In today's environment where traffic demands within a network are increasing rapidly, planning and designing a network are assuming great importance. Rapidly rising traffic within the network is leading to network congestion, requiring solutions to cope with the increasing demand. We address the question of network planning and design, focusing in particular on alleviation of congestion at digital-cross connect systems (DCSs) located at the nodes of a broadband transport network. We describe a constrained routing mechanism as part of a new design strategy, employing unique dynamically changing routing constraints. Also critical in network design and planning is the knowledge of DCS capacity lost to tie-trunks, when the requirement for DCS at a given node exceeds unity, and the DCSs need to be tied together to facilitate proper cross-connects. Therefore, this paper also provides a tie-trunk analysis, leading to mathematical expressions, which can act as useful guides in the judicious planning of DCSs at the nodes of the given network.

One way to improve the reliability of a network is through physical diversity, i.e., via routing of traffic between a given pair of nodes in the network over two or more physically-disjoint paths such that if a node or a physical link fails on one of the disjoint paths, not all of the traffic is lost. Alternatively, enough spare capacity may be allocated on the individual paths such that the lost traffic due to a node or physical link failure can be routed immediately over the predetermined paths. In this paper, we present optimal algorithms for K-disjoint paths (K/spl ges/2) in a graph of vertices (or nodes) and edges (or links). These algorithms are simpler than those given in the past. We discuss how such algorithms can be used in the design of survivable mesh networks based on the digital cross-connect systems (DCS). We also discuss the generation of optimal network topologies which permit K>2 disjoint paths and upon which survivable networks may be modeled. The study is of particular relevance to fiber networks.

Telecommunication fiber networks can be more complicated than the traditional graph-theoretic networks of nodes and links. This is due to practical and economic considerations. The paper considers two major types of deviations from the traditional graph-theoretic network, and provide an algorithm for the shortest pair of physically-disjoint paths between a given pair of nodes in the network. Such disjoint paths can be used for improving the reliability of the network, e.g., one path may be used as a back up while the other is actually used for transmission of data. Alternatively, the entire traffic between the given pair of nodes in the network may be divided equally over the two disjoint paths so that if a node or link on one of the paths fails, not all of the traffic is lost. Optimizing the length of disjoint paths helps in reducing the amount of fiber usage and network costs.>