Myung Ah Park

A dominating and absorbent set in a wireless ad-hoc network with different transmission ranges

Unlike a cellular or wired network, there is no base station or network infrastructure in a wireless ad-hoc network, in which nodes communicate with each other via peer communications. In order to make routing and flooding efficient in such an infrastructureless network, Connected Dominating Set (CDS) as a virtual backbone has been extensively studied. Most of the existing studies on the CDS problem have focused on unit disk graphs, where every node in a network has the same transmission range. However, nodes may have different powers due to difference in functionalities, power control, topology control, and so on. In this case, it is desirable to model such a network as a disk graph where each node has different transmission range. In this paper, we define Minimum Strongly Connected Dominating and Absorbent Set (MSCDAS) in a disk graph, which is the counterpart of minimum CDS in unit disk graph. We propose a constant approximation algorithm when the ratio of the maximum to the minimum in transmission range is bounded. We also present two heuristics and compare the performances of the proposed schemes through simulation.

On dual power assignment optimization for biconnectivity

Topology control is an important technology of wireless ad hoc networks to achieve energy efficiency and fault tolerance. In this paper, we study the dual power assignment problem for 2-edge connectivity and 2-vertex connectivity in the symmetric graphical model which is a combinatorial optimization problem from topology control technology.The problem is arisen from the following origin. In a wireless ad hoc network where each node can switch its transmission power between high-level and low-level, how can we establish a fault-tolerantly connected network topology in the most energy-efficient way? Specifically, the objective is to minimize the number of nodes assigned with high power and yet achieve 2-edge connectivity or 2-vertex connectivity.We addressed these optimization problems (2-edge connectivity and 2-vertex connectivity version) under the general graph model in (Wang et al. in Theor. Comput. Sci., 2008). In this paper, we propose a novel approximation algorithm, called Candidate Set Filtering algorithm, to compute nearly-optimal solutions. Specifically, our algorithm can achieve 3.67-approximation ratio for both 2-edge connectivity and 2-vertex connectivity, which improves the existing 4-approximation algorithms for these two cases.

Label prioritization in GMPLS-centric all-optical networks

When establishing lightpaths in an all-optical DWDM network, it is possible that concurrent lightpaths requests will block one another if the lightpaths attempt to reserve the same wavelength of the same link. In this paper, we propose a novel signaling mechanism, referred to as label prioritization, which attempts to reduce the backward-link blocking in GMPLS-centric all-optical networks by assigning different priorities to the suggested wavelengths of each connection request. The prioritization of the wavelength encourages concurrent lightpath requests to choose different wavelengths, thereby reducing the possibility that the requests will be blocked. The label prioritization mechanism consists of a signaling extension to GMPLS to support the label prioritization and a modification in the optical switch controller to support the signaling extension. Simulation results show that the label prioritization method can effectively reduce wavelength conflicts.

On approximate optimal dual power assignment for biconnectivity and edge-biconnectivity

Topology control is one of the major approaches to achieve energy efficiency as well as fault tolerance in wireless networks. In this paper, we study the dual power assignment problem for 2-edge connectivity and 2-vertex connectivity in the symmetric graphical model. The problem has arisen from the following practical origin. In a wireless ad hoc network where each node can switch its transmission power between high-level and low-level, how can we establish a fault-tolerant connected network topology in the most energy-efficient way? Specifically, the objective is to minimize the number of nodes assigned with high power and yet achieve 2-edge connectivity or 2-vertex connectivity. Note that to achieve a minimum number of high-power nodes is harder than an optimization problem in the same model whose objective is to minimize the total power cost. We first address these two optimization problems (2-edge connectivity and 2-vertex connectivity version) under the general graph model. Due to the NP-hardness, we propose an approximation algorithm, called prioritized edge selection algorithm, which achieves a 4-ratio approximation for 2-edge connectivity. After that, we modify the algorithm to solve the problem for 2-vertex connectivity and also achieve the same approximation ratio. We also show that the 4-ratio is tight for our algorithms in both cases.

Dial-up Internet access service system with automatic billing mechanism

Due to the rapid growth of the Internet, many Internet service providers (ISPs) have sprung up in Korea. The typical access of their dial-up Internet services is for user to subscribe to an ISP and pay a monthly flat rate. But the rate is relatively expensive to a large number of users with occasional access. Therefore they are unwilling to join the Internet. This causes a loss of users to the ISPs and an obstacle to the Internets growth. Meanwhile, as the contents providers (CPs) provide much better services, they tend to become commercial sites and, moreover, want to have their own billing method. The ISPs, therefore, have a need to provide an appropriate billing policy for the commercial CPs. We describe a dial-up Internet access service system with an automatic billing mechanism which is implemented to cope with the above trend. The system provides users with easy Internet access. It performs automatic billing based on the call connection time and the amount of data used. We expect, due to the system, the ISPs will attract a large number of new users and to be able to cope with changes in the CPs billing appropriately.

Embedding security into visual programming courses

A visual programming course can be set up in a way that draws a general audience from different disciplines in addition to serving majors. Thereby embedding security into a visual programming course can be effective not only in raising future security workforce, but also in promoting security awareness for non-majors. Moreover, an instructor can create a subsequent advanced course where students can reinforce and expand secure coding practices as well as learn security principles. However, most visual programming books that are suitable as textbooks usually do not deal with security issues. Even if they do, minimal discussion is usually included, even being without connection to security principles. Therefore, in order to imbed security into a visual programming course, instructors are required to spend enormous time in preparation. In this paper, we set out to provide a guideline for embedding security into a visual programming course. Specifically, we will discuss basic and advanced secure coding techniques along with related security principles.

Fault-Tolerant Dual Power Management in Wireless Sensor Networks

How to adjust the transmission power at each node to achieve global energy efficiency while maintaining the network connectivity, referred as power management problem, is the major target of various topology control technologies. Moreover, fault tolerance which is often modeled as 2-edge or 2-vertex connectivity is another desired feature in many applications. In this paper, we study the fault tolerant dual power assignment problem. With the assumption of dual universal transmission power levels, we aim to minimize the total number of nodes assigned to high power level such that the resultant network topology is 2-edge or 2-vertex connected. As the problems are NP-hard, we design a novel algorithm to compute nearly-optimal solutions. From the theoretical perspective, we prove that our algorithm can guarantee 3.67-approximation for both 2-edge connectivity and 2-vertex connectivity, which improves the existing best approximation algorithm. We also conduct some numerical experiments which show that results of our algorithm are at most 2 times of optimal solutions in average and have significant improvements compared to that of existing algorithm.

Service management for IN-based local number portability

ns liberalization has swept through the telecommunications industry, the issue of number portability has become increasingly important. Number portability is the key to open competition in local services. Local number portability (LNP) is a circuit switched network capability which allows an end-user to change service provider, location and/or service type without having to change his/her telephone number. There are several LNP solutions, but the industry considers the location routing number model the best way to implement LNP, which depends on intelligent network (IN) technology. In this paper, we propose TMN-based service management architecture for LNP which has an IN-based solution. Under the proposed architecture, we also describe the service management mechanism.