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ICT Today Nov/Dec

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Multimode Market Continues to Boom According to the 2017 Cisco Visual Networking Index, the amount of IP traffic is growing at an annual rate of 24 percent worldwide. The 2018 Cisco Global Cloud Index shows that global data center traffic is expected to increase from 6.8 zettabytes (ZB) in 2016 to 20.6 ZB in 2021. While the most significant growth is expected in the Asia Pacific region, every segment of the globe shows significant growth. This demand drives the need for higher speed networks, and consequently higher optical fiber volume in all regions. Among Cisco's other findings: there is almost five times more traffic inside the data center than from the data center to the user. When combined with data center interconnect traffic, this so-called "east-west traffic" accounts for more than 85 percent of total traffic. This helps to explain the demand for higher data center network speeds and more links between servers and switches. It is a truism that the enterprise data center is moving to the cloud. But what exactly does that mean? An obvious answer is that some enterprises are migrating to public cloud services offered by hyperscale vendors, such as Google, Microsoft, Amazon and others, but there are other approaches. An enterprise private cloud can provision service for its users in similar fashion to one of the hyperscale providers, but with owned rather than leased facilities. A combination of the two approaches can also be used. Cisco projects that the enterprise cloud, now the majority of the market, will continue to grow throughout the study period, reflecting a migration from legacy enterprise data centers, and in some cases, a pull back to in-house control from hyperscale providers. The public cloud will grow at an even faster pace, while the legacy enterprise data center will decrease. It is sometimes taken as fact that hyperscale data center customers only want singlemode fiber. However, Google, Alibaba and Baidu, for example, have deployed multimode fiber applications and continue to plan for its use in their roadmaps. The market is also seeing an increasing interest in multimode applications from other hyperscale players in the United States for 400G-SR4.2 (a standard to be discussed later) and 400G-SR8 for a variety of applications, including breakout. Given the distance advantages offered by singlemode fiber, why is multimode fiber still a preferred media? The reasons have to do with cable size, design and cost. How Multimode Fiber Stacks Up Until about 2010, copper had been used for data center server links. However, as server speeds increased, the link distance supported by copper twinaxial cable (twinax) and UTP Category5/6 cables significantly decreased, in some cases to as short as five to seven meters (m). For 40 Gb/s links, an 8-pair twinax cable is often used. However, a twinax cable is three or four times the diameter of a fiber cable (Figure 1). When large numbers of these cables are used, it significantly affects airflow around the rack, making it much more difficult to cool. By comparison, optical fiber cables, with their much smaller diameter, demand far less cable management space and are easier to manage. FIGURE 1: Size difference between copper twinax (8 pair) and duplex fiber solutions for 40 Gb/s. Among optical fiber types, multimode continues to be more cost-effective than singlemode for these shorter reach applications. While the cost of multimode fiber 8-9 mm 2-4 mm November/December 2018 I 21

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