Base-2 connectivity is a common type of fiber optic link in today’s 10G network, such as LC duplex or SC duplex connections. With Base-2 connectivity, the fiber links are based on increments of two fibers. However, this kind of connectivity can not meet the demands of 40G links for the reason that numerous 2-fiber patch cords in the data center will result in an unmanageable, unreliable mess. Therefore, Base-12 and Base-8 connectivity are introduced successively to develop a modular, high density, structured cabling system for 40G network. Then, which is more suitable for the 40G links, Base-8 or Base-12 connectivity?
This part will give a brief introduction to Base-12 connectivity and Base-8 connectivity respectively.
Inspired by the fact that the TIA/EIA-568A fiber color coding standards are based on groups of 12 fibers, it makes sense that high density connectivity can be based on an increment of the number 12. Thus the 12-fiber MTP connect and Base-12 connectivity were born in the mid-1990’s. In a Base-12 system, Base-12 connectivity makes use of links based on increments of 12 fibers with 12-fiber MTP connectors (as shown in the following figure).
Due to the quickly-changing technology associated with transceivers, switches and servers, data centers that want to keep up may need to use Base-8 connectivity. This is because the present, near future, and long term future is full of transceiver types which are based on either Base-2 or Base-8 connectivity. The Base-8 system still uses the MTP connector, but the links are built in increments of 8 fibers (as shown in the following figure). Thus there are 8-fiber trunk cables, 16-fiber trunk cables, 24-fiber trunk cables and so on.
It is known to us that transmission at 40G is mainly based on using eight fibers in the link–four for transmitting and four for receiving at 10G (as shown in the following figure). In addition, QSFP transceivers and MTP connectors are commonly used in the 40G network. Thus we can use Base-12 connectivity and Base-8 connectivity to connect to the QSFP ports.
If Base-12 connectivity is used in the 40G network, it is easy to figure out that plugging a 12-fiber connector into a QSFP transceiver only requiring eight fibers means four fibers are being unused. Thus, there appears Base-12 to Base-8 conversion modules or harnesses to enable the full utilization of the backbone fiber. The followings are three common solutions of Base-12 connectivity for 40G network:
Seen from the above picture, there are four unused fibers in solution 1, which leads to a significant and costly loss in fiber network utilization; solution 2 and solution 3 add additional MTP connectors and additional insertion loss into the whole link. In this case, Base-12 connectivity is not the optimal solution in 40G network both for cost and link performance reasons.
Unlike Base-12 connectivity, Base-8 connectivity enables 100% fiber utilization for QSFP transceivers without any additional cost and insertion loss of Base-12 to Base-8 conversion devices. And its cabling is much more simple and flexible (as shown in the following figure). The imperfection of Base-8 connectivity is that it does not provide as high connector fiber density as that of Base-12 connectivity.
Though Base-8 connectivity is superior to Base-12 connectivity in some aspects, both Base-8 and Base-12 connectivity will be used in the data center for many years to come. In fact, Base-8 connectivity isn’t an universal solution and Base-12 connectivity in some cases may still be more cost-effective. The following table clearly shows the benefits of Base-8 connectivity and Base-12 connectivity:
|Benefits of Base-8 Connectivity||Benefits of Base-12 Connectivity|
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