In the process of migrating to greater bandwidth 40G and 100G network, MTP cabling system which provides high density and high performance plays an important role. Whether to use 12-fiber or 24-fiber MPO cable has been a hot topic in higher speed networking migration. In my previous blog Choosing 24-Fiber MPO/MTP Cabling for 40/100G Migration, we have indicated that MPO 24 fiber cable is more suitable for 40G and 100G network. Besides, with active equipment planning to use a single 24-fiber MPO interface for 100G and the channel currently requiring 20 fibers, many IT managers are also considering the use of 24-fiber MPO solutions. However, before choosing 24-fiber MPO cable, there are some facts that should be noticed.
The Higher the Fiber Count, the Higher the Loss
Optical loss budget is a big concern among data center managers, and due to limitations in the protocol, standards now require a total connector loss budget of 1.0 dB for 40G and 100G, but a 24-fiber MPO connector typically has a loss of 0.5dB which is much higher than 0.2dB that 12-fiber MPO connector has. This is mainly due to the fact that the more the fiber count, the higher the loss. The higher loss of the 24-fiber MPO limits data center managers to having just two mated pairs in a channel.
Note: Current proper polishing technique can address 24-fiber MPO to meet the low loss requirement as 12 fiber MPO connector. For example, 24-fiber MTP trunk cable in fiber-mart.COM only has 0.35dB insertion loss.
The Higher the Fiber Count, the More Difficult to Control End-Face Geometry
In a quality fiber connector, the fibers protrude slightly beyond the ferrule. When two fibers are mated using the right pressure, the fibers will deform slightly to fill in any gaps and provide a solid mating. Any variance in the pressure can impact the insertion loss and return loss on a fiber-to-fiber basis. To achieve consistence pressure, it is important to have a very flat ferrule after polishing with all the fibers protruding equally. With higher count arrays, like 24-fiber MPOs, there are more fibers to control, which can significantly increase the odds for height variance. For example, in the following 72-fiber array, if we look at this graphic of the middle two rows of fibers, we can see the variance in the height profile. The height variance becomes even more pronounced across more rows of fibers. Besides, it is more difficult to achieve a flat ferrule polishing on a large array area.
Although the polishing technique has been significantly improved, there still exists limitation to achieve a flat end-face and equal pressure over the array.
Standards and Testing Remain an Issue to 24-fiber MPO Cabling
100GBase-SR4 standard has be a reality and that most of users is running 100G over 8 fibers, rather than 20, which will render the 24-fiber MPO a dated interface for 100G Ethernet. In addition, the MPO cabling testing is far more complicated than duplex cabling testing. You have to gain very professional training, tools understanding that you can efficiently conduct multifiber testing. In other words, if there is any issue with the multifiber cabling, it’s not easy to troubleshoot it.
It’s Still Your Choice
With the significant demand for higher speed 40GbE and 100GbE, MPO cabling has become more popular than ever. We have indicated that 24-fiber MPO cable reveals more advantages than 12-fiber MPO cable, however, before choosing it, there are more factors we have talked above that should be taken into consideration.