Theia: Simple and Cheap Networking for Ultra-Dense Data Centers.

Recent trends to pack data centers with more CPUs per rack have led to a scenario in which each individual rack may contain hundreds, or even thousands, of compute nodes using system-on-chip (SoC) architectures. At this increased scale, traditional rack-level star topologies with a top-of-rack (ToR) switch as the hub and servers as the leaves are no longer feasible in terms of monetary cost, physical space, and oversubscription. We propose Theia, an architecture to connect hundreds of SoC nodes within a rack, using inexpensive, low-latency, hardware elements to group the rack's servers into subsets which we term SubRacks. We then replace the traditional per-rack ToR with a low-latency, passive, circuit-style patch panel that interconnects these SubRacks. We explore alternatives for the rack-level topology implemented by this patch panel, and we consider approaches for interconnecting racks within a data center. Finally, we investigate options for routing over these new topologies. Our proposal of Theia is unique in that it offers the flexibility of a packet-switched networking over a fixed circuit topology.