Network topology

About: Network topology is a research topic. Over the lifetime, 52259 publications have been published within this topic receiving 1006627 citations.

Flexible optical wireless links and networks

Abstract: The worldwide demand for broadband communications is being met in many places by installed single-mode fiber networks. However, there is still a significant "first-mile" problem, which seriously limits the availability of broadband Internet access. Free-space optical wireless communications has emerged as a viable technology for bridging gaps in existing high-data-rate communications networks, and as a temporary backbone for rapidly deployable mobile wireless communication infrastructure. In this article we describe research designed to improve the performance of such networks along terrestrial paths, including the effects of atmospheric turbulence, obscuration, transmitter and receiver design, and topology control.

Defining an optimal topology for a group of logical switches

Abstract: A Layer 2 network switch fabric is partitionable into a plurality of virtual fabrics. A network switch chassis is partitionable into a plurality of logical switches, each of which may be associated with one of the virtual fabrics, including a base switch. Logical switches in multiple network switch chassis are connected by logical connections, such as logical inter-switch links that use physical connections, such as extended inter-switch links between base switches, for data transport. A topology of logical connections is established that balances competing metrics, such as robustness and scalability, while maintaining alignment with the topology of the physical connections. A topology factor allows establishing different topologies with different balances between the competing metrics.

FLSS: a fault-tolerant topology control algorithm for wireless networks

Abstract: Topology control algorithms usually reduce the number of links in a wireless network, which in turn decreases the degree of connectivity. The resulting network topology is more susceptible to system faults such as node failures and departures. In this paper, we consider k-vertex connectivity of a wireless network. We first present a centralized algorithm, Fault-tolerant Global Spanning Subgraph (FGSSk), which preserves k-vertex connectivity. FGSSk is min-max optimal, i.e., FGSSk minimizes the maximum transmission power used in the network, among all algorithms that preserve k-vertex connectivity. Based on FGSSk, we propose a localized algorithm, Fault-tolerant Local Spanning Subgraph (FLSSk). It is proved that FLSSk preserves k-vertex connectivity while maintaining bi-directionality of the network, and FLSSk is min-max optimal among all strictly localized algorithms. We then relax several widely used assumptions for topology control to enhance the practicality of FGSSk and FLSSk. Simulation results show that FLSSk is more power-efficient than other existing distributed/localized topology control algorithms.

The Performance of Neighbor-Joining Methods of Phylogenetic Reconstruction

Abstract: We analyze the performance of the popular class of neighbor-joining methods of phylogeny reconstruction In particular, we find conditions under which these methods will determine the correct tree topology and show that these perform as well as possible in a certain sense We also give indications of the performance of these methods when the conditions necessary to show that they determine the entire tree topology correctly, do not hold We use these results to demonstrate an upper bound on the amount of data necessary to reconstruct the topology with high confidence

Rate performance objectives of multihop wireless networks

Abstract: We consider the question of what performance metric to maximize when designing ad hoc wireless network protocols such as routing or MAC. We focus on maximizing rates under battery-lifetime and power constraints. Commonly used metrics are total capacity (in the case of cellular networks) and transport capacity (in the case of ad hoc networks). However, it is known in traditional wired networking that maximizing total capacity conflicts with fairness, and this is why fairness-oriented rate allocations, such as max-min fairness, are often used. We review this issue for wireless ad hoc networks. Indeed, the mathematical model for wireless networks has a specificity that makes some of the findings different. It has been reported in the literature on ultra wide band that gross unfairness occurs when maximizing total capacity or transport capacity, and we confirm by a theoretical analysis that this is a fundamental shortcoming of these metrics in wireless ad hoc networks, as it is for wired networks. The story is different for max-min fairness. Although it is perfectly viable for a wired network, it is much less so in our setting. We show that, in the limit of long battery lifetimes, the max-min allocation of rates always leads to strictly equal rates, regardless of the MAC layer, network topology, channel variations, or choice of routes and power constraints. This is due to the "solidarity" property of the set of feasible rates. This results in all flows receiving the rate of the worst flow, and leads to severe inefficiency. We show numerically that the problem persists when battery-lifetime constraints are finite. This generalizes the observation reported in the literature that, in heterogeneous settings, 802.11 allocates the worst rate to all stations, and shows that this is inherent to any protocol that implements max-min fairness. Utility fairness is an alternative to max-min fairness, which approximates rate allocation performed by TCP in the Internet. We analyze by numerical simulations different utility functions and we show that the proportional fairness of rates or transport rates, a particular instance of utility-based metrics, is robust and achieves a good tradeoff between efficiency and fairness, unlike total rate or maximum fairness. We thus recommend that metrics for the rate performance of mobile ad hoc networking protocols be based on proportional fairness.