Routing and Label Stacking in All-Optical Label Swapping Networks

Fast header processing in Optical Transport Networks (OTN) has been foreseen as one of the main challenges in All-Optical Packet Switched (AOPS) networks. The LASAGNE project aims at supporting All-Optical Label Swapping (AOLS), easing most of the header processing drawbacks in AOPS. However, AOLS is expensive mainly because each supported label requires the deployment of an All-Optical Logic Xor Gate (AOLXG). The number of AOLXG required in a switch is equal to the number of Label Swapped Paths (LSP) it forwards. As a result, the overall number of AOLXG used in a network equals the total number of hops employed. On the one hand, reducing the overall number of AOLXG implies using the shortest paths in the network. On the other hand, using shortest paths leads to network bottlenecks. The trade-off between the number of AOLXG installed and maximum link utilization is thus manifest. In this article, we study how labels can be stacked in order to reduce the overall number of AOLXG installed in the network. Consider a set of LSPs that share a set of consecutive links (a path segment) in the network. The first (last) node of the path segment pushes (pops) one label in the stacks of the LSPs. Intermediate nodes in the path segment would regard only one label for all LSPs, reducing the number of AOLXG installed. The AOLS LASAGNE implementation is modified in order to propose an architecture able to stack labels all-optically. Minimizing the number of AOLXG installed by means of label stacking leads to an extra tradeoff. To decrease that number, a routing solution aims at setting long LSPs that can be joined. As a consequence, a smaller label space incurs in longer delays. To analyze these trade-offs, an ILP model is proposed.