21846372
On monitoring transparent optical networks
Fault identification and localization problems in optical networks have become crucial. Due to network transparency and high data rates, optical networks are vulnerable to sophisticated attacks on the physical infrastructure, and hence require adequate fault monitoring in order to accurately identify and locate network failures. In transparent optical networks, faults may propagate to various parts of the network from the origin, and multiple alarms can be generated for a single failure. In order to reduce the number of redundant alarms, simplify fault localization, as well as lower financial investment in network monitoring equipment, fault monitor placement should be optimized for a given network. In this paper, we formulate a problem on the optimal placement of network monitoring devices and propose a solution approach. We provide a brief summary of available physical-layer monitoring devices, and present a scheme for optimal monitor placement.
9969836
Efficient route establishment and maintenance in wireless sensor networks with mobile base stations
The integration of ground wireless adhoc networks and airborne UAVs is a promising solution for realtime data collection in wireless sensor networks. Such networks play a vital role in many mission critical tasks such as forest fire-fighting and battlefield support. An important problem is to establish/maintain efficient routing structures in the ground sensor network for packet relaying. Our problem is unique in that the base stations are non-static, which necessitates frequent update of the routing structure. The performance of flooding based methods are evaluated. Particularly, in order to deal with non-uniform node density, we propose to introduce an artificial delay factor to control the flooding pattern. We mathematically prove that the delay should be proportional to local node density. Our simulation results show that the proposed method achieves good load balance among multiple base stations.
24043784
Efficient scheduling of transmissions in optical broadcast networks
All-optical networks (AONs) with a broadcast-star based physical topology offer the possibility of transmission scheduling to resolve channel and receiver conflicts. This paper considers the problem of scheduling packet transmissions in a wavelength-division multiplexed (WDM) optical network with tunable transmitters and fixed-tuned receivers. The scheduling problem is complicated by tuning latency, a limited number of channels, and arbitrary traffic demands. We first analyze scheduling all-to-all packet transmissions and obtain a new lower bound for the schedule length. The lower bound is achieved by an algorithm proposed by Pieris and Sasaki (1994). We then extend the analysis to the case of arbitrary traffic demands and obtain lower bounds for the schedule length. Two constructions for scheduling algorithms are provided through list scheduling and multigraphs. The upper bounds so obtained not only provide performance guarantees with arbitrary demands, but also nearly meet the lower bound in simulations.
6488428
Preserving survivability during logical topology reconfiguration in WDM ring networks
We consider the design of reconfiguring logical topologies over physical WDM ring networks. The logical topology consists of the same set of nodes as the physical topology, and the links of the logical topology are lightpaths established (or embedded) over the physical topology. The logical topology is said survivable if the failure of any single physical link does not disconnect the logical topology. In this paper, we consider the following problem: Given a logical topology with its survivable embedding over a physical ring network and a new logical topology to be reconfigured, find a sequence of lightpaths additions and deletions satisfying the given wavelengths and ports constraints such that the logical topology remains survivable throughout the reconfiguration.
800618
Packet filtering for congestion control under DoS attacks
Congestion control in IP networks is typically done at each router through queue management, and the network is entirely dependent on the end hosts to react congestion. However, when misbehaving flows exist and continue to send their packets in very high rates, the queue management schemes implemented in current IP routers reveal a significant shortcoming in protecting legitimate flows. Here, we propose a novel scheme for congestion control in IP networks. Our approach is a time-window based filtering mechanism implemented in a router and processed before a queue management policy is applied. Setting the window size properly and dropping packets reaching in the next window can catch the nonresponsive nature of misbehaving flows. The performance of our proposed scheme is demonstrated through extensive simulations using the NS2, simulator using a set of simulated traffic generated based on IP traces reported in http://www.nlnar.org.
550326
Efficient alarm management in optical networks
As the capacity of optical transport networks increases, rapid fault identification and localization become increasingly important. These problems are more challenging than in traditional electronic networks because of optical transparency. In a transparent optical network which does not regenerate optical signals, a fault may propagate to various parts of the network from the origin, and multiple alarms can be generated for a single failure. Efficient alarm management and filtering requires a careful selection and placement of network monitoring equipment. In this paper we survey the capabilities of current optical monitoring equipment and formulate a problem of selecting monitors to be placed throughout the network. Simulation results suggest that the number of monitors and generated alarms can be significantly reduced if monitor locations are selected judiciously.
195605809
Designing On-Chip Network Based on Optimal Latency Criteria
A new chip design paradigm, so called Network on Chip, has been introduced based on the demand of integration of many heterogeneous semiconductor intellectual property (IP) blocks. The Network on Chip design not only requires the good performance but also the minimization of several physical constraints such as the network latency, the used area as well as the power consumption of design. This paper analyzes the average latency of heterogeneous Network on Chip architectures in which the shortest path routing algorithm is applied. This average latency includes the queuing latency and the wire latency, and is calculated for general cases of allocating IPs onto the fixed generic switching architectures such as 2-D Mesh and Fat-Tree. With different allocation schemes of IPs, the network has different average latencies. Hence, this article presents an optimal search that adopts the Branch and Bound algorithm to find out the optimal mapping scheme to achieve the minimal network latency. This algorithm automatically map the desired IPs onto the target Network on Chip architecture with the criteria of lowest network latency. Some experiments of On Chip Multiprocessor Network application are simulated. The results show that the network latency is significantly saved with the optimized allocation scheme for the several cases of generic architectures of On Chip Multiprocessor Network application.
6409390
Java Memory Allocation with Lazy Worst Fit for Small Objects
Memory allocation is an important part of modern programming languages, including garbage-collected languages such as Java. We propose a fast memory allocation scheme for Java using lazy worst fit (LWF), where pointer increment is used as the primary allocation method and worst fit is used as a backup. We evaluated LWF on a working Java virtual machine with non-moving garbage collection, and the results show that LWF is practically useful since the overhead of fit allocation and the amount of fragmentation are low.
1950897
Secure reporting of traffic forwarding activity in mobile ad hoc networks
Nodes forward data on behalf of each other in mobile ad hoc networks. In a civilian application, nodes are assumed to be selfish and rational, i.e., they pursue their own self-interest. Hence, the ability to accurately measure traffic forwarding is critical to ensure proper network operation. These measurements are often used to credit nodes based on their level of participation, or to detect loss. Past solutions employ neighbor monitoring and reporting on node forwarding traffic. These methods are not applicable in civilian networks where neighbor nodes lack the desire or ability to perform the monitoring function. Such environments occur frequently in which neighbor hosts are resource constrained, or in networks where directional antennas are used and reliable monitoring is difficult or impossible. In this paper, we propose a protocol that uses nodes on the data path to securely produce packet forwarding reports. Reporting nodes are chosen randomly and secretly so that malicious nodes cannot modify their behavior based upon the monitoring point. The integrity and authenticity of reports are preserved through the use of secure link layer acknowledgments and monitoring reports. The robustness of the reporting mechanism is strengthened by forwarding the report to multiple destinations (source and destination). We explore the security, cost, and accuracy of our protocol.
38568907
Construction and shape analysis of PH quintic Hermite interpolants
In general, the problem of interpolating given first-order Hermite data (end points and derivatives) by quintic Pythagorean-hodograph (PH) curves has four distinct formal solutions. Ordinarily, only one of these interpolants is of acceptable shape. Previous interpolation algorithms have relied on explicitly constructing all four solutions, and invoking a suitable measure of shape—e.g., the absolute rotation index or elastic bending energy—to select the “good” interpolant. We introduce here a new means to differentiate among the solutions, namely, the winding number of the closed loop formed by a union of the hodographs of the PH quintic and of the unique “ordinary” cubic interpolant. We also show that, for “reasonable” Hermite data, the good PH quintic can be directly constructed with certainty, obviating the need to compute and compare all four solutions. Finally, we present an algorithm based on the subdivision, degree elevation, and convex hull properties of the Bernstein form, that gives rapidly convergent curvature bounds for PH curves, using only rational arithmetic operations on their coefficients.
11704041
Rational parametrization of canal surface by 4 dimensional Minkowski Pythagorean hodograph curves
Lorentzian geometry with a Minkowski Pythagorean hodograph (MPH) formalism in R/sup 3,1/ gives us a new and insightful method of rational parametrization of canal surfaces. Our previous works about MPH curves in R/sup 3,1/ shows that a curve /spl gamma/(t)=(x(t),y(t),z(t),r(t)) in R/sup 3,1/ can be represented by the PH representation map in Cl(3,1) which avoids the complex root finding algorithm. Our parametrization method gives us the flexibility to represent the canal surfaces within their fiber ambiguities. This paper constitutes the first step of our ongoing work which deals with the issues for canal surfaces in a truly new and intriguing manner such as finding rotation minimizing frames. We believe this is just the tip of the iceberg and the further work will yield many valuable applications in the area of canal surfaces.