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2-Fiber vs. 8-Fiber: Overcoming Data Center Cabling Challenges

Posted on Aug 3, 2022
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As data centers are expanding, the demand for higher data transfer rates keeps going up, and this increase is expected to continue. As a result, data center cabling has to meet the challenge of the ever-increasing data transfer rates. This article explains ways to achieve higher data transfer rates, and discusses how a 2-fiber duplex structured cabling solution stacks up against an 8-fiber parallel one to meet data center cabling challenges.

Ways to Achieve Higher Data Transfer Rates

Before we spend time discussing how to overcome data center cabling challenges with structured cabling solutions, we need to first start with different ways used to achieve the ever-increasing data transfer rates.

Increase the baud rate: The simplest way to achieve high data transfer rates. It's just increasing the rate that you can turn the laser on or off. This method works well for lower data rates such as 10G. As data rates get higher, it becomes problematic since signal-to-noise ratio starts to become an issue.

Increase the number of fibers: If you can use two fibers to create a 10G or 25G connection, you can also create a 40G or 100G connection with eight fibers. It can be realized by utilizing several pairs in a parallel transmission scenario.

Increase the number of wavelengths: This is most commonly referred to as wave division multiplexing (WDM). Several sources have to be used. The signal has to be multiplexed into a single fiber and then de-multiplexed once it is received.

Change modulation format: Compared to simple non-return to zero (NRZ), pulse amplitude modulation (PAM4) can allow transceivers to transmit four times the amount of data in the same time slot.

Regardless of which of these ways is used, in the end, either a 2-fiber duplex or 8-fiber parallel solution is used. Some 100G and early 400G solutions may use 16 or 32 fibers, but they all can be achieved with an 8-fiber infrastructure.

2-Fiber vs. 8-Fiber

Choosing a 2-fiber duplex or 8-fiber parallel solution is not a simple choice. Here we will take some time to explore both options. Each option is evaluated from different perspectives including price, power consumption, density, and flexibility.

Price

We know that for links shorter than 100 meters, multimode fiber and associated optics are used. For links greater than 100 meters, single-mode parallel optic links are a valid option. Thus, most hyperscale and cloud data centers only employ single-mode links.

For 2-fiber duplex connections, new components have to be developed to enable higher data transfer rates, driving up the overall cost. In contrast, 8-fiber parallel optic connections utilize existing technologies to build a more efficient system. In addition, 8-fiber parallel optics can use either four uncooled lasers or a single laser coupled with a waveguide splitter and four modulators. This means 8-fiber parallel optics is cheaper to manufacture.

Power Consumption

Power is arguably the single largest operating expense inside a data center. For this reason, data center owners and managers go to great length to lower power consumption anywhere in a data center. A single 10G connection consumes 1W of power. By contrast, a 40G parallel optic (8-fiber) utilizes 1.5W of power. Moreover, another thing to keep in mind is cooling. Generally speaking, you need 1 kW of cooling for every 1 kW of power consumed. So the reduction in power consumption of devices also translates to a reduction in power consumption due to cooling.

Density

A 8-fiber parallel optic links also provide a significantly denser solution. Most high-density SFP+ switch line cards are offered in a maximum of 48 ports. High-density QSFP line cards come with 36 ports. If you operate QSFP line cards in breakout mode, each of those ports can now be used as four 10G ports. So you can support up to 144 10G links with a single QSFP line card. This not only triples the density of switches but also decreases the number of line cards needed to support the network. This also means fewer power supplies, fan trays, supervisors, system controllers, fabric modules, and software licenses.

Flexibility

Compared to a 2-fiber structured cabling system, a base-8 structured cabling system grants more flexibility and clearer migration path to higher data transfer rates. With 8-fiber parallel optics, you can have an easier way to upgrade your system with maximum density and power savings. If you want to migrate your network from breakout 10/25G to native 40/100G, the existing 40/100G optics and line cards used in breakout mode can continue to be used to operate the 40/100G links.

from 10g to 400g

Meet the Challenge with Structured Cabling

Structured cabling is not a new concept. Many data center cabling systems use multifiber connectors referred to as preterminated trunk cables. Those preterminated trunk cables, usually from 12 to 144 fibers, are used to connect different areas of the data center. However, their bulky trunk sizes are too insufficient. These cables are now required to have fiber counts of 288, 432, and even 576 fibers in data center cabling systems. The use of base-8 high-fiber-count cables in structured cabling allows for greater fiber density in cable pathways. The system can also reduce the deployment time with fewer cable pulls as well as the overall installation cost.

Summary

New technology changes as well as future data center requirements will make data center cabling planning more challenging. High-fiber-count structured cabling based on 8-fiber connection may be a prime choice, but data center owners and managers still have to keep an eye on their data center cabling systems and plan for the future.

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