I included a few snippets from a paper published by ACG Research. The paper goes back to 2014 - pre-CloudXPress
The paper makes a case for an emerging DCI need and profile the case of Google and Facebook - and after reading it’s pretty easy to see the DCI purpose built solution Infinera came up with was meant to address these hyper-scale datacenter needs. I included the Google sections primarily below, as we already know enough about Facebook as a customer.
The growth of cloud-based services in consumer and business applications during the past five years has been spectacular. Projections are that this trajectory will continue during the next five years. By 2019 mobile network traffic is forecasted to increase tenfold. Half of this increase will be in video services, and an additional 10 percent will be in social networking applications. At the same time, business cloud computing services are expected to increase at a 40 percent average annual rate. By 2019 there will be 60 percent more data centers in the world’s metropolitan areas than there are today, and data center interconnect volumes will increase by more than 400 percent
Since the initial development of cloud-based services, the industry has recognized the need for data center interconnect (DCI). In the initial phases, providers deployed DCI solutions connecting end customer data centers to service providers’ data centers for offerings such as Infrastructure as a Service, hybrid cloud, Platform as a Service, and Software as a Service solutions. DCI has also been used to connect ecosystem partners with service providers’ data centers, for example in content distribution and compound application services.
New requirements for DCI have grown out of operators’ needs to deploy very high-capacity, high-speed, efficient transport between their own data center sites. In many cases we hear customer reports that their DC-DC traffic is growing faster than their DC-to-user traffic. The behavior and demand for cloudbased applications has forced operators to deploy highly interconnected internal data center sites, and their need for deploying DCI networks to support those applications has evolved alongside.
Cloud providers often lease wavelengths from traditional service providers to satisfy their DCI needs. However more and more cloud providers are deploying their own optical transport equipment over dark fiber as this provides superior economics in the face of a dramatic rise in DC-DC traffic. From the transport point of view, these deployments can be implemented using dedicated point-to-point optical links [Kevin: direct connect links like the Inphi solution] or using capacity on a shared optical network (metro or long haul). Choice of implementation is based on the required capacity, agility, available infrastructure, and overall cost. [Kevin: Note, these are the two solutions pre-DCI - note the point-to-point option]
Understanding that this mix of options has emerged for connecting cloud providers’ data centers in the market overall, let us turn our attention to the developments in hyper-scale providers’ services that are generating the need for a new class of DCI solution.
Google’s internal B4 WAN3 provides a dramatic example of the use of high-capacity, dedicated DCI between widely distributed internal sites. The B4 WAN communicates only between Google’s datacenter sites, is optimized for that purpose, and is separate from its customer-facing access network infrastructure.
To produce the B4 design, Google analyzed the pattern of its application communications for an extended time. In search, email, chat, video upload/download or other applications, Google identified needs for consistency in content across its data center sites; for high-quality experiences across its application portfolio; and for handling its own versions of the magnification effect efficiently across locations. Together these needs led to the design of a data center interconnect network of very large scale and with specific engineering requirements. The rate of growth of traffic between its data center sites is now greater than the rate of growth in its user-facing traffic—though both are large! The volumes carried between its data center sites are greater than the volumes flowing between its data centers and its users. The efficiency of its B4 DCI network is a fundamental enabler of Google’s ability to innovate and deliver its application portfolio globally, the Google Instant search enhancement as a recent example of that relationship.
If you want to see what Google B4 looks like now, you can see that here: https://youtu.be/zDAYZU4A3w0. Make sure you move yourself around as you watch - it’s in 3D.
And you can read more in the paper if you’re interested:
https://www.infinera.com/wp-content/uploads/2015/07/ACG-Rise…
Incidentally, the paper also lives on Infinera’s content servers. They must have thought it was a pretty good read, too. 
Best,
–Kevin