• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.489-490
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• 2009

오버레이 멀티캐스트는 네트워크 구조의 변경 없이 단지 종단 노드가 자신이 받은 패킷을 자신의 다음 노드에게 전달해주는 방법을 이용하여 멀티캐스트를 사용할 수 있는 기법이다. 본 연구에서는 실시간 멀티미디어 서비스를 위하여 트리를 구성할 때 오고가는 메시지 오버헤드를 줄이고 사용자들의 대기를 최소화 하기위한 빠른 조인과정을 고려한 오버레이 멀티캐스트 구성 알고리즘을 제안한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.923-926
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• 2008

오버레이 멀티캐스트는 하드웨어적인 인프라 구축 없이도 시스템의 자원과 네트워크 대역폭을 효율적으로 사용할 수 있는 기법이며 중간 노드의 이탈이 발생하게 될 경우 멀티캐스트 트리를 재구성 한다. 그러나 빈번한 멀티캐스트 트리의 재구성은 심각한 성능 저하를 가져오게 된다. 본 논문에서는 이러한 성능저하를 보완하기 위해 각 자식 노드들로부터 소스 노드에게 주기적으로 피드백 되어오는 정보를 기반으로 트리 성능 최적화 알고리즘을 제안한다. 제안된 모델은 서비스 하는 부모노드가 트리의 성능을 저하 시키는 원인으로 판단되어질 때 수행하는 메커니즘이고, 이 메커니즘을 수행하여 성능 최적화 트리를 구성함으로써 전체적인 서비스 트리의 성능을 향상시켰다.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1364-1367
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• 2007

오버레이 멀티캐스트는 기존의 IP 멀티캐스트와 달리 Infrastructure의 도움 없이 멀티캐스트 기능을 수행하지만 갑작스런 노드의 이탈이나 장애 발생 시 트리의 복구가 필요하다. 본 논문에서는 이를 위해 각 노드의 Out-degree 자원을 미리 예약하여 트리 복구 시 예약된 노드에게 서비스를 요청하는 방안을 제시한다. 제시된 방안은 백업 노드로 인해 신속한 트리의 복구가 가능하다. 시뮬레이션을 통해 제시한 방안이 기존의 방안에 비해 보다 작은 복구 시간을 필요로 하며 부모 노드의 이탈로 인해 많은 수의 노드가 영향을 받는 상황에서 더욱 효과적으로 동작함을 보여주고 있다.

• Journal of KIISE:Information Networking
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• v.29 no.5
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• pp.583-594
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• 2002

Assuring the security of group communications such as tole-conference and software distribution requires a common group key be shared among the legal members in a secure manner. Especially for large groups with frequent membership change, efficient rekey mechanism is essential for scalability. One of the most popular ways to provide sealable rekey is to partition the group into several subgroups. In this paper, we propose a two-layered key management scheme which combines DEP and CBT, a protocol in which subgroup manager cannot access the multicast data and another that has a multi-core, respectively. We also select sub-group key management protocols suitable for our structure and design new rekey protocols to exclude the subgroup managers from the multicast data. Compared to previous protocols based on CBT, our scheme provides forward secrecy, backward secrecy and scalability. This would reduce the number of encryption and decryption for a rekey message and would improve the efficiency number of rekey messages and the amount of information related to group members that group managers must maintain compared to DEP.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.90-95
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• 2000

In the Ordered Core Based Tree(OCBT) protocol, a core location is the most important feature to affect the performance. In this paper, the location placement of multiple level cores is studied. The proposed algorithm isthat each node in the network evaluates a sum of shortest path costs from all the other nodes and the entirenetwork is divided into a hierarchy region to have 3-logical level(Small, Medium, Large). The node to have thelowest cost in each S-Region is decided to be a core node. Then, the core nodes in the each S-Region evaluatea sum of shortest path costs from all the other core nodes in the same M-Region. The core node to have thelowest cost is decided to be the upper level core node. Similarly the highest level core node is decided in theL-Region. The proposed algoritthm is compared with conventional two methods to put the core nodes in thenetwork One is the random method to put the core nodes randomly. The other is the center method to locatethe core node at the nearest node from the center of each S-Region and then to locate the highest level corenode at the nearest core node from the center of the entire network. Extensive simulations are performed in theview of mean tree cost and join latency. Simulation results show that the proposed algorithm has betterperformance than random method or center method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.1
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• pp.22-37
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• 2013

Content distribution to a large number of concurrent clients stresses both server and network. While the server limitation can be circumvented by deploying server clusters, the network limitation is far less easy to cope with, due to the difficulty in measuring and balancing network load. In this paper, we use two useful network load metrics, the worst link stress (WLS) and the degree of interference (DOI), and formulate the problem as partitioning the clients into disjoint subsets subject to the server capacity constraint so that the WLS and the DOI are reduced for each session and also well balanced across the sessions. We present a network load-aware partition algorithm, which is practicable and effective in achieving the design goals. Through experiments on PlanetLab, we show that the proposed scheme has the remarkable advantages over existing schemes in reducing and balancing the network load. We expect the algorithm and performance metrics can be easily applied to various Internet applications, such as media streaming, multicast group member selection.

• Journal of Advanced Navigation Technology
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• v.13 no.5
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• pp.726-735
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• 2009

In this paper, we proposed a novel conditional access system to reduce the overhead transmission rate for messages which verify the entitlement of subscribers in bandwidth-limited system. We adapted a key update system with the tree structure which had been used for IP multicast to a group hierarchy for the subscriber groups or channel groups. We also analyzed the overhead transmission rate for periodic key update and aperiodic one for change in a subscriber. The numerical evaluations show that the proposed system can significantly reduce the overhead transmission rate for dynamic subscriber change up to several hundred thousands times for various system configuration.

• Journal of KIISE:Information Networking
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• v.27 no.3
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• pp.360-369
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• 2000

통신의 규모가 사용자 수와 지리적 범위 두 가지 측면에서 커짐에 따라 신뢰적인 멀티캐스트 프로토콜의 implosion 및 exposure 문제는 더욱 심각해진다. 본 논문은 트리 기반 신뢰적 멀티캐스트를 위한 효율적이고 확장성 있는 손실 복구 기법을 제안한다. 먼저 에러 비트맵 정보를 통하여 멀티캐스트 라우팅 트리와 유시한 논리적 트리를 구성함으로써 멀티캐스트 라우팅 트리에서 상위에 위치하는 수신자들이 재전송을 요청한 수신자의 신뢰성을 책임지도록 하고 또한 효율적인 복구를 위해 구성된 트리 상에 독립된 멀티캐스트 주소를 가지는 지역 그룹을 형성한다. 논리적 트리는 세션 멤버쉽이나 멀티캐스트 경로의 변화에 따라 적응적으로 재구성되는데 이는 멀티캐스트 세션의 진행 동안 논리적 트리와 멀티캐스트 라우팅 트리 사이에 불일치를 최소화함으로써 멤버쉽과 경로가 변하는 상황에서도 implosion과 exposure를 감소시키는 강점을 지닌다. 제안한 기법과 정적 트리기반의 신뢰적 멀티캐스트 프로토콜과의 시뮬레이션을 통한 비교는 세션의 크기가 증가할수록 제안한 적응형 트리 기반의 복구방식이 더욱 효율적임을 보여준다.

• Journal of KIISE:Information Networking
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• v.30 no.3
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• pp.377-386
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• 2003

In this paper, we present an application layer protocol to support secure wireless Internet services, called Application Layer Security(ALS). The drawbacks of the two traditional approaches to secure wireless applications motivated the development of ALS. One is that in the conventional application-specific security protocol such as Secure HyperText Transfer Protocol(S-HTTP), security mechanism is included in the application itself. This gives a disadvantage that the security services are available only to that particular application. The other is that a separate protocol layer is inserted between the application and transport layers, as in the Secure Sockets Layer(SSL)/Transport Layer Security(TLS). In this case, all channel data are encrypted regardless of the specific application's requirements, resulting in much waste of network resources. To overcome these problems, ALS is proposed to be implemented on top of HTTP so that it is independent of the various transport layer protocols, and provides a common security interface with security applications so that it greatly improves the portability of security applications. In addition, since ALS takes advantages of well-known TLS mechanism, it eliminates the danger of malicious attack and provides applications with various security services such as authentication, confidentiality integrity and digital signature, and partial encryption. We conclude this paper with an example of applying ALS to the solution of end-to-end security in a present commercial wireless protocol stack, Wireless Application Protocol.

• Journal of KIISE:Information Networking
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• v.35 no.5
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• pp.402-408
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• 2008

This paper considers the problem of minimizing network-wide broadcast latency in multi-rate wireless mesh networks where a node can dynamically adjust its link layer transmission rates to its neighbors. We propose a broadcast algorithm that complements existing broadcast construct algorithm which chooses a multicast node randomly when each candidate node has same metric. We consider the currently accumulated broadcast latency from source node to the each candidate node so far to choose the next broadcast node. The proposed broadcast algorithm for minimizing latency in a multi-rate mesh networks which exploit wireless advantage and the multi-rate nature of the network. Simulation based on current 802.11 parameters shows that proposed MinLink_WCDS algorithm improves overall latency than the previous existing broadcast algorithm.