport high data rates over relatively shorter or smaller distances. Multimode fiber has evolved from being optimized for multimegabit-per-second transmission, using light-emitting diode (LED) light sources, to being optimized to support multigigabit transmission using 850 nm vertical cavity surface emitting laser (VCSEL) sources – which tend to be more affordable than their singlemode counterparts.

This advancement in performance is clear, due to the classifications assigned to MMF by the standards bodies. OM1 and OM2 represented the earlier MMF types with low modal bandwidth and very limited support for higher speed optics. OM3 and OM4 represent the newer, laser-optimized MMFs that are typically installed in modern data centers today.

Considering Wideband Multimode Fiber (WBMMF) in the Data Center

When considering Wideband Multimode Fiber (WBMMF), we must first look at shortwave wavelength division multiplexing (SWDM). While OM3 and OM4 provide very high modal bandwidth at 850nm – the predominant wavelength that can be efficiently supported by VCSEL transmitters – SWDM supports improved performance across a single pair of multimode fibers, enabling additional wavelengths to be transmitted alongside 850nm. Because the modal bandwidth of OM3 and OM4 fibers were specified for laser operation at 850nm only, a new specification for optical fiber was required – with many data center managers now looking at WBMMF as the solution.

WBMMF optimizes the reach of SWDM transmission, to deliver four times the information across the same number of fiber strands over practical distances. Optimized to support the additional wavelengths required for SWDM operation (across 850nm to 950nm) WBMMF ensures not only more efficient support for future applications across the data center fabric, but also full compatibility with legacy applications because it remains fully compliant to OM4 specifications.

WBMMF standardization was completed in mid 2017, having been recognized by ISO/IEC and TIA standard bodies. The OM5 designation was also adopted for the inclusion of this new cabled optical fiber Category in the 3rd Edition of the ISO/IEC 11801 standard. Considering the future of OM5, the outlook is very positive. At the end of 2017, the IEEE agreed to initiate a project to define next generation multimode transmission using short wave division multiplexing, the transmission technology that OM5 was designed to support.

Benefits of Singlemode Fiber in the Data Center

Singlemode fiber (SMF), which is designed with a much smaller core, is the sensible and most realistic choice for longer-reach applications in the data center, such as extended runs in the fabric between leaf and spine switches, spine and routers, and into the transport network to connect data centers in different locations.

With a higher bandwidth, SMF does not have the modal dispersion limitations inherent in MMF. Therefore, SMF is used in applications where support for higher and next-generation bandwidths can absolutely be guaranteed. This means that SMF is a good choice for hyperscale and service provider data center owners to deploy, as it supports longer distances.

Large data centers and hyperscale data centers usually deploy SMF to connect multiple halls and extended equipment zones using a centralized cross-connects architecture at the MDA. They also typically employ a dedicated optical distribution frame (ODF). By deploying an ODF, technicians can make sure that cables are sustained at an optimum length for transmission, whilst other data halls and equipment zones can be efficiently patched to one another with minimum disruption to service and networking equipment.

Fiber Connectors as the Final Consideration

Clearly both MMF and SMF have their advantages and disadvantages – which option a data center designer chooses, will depend on a range of factors from budget to use case and more.

However, data center designers should also consider the use and choice of fiber connectors as part of a fiber selection process.

Having evolved alongside fiber-optic cabling, driven by increasing fiber density, fiber connectors work to pull the whole system together. As a brief look at fiber connector evolution, in the early 2000s the duplex LC connector emerged as the predominant two-fiber type, and remains so today. While the evolution of the duplex connector was underway, array connectors (parallel optics) were also progressing. The multifiber push-on (MPO), which was first deployed in public networks, had become a firm first choice for rapidly deploying cabling into data centers. Finally due to its compact size, the MPO allows 12 or more fibers to be terminated in a compact plug, occupying the same space as a duplex LC. The MPO’s high density enables installation of preterminated, high-strand-count cables, while eliminating the time-consuming process of field installing connectors on site.

Find out more about the fiber types and considerations that should be made to enhance and futureproof today’s data centers here.


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