The conventional lightpath is an end-to-end system that is exclusively occupied by its source and destination nodes, with no wavelength multiplexing between the multiple intermediate nodes along the lightpath. Thus if there are not enough IP streams to share the lightpath, the wavelength capacity is severely underutilized for low-rate IP bursts unless the wavelength is filled up by the efficiently aggregated IP traffic. The light trail is an architecture concept that has been proposed as a novel architecture designed for carrying finer granularity IP traffic. A light trail is a unidirectional optical trail between the start node and the end node [111, 173]. It is similar to a lightpath with one important difference in that the intermediate nodes can also access this unidirectional trail. Moreover, the light trail architecture, as detailed later on, does not involve any active switching components. However, these differences make the light trail an ideal candidate for traffic grooming. In light trails, the wavelength is shared in time by the nodes on the light trail. Medium access is arbitrated by a control protocol among the nodes that have data ready to transmit at the same time. In a simple algorithm, upstream nodes have a higher priority compared to the nodes downstream.

Current technologies that transport IP-centric traffic in optical networks are often too expensive, due to their reliance on an expensive optical and opto-electronic approach. Consumers generate diverse granularity traffic and service providers need technologies that are affordable and seamlessly upgradable. The exclusion of...