Hyeong-Ah Choi

Loopback recovery from double-link failures in optical mesh networks

Network survivability is a crucial requirement in high-speed optical networks. Typical approaches of providing survivability have considered the failure of a single component such as a link or a node. We motivate the need for considering double-link failures and present three loopback methods for handling such failures. In the first two methods, two edge-disjoint backup paths are computed for each link for rerouting traffic when a pair of links fails. These methods require the identification of the failed links before recovery can be completed. The third method requires the precomputation of a single backup path and does not require link identification before recovery. An algorithm that precomputes backup paths for links in order to tolerate double-link failures is then presented. Numerical results comparing the performance of our algorithm with other approaches suggest that it is possible to achieve almost 100% recovery from double-link failures with a moderate increase in backup capacity. A remarkable feature of our approach is that it is possible to trade off capacity for restorability by choosing a subset of double-link failures and designing backup paths using our algorithm for only those failure scenarios.

Construction of optimal multicast trees based on the parameterized communication model

Many tree-based multicast algorithms have been proposed to provide an efficient software implementation on parallel platforms without hardware multicast support. These algorithms are either architecture-dependent (not portable) or architecture-independent (portable) but do not provide good performance when ported to different parallel platforms. Based on the LogP model, the proposed parameterized communication model can more accurately characterize the communication network of parallel platforms. The model encompasses a number of critical system parameters which can be easily measured on a given parallel platform. Based on the model, efficient methods to construct optimal multicast trees are proposed for both 1-port and /spl alpha/-port communication architectures. Experimental results conducted on the IBR/SP at Argonne National Laboratory are presented to compare the performance of the optimal multicast tree with two other known free-based multicast algorithms. We claim that our proposed multicast algorithms can be ported to different parallel platforms and provide a near-optimal performance as the truly machine-specific optimal performance is achievable only when the underlying detailed network characteristics are considered.

Graph bipartization and via minimization

The vertex- (respectively, edge-) deletion graph bipartization problem is the problem of deleting a set of vertices (respectively, edges) from a graph so as to make the remaining graph bipartite. This paper first shows that the vertex-deletion graph bipartization problem has a solution of size k or less if and only if the edge-deletion graph bipartization problem has a solution of size k or less, when the maximum vertex degree is limited to three. This immediately implies that (1) the vertex-deletion graph bipartization problem is NP-complete for cubic graphs, and (2) the minimum vertex-deletion graph bipartization problem is solvable in polynomial time for planar graphs when the maximum vertex degree is limited to three. It is then proved that the vertex-deletion graph bipartization problem is NP-complete for planar graphs when the maximum vertex degree exceeds three. Using this result, it is finally shown that the via minimization problem, which arises in the design of integrated circuits and printed ci...

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.

Detecting Stations Cheating on Backoff Rules in 802.11 Networks Using Sequential Analysis

As the commercial success of the IEEE 802.11 protocol has made wireless infrastructure widely deployed, user organizations are increasingly concerned about the new vulnerabilities to their networks. While various security issues have been extensively studied, the threats posed by denial-of-service (DoS) attacks have not been fully exploited. In this paper, we consider DoS attacks posed by cheating on the backoff rules in the IEEE 802.11 DCF protocol and propose a scheme detecting such adversaries. Our scheme is based on the sequential hypothesis testing. We first develop analytical models for packet interarrival time distribution from each station in the network where multiple cheating stations co-exist. Using the characterization of this probability distribution, we develop an algorithm to detect cheating stations based on the throughout degradations observed at normal stations. Our simulation results show that the proposed algorithm only requires very small number of observations of packets with very small value (i.e., less than 0.1%) of false positive and false negative decisions. That is, our proposed algorithm performs significantly fast and also accurately.

Scheduling multirate sessions in time division multiplexed wavelength-routing networks

We consider multiwavelength wavelength-routing networks operating in circuit-switched mode. Wavelength utilization is poor in such networks if sessions require only a fraction of a wavelengths capacity. An all-optical approach to improve wavelength utilization is to use time division multiplexing (TDM) on each wavelength, and switch time slots and wavelengths. In this paper, we address the off-line multirate session scheduling problem, i.e., the problem of assigning time slots and wavelengths to a given static set of multirate sessions, in ring topologies. Given a set of sessions and their relative rates, our objective is to maximize network throughput. This objective translates to the problem of minimizing the maximum length of a TDM frame over all wavelengths. We first show that the off-line single-rate session scheduling problem is equivalent to the off-line wavelength assignment problem, and hence obtain bounds on frame length. We then present scheduling algorithms with provable worst-case bounds on frame length for multirate session scheduling.

Circuit-switched broadcasting in torus and mesh networks

We consider the problem of broadcasting on torus and mesh networks using circuit-switched, half-duplex, and link-bound communication. In this paper, we obtain an optimal broadcasting algorithm that uses pd time steps for a d-dimensional torus with (2d+1)/sup p/ nodes in each side of the torus. Using this algorithm, we show that a broadcasting on a d-dimensional mesh with the same size can be done in pd+p+d-1 time steps.

Active monitoring and alarm management for fault localization in transparent all-optical networks

Achieving accurate and efficient fault localization in large transparent all-optical networks (TONs) is an important and challenging problem due to unique fault-propagation, time constraints, and scalability requirements. In this paper, we introduce a novel technique for optimizing the speed of fault-localization through the selection of an active set of monitors for centralized and hierarchically-distributed management. The proposed technique is capable of providing multiple levels of fault-localization-granularity, from individual discrete optical components to the entire monitoring domains. We formulate and prove the NP-completeness of the optimal monitor activation problem and present its Integer Linear Program (ILP) formulation. Furthermore, we propose a novel heuristic whose solution quality is verified by comparing it with an ILP. Extensive simulation results provide supporting analysis and comparisons of achievable alarm-vector reduction, localization coverage, and time complexity, for flat and hierarchically distributed monitoring approaches. The impact of network connectivity on fault localization complexity in randomly generated topologies is also studied. Results demonstrate the effectiveness of the proposed technique in efficient and scalable monitoring of transparent optical networks.

Securing smart home: Technologies, security challenges, and security requirements

Smart homes are gaining vast popularity as the most promising application of the emerging Internet of Things (IoT) technology. Exploiting the high level of connectivity present in current electronic devices (such as smartphones, tablets, and multimedia systems), smart homes provide innovative, automated and interactive services for residential customers through distributed and collaborative operations. As these types of networks become enormously popular, it is fundamental to provide the adequate level of protection against cyber-attacks for the residential customers. However, the resource-constrained nature of many of the devices present in a smart home environment, does not permit to implement the standard security solutions and therefore smart homes currently present security vulnerabilities. In this paper the security challenges and threats to the existing solutions suited for smart homes are examined in detail with the objective of fostering the development of practical solutions to secure the smart homes.

On wavelength assignment in WDM optical networks

We address the problem of assigning wavelengths to paths (connections) in optical wavelength division multiplexed networks. The problem is formulated as follows: given the physical topology of a network with each edge of two opposite directed fiber links and a set of directed paths with no more than L paths over any fiber link, we assign a wavelength to each path in such a way that no two paths are assigned the same wavelength if they share a directed physical link. In this paper, we first prove that the problem is NP-complete for arbitrary network topologies. Our NP-completeness result is obtained through a polynomial time reduction from the graph k-colorability problem. This reduction implies that no polynomial time algorithm can solve the problem with the number of wavelengths bounded by a constant times L for the class of network topologies including meshes. We then consider tree topologies. For star networks (i.e. the length of any path is bounded by two), we give a polynomial time algorithm that requires L wavelengths. For trees with path lengths larger than two, we show that the problem is NP-complete and present a heuristic algorithm based on the polynomial time algorithm for star topologies. Our heuristic algorithm may require 2L wavelengths in the worst-case, but the simulation result shows that the average-case performance significantly outperforms the worst-case bound. This suggests that fewer excess wavelengths are required when most of the load is local.