• Proceedings of the Korea Multimedia Society Conference
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• 2004.05a
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• pp.417-420
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• 2004

Ad hoc network는 유선 백본 없이 이동 노드들로만 구성된 네트워크로서 이동 노드들의 움직임이 빈번히 발생하기 때문에 네트워크의 안정성을 유지하기가 어렵다. 또한 중앙 집중화된 보안 기반구조가 아니기 때문에 보안 공격을 받기가 쉽고 노드들이 쉽게 손상될 수 있다. 기존의 보안 방법 중의 하나인 threshold cryptography는 키의 유지와 분배를 위한 효율적인 구조를 제공하였으나 라우팅의 오버헤드가 증가하였고, 네트워크 전역의 트래픽이 증가되었다. 게다가 서비스 거부 공격과 wormhole과 같은 공격은 ARP 또는 IP spoofing을 통하여 쉽게 받을 수 있다. 본 논문에서는 threshold cryptography에 의해 야기되는 오버헤드를 줄이고 노드간의 인증된 패킷 전달을 돕기 위한 새로운 접근 방법을 제안한다.

• Proceedings of the Korea Multimedia Society Conference
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• 2002.05c
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• pp.385-389
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• 2002

Ad-hoc 무선망은 고정된 유선망을 가지지 않고 이동 노드들로만 구성된 망이다. 여러 가지 이동 노드에 대한 이동 제약이 없고, 유선망이나 기지국 같은 기반 구조를 필요를 하지 않기 때문에 여러 환경에 적용이 가능하다. 그러나 라우터들 사이의 이동성과 다른 연결 요소들의 가변적인 요소는 잠재적으로 속도감 있고 예측 불가능하게 변하는 망을 가져올 수 있다. 이에 따른 패킷의 손실이 무선 네트워크에서 자주 발생하게 된다. 최근 몇 년 동안 Ad-hoc망에서 사용되는 라우팅 프로토콜의 각각에 대한 성능을 분석하는 연구가 있었지만, Ad-hoc 무선망에서 특정한 프로토콜의 TCP 버전별 비교 분석에 대한 연구가 미비한 실정이다. 따라서 본 논문에서는 무선 네트워크가 가지는 단점을 보완하고 트래픽 성능을 향상시키기 위한 한 방편으로, Ad-hoc 라우팅 알고리즘인 DSR 프로토콜을 이용하여 TCP Tahoe, Sack, Reno 버전별로 토폴로지의 크기의 변화와 이동 노드의 이동 속도의 변화에 따라 트래픽의 성능을 모의 실험하여 비교 분석하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.95-101
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• 2005

In this paper, some performance characteristics of multimedia traffic for mobile ad-hoc networks is studied with simulations. Synthetic streaming video is considered as the multimedia traffic for MPEG-coded video in the simulation. The synthetic video stream is generated with a video stream generation algorithm. The algorithm generate VBR traffics for MPEG video streams with special predefined GOP(group of pictures) patterns that is consisted of a sequence of I(intra-coded), P(predicted-coded) and B(bidirectional-coded) frames. The synthetic VBR streams is transmitted through UDP protocol with on-demand mobile ad-hoc network routing protocols like as AODV and DSR. And performances for video streams through mobile ad-hoc networks is evaluated, the throughputs is compared between data and video traffics.

• Journal of Korea Multimedia Society
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• v.13 no.8
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• pp.1221-1234
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• 2010

MANET(Mobile Ad-hoc Network)s have been researched primary at routing protocols and at the guarantees of QoS(Quality of Service) for mobile environments. Otherwise the Ubiquitous Sensor Networks (USNs) have some limitations in power energies and in processing of sensing data, as well as their network topologies are frequently changed by fading off and node failures. Thus we should redesign network protocols with concerning to energy efficiency for the USNs above all. In this paper, we focus on the protocol interface for managing for USNs based on the surveys. And then we figure the topology of USNs out and design the network protocol interface to make power saved, with data gathering and processing more efficient using our designed packet structures.

• The Transactions of the Korea Information Processing Society
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• v.5 no.5
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• pp.1274-1284
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• 1998

Multicasting plays an important role in providing multimedia services like audio and video conferencing and has been actively studied for many years. The study of multicasting has been mainly focused on finding a low-cost tree on the assumption that every edge of the tree has enough link capacity to be allocated to the amound of bandwidth required by a service. In some cases, however, a multicasting tree whose some edges do not have enough bandwidth to be allocated may exist. A typical example of this case is to multicast among the group users located in the different sub-networks in the interconnected networks composed of the high bandwidth networks such as B-ISDN and the low bandwidth networks such as PSTN and PSDN. This paper proposes a novel multicasting protocol for providing multimedia services in a wide area network interconnected by multiple heterogeneous networks. First, the paper discusses the inherent limitation of present multicasting protocols for the case. Second, se introduce a new concept, multiple QoS's for a service, which extends the implicit assumption that only one QoS is assigned to a service in order to overcome this limitation. Third, our multicasting protocol is designed based on the current Internet protocol stacks. Last, we perform simulations for possible scenarios to provide multimedia services in the network and analyze their pros and cons.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.109-113
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• 2011

In intelligent subway systems, UWB-based WiMedia D-MAC Protocol can be considered to send and receive multimedia data which requires high data rate. However, network devices which do not exist within 10 meters, the limited communication rage, can not communicate with each other because WiMedia does not support multi-hop communications. In this paper, we developed the algorithm to select a relaying device for multi-hop routing on WiMedia networks. In the first step, each device acquires information of neighbors through beacon and decides whether it is a normal or relaying device using the acquired information. In the next step, all devices can create the 2-hop routing table using the information received via relaying devices and the whole routing table for all devices on networks, eventually.

• Journal of Korea Multimedia Society
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• v.10 no.2
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• pp.269-277
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• 2007

Network clustering has been proposed to provide that sensor nodes minimize energy and maximize a network lifetime by configuring clusters, Although dynamic clustering brings extra overhead like as head changing, head advertisement, it may diminish the gain in energy consumption to report attribute tasks by using cluster heads. Therefore, this paper proposes a new routing algorithm which configures cluster to reduce the number of messages when establishing paths and reports to the sink by way of cluster heads when responding sens ing tasks. All sensor nodes only broadcast bitmap once and maintain a bitmap table expressed by bits, allowing them to reduce node energy and to prolong the network lifetime. After broadcasting, each node only updates the bitmap without propagation when the adjacent nodes broad cast same query messages, This mechanism makes nodes to have abundant paths. By modifying the query which requests sensing tasks, the size of cluster is designed dynamically, We try to divide cluster by considering the number of nodes. Then, all nodes in a certain cluster must report to the sub- sink node, The proposed routing protocol finds easily an appropriate path to report tasks and reduces the number of required messages for the routing establishment, which sensor nodes minimize energy and maximize a network lifetime.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1178-1181
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• 2009

Geographic forwarding algorithms을 사용하는 Georouting protocol에서는 route maintenance을 위해서 고정된 주기마다 beacon message을 이웃노드에 전송하는 fixed periodical beacon based route algorithm을 사용하여 mobile node 정보를 습득한다. Fixed periodical beacon scheme에서의 기존 연구 이슈는 이웃노드 정보의 신뢰성을 유지하기 위해서 다양한 mobility environment 환경에 맞도록 beacon 전송주기를 적절히 결정하는 연구가 진행되어 왔다. 이와 같은 연구에서는 long periodical interval 사용 시 이웃노드의 위치정보 error을 발생시킬 확률이 높으며 또한 short periodical interval 의 경우 네트워크 내에 high route overhead 을 유발시키는 단점을 가지고 있다. 따라서 고정된 주기 방법은 다양한 mobility environment에 잘 적용되지 못하며 또한 mobility environment 에서 발생하는 route maintenance 내에 이웃노드 정보에 대한 불확실성 문제가 빈번이 발생하여 경로 설정에 잘못된 정보를 제공하여 경로 신뢰성(path reliability)과 낮은 전송률 (transmission rate)을 야기한다. 본 논문에서는 이런 이웃노드 정보의 불확실성 문제를 극복하기 위해서 mobile node가 스스로 자신의 위치를 체크하여 routing table을 능동적으로 갱신하는 방법을 이용하여 이 문제를 극복할 수 있도록 하였다. 모의 실험은 ns2를 이용하여 실시하였으며 결과는 low/high mobility scenario에서는 기존 방법 보다 routing overhead 을 줄이면서 높은 전송률 (transmission rate)을 보인다.

• Journal of the Institute of Convergence Signal Processing
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• v.7 no.2
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• pp.45-52
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• 2006

Mobile Ad-hoc Network(MANET) could be applied to various applications by virtue of its characteristics such as self-organizing and infrastructure-free network. This paper proposes a multimedia application service model for MANET, called multi-hop Relay(mRelay) system. It supports a multi-hop communication-based multimedia service interworked with Internet by using an unmanned moving robot with wireless multimedia communication function as a mRelay terminal. The modified AODV routing protocol was applied to the terminal and it was verified that composition and maintenance of mobile Ad-hoc network in mRelay system under the various indoor scenarios were successful and stable multi-hop multimedia services were possible. The mRelay system can be applicable to various application services of mobile Ad-hoc networks.

• Journal of KIISE:Information Networking
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• v.36 no.5
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• pp.456-469
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• 2009

We develop a new wireless link quality metric, ECOT(Estimated Channel Occupancy Time) that enables a high throughput route setup in wireless mesh networks. The key feature of ECOT is to be applicable to diverse mesh network environments where IEEE 802.11 MAC (Medium Access Control) variants are used. We take into account the exact operational features of 802.11 MAC protocols, such as 802.11 DCF(Distributed Coordination Function), 802.11e EDCA(Enhanced Distributed Channel Access) with BACK (Block Acknowledgement), and 802.11n A-MPDU(Aggregate MAC Protocol Data Unit), and derive the integrated link metric based on which a high throughput end-to-end path is established. Through extensive simulation in random-topology settings, we evaluate the performance of proposed link metric and present that ECOT shows 8.5 to 354.4% throughput gain over existing link metrics.