Young-Cheol Bang

An Adaptable Mobility-Aware Clustering Algorithm in vehicular networks

The forthcoming Intelligent Transportation System aims to achieve safety and productivity in transportation using vehicular ad hoc networks (VANETs) to support the communications system required. Currently, some clustering approaches have been proposed to improve the performance of VANETs due to their dynamic nature, high scalability and load balancing results. However, the host mobility and the constantly topology change continue to be main problems of this technique due to the lack of models which represent the vehicular behavior and the group mobility patterns. Therefore, we propose an Adaptable Mobility-Aware Clustering Algorithm based on Destination positions (AMACAD) to accurately follow the mobility pattern of the network prolonging the cluster lifetime and reducing the global overhead. In an effort to show the efficiency of AMACAD, a set of simulation was executed. The obtained results reveal an outstanding performance in terms of the lifetime of the cluster heads, lifetime of the members and the re-affiliation rate under varying speeds and transmission ranges.

On Efficient Core Selection for Reducing Multicast Delay Variation under Delay Constraints

With the proliferation of multimedia group applications, the construction of multicast trees satisfying the Quality of Service (QoS) requirements is becoming a problem of the prime importance. An essential factor of these real-time application is to optimize the Delay- and delay Variation-Bounded Multicast Tree (DVBMT) problem. This problem is to satisfy the minimum delay variation and the end-to-end delay within an upper bound. The DVBMT problem is known as NP-complete problem. The representative algorithms for the problem are DVMA, DDVCA, and so on. In this paper, we show that the proposed algorithm outperforms any other algorithm. The efficiency of our algorithm is verified through the performance evaluation and the enhancement is up to about 13.5% in terms of the multicast delay variation. The time complexity of our algorithm is O(mn 2 ) which is comparable to well known DDVCA.

An Energy-Aware Multipath Routing Algorithm in Wireless Sensor Networks

One of the major challenges facing the design of a routing protocol for Wireless Sensor Networks (WSNs) is to find the most reliable path between the source and sink node. Furthermore, a routing protocol for WSN should be well aware of sensor limitations. In this paper, we present an energy efficient, scalable, and distributed node disjoint multipath routing algorithm. The proposed algorithm, the Energy-aware Multipath Routing Algorithm (EMRA), adjusts traffic flows via a novel load balancing scheme. EMRA has a higher average node energy efficiency, lower control overhead, and a shorter average delay than those of well-known previous works. Moreover, since EMRA takes into consideration network reliability, it is useful for delivering data in unreliable environments.

NetLets: measurement-based routing daemons for low end-to-end delays over networks

Routing in the Internet is based on the best-effort mechanism, wherein the routers generally forward packets to minimize the number of hops to the destination. Furthermore, all packets of a type are treated the same independent of their size. We propose the framework of NetLets to enable the applications to send data packets to the destination with certain guarantees on the end-to-end delay. NetLets employ in situ instruments to measure the effective bandwidth and propagation delays on the links, and compute the paths with minimum measured end-to-end delay for data packets of various sizes. Based on experiments over local area networks, the paths selected by NetLets indeed achieve the minimum end-to-end delay, and our method outperformed the best-effort mechanism based on the hop count. We also describe an implementation of NetLets over the Internet to illustrate their viability for wide-area networks.

Discord model for detecting unexpected demands in mobile networks

Predicting the number of calls in a cell in average must be an important issue in mobile computing. It is quite useful in performance modeling and usually assumed as a random Poisson value. For effective management of cellular networks, the average number of calls should be carefully traced and the unexpected changes in the numbers need to be promptly detected. In this paper, we propose an efficient algorithm detecting those changes in the behavior of users based on the technique proposed for point-of-change problem just in terms of the number of call arrivals. Computer simulation reveals the proposed method effectively detect the discord, and the developed model is very accurate that the difference is as small as mostly less than 1%.

On Core Selection Algorithm for Reducing Delay Variation of Many-to-Many Multicasts with Delay-Bounds

With the proliferation of multimedia group applications, the construction of multicast trees satisfying the quality of service (QoS) requirements is becoming a problem of the prime importance. In this paper, we study the core selection problem that should produce the improved delay-bounded multicast tree in terms of the delay variation that is known to be NP-complete [8]. A solution to this problem is required to provide decent real-time communication services such as on-line games, shopping, and teleconferencing. Performance comparison shows that our proposed scheme outperforms that of DDVCA [18] that is known to be most effective so far in any network topology. The enhancement is up to about 11.1% in terms of normalized surcharge for DDVCA. The time complexity of our algorithm is O(mn2).

On Multicasting with Minimum Costs for the Internet Topology

We have developed and evaluated a novel heuristic algorithm for the construction of a multicast tree with minimizing tree costs. Our algorithm works on directed asymmetric networks and is shown here to have a perform gain in terms of tree costs for Internet like networks over existing algorithms. The time complexity of our algorithm is O(D×m) for a m-arc network with D number of members in the multicast group and is comparable to well-known algorithms for multicast tree construction. We have performed empirical evaluation that compares our algorithms with the others on large networks.

Efficient Algorithm for Reducing Delay Variation on Bounded Multicast Trees

With the proliferation of multimedia group applications, the construction of multicast trees satisfying QoS requirements is becoming a problem of prime importance. In this paper, we study the delay- and delay variation-bounded multicast tree (DVBMT) problem which is NP-complete. The problem is to construct a spanning tree for destination node, which has the minimized multicast delay variation, and the delay on the path from the source to each destination is bounded. A solution to this problem is required to provide decent real-time communication services such as on-line games, shopping, and teleconferencing. Performance comparison shows that the proposed scheme outperforms DDVCA which is known to be effective so far in any network topology. The enhancement is up to about 3.6%~11.1% in terms of normalized surcharge for DDVCA. The time complexity of our algorithm is O(mn 2).

New Parameter for Balancing Two Independent Measures in Routing Path

The end-to-end characteristic is an important factor for QoS support. Since network users and their required bandwidths for applications increase, the efficient usage of networks has been intensively investigated for the better utilization of network resources. The distributed adaptive routing is the typical routing algorithm that is used in the current Internet. If the parameter we concern is to measure the delay on that link, then the shortest path algorithm obtains the least delay path P LD . Also, if the parameter is to measure of the link cost, then the shortest path algorithm calculates the least cost path P LC . The delay constrained least cost (DCLC) path problem has been shown to be NP-hard. The path cost of P LD is relatively more expensive than that of P LC , and the path delay of P LC is relatively higher than that of P LD in DCLC problem. In this paper, we propose an effective parameter that is the probabilistic combination of cost and delay. It significantly contributes to identify the low cost and low delay unicasting path, and improves the path cost with the acceptable delay.

On algorithm for efficiently combining two independent measures in routing paths

This paper investigates the routing efficiency problem with quality of service (QoS). A solution to this problem is needed to provide real-time communication service to connection-oriented applications, such as video and voice transmissions. We propose a new weight parameter by efficiently combining two independent measures, the cost and the delay. The weight ω plays on important role in combining the two measures. If the ω approaches 0, then the path delay is low. Otherwise the path cost is low. Therefore if we decide an ω, we then find the efficient routing path. A case study shows various routing paths for each ω. We also use simulations to show the variety of paths for each ω. When network users have various QoS requirements, the proposed weight parameter is very informative.