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Over the past five years, coherent transmission technologies have delivered more than an order of magnitude improvement in the capacity- reach product for long-haul DWDM transmission systems. This article provides a working definition of "coherent transmission" based on current market realities; provides a functional model for beyond 100G coherent systems, and then examines five key technologies that will deliver beyond 100G: evolving transmitter technologies, including Nyquist pulse shaping and nonlinear compensation of transmitter devices; nonlinear compensation for the propagation effect; further advances in FEC technology; flexible grid DWDM and coherent super-channels. In each case we explain the factors in terms of optical or electronic component performance that are most likely to result in system performance limitations, and discuss engineering strategies to mitigate those limitations. [ABSTRACT FROM AUTHOR]

We present the on-demand link vector (OLIVE) protocol, a routing protocol for ad hoc networks based on link-state information that is free of routing loops and supports destination-based packet forwarding. Routers exchange routing information reactively for each destination in the form of complete paths, and each node creates a labeled source graph based on the paths advertised by its neighbors. A node originates a broadcast route request (RREQ) to obtain a route for a destination for which a complete path does not exist in its source graph. When the original path breaks, a node can select an alternative path based on information reported by neighbors, and a node can send a unicast RREQ to verify that the route is still active. A node that cannot find any alternate path to a destination sends route errors reliably to those neighbors that were using it as next hop to the destination. Using simulation experiments in ns2, OLIVE is shown to outperform dynamic source routing, ad hoc on-demand distance vector, optimized link-state routing protocol, and topology broadcast based on reverse-path forwarding, in terms of control overhead, throughput, and average network delay, while maintaining loop-free routing with no need for source routes. [ABSTRACT FROM AUTHOR]