  An optical circuit-switched network core has the potential to overcome the
inherent challenges of a conventional electrical packet-switched core of
today's compute clusters. As optical circuit switches (OCS) directly handle the
photon beams without any optical-electrical-optical (O/E/O) conversion and
packet processing, OCS-based network cores have the following desirable
properties: a) agnostic to data-rate, b) negligible/zero power consumption, c)
no need of transceivers, d) negligible forwarding latency, and e) no need for
frequent upgrade. Unfortunately, OCS can only provide point-to-point (unicast)
circuits. They do not have built-in support for one-to-many (multicast)
communication, yet multicast is fundamental to a plethora of data-intensive
applications running on compute clusters nowadays. In this paper, we propose
Shufflecast, a novel optical network architecture for next-generation compute
clusters that can support high-performance multicast satisfying all the
properties of an OCS-based network core. Shufflecast leverages small fanout,
inexpensive, passive optical splitters to connect the Top-of-rack (ToR) switch
ports, ensuring data-rate agnostic, low-power, physical-layer multicast. We
thoroughly analyze Shufflecast's highly scalable data plane, light-weight
control plane, and graceful failure handling. Further, we implement a complete
prototype of Shufflecast in our testbed and extensively evaluate the network.
Shufflecast is more power-efficient than the state-of-the-art multicast
mechanisms. Also, Shufflecast is more cost-efficient than a conventional
packet-switched network. By adding Shufflecast alongside an OCS-based unicast
network, an all-optical network core with the aforementioned desirable
properties supporting both unicast and multicast can be realized.
