• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.6
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• pp.29-36
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• 2016

A wireless passive sensor network is a network which, by letting separate RF sources supply energy to sensor nodes, is able to live an eternal life without batteries. Against expectations about an eternal life, however, a wireless passive sensor network still has many problems; scarcity of energy, non-simultaneity of energy reception and data transmission and inefficiency in resource allocation. In this paper, we focus on a wireless passive sensor network providing a packet service which is tolerable to packet losses but requires timely delivery of packets. Perceiving the practical constraints, we then consider a contending-type MAC scheme, rooted in framed and slotted ALOHA, for supporting many sensor nodes to deliver packets to a sink node. Next, we investigate the network-wide throughput achieved by the MAC scheme when the packets transmitted by geographically scattered sensor nodes experience path losses hence capture phenomena. Especially, we derive an exact formula of network-wide throughput in a closed form when 2 sensor nodes reside in the network. By controlling design parameters, we finally optimize the contending-type MAC scheme as to attain the maximum network-wide throughput.

• Annual Conference of KIPS
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• 2003.05b
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• pp.1377-1380
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• 2003

계층적 모바일 IPv6는 이동 노드의 지역적인 이동시 보다 빠르고 효과적으로 서비스를 제공하기 위하여 네트워치를 계층적으로 구성한 프로토콜로써, 모바일 IPv6의 단점인 핸드오프시의 긴 지연시간을 단축시켜 손실되는 패킷을 줄이며, 외부로 전송되는 트래픽의 양을 감소시키는 장점이 있다. 따라서 많은 양의 데이타 처리가 필요한 멀티미디어 통신이나, 신속한 서비스를 필요로 하는 실시간 통신에 적용이 가능하다. 본 논문에서는 기존의 모바일 IPv6와 계층적 모바일 IPv6를 구현하여 핸드오프 지연시간과 패킷 손실량을 측정하고 성능 비교를 통하여 계층적 모바일 IPv6의 성능 향상을 확인하였다.

• Journal of KIISE:Information Networking
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• v.28 no.1
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• pp.143-153
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• 2001

본 논문에서는 에드-혹 망의 멀티캐스트 라우팅 프로토콜인 ODMRP(On-Demand Multicast Routing Protocol)를 확장한 PatchODMRP를 제안한다. ODMRP는 네트워크 상에서 멀티캐스트그룹의 송신원으로부터 수신원에 이르는 경로 상에 있는 노드들을 FG(Forwarding Group) 노드로 선출하여 이들이 해당 멀티캐스트그룹에 속하는 패킷을 모두 플러딩하도록 함으로써 멀티캐스트 그룹데이타 전송을 담당하는 메쉬를 구성하도록 하는 방안이다. 그런데 ODMRP는 주기적으로 이 메쉬를 구성하는 FG 노드들을 재 선정하기 때문에 이 주기가 길어지면 메쉬 구성이 네트워크 노드들의 이동성을 따라가지 못해 메쉬분리가 발생하고 데이터가 손실될수 있다. 반면에 이 주기를 짧게 하면 오버헤드가 지나치게 커질수 있다. 특히 송신원의 수가 적은 경우 ODMRP의 메쉬는 매우 성기게 형성되는데 이때 호스트들의 이동성이 크면 메쉬 연결을 유지하기 위하여 이 주기를 짧게 잡아주거나 높은 데이터 손실율을 감수해야한다. 본 논문에서는 이 문제점을 해결하고자 각 FG 노드들이 BEACON 신호를 이용해 자신에 인접한 메쉬에 손실이 발생한 것을 인지하고 이를 국부적인 플러딩을 통하여 빠르게 복구하는 메커니즘을 ODMRP에 추가한 PatchODMRP 방식을 제안한다. 시뮬레이션을 통하여 기존의 ODMRP와 제안하는 PatchODMRP의 성능을 비교한 결과 PatchODMRP가 호스트의 이동성에 훨씬 강하며 ODMRP에 비하여 낮은 오버헤드로 높은 데이터 전송률을 제공할 수 있음을 보여주었다.

• Journal of KIISE:Information Networking
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• v.35 no.5
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• pp.374-383
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• 2008

IEEE 802.11 WLANs support various data rates in order to adapt to wireless channel condition. It is known that when some WLAN stations use a lower data rate than the others, total throughput is considerably degraded. The concept of temporal fairness which provides equal time to all stations has been introduced to alleviate this performance anomaly problem. However, most previous mechanisms assume that stations have infinite backlogs in the MAC layer and do not consider transport layer. In this paper, we first examine and analyze the performance of previous methods considering transport layer protocols. We then propose two new temporal fairness guarantee methods: AP priority and dynamic CWmin adjustment. We carried out extensive performance study via ns-2 computer simulations. The results show that the proposed methods provide temporal fairness and improve the throughput of WLANs in various environments.

• Journal of KIISE:Information Networking
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• v.35 no.3
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• pp.215-226
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• 2008

As sensor networks are used in various and dynamic applications, the function of sink-to-sensors reliable multicasting such as for task reprogramming is newly required. NAK-based error recovery schemes have been proposed for energy efficient reliable multicasting. However, these schemes have incompleteness problems such as the last packet loss. This paper introduces an ACK-based error recovery scheme, RM2I(Reliable Multicast with Implicit ACK and Indirect Recovery). It utilizes wireless multicast advantage in which a packet may be delivered to all of its omni-directional neighbor nodes. When a sender overhears a packet which its receiver forwards to the next nodes, it may interpret it as an ACK from the receiver. We call it an Implicit ACK. In Indirect Recovery, when a node receives a packet from neighbor nodes which are not its direct upstream node, it saves and utilizes it for error recovery. Using NS-2 simulator, we have analyzed their effects. We have also compared RM2I with the NAK-based error recovery scheme. In results, RM2I shows comparable performances to the ideal NAK-based scheme, except where Implicit ACK and Indirect Recovery do not occur at the edges of the networks.

• Journal of KIISE:Information Networking
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• v.29 no.1
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• pp.15-23
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• 2002

We present a new MDA-based Mobile-IPv6 multicast routing algorithm for wirelese service operators to offer Mobile-IP over IMT-2000 service under IMT-2000 network by taking advantage of the existing infrastructure for IMT-2000 multimedia application services. The extended IMT-2000 system architectures use an PDSNs (i.e. IWFs), and the home network (i.e. Internet) backbone and intermediate network are composed of ATM entities. A key feature of the new protocol is the use of MDA(Multicast Delivery Agent) to reduce delivery path length of the multicast datagram. We show that proposed protocol is efficient in terms of various performance measures such as multicast traffic load, multicast related handoff, and average routing length when we implement it using the Mobile-IPv6. Particularly, the number of tunneling and average routing length of datagram are reduced relatively, the multicast traffic load is also decreased.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.252-259
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• 2003

In the case of link congestion, most of the existing ad-hoc routing protocols like AODV and DSR do not try to discover a new route if there is no change in the network topology. Hence, with low mobility, traffic may get concentrated on some specific nodes. Since mobile devices have low battery power and low computing capability, traffic concentration on a specific node is not a desirable phenomenon. Therefore, in this paper, we propose a new protocol called SLAP (Simple Load-balancing Ad-hoc routing Protocol) which resolves the traffic concentration problem by letting each node check its own load situation and give up its role as a packet forwarder gracefully in the case of high traffic load. We compare the performance of SLAP with that of AODV and DSR in terms of the forwarding traffic distribution.

• Journal of KIISE:Information Networking
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• v.35 no.6
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• pp.497-509
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• 2008

Various algorithms and architectures for efficient packet classification have been widely studied. Packet classification algorithms based on a decision tree structure such as HiCuts and HyperCuts are known to be the best by exploiting the geometrical representation of rules in a classifier. However, the algorithms are not practical since they involve complicated heuristics in selecting a dimension of cuts and determining the number of cuts at each node of the decision tree. Moreover, the cutting is not efficient enough since the cutting is based on regular interval which is not related to the actual range that each rule covers. In this paper, we proposed a new efficient packet classification algorithm using a range cutting. The proposed algorithm primarily finds out the ranges that each rule covers in 2-dimensional prefix plane and performs cutting according to the ranges. Hence, the proposed algorithm constructs a very efficient decision tree. The cutting applied to each node of the decision tree is optimal and deterministic not involving the complicated heuristics. Simulation results for rule sets generated using class-bench databases show that the proposed algorithm has better performance in average search speed and consumes up to 3-300 times less memory space compared with previous cutting algorithms.

• The Transactions of the Korea Information Processing Society
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• v.4 no.1
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• pp.237-245
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• 1997

In this paper, a flow control mechanism is proposed which is based on the priority control between communication path of a node. In this scheme, demanding length of a data queue for any pre-defined, then each node in that path is forced to maintains buffer size under the limit by controlling priority level of the path. The communication path which requires higher bandwidth sets its demanding queue length smaller. By providing relationship between the priority of a path and length of its queue, the high bandwidth requesting path has a better chance to get high bandwidth by defining the smaller demanding queue size. And also, by forcing a path which has high flow rate to maintain small queue size in the path of the communication, the scheme keep the transmission delay of the path small. The size of the demanding queue of a path is regularly adjusted to meet the applications requirement, and the load status of the network during the life time of the communication. The priority control based on the demanding queue size is also provided in the intermediate nodes as well as the end nodes. By that the flow control can provide a quicker result than end to-end flow control, it provides better performance advantage especially for the high speed network.

• Journal of KIISE:Information Networking
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• v.34 no.5
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• pp.328-339
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• 2007

Conventional topology-based routing protocols are not suitable for inter-vehicular communication, where frequent route updates are necessary due to continuous and abrupt changes in network topology Position-based routing protocols are widely accepted to better serve their purpose in such a scenario as they do not require path discovery or maintenance. However they have to deal with the overhead of the location service and inaccurate position information. This paper proposes the MMFP (Multi-hop MAC Forwarding Protocol) for inter-vehicle communication that relies on reachability information collected from received packets in making a forwarding decision without path discovery. The MMFP is designed as an extension to the IEEE 802.11 MAC layer to ensure accuracy in its time-critical operations. This paper also presents some simulation results that demonstrate the superior performance of the MMFP over AODV in a realistic inter-vehicular communication.