Times are changing in the data center. For decades data centers were wired with orange multi-mode fiber optic cable. MMF is the choice for the data center connections because it is smaller and faster than copper and cheaper and more forgiving than single-mode fiber optic cables typically used for long-haul transmissions. The orange flavor of MMF was pulled into data centers to deploy Gigabit Ethernet.
This type of MMF would work with links up to 600 meters. MMF uses the 850 nm and 1300 nm wavelength to transmit data. The typical MMF is 62.5/125 µm which means it has a core size of 62.5 micrometers (µm) and a cladding diameter of 125 µm, OM1 (“OM” stands for optical multi-mode). The second generation of MMF is 50/125 µm (OM2). These cables used LED transmitters. Newer installations often used laser-optimized 50/125 µm multi-mode fiber (OM3). MMF that meets this designation has enough bandwidth to support 10 Gigabit Ethernet (GigE) up to 300 meters.
10 GigE is a great technology, but many organizations have outgrown it. New variants of Ethernet can reach speeds of 25 Gbps, 40 Gbps, 100 Gbps, and soon, up to 800 GigE is needed to keep up with the new requirements of enterprise and cloud data centers.
The industry determined that a new type of fiber was needed to physically pass the bits back and forth at these new speeds and yet maintain backward compatibility with older installations. In October 2016, the international cabling standards development body International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) decided that the new standard would be called OM5.
Cabling Installation & Maintenance magazine reports that the new OM5 standard was developed to meet the increasing bandwidth demands but keep up compatibility with older MMF installations, “The standard specifies 50/125-micron laser-optimized fiber that is optimized for enhanced performance for single-wavelength or multi-wavelength transmission systems with wavelengths in the vicinity of 850nm to 950nm.”
Sr. Fiber Product Manager at Legrand Randy Harris, explained that OM5 fiber is a new type of 50-micron core, laser-optimized multimode fiber (LOMF) designed to provide better performance for applications using wavelength division multiplexing (WDM). It operates over a wider window in the range of 850nm to 953nm to support at least four wavelengths. Swiss-based cabling provider R&M says OM5 fiber-optic cabling supports duplex transmission by sending four wavelengths over a single multimode fiber to create future bandwidths up to 200 Gbps.
Cindy Montstream explained in an article published in Cabling Installation & Maintenance magazine in September 2016,
The 40 GE SWDM4 and 100 GE SWDM4 specifications support transmission over duplex OM3, OM4, and OM5 multimode fiber types. Maximum reaches vary from 75 to 440 meters depending on data rate and fiber type. The group added that in the future, SWDM technology could be leveraged to enable 200-, 400-, and 800-Gbit/sec Ethernet traffic on multimode fiber cabling as well.
In June 2016, a Telecommunications Industry Association (TIA) TR-42 subcommittee approved the new standard, which specifies wideband multimode fiber. In February 2017, the TIA TR-42.12 Optical Fibers and Cables subcommittee approved lime green as the OM5 jacket color. At that time it also approved a project to develop Addendum 2 to the TIA-598-D standard.
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The evolution of Ethernet is driving changes in the data center. The IEEE has developed a couple of new standards for Ethernet, which I wrote about here. The new standards include IEEE 802.3by, which covers 25 Gb/s switch interconnects for data centers.
In well-done cable installations cables can be distinguished by jacket color:
- Orange jackets indicate legacy 62.5/125 µm (OM1) and 50/125 µm (OM2) fiber-optic cabling
- Aqua jackets show 50/125 µm “laser-optimized” OM3 and OM4 fiber fiber-optic cabling
- Lime-green jackets 50/125 µm “laser-optimized” OM5 fiber-optic cabling
- Yellow jackets indicate single-mode fiber-optic cabling
It took decades to install all the orange old-school MMF, it is going to take several more decades to get it all uninstalled.
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Ralph Bach has been in IT long enough to know better and has blogged from his Bach Seat about IT, careers, and anything else that catches his attention since 2005. You can follow him on LinkedIn, Facebook, and Twitter. Email the Bach Seat here.
