Optical Data Center Networks: Architecture, Performance, and Energy Efficiency

In a data center, servers communicate with each other to store and handle a large amount of data. Thus, the network within a data center affects the performance of the data center; the lack of bandwidth between servers increases the time to obtain the required data from the other servers. The energy consumption is also one of the important problems in a data center. The energy consumed by the data center increases as the amount of data handled by the data center becomes large. The network within a data center consumes a non-negligible fraction of the energy consumed in a data center. Therefore, the data center network should provide the sufficiently large bandwidth between servers with a small energy consumption. One approach to achieve this is the optical data center network, which uses the optical switches, because optical switches provides a large bandwidth between their ports with a small energy consumption. There are two kinds of optical switches; optical packet switches and optical circuit switches. In this chapter, we explain the overview of the architectures of these optical switches. Then, we introduce two approaches of optical data center networks. The first approach is the application of the optical packet switches, and focuses on the bandwidth provided for all-to-all communication. In this approach, we introduce the network structure that uses the large bandwidth of optical packet switches. The other approach is the application of the optical circuit switches, whose energy consumption is much smaller than that of the packet switches, and aims to minimize the energy consumption. In this network, the optical circuit switches are used to construct the core of the data center network, and the packet switches are connected to the optical circuit switches. The connection between packet switches are changed by setting the optical circuit switches. By setting the optical circuit switch so as to minimize the number of required ports of the packet switches considering the current traffic, we reduce the energy consumption.