In its first 27 years of existence we saw the introduction of six Ethernet rates – 10Mbps, 100Mbps, 1Gbps, 10Gbps 40Gbps and 100Gbps. And the Ethernet community is now working feverously to introduce six new rates -- 2.5Gbps, 5Gbps, 25Gbps 50Gbps, 200Gbps and 400Gbps-- in the next three years.
Higher Ethernet rates used to be introduced when industry bandwidth requirements drove the need for speed. But with Ethernet’s success, it soon became apparent that one new advance could satisfy the requirements of each Ethernet application space. This was clearly illustrated nearly 10 years ago when it was recognized that computing and networking were growing at different rates. This led to 40Gbps being selected as the next rate for servers beyond 10Gbps, while 100Gbps was selected as the next networking rate.
The industry, however, has a funny way of taking an Ethernet solution and applying it as it sees fit. Rather than use 40GbE as a server solution, the industry applied it in conjunction with 10GbE. This combination of 10GbE and 40GbE served to fuel the growth of hyper scale data centers, and while this has had a dramatic impact on the industry overall, it served to unchain Ethernet and lead to its next evolutionary step – introduction of rates targeted at applications, as opposed to force-fitting given Ethernet rates to given applications.
Figure 1- Ethernet Alliance Ethernet 2016 Roadmap
For example, 70 billion meters of deployed of Cat 5e and Cat 6 cabling, not capable of supporting the upgrade to 10GbE, led to the initiation of an Ethernet project to develop 2.5GbE and 5GbE BASE-T. These new specifications can be applied to the deployed cable infrastructure giving a needed speed-boost to campus and enterprise applications that are looking to deploy the next wireless standard, 802.11ac, that will drive the uplinks of wireless access points beyond today’s GbE uplinks.
So, while we saw 10GbE/40GbE data centers quickly being deployed, the industry recognized a couple of things. First, a higher density solution for 100GbE was necessary, and the easiest way to enable it was to reduce the width of the electrical interface from 10 lanes of 10Gbps to 4 lanes of 25Gbps. The industry also recognized the need for a higher speed of Ethernet beyond 100Gbps, which led to the industry effort to develop 400GbE.
The development of this higher speed Ethernet was different than the development of 40GbE and 100GbE, as new technologies were needed to develop a practical 400GbE solution. Figure 2 illustrates the options that can be considered during the development of new higher speed solutions, and how it was applied to the development of the target 400GbE specifications. More fibers running at 25Gbps was selected as the solution for operation over 100m of MMF. In the case of the solutions running over single mode fiber, operation at 50Gbps or greater was selected, and PAM4, a higher order modulation scheme, was chosen. And, while the 500m solution is running PAM4 at 100Gbps over 4 fibers, the 2km and 10km solutions added additional optical lambdas, and are running 8 lambdas at 50Gbps.
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