Summer 2018 Optical Connections Magazine


change,” reported the Facebook technical team in a blog. “This, in turn, results in significant eciencies, power savings, and increased flexibility.” 400 G ZR: Prospects and Challenges Up until recently, one of the limitations of using higher order modulation formats and DWDM to boost DCI bandwidth was the requirement to use proprietary optical modules at each end of a link. Responding to input from a number of large scale datacentre players, the Optical Internetworking Forum (OIF) began working to standardise what turned out to be 400 Gigabit Ethernet DCI links operating over distances of 80 km, or somewhat above. The result is the low cost 400G ZR standard now being adopted by builders and operators. Along with greater freedom in investment decisions and increased supply chain flexibility, 400 G ZR aims to provide a low cost, low power and a low footprint solution for DCI applications over up to 120 km distances. But there is some unfinished 400 G ZR business. “One key challenge of commercialising 400 ZR is fitting the coherent digital signal processor and electro-optics component within a very small footprint and power envelope,” suggests Xenos. “Also, product development with new 7 nm complementary metal-oxide- semiconductor technology will be required, which is a significant investment for component suppliers.” She concludes that 400 G ZR will address a limited set of applications. “It cannot operate for reaches beyond 120 km, and will not be compatible with metro ROADM networks, which are deployed by many ICPs, multi-tenant datacentres, enterprises and service providers today.” MIXED FORTUNES AHEAD Experts predict that dierent types of player will have an impact on, and be impacted by, future DCI market expansion

making the patch panel just as responsive and agile as the rest of the datacentre.”

that ICPs will continue to globalise their core businesses, driving more subsea DCI growth, and 4K video rollouts will drive DCI growth for CSPs. Writing on the Ovum Straight Talk briefing service in 2018, Redpath suggests that vendors need to find avenues to achieve trusted partner status with ICPs: “The ability to meet unforecasted short-lead-time orders is one way in which vendors can endear themselves to their ICP clients.” Meantime, although Ovum finds that beyond US borders most CSPs have a strong position in the DCI market in their territories, DCI solutions for the CSP community will need to meet multiservice requirements and will require a path to 5G. Again, IHS Markit observes that, while traditional carriers have adopted Optical Transport Network (OTN), ICPs have standardised on Ethernet as the preferred technology providing sub-wavelength aggregation and switching. “With no legacy TDM trac or connection- oriented services to support, the business case for introducing OTN services, OAM and/or OTN switching infrastructure is less apparent,” according to Adams. In any event, there will be testing times for DCI solutions vendors. “Bandwidth growth is a certainty, but individual vendor revenue growth is not; the DCI market is intensely competitive, and in the past, ICPs have in some cases bypassed the system vendors,” observes Redpath. “For vendors, there is no rest for the wicked, nor for the virtuous; they must keep the long game in mind.”

DCI DISAGGREGATION IHS Markit believes that the growth in the compact DCI equipment sector noted in its report represents a broader industry trend toward optical equipment disaggregation. In this, dierent functions in the optical network can be addressed by open hardware platforms and linked together through SDN controllers and applications. “As disaggregated equipment configurations get proven out in DCI applications, we can see usage expanding to address other areas in metro optical and enterprise applications,” comments Heidi Adams, senior research director, IP and optical networks, IHS Markit. “Requirements for compact, modular systems extend beyond the transponder or muxponder to the photonic line system,” adds Xenos. She instances her company’s new 6500 Reconfigurable Line System (RLS) as an example of a solution optimised for photonic layer functionality, and able to be configured for simple functions such as line amplification or more robust configurations, such as full Colourless- Directionless-Contentionless ROADM, allowing it to fit into a variety of disaggregated line system applications. One famous case of disaggregation to meet extraordinary demands on network capacity and deliver very flexible scalability is Facebook’s (somewhat confusingly named) Fabric Aggregator. Rather than keep on expanding traditional datacentre switching and associated equipment, Facebook has built distributed network systems using simple, smaller, interchangeable building blocks such as the group’s own Wedge 100 switch, the Facebook Open Switching System (FBOSS) software stack, and a cabling assembly unit to emulate the backplane functionality of classic chassis arrangements. “With this approach, we can scale the capacity, interchange the building blocks, and change the cable assembly quickly as our requirements



Photonics (SiPh) is a

technology with considerable appeal for

streamlining optical datacentre

networking. “Interest is fueled mainly by Google, Apple, Facebook, Amazon, and Microsoft (GAFAM) due to several advantages: low cost, higher integration, more embedded functionalities, higher interconnect density, lower power consumption, and better reliability compared with legacy optics,” observes Dr. Eric Mounier, senior technology & market analyst at Yole Développement. “But challenges are still present, especially for laser source integration, modulator eciency, lower-cost packaging, and integration.”

in some dierent ways. For example,

Ian Redpath, leader at Ovum’s

Optical Networks, Optical Components and Core Switching practice, argues


ISSUE 13 | Q2 2018

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