Optical switching in next-generation data centers

This thesis presents advanced optical connectivity solutions for next-generation data centers, spanning millions of processing cores. The wavelength routing of optical packets based on arrayed waveguide gratings (AWGs), tunable wavelength converters (TWCs), and fiber delay lines (FDLs) is a disruptive technology for capacity, footprint, and flexibility requirements of massive cloud data centers. We develop a wavelength-division multiplexed (WDM) design based on Birkhoff-von Neumann architecture as a bit-rate transparent, scalable solution to switching bottlenecks in data center networks. As no mature all-optical buffering technology is currently available, central to our design is the buffering strategy that we adopt to store contending packets. Due to the limited number of FDLs, packet drops are common in optical packet switching (OPS) data centers and limit the network throughput. In a practical scenario, physical layer impairments, predominantly amplified spontaneous emission (ASE) noise and crosstalk, degrade Q-factor and lead to additional packet drops. To examine the performance of optical buffer units more accurately, we develop a unified analysis framework, integrating the network layer and the physical layer effects. Using this framework, we refine our architectures and provide guidelines for minimizing the physical layer impact. Besides, optical switch designs should not neglect the diversity of data center traffic patterns when developing connectivity solutions. Empirical studies of data center network traffic reveal that server traffic exhibits strong spatial and temporal correlations. We examine the effectiveness of an AWG-based load balancer with round-robin tuning TWCs in resolving congestion penalties in the data center network. Our cross-layer analysis suggests that the physical layer impairments due to the load balancer hardware could counteract its potential gains and lead to significant throughput degradation. To resolve this challenge, we develop a novel modular router architecture based on WDM shared recirculation buffers that integrates the functions of load balancing and routing and maximizes the optical buffering gains. The router employs a load-balancing scheduler to maximize throughput and minimize delay. Our mathematical analysis and Monte Carlo simulations show that the consolidation of optical buffer slots into WDM FDLs accompanied with internal load balancing leads to a virtually lossless router, resilient to data center traffic anomalies.