Design of hybrid optical network architectures incorporating line systems

Multiring architectures are widely used as the design approach for survivable optical core networks, particularly when the rings that can be constructed are not constrained by geographical distances between nodes in the network. This is because traffic flows can be rapidly restored using ring protection mechanisms, and costs can be minimised using add-drop multiplexers (ADMs) at the nodes for inserting and extracting optical signals from a ring. There are, however, situations where a network architecture based solely on rings is not cost-effective or even possible. Multiring architectures are not possible where geographical distances are too large for rings to be formed, so the design of such a network must resort to using point-to-point line systems. Also, these architectures may not be cost-effective in the situation where routing traffic demands using shortest paths in the network results in asymmetric link loads within the network. In this paper we investigate the introduction of line systems into a network architecture to absorb traffic load in particularly heavily-loaded corridors within the network. By using ADMs at intermediate nodes along the line system, we are able to extend the concept of point-to-point line systems to multihop line systems, in which optical signals can be added or dropped at these intermediate nodes. We present a tool for designing hybrid architectures, and demonstrate the reduction in cost that can be achieved by the use of hybrid network architectures.