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Performance Evaluation of Dynamic CCA-ED Threshold Control Scheme for WLAN
Minseok Oh(오민석),Hyeonho Na(나현호) 한국정보기술학회 2015 한국정보기술학회논문지 Vol.13 No.12
An effort has been made to achieve and maintain a high data rate, which is actually experienced by the users and less affected by the nearby devices even in a Wi-Fi dense area. An IEEE 802.11ax TG (task group) was formed to standardize these efforts, so called HEW (high efficiency WLAN). As a way of alleviating the effect of nearby devices, the IEEE 802.11ax TG is considering a scheme which changes the CCA (clear channel assessment) threshold dynamically. In this paper we explain how the scheme tries to resolve the hidden terminal problem and the exposed terminal problem at the same time. We also analyze the performance of the dynamic CCA threshold control scheme in various density of APs/STAs through simulation.
Security Challenges and Solutions in Wireless Mesh Networks
Minseok Oh(오민석) 한국정보기술학회 2012 한국정보기술학회논문지 Vol.10 No.2
A promising, low-cost alternative for providing last-mile wireless connectivity is the concept of Wireless Mesh Networks (WMN). The true potential of any network, however, cannot be exploited without considering and adequately addressing the security issues. The broadcast nature of transmission and the dependency on the intermediate nodes for routing the user traffic leads to security vulnerabilities making the WMN prone to various attacks. In this paper, we will discuss the security vulnerabilities in multi-hop wireless networks that are relevant to the WMN. We will consider the attacks in the MAC layer in the WMN in detail and the possible solution mechanisms in the MAC layer to prevent and detect these attacks.
A Comprehensive Study on Fault Management Approaches in Communication Networks
Minseok Oh 한국정보기술학회 2012 한국정보기술학회논문지 Vol.10 No.1
Although fault management has been a subject of research from the earliest days of networking, it is still considered a hard problem and there still exist communication networks that cannot be well managed for faults. Furthermore, while solutions have been found to many fault management problems, the networking community is still locked in debates over which solutions are preferred. In this paper we make it clear why fault identification and alarm correlation in communication systems are difficult, then carry out a systematic inquiry to discover the characteristics of alarms in communication networks and finally studies the currently available fault diagnosis methods. This article will provide an essential, comprehensive, and solid ground for those who research on the fault management in communication networks.
Provisioning Transmission Paths Given Alarm Collecting Agents
Minseok Oh 한국정보기술학회 2009 한국정보기술학회논문지 Vol.7 No.2
For a reliable communication, all the alarms generated from a node should be delivered to a network management center. In general, before a management center receives alarms, they are collected through agents. It may be ideal for an agent to reside in every communication node, but it will use up the node's resource, such as processing power and communication bandwidth, as well as increase the cost of the node. When agents are deployed in a few selected nodes, however, there are chances that multiple fault may prohibit alarms from reaching the alarm collecting agents assuming the alarms travel along the provisioned path, as does usually in a WAN, such as in SDH/SONET. This paper investigates a way of finding the shortest path while a newly provisioned path does not cause multiple faults to block alarms basing on Bellman-Ford algorithm, and the proposed algorithm is proven mathematically.
Minseok Oh 한국정보기술학회 2008 한국정보기술학회논문지 Vol.6 No.6
In SDH/SONET, ADMs make it possible to have a ring network. The ring topology provides certain advantages in executing a fault localization process. Each section in SDH/SONET may exhibit a different characteristic in terms of its failure, which results in different probabilities of failure. A failure in the section layer produces alarms which are consequently delivered to the fault management center. Once they are collected, those received alarms are checked to find a possible fault section. Each lookup process may be associated with a certain cost or delay, which we want to minimize in this investigation. As a sequential work from the previous study, this paper proposes a minimum cost search tree algorithm for localizing a section failure in a SDH/SONET ring network in light of the search delay, given the probability of each section.
A Performance Comparison of Two Mesh Routing Protocols
Minseok Oh 한국정보기술학회 2011 Proceedings of KIIT Conference Vol.2011 No.5
In this paper, we compare two mesh routing protocols, BATMAN-ADV and FLAME, which run on Layer 2 of the OSI reference model. Those are a few protocols available in software package incorporated into the OpenWrt OS for embedded systems. Our experiments involves the throughput and delay performance on a linear mesh network over varying number of hops between end nodes. We have used 5.8 ㎓ channel bands to avoid any interference with existing 802.11g radios. The results show that BATMAN-ADV performs better than FLAME slightly. The better performance is due to the elaborate routing mechanism and up-to-date release of BATMAN-ADV compared to FLAME.
Minseok Oh(오민석) 한국정보기술학회 2008 한국정보기술학회논문지 Vol.6 No.5
In SDH/SONET, ADMs (add/drop multiplexers) make it possible to have a ring network. The ring topology provides certain advantages in executing a fault localization process. A failure in the session layer produces alarms which are consequently delivered to the fault management center. Once they are collected, those received alarms are checked to find a possible fault session. Each lookup process may be associated with a certain cost or delay, which we want to minimize in this investigation. This paper proposes a minimum cost search tree algorithm for localizing a session failure in a SDH/SONET ring network in light of the search delay. Among the received alarms some may not help localize the fault so that the cost of binary search tree can be further minimized by filtering out those redundant alarms. We also propose an algorithm to form a binary search tree for the reduced alarm set.
Pulse Dual Slope Modulation for VLC
( Minseok Oh ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.4
In the field of visible light communication (VLC), light-emitting diodes (LEDs) are used for transmitting data via visible light. In this study, we analyze pulse dual slope modulation (PDSM) as a means of delivering information in VLC. PDSM involves the modulation of symmetrical slope pulses to encode binary 0s and 1s, and owing to the moderately increasing and decreasing pulse shapes that are created, this method enables more spectral efficiency than the variable pulse position modulation (VPPM) technique currently adopted in IEEE 802.15.7. In particular, PDSM allows for the avoidance of intra-frame flicker by providing idle pulses in a spectrum-efficient way. A simple detection scheme is proposed for PDSMsignals, and its bit error rate (BER) is analyzed mathematically at varying slopes to validate the process through simulation. The BER performance of PDSM detection using dual sampling is compared to the performances of PDSM and VPPM using correlation detection. It is found that, when the probability of idle pulse transmission is less than 0.08 and higher than 0, the BER of dual sampling PDSM is lower than that of PDSM using correlation detection over the entire light intensity range.