Optical transmission has long been the established choice for nonwireless data transmission spanning distances longer than a few tens of meters, due to its high bandwidth and electromagnetic noise immunity. Most current high-bandwidth networks are essentially a group of fiber-optic links connected by nodes whose function is to forward incoming data to the appropriate output. The input to these nodes is data in optical form, and their output is also data in optical form. Thus, it makes sense to also process the data in the optical domain in order to have simple node architectures that improve reliability, performance, and cost. However, optical node technology cannot yet match the flexibility of electronic technology: The main roadblocks are the lack of random-access optical memories and of optical processors. Industry has addressed this lack by creating two kinds of nodes that achieve opposite extremes in the trade-off between efficiency and complexity: electronic packet switching () nodes and optical circuit switching () nodes.