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The difference between 8-core fiber optic cable and 12-core fiber optic cable

2022-09-13
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"While 12-fiber connectivity technology will still have a place in the data center industry, in the long run, 8-fiber technology will be more and more adopted by data centers."

 

Definition of 8-core fiber optic cable

When it comes to fiber optic connections, various terms are used to describe the cable, depending on the type of connector used and the number of fiber cores used in the cable. 2-core cables are easier to understand and identify. When using a 2-fiber connection, the cable is in increments of two fibers, such as the common LC duplex or SC duplex connectors.

 

For comparison, when using fiber optic cable with 12-fiber connection technology, 12-fiber MTP© connectors are used in increments of 12 fibers. More recently, 8-pin connectivity solutions have begun to emerge. The 8-fiber system will still use MTP-type connectors, including eight-fiber connectors, but the cables will be manufactured in eight-fiber increments. For example, in an 8-core system, there is no trunk cable with 12 fibers, but a trunk cable with 8 fibers, a trunk cable with 16 fibers, a trunk cable with 24 fibers, and a trunk cable with 32 fibers; all 8 Core trunk cables are in increments of eight.

fiber optic cable

Review: Origin of 12-fiber cable

The 12-fiber connection technology was introduced in the mid-1990s by IBM and Corning. At the time, the two companies were working on a modular, high-density structured fiber optic cable system that could be rapidly deployed into a data center, while still allowing maximum port density in a rack. After the data center has grown from only a few fiber optic connectors to thousands of fiber optic ports, it is obvious that the patch cords connecting two-core optical fibers in series in the data center will cause a messy dilemma that is difficult to manage and has poor reliability.

 

Since the TIA/EIA-568A fiber color coding standard is formulated for 12-core fiber optic cables, high-density connections can be used to achieve digital 12-increment connection technology. Therefore, 12-core fiber MTP connectors and 12-core fiber optic cables Connectivity technology came into being. Since then, trunk cables with increments of 12-core fibers and even 144-core fibers have been introduced and deployed worldwide.

 

The 12-core trunk optical cable is generally used for the network backbone, which is directly connected from the main wiring and connected to the partitioned wiring area. At this time, the amount of optical fibers is large, and the density of optical cables is high. Most fiber ports require two fibers to connect to ports on servers, switches, and storage devices, so 12-fiber to 2-fiber patch panels and breakout cords are required to provide two-fiber ports with two fibers fiber optic interface. Since the number 12 is divisible by the number 2, we can easily provide a two-fiber interface for network equipment to implement a complete optical fiber application for a 12-core trunk cable.

 

The difference between 8-core and 12-core fiber optic cable

The rise of 8-fiber cables

For nearly 20 years, 12-fiber fiber optic connection technology has served the data center industry well. Due to the explosion in deployments of 12-fiber MTP connectors in recent years, MTP is now the established standard in many data center backbone networks. But times are changing, and 8-pin connection technology is becoming more common these days. On the one hand, this is due to a shift in the types of transceivers that switch, server and memory manufacturers use 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.

 

Technological innovations in transceivers are changing rapidly, but anyone who has installed a 40G line knows that one of the most common types of transceivers, QSFP transceivers, uses eight-fiber fiber optic cables. We can connect to QSFP ports using 12-fiber connection technology, and in fact, many people who use 40G lines do use 12-fiber connection technology in trunk networks these days. However, as anyone who has learned basic math knows, plugging a 12-fiber connector into a transceiver that requires only eight fibers means four fibers are not useful. There are solutions on the market that achieve 100% full utilization of the backbone fiber in this solution through 12-fiber to 8-fiber conversion modules or breakout cables, but this adds extra MTP connectors and insertion loss to the cable. Generally speaking, this is not the best solution in terms of cost or cable performance, so the industry also recognizes the need for a more reasonable solution.

 

This solution is the 8-core fiber optic cable connection technology. Talking with major transceiver, switch, server, and storage manufacturers, it is clear that the current, near-term and long-term future will be the era of transceivers supporting 2-fiber or 8-fiber fiber optic connectivity technologies. . In other words, the development trend in the field of 40G-400G Ethernet data transmission is the connection solution of two and eight fibers.

 

In the process of developing to 400G, some solutions with shorter usage time will be adopted, such as the first and second generation OM3/OM4 parallel transmission technology, in which 32-core and 16-core fiber optic cable solutions are recommended. But Corning learned from discussions with prominent transceiver, switch, server, and storage vendors that due to manufacturing costs and connector complexity (say, you really want to add a 32-fiber connector to your network) ?), people don't expect widespread use of this solution. Therefore, for the 400G network with parallel transmission through OM3/OM4 fiber, the third-generation solution—the 8-core fiber optic cable solution is expected to gain wide acceptance in the market.

 

Because the number eight is divisible by the number two, the 8-core fiber optic backbone network connection technology can be easily applied in the two-core fiber transceiver system like the 12-core fiber optic cable connection technology. At the same time, 8-fiber cable connection technology provides the most flexibility for the most widely used 40G, 100G and 400G transceivers, and 12-fiber cable connection technology is not the best solution for eight-fiber transceiver systems. In short, 8-core fiber optic cable connection technology is the best solution for future 400G data transmission requirements.

 

Can 8-core fiber optic cable and 12-core fiber optic cable be used at the same time?

Not necessarily. It depends on our understanding of "simultaneous use". If it is understood as directly mixing components and plugging an 8-fiber trunk cable into a 12-fiber module, the answer is definitely "no". According to the design purpose, these two components cannot be directly inserted into each other's components. Similarly, the appearance of the 12-core fiber optic cable and the 8-core fiber optic cable are different in design, so the 8-core fiber optic cable and the 12-core fiber optic cable cannot be mixed in the same fiber optic cable connection at the same time. fiber optic cable assemblies.

 

A major appearance difference between the two types of optical cables is that the connectors at both ends of the 12-core trunk cable generally do not have positioning pins, and a wiring module with positioning pins is required. However, the new 8-core trunk cable is manufactured with positioning pins on the connectors at both ends. Therefore, the 8-fiber trunk cable definitely cannot be plugged into the 12-fiber cable patch module, because that means we are trying to connect two connectors with alignment pins together. The reason for this change in the trunk cable plug scheme is that it has the added advantage of ensuring that the 8-fiber MTP cable ends will always use the connector without locating pins whenever the cable is used in the network. This simplifies network deployment and eliminates the need to buy a lot of MTP patch cords with locating pin headers.

 

But if "simultaneous use" is understood as the simultaneous use of 8-fiber cable and 12-fiber cable connection technology in the same data center, then the answer is "yes", with one condition. This condition is that the 8-core optical cable and the 12-core optical cable must be used separately, because we have mentioned earlier that the components of the 8-core optical cable and the 12-core optical cable are not interchangeable, and in the same optical cable link, the 8-core optical cable and the 12-core optical cable are not interchangeable. Fiber optic cable assemblies cannot be plugged into each other. Therefore, some care must be taken when managing the physical layer infrastructure of the data center to ensure that 8-fiber and 12-fiber cable assemblies are not mixed in the same cable link.

 

Comparison of 8-fiber cable and 12-fiber cable: how to choose?

 

Because 12 is significantly larger than 8, 12-fiber cable connection technology does have an advantage in terms of connector fiber density compared to 8-fiber cable connection technology, so a large number of fibers can be installed faster when using 12-fiber cable connection technology. However, since 40G and 100G are deployed in higher numbers of lines using eight fiber transceivers, the advantage of keeping the number of fibers in the MTP backbone connection technology consistent with the number of transceiver fibers trumps 12 fibers. The density advantage of fiber optic cable connection technology.

 

Additionally, when using MTP-to-LC duplex breakout patch cords to connect to switch line cards, the 8-pin breakout patch cords can be easily routed to the ports of all common line cards, since all common line cards have port counts that are divisible by four (Because an 8-pin breakout cord provides a four-way LC duplex connection). In the case of 12-pin breakout patch cords that provide six LC duplex connections, those breakout 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. The comparative advantages of 8-fiber cable and 12-fiber cable connection technology deployed in data centers are detailed in the table below.

 

Advantages of 8-core fiber optic cable

The best choice for two-fiber and eight-fiber transceiver technology

Ensure that the transceiver system of eight-core fiber achieves 100% fiber utilization, and the conversion equipment from 12-core fiber optic cable to 8-core fiber optic cable will not increase the cost and insertion loss

 

Breakout jumpers can be easily routed to ports on all common line cards of the switch

 

Only MTP jumpers without alignment pins are required for any connection in the link

 

The most flexible solution for 40G, 100G and 400G data transmission networks

 

Advantages of 12-fiber cable

Greater fiber density per connector than 8-core fiber optic cable

Compatible with large-scale fiber counts installed in existing 12-fiber MTP deployments

 

While the density of fiber used per connector cannot be ignored, most people are more concerned with migrating to 40G and 100G speeds faster. For now, anyone planning to migrate their data center to a 40G or 100G network in the near term will find it more advantageous to use 8-fiber cabling technology.

 

Epilogue

For many years to come, data centers will continue to use 8-fiber cable and 12-fiber cable connection technology. Both methods have their own advantages and have their own place in the data center field, and whether to use 40G and 100G data transmission is a key determining factor. If your data center is using 12-fiber cabling technology and you're comfortable with it, you can rest assured to continue using 12-fiber cabling technology. 8-fiber cabling technology is just one option in the network designer's toolkit to ensure data centers are cost-effective, have a future-proof network, and easily migrate to 400G transport networks.

 

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