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A Transparent Failover Mechanism for a Mobile Network with Multiple Mobile Routers
Nakjung Choi,JihoRyu,Eunkyoung Paik,Taekyoung Kwon,Yanghee Choi IEEE 2007 IEEE communications letters Vol.11 No.7
<P>In a mobile network that is multihomed by multiple mobile routers, a mobile router that loses link connectivity can be replaced by the other mobile routers. We propose a transparent failover mechanism (TFM) to provide seamless Internet services to nodes in the mobile network, which is validated by implementing a real test-bed. Compared to the network mobility basic support protocol, TFM does not require the nodes attached to the failed mobile router to change their addresses, and hence has two advantages: (a) IP connectivity is maintained transparently, and (b) failover is quickly accomplished by avoiding the address re-configuration process in each node.</P>
Exploiting Multi-User Diversity for Uplink Throughput in IEEE 802.11 WLANs
Nakjung Choi,Yongho Seok,Taekyoung Kwon IEEE 2013 IEEE COMMUNICATIONS LETTERS Vol.17 No.9
<P>In multi-rate 802.11 networks, stations with better uplink conditions should access the shared channel more frequently than the ones with worse uplink conditions to enhance the aggregated throughput, which is referred to as multi-user diversity. In this letter, we propose Adaptive Basic Rate Set (ABRS) that uses the time gap between DIFS and EIFS for a prioritized channel access while minimizing starvation. ABRS requires the change in the firmware only at access points with no modification to the standard. Simulation results reveal that ABRS effectively prioritizes stations with higher bit rates; the aggregate uplink throughput is improved up to about 30-70% even in mobility scenarios.</P>
A Fog Operating System for User-Oriented IoT Services: Challenges and Research Directions
Choi, Nakjung,Kim, Daewoo,Lee, Sung-Ju,Yi, Yung Institute of Electrical and Electronics Engineers 2017 IEEE communications magazine Vol.55 No.8
<P>As the proliferation of mobile devices has ignited cloud computing, it is expected that increasing development and deployment of IoT services will expedite the era of fog computing. Fog computing brings computing, storage, and networking even closer to end users and devices for services with better QoS. We introduce FogOS, a fog computing architecture for IoT services. We take the perspective of designing an operating system, practicing the architectural lessons from the long history of operating systems. We focus on addressing the challenges raised by the diversity and heterogeneity of IoT services and edge devices that are owned by individuals and different owners, and presenting how FogOS is designed to effectively and efficiently provide and manage such IoT services. We provide a city-scale surveillance use case to demonstrate FogOS in action.</P>
IEEE 802.11 기반 무선랜에서 TCP 인지 서브 계층 TAS
최낙중(Nakjung Choi),정하경(Hakyung Jung),류지호(Jiho Ryu),석용호(Yongho Seok),최양희(Yanghee Choi),권태경(Taekyoung Kwon) 한국정보과학회 2006 정보과학회논문지 : 정보통신 Vol.33 No.5
본 논문은 IEEE 802.11 기반 무선랜 환경에서 TCP 성능을 향상시키기 위한 새로운 분할TCP 기법을 소개한다. IEEE 802.11 기반 무선랜 환경에서는 유선 환경과는 달리 TCP 데이타 흐름(flow)이 많은 데이타를 보내려고 시도하지 않기 때문에 TCP 데이타 흐름 성능 저하의 주요한 원인이 된다. 본 논문에서는 이런 문제를 완화하여 TCP 데이타 흐름의 성능을 향상시키기 위한 TAS(TCP-Aware Sub-layer) 기법을 제안한다. TAS 기법은 하나의 TCP 데이타 흐름을 AP 등의 분할 지점을 기점으로 두 개의 TCP 데이타 흐름으로 나누는 기존의 분할 연결(split-connection) 기법을 확장한 개념이다. TAS를 기반으로 동작하는 무선 노드는 실제로 TCP ACK을 수신하는 것이 아니라, 수신된MAC ACK을 이용하여 TCP ACK을 에뮬레이션한다. NS2 모의 실험을 통하여 제안된 기법인 TAS 기법의 성능을 기존 TCP 기법, I-TCP (Indirect TCP) 기법의 성능과 비교하였으며 모의 실험 결과는 TAS 기법이 다른 기법들에 비하여 시간당 처리량과 자원 할당의 형평성 측면에서 더 좋은 성능을 보인다는 것을 증명한다. 또한 절전 모드의 경우, 전송 지연 시간도 줄일 수 있다. This paper introduces a new split-TCP approach for improving TCP performance over IEEE 802.11-based wireless LANs. TCP over wireless LANs differently from wired networks is not aggressive, which is a fundamental reason for poor performance. Therefore, we propose TAS (TCP-Aware Sub-layer) to migigate this problem. Our scheme extends the split-connection approach that divides a connection into two different connections at a split point such as an access point (AP). Using TAS, a wireless node emulates TCP ACK packets using MAC ACK frames, instead of receiving real TCP ACK packets. We compared TAS with both normal TCP and I-TCP (Indirect TCP) by NS2 simulation. Results show that TAS achieves higher throughput, more fair resource allocation and, in power-saving mode, shorter delays.
An Iterative Analysis of Single-Hop B-MAC Networks Under Poisson Traffic
정성환,Nakjung Choi,Taekyoung Kwon 한국통신학회 2012 Journal of communications and networks Vol.14 No.1
The Berkeley-medium access control (B-MAC) is a lightweight, configurable and asynchronous duty cycle medium access control (MAC) protocol in wireless sensor networks. This article presents an analytic modelling of single-hop B-MAC protocol under a Poisson traffic assumption.Our model considers important B-MAC parameters such as the sleep cycle, the two stage backoff mechanism, and the extended preamble. The service delay of an arriving packet and the energy consumption are calculated by an iterative method. The simulation results verify that the proposed analytic model can accurately estimate the performance of singlehop B-MAC with different operating environments.
모바일 IPv6 라우터에서 플로우 측정을 이용한 핸드오버 모니터링
손현구(Hyeongu Son),최낙중(Nakjung Choi),최양희(Yanghee Choi),이영석(Youngseok Lee) 한국정보과학회 2009 정보과학회논문지 : 정보통신 Vol.36 No.5
본 논문에서는 모바일 IPv6 망에서 트래픽을 모니터링하고 사용자의 이동성 정보를 분석하는 방법을 제안한다. 제안하는 방법에서는 트래픽 모니터링을 위한 별도의 소프트웨어를 단말에 설치하지 않고 라우터에서 패킷들을 모니터링하여 핸드오버 지연시간을 분석한다. 라우터에서 플로우 기반 트래픽 모니터링을 수행하기 위하여 표준 플로우 기반 트래픽 모니터링 방법인 IPFIX를 사용한다. 따라서, 단말과 상관없이 라우터에서의 모니터링만으로 사용자의 이동성에 대한 정보를 분석할 수 있는 장점을 가진다. 제안한 방법을 검증하기 위하여 실제 구축된 802.11 기반의 모바일 IPv6 망에서 이동성 실험을 수행하여 핸드오버를 측정하고 분석하였다. 실험을 통하여 분석된 결과 다운로드의 핸드오버 지연시간 측정 결과는 약간의 오차를 포함하였지만, 업로드의 핸드오버 지연시간 측정은 정확한 결과를 보여주었다. In this paper, we propose a method of monitoring traffic and analyzing information of handover in mobile IPv6 networks. Our proposed method analyzes handover latency through monitoring packets at routers without installing monitoring applications at mobilenodes. For this purpose, we employ a flow-based traffic monitoring standard called IPFIX to perform the traffic measurement function the packets at the routers. Therefore, our method is useful in that we could easily obtain information regarding handover of mobile nodes by only monitoring traffic at the routers. In order to verify the proposed method, we carried out experiments in a real 802.11-based mobile IPv6 network testbed. From our experimental results, it was shown that the calculated handover latency for uploading traffic is accurate with less accuracy of analyzing the handover latency for downloading traffic.
HAVS: hybrid adaptive video streaming for mobile devices
Hwang, Jaehyun,Lee, Junghwan,Choi, Nakjung,Yoo, Chuck IEEE 2014 IEEE transactions on consumer electronics Vol.60 No.2
<P>This paper presents a new Scalable Video Codec (SVC)-based hybrid adaptive video streaming scheme, named HAVS, for mobile devices in wireless environments. The proposed approach takes two existing video streaming technologies, viz., progressive download and adaptive streaming, and switches them in a hybrid manner. To this end, HAVS employs the H.264/SVC encoding scheme, where each video chunk is encoded into one base layer and several enhancement layers. Since clients request the base layer every time a video is streamed, HAVS performs progressive download for the base layer and adaptive streaming for the enhancement layers. Through wireless test-bed experiments, it is demonstrated that the proposed scheme can be easily implemented on mobile devices without any server-side modification. This scheme effectively prevents video freeze thereby providing better quality video streaming than the existing non-hybrid streaming technologies.</P>