Optical Connectivity Trends in the Data Center

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Migration from 10G to 40G and 100G with OM3/OM4 Multimode Fiber

 

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Written By:
Doug Coleman, Manager Technology and Standards, Corning Cable Systems; 

David Kozischek, Marketing Manager Enterprise Networks, Corning Cable Systems; 
Carol Sparks, Manager Transmission & Application, Corning Cable Systems

 

Why is OM3/OM4 connectivity the dominate media in the Data Center?

OM3/OM4 multimode connectivity provides the lowest price per circuit when compared to OS2 single-mode connectivity and OM3/OM4 supports an easy migration to 10G/40G/100G data rates at required distances in the data center.  10/40/100G transceivers (SFP+, QSFP, CXP) that operate with OM3/OM4 connectivity utilize a 850nm vertical cavity surface emitting laser (VCSEL) light source that is very economical to manufacture and is easy to package into the transceiver transmitting optical subassembly (TOSA).

 

10G OM3/OM4 Connectivity

The IEEE 802.3ae 10G standard released in 2002  included 10GBASE-SR OM3 guidance that supports operation at 850nm with duplex fiber serial transmission. Even though duplex fiber implied duplex LC connectivity throughout the channel, 12F MPO terminated cables emerged as a primary choice for deployment in data-center backbone applications. The 12F MPO terminated trunk cable provided the highest fiber packing density to maximize pathway and space utilization in ducts, raceways, and patch panels.

An MPO connectorized backbone cable typically is terminated in patch panels using one of two methods that break-out the 12F MPO to six 2F duplex LC (Figure 1). The first 10G connection type is called Method 1.  Method 1 is normally used in an interconnect application where a harness assembly is used on the front of the patch panel. Harness assemblies are used to break out the 12F MPO connectors terminated on trunk cables into simplex- or duplex-style connectors. The harness assembly interconnects with the backbone cable at the patch panel MPO connector adapter.  Figure 1 shows an MPO connector, a typical MPO to LC module, an MPO panel and a 12F MPO to duplex harness.

Another method for deploying 10G in the data center is called Method 2. Method 2 is used in both interconnect and cross-connect applications where an MPO connector module is used. MPO connector modules are used to break out the 12F MPO connectors terminated on a backbone cable into simplex or duplex style connectors. Simplex and duplex style jumper patch cords then can be used to patch into 10G system equipment ports, patch panels, or client outlets. The MPO module features simplex or duplex port adapters across the front and one or two MPO connector adapters across the back. Fiber polarity is maintained with an integrated wiring configuration built into the module that ensures proper transmitter-to-receiver continuity throughout the system.

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Figure 1.  Breakout of 12F MPO backbone to duplex for 10G connectivity.

 

Migration from duplex fiber transmission to 40/100G parallel optics

Cabling migration from 10G to 40G to 100G in an MPO based system is a simple and easy deployment. Starting with a 10G configuration, a base 12F MPO backbone cable is deployed between the 10G switches. As discussed earlier, modules or harnesses are used at the end to transition from the 12F MPO to LC duplex. These breakout configurations enable connectivity into the switch.  Figure 2 illustrates a module solution.

 

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Figure 2: 10G over 12F MPO backbone cabling.

 

Inspection of Figure 3 shows that 40G uses only eight of the 12 fibers, with the inside 4 fibers unused. If a conversion harness or module is not implemented, the four unused fibers result in 33% dark trunk fibers. To provide 100 percent trunk fiber connectivity usage, conversion modules and harness are used to break out the 12F trunk connectivity into 8F connectivity for mating to electronics.

 

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Figure 3: 40G parallel optic transmission lanes and 12F MPO connector end face.

 

When the switches migrate to 40G, the 10G module or harness is removed and should be replaced by a conversion module or conversion harness (Figures 4 and 5). Alternatively, an MPO adapter panel can be used, resulting in 67% trunk fiber utilization (Figure 6). In any of these deployment options, the use of an MPO terminated jumper is needed to establish connectivity between the switches. For 100GBASE-SR4 networks all Figures 4-6 cabling is applicable.

 

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Figure 4-6: 40G over 12-fiber MPO cabling solutions

 

Figure 4: Uses conversion modules resulting in 100% trunk fiber utilization.
Figure 5: Uses conversion harnesses resulting in 100% trunk fiber utilization.
Figure 6: Uses panels and jumpers resulting in 67% trunk fiber utilization.

 

100GBASE-SR10 networks require a 24 fiber jumper to establish a link. Systems that use 12 fiber MPO backbone cabling will need a 24F to (2) 12F jumper (Figure 7).

 

 

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Figure 7: 100G over 12F MPO cabling.

 

Multiple loss performance tiers are available for MPO connectivity solutions. Just as connector loss must be considered with currently deployed applications such as 10 Gigabit Ethernet, insertion loss is also a critical factor for 40 and 100 Gigabit Ethernet applications. For example, IEEE 802.3 defines a maximum distance of 300 meters on OM3 multimode fiber for 10 Gigabit Ethernet (10GBASE-SR). To achieve this distance, a total link loss of 2.6 dB is needed which includes a maximum allocated connector loss of <1.5 dB.  As the total connector loss in the channel increases above 1.5 dB, the supportable distance decreases. When extended distances or multiple connector matings are required, low-loss performance modules and connectivity may be necessary. Table 1 summarizes the IEEE 802.3 standards for distance and link loss.

 

 

100 Gbit Ethernet* 802.3bm  100GBASE-SR4  100.00 OM3 8 70  1.75

100 Gbit Ethernet* 802.3bm  100GBASE-SR4  100.00 OM4 8 100 1.86

 

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Table 1. IEEE 802.3 maximum length and channel insertion loss for 40 and 100G Ethernet.   

 

Preparing for the Future

To best meet the needs of the future, MPO-based connectivity utilizing OM3 or OM4 fiber is the ideal solution in the data center. With inherent modularity and optimization for a flexible, TIA-942-compliant structured cabling installation, MPO-based optical fiber systems can be installed for use in today’s 10G networks, while providing an easy migration path to future higher speed technologies such as 40 and 100 Gigabit Ethernet.

 

The IEEE 802.3ae 10G standard released in 2002  included 10GBASE-SR OM3 guidance that supports operation at 850nm with duplex fiber serial transmission. Even though duplex fiber implied duplex LC connectivity throughout the channel, 12F MPO terminated cables emerged as a primary choice for deployment in data-center backbone applications. The 12F MPO terminated trunk cable provided the highest fiber packing density to maximize pathway and space utilization in ducts, raceways, and patch panels.

 

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*Pending 802.3bm guidance

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