• Annual Conference of KIPS
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• 2005.05a
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• pp.1339-1342
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• 2005

이기종 네트워크들이 계층적인 구조로 결합되어 있는 오버레이 네트워크 환경에서 이동 단말(Mobile Terminal:MT)의 끊김없는 이동성 지원을 위해서는, 패킷 손실 및 호 단절 현상을 최소화할 수 있는 최적의 핸드오버 시점을 결정할 수 있어야 한다. 기존의 수직적 핸드오버 기법은, 단순히 MT의 위치 정보를 바탕으로 핸드오버 수행을 예측하고 결정하였다. 하지만 이 기법은, MT의 위치와 관계없이 네트워크의 과부하로 인한 패킷 손실 및 호 단절 현상이 발생할 수 있기 때문에, 네트워크의 과부하에 따른 핸드오버 시점을 간과하는 문제점을 노출하였다. 하루가 다르게 인터넷 트래픽이 급증하는 현실에서, 네트워크의 과부하를 고려하는 핸드오버 기법이 필요한 때이다. 따라서 본 논문에서는 MT의 위치와 네트워크의 부하를 모두 고려하여 핸드오버 시점을 결정할 수 있는 핸드오버 맵(Handover-Map:H-Map)의 개념을 제안한다. 그리고 핸드오버 동기화 현상을 최소화하기 위해 향상된 H-Map을 기반으로 차별화된 핸드오버 시점을 부여하는 VAH(Vertical handover on Advanced H-Map) 기법을 소개하고, 이의 성능을 기존기법과 비교한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1732-1750
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• 2016

Recently, Peer-to-Peer (P2P) live streaming assisted by the cloud computing has attracted considerable attention to improve the reliability of the P2P such as the resilience to peer churn and the shortage of upload capacity. The cost of cloud-assistance is comprised of the number of requests issued to the cloud and the amount of data fetched from the cloud. In this paper, we propose three techniques to reduce the cost of such a cloud-assistance.More concretely, in the proposed method, 1) each peer which lost its parent in the overlay can find a new parent by referring to the information registered in the cloud, 2) several peers which proactively fetch chunks from the cloud are dynamically invested, and 3) the number of requests issued to the cloud is reduced by allowing peers to fetch a collection of chunks using a single request. The performance of the proposed method is evaluated by simulation. The simulation results indicate that it reduces the cost of conventional scheme by 46% while guaranteeing the quality of live streaming service.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1732-1743
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• 1998

In this paper, we have proposed a channel assignment shceme for the multiple traffic class environment where the traffic volume varies with time. Our basic idea is to assign radio channels considering the characteristics of each traffic class and mobile speed and change the number of allocated channels for each traffic class according to vaiation of traffic volume. To evalute the perfomance of our proposed algorithms, we conducted analyical and simulation studies. We derived new call blocking probability and hand-off failure probability of the proposed scheme analytically. The simulatioh results show that our proposed algorithms can grantee GOS of each traffic class and provide a fairness between the new call and the hand-off call.

• Journal of Communications and Networks
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• v.7 no.1
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• pp.76-86
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• 2005

Today's wireless access networks consist of several tiers that overlap each other. Provisioning of real time undisrupted communication to mobile users, anywhere and anytime through these heterogeneous overlay networks, is a challenging task. We extend the end-to-end approach for the handoff management in hybrid wireless data network by designing a fully mobile-controlled handoff for mobile devices equipped with dual mode interfaces. By handoff, we mean switching the communication between interfaces connected to different subnets. This mobile-controlled handoff scheme reduces the service disruption time during both horizontal and vertical handoffs and does not require any modification in the access networks. We exploit the IP diversity created by the dual interfaces in the overlapping area by simultaneously connecting to different subnets and networks. Power saving is achieved by activating both interfaces only during the handoff period. The performance evaluation of the handoff is carried out by a simple mathematical analysis. The analysis shows that with proper network engineering, exploiting the speed of mobile node and overlapping area between subnets can reduce service disruption and power consumption during handoff significantly. We believe that with more powerful network interfaces our proposal of dual interfaces can be realized.

• Journal of the Korea Society of Computer and Information
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• v.17 no.2
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• pp.95-103
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• 2012

In this paper, we propose an efficient mobile P2P streaming architecture to minimize playback jitters in P2P overlay networks based on wired/wireless networks even though mobile peers experience the handover. In this architecture, mobile peers receive data in a push manner to maximize the data receiving speed before and after the handover. In addition, they can maintain the buffering above a specific level through handover prediction and re-selection of neighbor peers. By simulation experiments, we show that our proposed architecture can improve the performance significantly when the handover occurs compared to the existing mesh structure.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.11
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• pp.1-11
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• 2009

A content based pub/sub (Publish/subscribe) services at the peer-to-peer network has the requirements about how to distribute contents information of subscriber and to delivery the events efficiently. For satisfying the requirements, a DHT(Distributed Hash Table) based pub/sub overlay networking and tree type topology based network construction using filter technique have been proposed. The DHT based technique is suitable for topic based pub/sub service but it's not good contents based service that has the variable requirements. And also filter based tree topology networking is not efficient at the environment where the user requirements are distributed. In this paper we propose the R-Tree algorithm based pub/sub overlay network construction method. The proposed scheme provides cost effective event delivery method by mapping user requirement to multi-dimension and hierarchical grouping of the requirements. It is verified by simulation at the variable environment of user requirements and events.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.1
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• pp.5-25
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• 2009

In recent years the popularity of multi-hop wireless networks has been growing. Its flexible topology and abundant routing path enables many types of applications. However, the lack of a centralized controller often makes it difficult to design a reliable service in multi-hop wireless networks. While packet routing has been the center of attention for decades, recent research focuses on data discovery such as file sharing in multi-hop wireless networks. Although there are many peer-to-peer lookup (P2P-lookup) schemes for wired networks, they have inherent limitations for multi-hop wireless networks. First, a wired P2P-lookup builds a search structure on the overlay network and disregards the underlying topology. Second, the performance guarantee often relies on specific topology models such as random graphs, which do not apply to multi-hop wireless networks. Past studies on wireless P2P-lookup either combined existing solutions with known routing algorithms or proposed tree-based routing, which is prone to traffic congestion. In this paper, we present two wireless P2P-lookup schemes that strictly build a topology-dependent structure. We first propose the Ring Interval Graph Search (RIGS) that constructs a DHT only through direct connections between the nodes. We then propose the ValleyWalk, a loosely-structured scheme that requires simple local hints for query routing. Packet-level simulations showed that RIGS can find the target with near-shortest search length and ValleyWalk can find the target with near-shortest search length when there is at least 5% object replication. We also provide an analytic bound on the search length of ValleyWalk.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.4
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• pp.695-707
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• 2013

DHT(Distributed Hash Table) networks such as Kademlia are vulnerable to the ID mapping attack caused by the voluntary DHT mapping structure where the location of a node is solely determined by itself on the network topology. This causes security problems such as eclipse, DRDoS and botnet C&C on DHT networks. To prevent ID mapping attacks, we propose a non-voluntary DHT mapping scheme and perform analysis on NAT compatibility, attack resistance, and network dynamicity. Analysis results show that our approach may have an equivalent level of attack resistance comparing with other defense mechanisms and overcome their limitations including NAT compatibility and network dynamicity.

• Journal of IKEEE
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• v.17 no.4
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• pp.459-468
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• 2013

Under nonlinear characteristics of frames, we propose the frame interpolation using GRNN to enhance the visual picture quality. By full search with block size of 128x128~1x1 to reduce blocky artifact and image overlay, we select the frame having block of minimum error and re-estimate the nonlinear moving vector using GRNN. We compare our scheme with forward(backward) motion compensation, bidirectional motion compensation when the object movement is large or the object image includes zoom-in and zoom-out or camera focus has changed. Experimental results show that the proposed method provides better performance in subjective image quality compared to conventional MCFI methods.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.217-228
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• 2011

In centralize CDN systems, the content server selection is performed by service node for every user request, and the selected node is notified to the user. In this paper, we present distributed CDN architecture and algorithm in which the request from a user is delivered to the content source by a P2P algorithm utilizing DHT(distributed hash table) through the overlay network and the user selects one of the source nodes based on real-time user-centric criteria. For this purpose, we propose a modified Pastry algorithm for contents registration, search and selection, in addition to the distributed architecture. The proposed architecture has the advantages of load balancing, traffic balancing, scalability, fault-tolerance due to the self-configuration, self-healing attributes of distributed architecture. Various simulation shows the feasibility of the proposed architecture and algorithm, and the performance is compared and discussed for the variations of the proposed scheme.