A light path is essentially an optical channel that can be employed to transmit circuit-switched traffic and may span across multiple fiber links. Its configuration is determined by the assignment of a specific wavelength. When wavelength converters are not available, a light path will be constrained to use the same wavelength. Moreover, a light path has the capability to establish logical or virtual connections between nodes that could be geographically distant from one another.
It not only carries the direct traffic between the interconnected nodes but also traffic originating from nodes upstream of the source to nodes upstream of the destination.
A primary goal of light path communication is to minimize the number of hops a packet needs to traverse. In the context of light path communication, the network employs an equal number of transmitters and receivers because each light path functions on a point-to-point basis. However, this approach does not fully exploit all available wavelengths on the fiber links within the network, nor does it maximize the switching capacity of each Wavelength Routing Switch (WRS).
We formulate the light-tree-based virtual topology design problem as an optimization problem with one of two possible objective functions: for a given traffic matrix,
- Minimize the network-wide average packet hop distance, or,
- Minimize the total number of transceivers in the network