Showing papers by "Seung-Woo Seo published in 2008"

Performance Analysis of IEEE802.11 Wireless Mesh Networks

Abstract: The wireless mesh network is emerging as a promising technology in providing economical and scalable broadband Internet accesses to communities. The backbone of the wireless mesh network consists of mesh routers, which connect each other in an ad hoc manner via wireless links. The presence of backbone mesh routers and utilization of multiple channels and interfaces allow the wireless mesh network to have better capacity than that of the infrastructure-free ad hoc network formed by mesh clients directly. A special type of the mesh routers, referred to as gateway nodes, is capable of Internet connection, and other mesh routers and associated terminal clients have to access the Internet through the gateway nodes. In this paper, we present the analytically traceable stochastic models to characterize the average delay and throughput performance in wireless mesh networks. We model the forwarding mesh routers as an open queuing network. The analytical model takes into account the mesh router density, the random packet arrival process, the degree of locality of traffic and the collision avoidance mechanism of the IEEE802.11 DCF random access MAC. Our simulation results suggest that the analytical results are quite accurate, which can provide valuable insights in system performance and an effective guideline for the scalable design and optimization in wireless mesh networks.

Optimal level-homogeneous tree structure for logical key hierarchy

Abstract: Many attempts have been made to reduce the number of re keying messages in group key management by optimizing the tree structure for logical key hierarchy (LKH) (X.S. Li et al., 2001), (W.T. Zhu, 2005). Contrary to the conventional assumption of complete alpha-ary trees, we investigate in this paper into more general tree structures called complete level-homogeneous trees. Specifically, we derive an analytical model of the average number of re keying messages in the complete level-homogeneous trees. Furthermore, since we found from the analysis results that no definite optimal tree structure is identified in terms of the conventional cost metric, we propose an algorithm that finds one of the candidate tree structures. As an another approach, in order to determine a definite optimal tree structure, we also propose a new cost metric that considers member dynamics as well as the average number of re keying messages.

L+1-MWM: A Fast Pattern Matching Algorithm for High-Speed Packet Filtering

Abstract: A signature-based network intrusion detection system (NIDS) identifies intrusions by comparing the data traffic with known signature patterns. In this process, matching of packet strings against signature patterns dominates the overall system performance. The MWM algorithm has been known as the fastest pattern matching algorithm when the patterns in a rule set rarely appear in packets. However, the matching time does not decrease if the length of the shortest pattern in a signature group is too short. In this paper, by extending the length of the shortest pattern, we minimize the pattern matching time of the algorithm which uses multi-byte unit. For example, when the length of the shortest pattern is less than 5, the proposed algorithm shows 38.87% enhancement in average.

Multi-directional emergency exit light and emergency lighting system and method using the same

Abstract: The present invention relates to a multi-directional emergency exit light, and an emergency lighting system and method using the emergency exit light, which can select a suitable route while ensuring that a dangerous region is avoided, and can indicate a suitable direction. A multi-directional emergency exit light of the present invention performs guidance along an escape route. The multi-directional emergency exit light (100) includes a power supply device (140) for supplying power. A multi-direction indication device (120) is capable of indicating a plurality of guiding directions, and indicates a specific guiding direction under control of a microprocessor module (150). The microprocessor module (150) sets a guiding direction on a basis of certain criteria, and performing control so that the multi-direction indication device indicates the guiding direction.

Method of detecting character string pattern at high speed using layered shift tables

Abstract: A character string pattern matching method for detecting the presence of at least one of N (N is a natural number equal to or greater than 2) patterns in specific text shifts a detection location across text by a maximum shift length using single-byte character-based layered SHIFT tables, thereby increasing a pattern matching speed as compared with the prior art pattern matching algorithms.

Throughput Model of IEEE 802.11e EDCF with Consideration of Delay Bound Constraint

Abstract: In this paper, we present an accurate throughput model of the IEEE 802.11e enhanced distributed coordination function (EDCF). Compared to the previous models, we newly consider a delay bound by predicting an effective retry limit and applying the retry limit to our model. To support this, the accurate description of the performance in a non-saturation condition is necessary, which is achieved by newly considering a queue length and a queue limit in the Markov chain. Simulation results show that our model is accurate in predicting the system throughput.

A Load Balancing Scheme for Birkhoff-von Neumann Input-Queued Switches

Abstract: In this paper, we propose a novel load-balancing scheme for the Birkhoff-von Neumann input-queued (BvN-IQ) switch, which we call the cyclic exchange. According to the cyclic exchange scheme, in each time slot each linecard transfers a cell from its non-empty VOQ to the empty VOQ of another linecard which is destined for the same output. In order to guarantee the cell sequence in this procedure, we propose a simple rule of selecting the cells to be transferred for load balancing, and prove the sequence guarantee by the proposed rule. Since the cyclic exchange is performed locally between two linecards, its communication and computation overhead is not too heavy to implement. To be specific, the communication overhead of the proposed scheme is the transmission of N bits and its computation overhead corresponds to a priority encoder with a fixed highest priority. The simulation results show that the proposed scheme achieves 100% throughput asymptotically and shorter delay than the two-stage switch.

Procédé de détection de motif de chaîne de caractères à une vitesse élevée utilisant des tables de décalage stratifiées

Abstract: L'invention porte sur un procede de reconnaissance de motif de chaine de caracteres pour detecter la presence d'au moins l'un de N motifs (N est un entier naturel egal ou superieur a 2), dans un texte specifique. L'invention porte sur un procede de reconnaissance de motif de chaine de caracteres qui decale un emplacement de detection a travers un texte par une longueur de decalage maximale a l'aide de tables de DECALAGE stratifiees a base de caractere a un seul octet, augmentant ainsi une vitesse de reconnaissance de motif par rapport aux algorithmes de reconnaissance de motif de l'etat de la technique.