Distribution of data received at a central receiving station to their final destination is done by switches and routers. Though the terms switching and routing are used interchangeably, there are some differences about the way they work and the level of their operation. A switch is a dedicated service. For instance, an electro-mechanical switch connected to household electrical equipment provides a dedicated connectivity between the switch and the equipment. More advanced electronic switching (e.g. that used in a phone service) does not provide a dedicated physical connectivity but provides a dedicated time slot. Such circuits are called virtual circuits.

In packet switching , a message is divided into small segments called packets . Each packet is transmitted individually and may follow different paths to the destination. After all packets have arrived at the destination, they are re-assembled to form the original message. A packet has a header which identifies destination. Routers read the information on the header and decide on the best route for a packet based on the network condition.

Wavelength routing is a process in which arriving optical signals are directed to different output ports depending on the wavelength of the input. A network which uses this procedure is called a wavelength routed network . A wavelength router may be looked upon as a fixed wavelength demultiplexer which directs different wavelengths to different ports. A wavelength which is used for one destination is not available for another destination. Thus the device must also have wavelength converters in addition to optical cross connects. By changing the wavelength of an arriving input signal, one can change the destination port of the signal.
A wavelength routing network has edge nodes which provide interface between the optical layer and other systems such as IP routers, ATM switches etc. All switching inside the optical layer is done by OXCs which may work in conjunction with wavelength converters.
Wavelength routing requires that a route must be defined in the network which connects a source (input) with the destination. Such an optical path is called a light path (also called a clear path. as the signal does not undergo any conversion from optical to electrical domain in its passage from the source to destination.)

In the figure shown, the edge nodes are marked E-1 to E-5 which are connected by fibers to all optical portion of the network. Two optical paths, one from E-1 to E-3 and another from E-2 to E-4 are shown in the figure. A wavelength which is being used for one of the light paths is not available for another path. In the optical domain there is no conversion from photon signal to electrical signal.