A cross-layer SDN control plane for optical multicast-featured datacenters

The increasing number of datacenter applications with heavy one-to-many communications has motivated the proposal of optical multicast-featured datacenter architectures. These solutions use optical power splitters to duplicate the optical signal from the input port to all the output ports on the fly, thus are promising for fast, reliable, economical, and energy-efficient group data delivery. Figure 1 illustrates how optical power splitters can be inserted into a datacenter. In case of heavy multicast communications from a particular sender to a group of receivers, an optical power splitter can be connected to these servers statically. They can also be placed to the level of Top-of-Rack (ToR) switches to aggregate traffic, so that a set of servers beneath the sender ToR switch can multicast to another set of servers across the destination ToR switches. Dynamic allocation of optical power splitters can be achieved by having a high-radix optical space switch, e.g. a 3D MEMS switch, as a connectivity substrate [5]. The key challenge of these architectures lies in fitting optical data duplication in the picture of the existing network stack. Optical power splitters can only send data unidirectionally, from input to output but not vice versa. Today’s unicast routing protocols assume bidirectional links and thus are ignorant of these additional optical paths. Since multicast routing protocols depend on unicast routing protocols for topology discovery, multicast trees will not be built over the optical splitters. Utilizing the optical multicast function requires multicast data delivery to be performed over the optical power split-