12-core connection technology uses fiber optic cable in increments of 12 fibers using MTP connectors for 12 fibers. More recently, 8-core connectivity solutions are beginning to emerge. 8-core systems will still use MTP-type connectors, including connectors for eight fibers, but manufacture the fiber optic cable in eight-fiber increments. For example, instead of a 12-fiber backbone, an 8-fiber backbone, a 16-fiber backbone, a 24-fiber backbone, and a 32-fiber backbone are used in 8-core systems; all 8-fiber backbone cables are in figure-eight increments.
With the introduction of 12-core connectivity in the mid-1990s, it became clear that stringing two-core fiber patch cords all over the data center would create a cluttered dilemma of unmanageability and reliability as the data center grew from just a few fiber connectors to thousands of fiber ports. Since the TIA/EIA-568A fiber color coding standard was developed for 12-cell fiber optic cable, high-density connections could be implemented in increments of the number 12, so 12-cell fiber MTP connectors and 12-cell fiber optic cable connection technology was born. Since then, backbone cables in 12-core fiber and even 144-core fiber increments have been introduced and deployed worldwide. 12-core backbone cables are typically used for network backbones that exit from the main distribution line and connect to partitioned wiring areas, where fiber usage is high and cable usage density is high. Most fiber ports require two fibers to connect to ports on servers, switches, and storage devices, so 12-cell to 2-cell patch panels and branch patch cords are required to provide a two-cell fiber interface to the two-cell fiber ports. Since the number 12 is divisible by the number 2, we can easily provide a two-core fiber interface to network devices for a complete fiber application with a 12-core backbone cable.
Data Center Cabling
For nearly 20 years, 12-conductor fiber optic cable connectivity has served the data center industry well. Due to the dramatic increase in deployments of 12-fiber MTP connectors in recent years, MTP has now become the accepted standard in many data center backbone networks. But times are changing, and more recently 8-conductor connectivity has become increasingly common. On the one hand, this is due to a shift in the types of transceivers that switch, server and storage manufacturers are using in their equipment, and on the other hand, the direction of transceiver development is leading the industry from 10G Ethernet to 40G, 100G and even 400G. The technology in the transceiver space is changing rapidly, but anyone who has installed a 40G line knows that one of the most common transceiver types, the QSFP transceiver, uses exactly eight cores of fiber optic cable. We can connect to QSFP ports using 12-core connection technology, and indeed, many people using 40G lines do use 12-core connection technology in their trunk networks today. However, anyone who has studied basic math knows that plugging a 12-fiber connector into a transceiver that only requires eight fibers means that four fibers are not being used. There are solutions on the market that achieve 100% full utilization of the backbone fiber in this scenario with 12-conductor to 8-conductor conversion modules or branch patch cords, but this adds additional MTP connectors and insertion loss to the fiber cable. Generally speaking, this is not an optimal solution in terms of cost or cable performance, so the industry has recognized the need for a more reasonable solution. That solution is 8-cell fiber optic cable connection technology. Talking to the major transceiver, switch, server and memory manufacturers, it is clear that the current, near and long term future will be the era of transceivers supporting 2 or 8 core fiber optic connectivity. In other words, the trend in the 40G-400G Ethernet data transmission space is toward two- and eight-fiber connectivity solutions.
The move to 400G will see the adoption of shorter term solutions such as the first and second generation OM3/OM4 parallel transmission technologies, where 32- and 16-cell fiber solutions are recommended. But Corning's discussions with prominent transceiver, switch, server and memory vendors have revealed that because of manufacturing costs and connector complexity (for example, do you really want to add a 32-fiber connector to your network?) For this reason, they did not want to use this solution extensively. Therefore, for 400G networks with parallel transmission over OM3/OM4 fiber, the third-generation solution, the 8-cell solution, is expected to gain widespread acceptance in the market. Because the number eight is divisible by the number two, the 8-cell fiber optic backbone connection can be used as easily as the 12-cell fiber optic connection in a two-cell fiber optic transceiver system. At the same time, 8-cell cable connectivity offers the most flexibility for the most widely used 40G, 100G and 400G transceivers, while 12-cell cable connectivity is not the best solution for an eight-fiber transceiver system. In short, 8-core fiber optic cable connection technology is the best solution for future 400G data transmission requirements.
Can 8-core and 12-core fiber optic cables be used together?
Not necessarily. It depends on what we mean by "simultaneous use". If you think of it as a straight mix of components and plugging an 8-core backbone cable into a 12-fiber module, the answer is definitely "no." The two types of assemblies are not designed to be plugged directly into each other, nor are 12- and 8-fiber cables designed to look the same, so you cannot mix 8- and 12-fiber assemblies in the same cable connection. A major cosmetic difference between the two types of cables is that the connectors at the ends of 12-core backbone cables generally do not have locating pins, and require the use of junction blocks with locating pins. The newer 8-conductor backbone cables are manufactured with locating pins on the connectors at both ends. Therefore, the 8-conductor backbone cable will definitely not fit into the 12-conductor cable terminal block, because that would mean trying to connect two connectors with locating pins together. The reason for this change in the backbone plug scheme is that it is more advantageous to ensure that whenever fiber optic cable is used in the network, the 8-conductor MTP jumper can always be used without locating pins on both ends of the connector. This simplifies network deployment and eliminates the need to purchase large quantities of header MTP patch cords with locating pin connectors. However, if "simultaneous use" is understood to mean using both 8- and 12-conductor fiber optic cable connection technology in the same data center, then the answer is "yes," but with one condition. This condition is that the 8-core and 12-core cables must be used separately because, as we mentioned earlier, the 8-core and 12-core components are inherently non-interchangeable and the 8-core and 12-core components cannot be plugged into each other in the same cable link. Therefore, a little care should be taken when managing the physical layer infrastructure of the data center to ensure that 8-core and 12-core cable assemblies are not mixed in the same cable link.
8-core versus 12-core fiber optic cable: How do I choose?
Because 12 is significantly larger than 8, 12-cell cable connection technology does have an advantage in terms of connector fiber usage density compared to 8-cell cable connection technology, and therefore allows for faster installation of large amounts of fiber when using 12-cell cable connection technology. However, because of the higher number of 40G and 100G line deployments, where eight-fiber transceivers are used, the advantage of keeping the number of fibers in the MTP backbone consistent with the number of transceiver fibers outweighs the density advantage of 12-fiber connections. In addition, when using MTP to LC duplex branch patch cords to connect to switch line cards, 8-cell branch patch cords can be easily routed to ports on all common line cards because the number of ports on all common line cards is divisible by the number four (since 8-cell branch patch cords provide four LC duplex connections). In the case of 12-cell branch patch cords that provide six LC duplex connections, these branch patch cords cannot be easily routed to line cards with 16 or 32 ports because the numbers 16 and 32 are not divisible by the number six.
While the density of fiber used per connector is not negligible, most people are more concerned about migrating to 40G and 100G speeds faster. Anyone planning to migrate their data center to a 40G or 100G network in the near future will now find it advantageous to use 8-cell fiber optic cable connectivity.
