Chapter 12 - Photonic Packet Switching

Abstract

Optical networks that are capable of providing packet-switched service at the optical layer are called photonic packet-switched (PPS) networks. Packet-switched services are provided today using electronic switches by many networks, such as IP and Ethernet networks. The focus of this chapter is networks, where the packet-switching functions are performed optically. The goal of PPS networks is to provide the same services that electronic packet-switched networks provide, but at much higher speeds. The state of optical packet-switching technology is somewhat analogous to the state of electronic circuits before the integrated circuit was invented. All the building blocks needed for optical packet switching are in a fairly rudimentary state today and in research laboratories; they are either difficult to realize, very bulky, or very expensive. Fast optical switches have relatively high losses, including polarization-dependent losses, and are not amenable to integration. Optical wavelength converters are still in their infancy. Temperature dependence of individual components can also be a significant problem when multiplexing, demultiplexing, or synchronizing signals at high bit rates. The optical layer continues to provide circuit-switched services, with packet-switching functions being done in the electronic domain by IP routers or Ethernet switches. PPS, particularly with burst switching, is being positioned as a possible future replacement for the optical circuit layer, while still retaining electronic packet switching at the higher layers. Using an underlying optical packet layer instead of a circuit layer will help improve link utilizations.