Fiber cabling keeps up with zettabyte era

The increased migration of applications and workloads to cloud architectures and the surge in number of devices connected to cloud or IP networks are generating unprecedented volume, velocity and variety of data flowing through data centers. According to the Cisco Visual Networking Index forecast, global IP traffic will nearly triple from 2016 to 2021.

Last year, the annual global IP traffic surpassed 1 zettabyte (ZB) or one billion terabytes. This will hit 3.3 ZB per year by 2021, of which 82% will be video traffic. Cloud traffic, meanwhile, is expected to rise 3.7-fold, up from 3.9 ZB per year in 2015 to 14.1 ZB per year by 2020.

By then, 92% of workloads will be processed by cloud data centers with only 8% processed by traditional data centers.

“The fundamental problem that all data centers are going to have is to handle and move all that data around,” says Russell Dearnley, senior manager of Data Center Connectivity at Panduit Corp. “You need pipes big enough to move that data from one machine to another.”

Currently, the most efficient way for moving large volumes of data is through fiber optic cabling. Developments in four areas have boosted data transfer rates over such cables.

More data at faster rate

“One is the speed at which the laser can switch on and off,” says Dearnley. “Up until recently, 10 Gbps has been about the fastest they could turn on and off. And now, we’re starting to introduce lasers that can turn on and off at 25 Gbps and within two to three years, we’ll be using lasers that switch on and off at 50 Gbps. We’re going to five times the speed in a space of two to three years.”

Another way of increasing data transfer rate is to use parallel optics. For example, an incoming 40 Gb signal is split into four 10 Gb signals, which are transmitted down four fibers. “At the other end, you combine it all back again and you’ve got your full 40 Gb or in the case of 100 Gb, you split it up into 25 Gb signals and then multiplex them back together,” explains Dearnley.

Advances in opto-electronics have also helped to increase the bit rate in the channel without increasing the required bandwidth. Instead of lasers just turning on and off, which is the most simple pulse amplitude modulation (PAM) scheme, the number of signal levels is increased. In 4-level PAM or PAM-4, for example, the amplitude levels are doubled from two to four, each represented by a two-bit signal – 00, 11, 01 and 10. “So, you now have basically four levels of information,” says Dearnley. “That’s another way of doubling the [data rate].”

The fourth area of enhancement is wavelength division multiplexing. “Instead of just sending that one wavelength down the fiber, you send more than one,” adds Dearnley. “The first commercial application in the marketplace is Cisco’s BiDi optical technology, where they were using two wavelengths, one wavelength in one direction and another in the reverse direction. Because they are independent, they don’t interfere so you can actually put twice as much information on the fiber.”

Further, the SWDM Alliance is promoting the adoption of shortwave wavelength division multiplexing (SWDM) as a cost-effective means of transmitting multiple channels over duplex multimode fiber at data rates at or above 40 Gbps. The alliance is now focused on 40 Gbps using four 10 Gbps wavelengths, to generate individual data streams multiplexed onto a single fiber pair. It combines the four technological advancements described above in various different ways to increase data rate over multi-mode fiber.

Matching fiber

To support the high data rates of SWDM applications as well as at least legacy OM4 applications on multi-mode fiber, the Telecommunications Industry Association (TIA) published in June 2017 a new fiber specification that defines Wideband Multimode Fiber (WBMMF), which will be referred to as OM5 in the 3rd edition of ISO/IEC 11801: Information Technology – Generic Cabling for Customer Premises.

Additionally, hyper-scale, web-scale data centers that deploy millions of circuits are beginning to use more and more single-mode applications. With economies of scale, the price difference between multi-mode fiber optics, which have been the predominant choice within the data center, and single-mode fiber optics, which offer longer transmission distance and more bandwidth, is decreasing.

“I don’t think multi-mode will ever go away,” Dearnley predicts. “I think there are just going to be different applications but I think single-mode will become somewhat more significant in data centers, especially large data centers.”

The main challenge is to get the cost of single-mode optics down to a level feasible for applications in data centers. Still, single-mode cabling is inherently suited for data transmissions over longer distances than multi-mode cabling.

But undeniably, the use of fiber optics will become more prevalent in the data center as IT organizations grapple with the rapid rate of data traffic growth in the zettabyte era.