Choosing 24-Fiber MPO/MTP Cabling for 40/100G Migration

In 2002, the IEEE ratified the 802.3ae standard for 10GbE over duplex fibers (one fiber transmits and the other receives) terminated with duplex LC-style connectors and vertical cavity surface-emitting laser (VCSEL) transceivers. With the increasing need for high speed data transmission, in 2010, the IEEE ratified the 802.3ba standard for 40/100G to satisfy this demand. Similar to how transportation highways are scaled to support increased traffic with multiple lanes at the same speed, the 40/100G standards use parallel optics, or multiple lanes of fiber transmitting at the same speed. Running 40G requires 8 fibers, with 4 fibers each transmitting at 10Gbit/s and 4 fibers each receiving at 10Gbit/s. Running 100G requires a total of 20 fibers, with 10 transmitting at 10Gbit/s and 10 receiving at 10Gbit/s. Both scenarios call for high-density MPO-style connectors, which can be either 12-fiber or 24-fiber. However, 24-fiber MPO/MTP cabling is often considered to be the better solution for 40/100G migration. Why? Reading this post and you will get the reasons.

12-Fiber and 24-Fiber MPO/MTP Cabling

A 12-fiber MPO/MTP connector is used for 40G Ethernet. Among the 12 fibers, only 8 optical fibers are required—4 for Tx and 4 for Rx, and each channel has a transmission rate of 10Gbps (typically 40G applications use only the 4 left and 4 right optical fibers of the 12-fiber MPO/MTP connector, while the inner 4 optical fibers are left unused). To run 100GbE, there are two solutions. One is to use two 12-fiber MPO/MTP connectors—one transmitting 10Gbit/s on 10 fibers and the other receiving 10Gbit/s on 10 fibers. The other solution is to use a 24-fiber MPO/MTP connector—20 fibers in the middle of the connector transmitting and receiving at 10Gbit/s and the 2 top and bottom on the left and right unused. 12-fiber can be both used for 40/100G solutions, but why said the 24-fiber is better than 12-fiber? The following part will explain in details. The image below shows different construction of 12-fiber and 24-fiber MPO/MTP.

12-fiber vs. 24-fiber

Why Is the 24-Fiber the Right Migration Path to 40/100G?
Fiber Utilization to the Extreme

Using 24-fiber trunk cables with 24-fiber MPO/MTP connectors on both ends to connect from the back of the switch panel to the equipment distribution area can utilize the fibers to the extreme. As we have mentioned above, 40G will uses 8 fibers (4 Tx and 4 Rx) of the total 12-fiber trunk cable with 12-fiber MPO/MTP connectors, leaving 4 fibers unused. Nevertheless, when three 40G links are using three separate 12-fiber trunk cables, it will result in a total of 12 unused fibers, or 4 fibers unused for each trunk, which can be a waste. With the use of 24-fiber, running three 40G links will use all 24 fibers of the trunk cable, which recoups 33 percent of the fibers that could be lost with 12-fiber trunk cables, providing a much better return on investment. For 100G applications, which require 20 fibers (10 Tx and 10 Rx), a 24-fiber trunk cable can provide a single 100G link instead of using two 12-fiber trunk cables.

Spacing Saving

With more and more patch cables and optical equipment used in data centers, space is a premium. Using 24-fiber trunk cable will cause less cable congestion in already-crowded pathways, which can save more space and make cable management easier. For example, for a 40G application, it takes three 12-fiber trunk cables to provide the same number of links as a single 24-fiber trunk cable which can take about 1.5 times more pathway space.

Increasing Fiber Density

With today’s large core switches occupying upwards of one-third of an entire rack, density in fiber switch panels is critical. 24-fiber MPO connectors offer a small footprint which can ultimately provide increased density in fiber panels at the switch location.

Cost Effective

The 24-fiber data center fiber trunking and interconnect solution offers a simple and cost effective migration path from 10G-40G-100G, providing future-readiness for three generations of active equipment. With 24-fiber trunk cables effectively supporting all three applications (shown in the following picture), there is no need to recable the pathway from the back of the switch panel to the equipment distribution area.

24-fiber for 10, 40 and 100G applications


With increasing concerns about the cost to upgrade and the complexity involved, data center managers need a solution that simplifies the process and provides better return on investment, while meeting both current and future needs. Taking the advantages of maximum fiber utilization, space and cost saving and high density, it is no doubt that 24-fiber MPO/MTP cabling is better solution for 40/100G migration.

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