Previous networks used electronics for both the medium of transmission and the processing technology. Hence, the transmission and processing bandwidths at nodes were approximately of the same order. Electronic technology advanced simultaneously on the transmission and processing sides, leading to a matched growth in the evolution of the networks. With the shift to optical technology, the transmission capacity has taken a quantum leap while the processing capacity has seen only modest improvements in electronics. Optical processing is currently in its infancy and therefore the backbone networks are likely to remain circuit-switched with the possibility of having optical switching at intermediate nodes.

The increase in the transmission capacity in terms of multiple wavelengths each operating at a few tens of gigabits per second with multiple time slots within a wavelength requires an equivalent increase in the electronic processing for efficient operation of the networks. However, it is impractical to match the power of the optical technology with that of electronics if the nodes were to process all the information that is received from different links they are connected to. Hence, the switching trends depend on having multiple simple processing devices that work independently on parts of the information that is received at a node. Such a network model is referred to as a trunk-switched network (TSN). A TSN is a two-level network model in which a link is considered as multiple channels and channels are combined together to form groups called trunks. This conceptual architecture is capable of grooming subwavelength level traffic over a link.