6.3 Network Architecture Classification

In order to efficiently use the huge bandwidth that optical channels can support, it is necessary to use, in synergy, wavelength, and time and space division multiplexing. In order to establish a circuit connection between two users, a path, time slot(s), and wavelength(s) have to be allocated, avoiding collision (blocking) with other simultaneous connections. The blocking probability is the main measure of quality of service in circuit-switched network [39 41].

The architecture may be purely optical or may include one or more logical network overlays. In the first case, it may use a simple passive broadcast star and a tree topology, or each connection can be routed independently through the network on its own optical frequency through static or dynamic optical routers, WSCX, or wavelength reuse through WICX. In the second case, electronically switched overlays are used on the transparent optical physical network.

The evident explosion in interest in the Internet creates a demand for a considerable increase of capacity and quality in international networking. Much work is devoted to switched DWDM networks with or without wavelength translations. Work is still underway to reach a consensus on what is really required and feasible. Among many other interesting publications see for instance [42, 43].