• International Journal of Fuzzy Logic and Intelligent Systems
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• v.2 no.3
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• pp.194-197
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• 2002

This paper considers the problem of routing connections in a optical multi tree networks using WDM (Wavelength Division Multiplexing), where each connection between a pair of nodes in the network is assigned a path through the network and a wavelength on that path, so that connections whose paths share a common link in the network are assigned different wavelengths. The problem of optimal coloring of the paths on the optical multi-networks is NP-hard[1], but if that is the coloring of all paths, then there exists efficient polynomial time algorithm. In this paper, using a "divide & conquer" method, we give efficient algorithm to assign wavelengths to all the paths of a tree network based on the theory of [7]. Here, our time complexity is 0(n4log n).

• Journal of the Korea Society of Computer and Information
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• v.21 no.9
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• pp.79-84
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• 2016

In this paper we consider the problem of finding the triplet (S,${\pi}$,f), where $S{\subseteq}V$, ${\pi}$ is a sequence of nodes in S and $f:V{\backslash}S{\rightarrow}S$ for a given complete graph G=(V,E). In particular, there exist two costs, $c^V_{uv}$ and $c^D_{uv}$ for $(u,v){\in}E$, and the cost of triplet (S,${\pi}$,f) is defined as $\sum_{i=1}^{{\mid}S{\mid}}c^V_{{\pi}(i){\pi}(i+1)}+2$ ${\sum_{u{\in}V{\backslash}S}c^D_{uf(u)}$. This problem is motivated by the integrated routing of the vehicle and drone for urban delivery services. Since a well-known NP-complete TSP (Traveling Salesman Problem) is a special case of our problem, we cannot expect to have any polynomial-time algorithm unless P=NP. Furthermore, for practical purposes, we may not rely on time-exhaustive enumeration method such as branch-and-bound and branch-and-cut. This paper suggests the simple heuristic which is motivated by the MST (minimum spanning tree)-based approximation algorithm and neighborhood search heuristic for TSP.

• Journal of the Korea Society of Computer and Information
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• v.13 no.4
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• pp.177-184
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• 2008

The design goal of protocols in wireless sensor networks (WSN) is mainly energy efficiency because of their stringent resource and energy constraints. In this paper, we propose a simple cross-layered protocol for WSNs, so called EATD(Energy-Aware Tree based Delivery scheme). EATD is a tree-based energy aware data delivery algorithm by using a SYNC packet with link and node cost to maximize the network lifetime. Our simulation results show significant improvements compared with existing schemes in terms of energy efficiency and delay.

• Spatial Information Research
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• v.19 no.5
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• pp.63-74
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• 2011

Recently, there has been much interest in the spatial query which energy-efficiently acquires sensor readings from sensor nodes inside specified geographical area of interests. The centralized approach which performs the spatial query at a server after acquiring all sensor readings, though simple, it incurs high wireless transmission cost in accessing all sensor nodes. In order to remove the high wireless transmission cost, various in-network spatial indexing schemes have been proposed. They have focused on reducing the transmission cost by performing distributed spatial filtering on sensor nodes. However, these in-network spatial indexing schemes have a problem which cannot optimize both the spatial filtering and the wireless routing among sensor nodes, because these schemes have been developed by simply applying the existing spatial indexing schemes into the in-network environment. Therefore, we propose a new distributed spatial indexing scheme of the GR-tree. The GR-tree which form s a MBR-based tree structure, can reduce the wireless transmission cost by optimizing both the efficient spatial filtering and the wireless routing. Finally, we compare the existing spatial indexing scheme through extensive experiments and clarify our approach's distinguished features.

• Journal of KIISE:Information Networking
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• v.34 no.2
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• pp.120-133
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• 2007

A multicast tree includes several, possibly a large number of, paths connecting source-receiver pairs, and network failure may disable part of the multicast tree. Reconstruction of the entire multicast tree to recover from a component failure is highly undesirable, because some group members have to suffer service disruptions even though the communication paths to/from them are not affected by the failure. To limit reconfiguration region and to maximize the likelihood of successful reconfiguration, we propose and evaluate a pre-planned reconfiguration policy for QoS multicast sessions. Specifically, we equip a reconfiguration path (RP) with each end-to-end path that connects a source-receiver pair in the multicast tree, and reserve resources in advance along the RPs. Efficient resource-sharing techniques are applied to reduce the amount of resources reserved for RPs but not used in the absence of failures. This way, we prevent uncontrolled competition among different multicast sessions which may simultaneously try to recover from failures. We evaluate the performance of the proposed scheme using simulation on randomly-generated networks. We use the shortest-path routing for QoS multicast sessions, and simulate both source-based and shared multicast trees. The evaluation results indicates that successful pre-planned reconfiguration can be achieved for all group members with reasonable overhead. Our scheme is also shown to adapt well to dynamic changes of group membership.

• Journal of the Korean Operations Research and Management Science Society
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• v.19 no.1
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• pp.153-168
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• 1994

This paper is concerned with the development of tree-search algorithm for the exact solution to the vehicle problem (VRP), where set of vehicles of known capacity based at depot, have to be routed in order to supply customers with known requirements. When is required is to design routes, so that the total cost (i. e. total route length or time duration, ect.) is minimized. For obtianing the exact solution, the most important factors are the value of bound and branching strategy. Using the bound based on with bound ascent procedures from subgradient and state-space ascents, the incorporation of bounds into tree search algorithm to solve the problem is shown. Computational results of the corresponding algorithm show that VRPs with up to 40 customers can be solved optimally with this algorithm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.601-602
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• 2006

The primary role of MRP(Material Requirement Planning) is to make a production plan so that we have an exact quantity of right materials on needed time at right place. But the ignorance on capacity constraints makes some problems whenever production schedule is established. To increase the performance of MRP system, a novel approach which is based on new input data structure is suggested. The new input data structure includes all the information about Material BOM, Routing and resource data so that we can easily examine the usage of resources and generate higher performance production plans.

• Electronics and Telecommunications Trends
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• v.14 no.5 s.59
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• pp.99-110
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• 1999

본 논문은 지금까지 제안되어 온 인터넷 멀티캐스트 라우팅 프로토콜에 대하여 살펴본다. 지금까지 제안되어 온 방식들은 크게 SBT(Source Based Tree) 및 CBT(Center Based Tree) 방식으로 분류할 수 있다. SBT 방식은 하나의 송신자에서 각 수신자에 이르는 최단 경로 트리를 구하여, 데이터 전송지연 시간 측면에서 효율적인 반면에, 불필요한 제어 메시지의 수가 많이 발생하여 확장성(scalability) 문제를 갖는다. 반면에 CBT 방식은 여러 송신자가 멀티캐스트 트리를 공유하는 공유형(shared) 트리 구성 방식이며, 송신자와 수신자 모두 센터(center) 노드에 이르는 최단 경로를 통해 데이터를 주고 받는다. 이 방식은 SBT 방식에 비해 확장성 측면에서 효율적인 반면에 전송지연 시간이 길다. 향후의 관련 연구에서는 확장성과 전송지연 및 네트워크 자원의 효율적인 이용을 고려한 멀티캐스트 라우팅 기법이 개발되어야 할 것이다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.12
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• pp.4343-4355
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• 2014

Multicast group communication has many advantages in data centers and thus is widely used by many applications. It can efficiently reduce the network traffic and improve the application throughput. For the multicast application in data centers, an essential problem is how to find a minimal multicast tree, which has been proved to be NP-hard. In this paper, we propose an approximation tree-building method for the minimal multicast problem, named HD（Hamming Distance）-based multicast tree. Consider that many new network structures have been proposed for data centers. We choose three representative ones, including BCube, FBFLY, and HyperX, whose topological structures can be regarded as the generalized hypercube. Given a multicast group in BCube, the HD-based method can jointly schedule the path from each of receiver to the only sender among multiple disjoint paths; hence, it can quickly construct an efficient multicast tree with the low cost. The experimental results demonstrate that our method consumes less time to construct an efficient multicast tree, while considerably reduces the cost of the multicast tree compared to the representative methods. Our approach for BCube can also be adapted to other generalized hypercube network structures for data centers after minimal modifications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.660-666
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• 2014

In this paper, we consider a classification criteria of sensor nodes based on equipment function, and propose a routing search algorithm between node when an IP-USN is applied inside a ship. whereas a tree-type routing algorithm is applied to the limited mobile enviroment, such as engine room or machine room, a mesh-type routing alogrithm is to free mobile enviroment, such as passager corridor liviing quarters or restanrats areas. For mesh-type routing, it is necessary to maintain a seamless route path between a sink node and sensor nodes for which we consider a novel message exchange periodically. We proposed a new message, RDES message, which is issued periodically to update the topology of sensor node and check a connectivity between nodes.