Switch control: Bridging the last mile for optical data centers

To overcome the bandwidth bottleneck of electrical switches in data center networks (DCNs), switching the traffic in the optical domain has been much investigated as a future-proof solution supplying ultra-bandwidth. To date, many optical switch solutions have been investigated, exploiting various building blocks, such as 3D MEMS, LCoS display matrices, Mach-Zehnder interferometers, tunable lasers and AWGRs, and SOAs. Despite the promises held by the optical switching technology, the practical implementation of the optical DCNs is actually facing several challenges. As the main unresolved challenge, a nanoseconds-scale control system is essential to control the optical switch for traffic forwarding. Fast switch reconfiguration time including both hardware switching time (e.g. nanoseconds for SOA-based switch) and controlling overhead is essential as it determines the network throughput and latency performance. Moreover, the precise time synchronization of the switching network and the packet contention resolution also need effective scheduling at the switch control plane. In this chapter we first introduce the important role and prospect of the switch fabric control in the first section. In the second section, the switch control classification is presented. The technical challenge that limits the implementation of optical switch control is the content of the third section. The fourth section of this chapter is the state of the art of current switch control solutions. Finally, we will summarize this chapter and provide an outlook on future applications. This chapter will cover the switch fabric control from the fundamentals to recent developments, which is an important part of the topic of "Optical Switching: Device Technology and Application in Networks". This chapter will provide quick expertise on the most recent switch control technologies for researchers, senior graduate and post-graduate students, and professionals working in the telecommunications industry.