  To cater to the demands of our rapidly growing Internet traffic, backbone
networks need high-degree reconfigurable optical add/drop multiplexers (ROADMs)
to simultaneously support multiple pairs of bi-directional fibers on each link.
However, the traditional ROADM architecture based on the Spanke network is too
complex to be directly scaled up to construct high-degree ROADMs. In addition,
the widely deployed Spine-Leaf datacenter networks (DCNs) based on electrical
switches consume too much power and exhibit high packet latency. Because of
these issues, Clos networks are considered as promising alternatives for
constructing large-scale ROADMs and all-optical DCNs. In this article, we look
at a next-generation Clos-based ROADM architecture and show that it indeed
provides better blocking performance with lower element and fiber complexities
compared with a traditional Spanke-based ROADM architecture. We also discuss
the application of a Clos network in all-optical DCNs to show that it can be
used to effectively construct large-scale DCNs with significantly greater
flexibility in supporting a variety of multicast services and in combining
different network topologies.
