A key element of past, current, and future telecommunication infrastructures is the switching node. In recent years, packet switching has taken a dominant role over circuit switching, so that current switching nodes are often packet switches and routers. While a deeper penetration of optical technologies in the switching realm will most likely reintroduce forms of circuit switching, which are more suited to realizations in the optical domain, and optical cross-connects [1, Section 7.4] may end up playing an important role in networking in the long term, we focus in this chapter on high-performance packet switches.

Despite several ups and downs in the telecom market, the amount of information to be transported by networks has been constantly increasing with time. Both the success of new applications and of the peer-to-peer paradigm, and the availability of large access bandwidths (few Mb/s on xDSLs and broadband wireless, but often up to 10's or 100's of Mb/s per residential connection, as currently offered in Passive Optical Networks – PONs), are causing a constant increase of the traffic offered to the Internet and to networking infrastructures in general. The traffic increase rate is fast, and several studies show that it is even faster than the growth rate of electronic technologies (typically embodied by Moore's law, predicting a two-fold performance and capacity increase every 18 months).