FAQS

What is Wavelength Division Multiplexing (WDM) Technology?

Wavelength division multiplexing (WDM) allows multiple wavelengths, typically 2 or 4 wavelengths over a single fiber.  The IEEE 802.3bs 200 Gb/s & 400 Gb/s Ethernet Task Force in 2016 added 200 Gb/s capability to support a cost and performance optimized migration path to 400 Gb/s that includes support for 200 Gb/s with at least 2 km of SMF (4l WDM duplex fiber) and at least 10 km of SMF (4 l WDM duplex fiber).

What changes were made to ANSI/TIA-942 when it was updated in 2017?

Some important changes to TIA-942-B Data Center Standard include:

  • Added MPO-16, MPO-32 (ANSI/TIA-604-18) and MPO-24 (ANSI/TIA-604-5)
  • Added Category 8
  • Changed recommendation to category 6A or higher
  • Added wideband laser-optimized 50/125 µm multimode (OM5)
  • Added 75-ohm broadband coaxial cables and connectors (ANSI/TIA-568.C-4)
  • Added recommendations for fiber in non-continuous pathways that could cause micro bends
  • Recommends that cabinets be at 1200 mm (48”) deep and to consider cabinets wider than 600 mm (24”) wide
  • Recommends considering pre-terminated cabling to reduce installation time and improve consistency and quality of terminations
  • Recommends considering need for proper labeling, cable routing, cable management, and ability to insert and remove cords without disrupting existing or adjacent connections
  • Maximum cable lengths for direct attach cabling in EDAs reduced from 10 m (33 ft.) to 7 m (23 ft.). (Direct attach cabling between rows is not recommended).

Other relevant changes include:

  • Change in return loss for single-mode fiber from minimum 26dB to minimum of 35dB, making field terminations more difficult
  • Polarity in Testing; used to be covered in ANSI/TIA -568.0-D and now is addressed in 568.3-D.
What types of connectors are used in Data Center applications?

In fiber optic systems for data centers, LC, SC and MPO optical fiber connectors are often used.

  • SC (square connector) connectors have a push-pull coupling end face with a spring-loaded ceramic ferrule, and is ideal in data center applications.
  • LC (Lucent connector) connectors – also push-pull connectors – came along after SC connectors, and feature a smaller ferrule (for this reason, it’s known as a “small form-factor connector”). Its smaller size makes it ideal for dense data center racks and panels.
  • MPO connectors are used for ribbon cables with anywhere from eight to 24 fibers.

 

What type of fiber do you recommend for data center applications?

To support the high bandwidths required in data centers, most companies are installing at least OM4, laser optimized multimode fiber. Some companies are installing single-mode fiber, but that requires more expensive optics. A new option that is emerging is OM5, a wide bandwidth multimode fiber which allows short wavelength division multiplexing. This means the fiber can carry multiple wavelengths of light over the same fiber, increasing bandwidth significantly and yet still allowing the use of lower cost multimode optics.

What is wide band multimode fiber and how is it used?

WBMMF is a relatively new fiber medium specified in ANSI/TIA-492AAAE and given the designation of OM5 multimode fiber by ISO/IEC and TIA. This 50/125 µm multimode laser optimized fiber was originally developed to support Short Wavelength Division Multiplexing (SWDM) and supports 4 wavelengths of 25Gb/s transmission for an aggregated 100 Gb/s transmission on a duplex LC link, a popular and familiar interface in the data center. WBMMF supports four wavelengths between 850 nm and 953 nm, using multimode optics. WBMMF was designed for use in data centers.

How does WDM technology differ from parallel optics?

Whereas Wavelength Division Multiplexing (WDM) utilizes a single fiber, parallel optics uses multiple fibers and lanes at various transmission rates. At the 25G transmission rate and at 100 meters, for example, IEEE’s 400 Gb/s migration path requires 16 lanes (16 MMFs to transmit and 16 to receive) for a total of 32 multimode fibers. This parallel configuration launched new 16-fiber and dual-row 32-fiber MPO connectors for which TIA recently published a standard. At 500 meters for SMF, four lanes / 8 fibers total are required by the IEEE for 400 Gb/s. Currently, the IEEE P802.3cd is defining standards for 50 Gb/s, as well as next generation 100 Gb/s and 200 Gb/s Ethernet. Published release is expected in Q3 of 2018.

Will WDM/SWDM ultimately replace parallel fiber optic solutions?

The consensus among FOTC members is that both solutions will coexist and depend upon specific data center network goals and applications. Employing parallel fiber solutions are currently necessary to transition between speeds, so that breakout capability is essential.

What’s the difference between Tier 1 and Tier 2 Testing?

Tier 1 testing looks at loss, length and polarity. While Tier 1 fiber optic tests can identify problems in terms of pass or fail, they cannot determine the root cause or location of the problem. Tier 2 fiber optic testing is used to pinpoint root-cause locations and the amount of loss and optical return loss (ORL) from each problem contributor and is performed selectively in addition to Tier 1 testing under specific conditions and situations. Tier 2 fiber testing provides a deeper level of link visibility unlike any other fiber infrastructure tests. The optical time-domain reflectometer (OTDR) is used to perform Tier 2 fiber optic testing.

Should I install singlemode or multimode fiber in my network?

While some people choose to install singlemode fiber because of it’s high bandwidth, multimode fiber continues to be a popular choice for enterprise applications. Newer grades of multimode fiber, such as OM4 laser optimized fiber and OM5, wideband multimode fiber, have the bandwidth to support most applications over the distances required, plus the cost for the optics remains lower than the cost of singlemode optics.

In TIA standards what is the difference between a TSB and an Addendum?

A TSB is a Telecommunications Services Bulletin. It is purely informational: we might look at a subject, collect information and share it with the industry. There is no normative information, – no “shall” statements. TSBs are often stepping stones in the standards process as we start to explore topics that might become part of a standard. In fact, a TSB can be referenced by a standard. An addendum is an official addition to a publish standard. Anything in the addendum has the same enforcement as a full, published standard. The contents can be normative or informative depending on the content and how the engineering committee positions the material as an addendum

Can the same fiber optic transceivers that are used with OM3 fiber, like SFP + 10Gbps pluggable modules, be used with OM4 fiber or are there new transceiver types that need to be used?

Yes, you can use the same fiber-optic transceivers for both OM3 and OM4 fibers because the two fiber types are basically the same except that OM4 fiber has higher bandwidth. The IEEE 10Gbps Ethernet standard states that 300m OM3 and 400m OM4 link lengths are supported with 10GBASE-S compliant transceivers.

Are Bend Insensitive Multimode Fiber approved by standards?

Yes. ANSI/TIA/EIA-568B.3 sets performance specifications, minimum bend radius standards and maximum pulling tensions for 50/125-micron and 62.5/125-micron fiber optic cables. For inside plant cable, the fiber cable bend radius is 10 times the cable’s outside diameter under no pull load, and 15 times the cable’s outside diameter when subject to tensile load performance measurements and qualification processes. If you are interested learning more about the status of BIMMF or participating in the discussion you can access the schedule for TR-42.12 here and download recent meeting reports.

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