Hwa-Chun Lin

National Tsing Hua University, Hsin-chu-hsien, Taiwan, Taiwan

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Publications (39)20.55 Total impact

  • Hwa-Chun Lin, Chien-Yi Ho
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    ABSTRACT: This paper proposes a distributed location management strategy called weighted sliding-frame strategy for wireless mobile networks in which the processing speeds of the location information databases (LIDs) are heterogeneous. In the proposed strategy, a number of consecutively numbered location information databases are arranged into a frame. A frame of location information databases overlaps with the next frame except one database. Each frame is assigned a weight which is used to distribute the location information of the mobile hosts among the frames. The number of mobile hosts whose location information are stored in a frame is proportional to the weight assigned the frame. A nonlinear convex programming problem is formulated and solved numerically in order to find the set of weights that minimize the average database response time. Our numerical results show that the proposed weighted sliding-frame strategy is able to properly distribute the location information of the mobile hosts among the frames such that the average database response time is significantly lower than that of the sliding-frame strategy proposed in our previous work.
    Proceedings of IEEE International Conference on Communications, ICC 2010, Cape Town, South Africa, 23-27 May 2010; 01/2010
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    ABSTRACT: This paper proposes a new approach to designing alternate routing algorithms for all-optical wavelength-division multiplexing networks in order to reduce the connection blocking probability. The key idea is to try to route traffic in approximately the optimal way of splitting the traffic among the multiple routing paths between each source-destination pair. The optimal way of splitting the traffic among the multiple routing paths between each source–destination pair is obtained by solving a nonlinear multicommodity flow optimization problem. Two alternate routing algorithms, namely, traffic intensity based fixed-alternate routing algorithm and traffic intensity based dynamic-alternate routing algorithm, are proposed based on this approach. Simulations are performed to study the performances of the proposed alternate routing algorithms. Our simulation results show that the alternate routing algorithms designed according to the optimal way of splitting the traffic can effectively reduce the connection blocking probability.
    Journal of Lightwave Technology 11/2008; 22(26):3604-3616. · 2.56 Impact Factor
  • Hwa-Chun Lin, Chien-Yi Ho
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    ABSTRACT: This paper proposes a distributed location management strategy for wireless mobile networks. In the proposed strategy, a number of consecutively numbered location information databases (LIDs) are arranged into a frame. A frame of LIDs overlaps with the next frame except one database. The location information of a mobile host is replicated and stored in the databases in the same frame. When the location area of a mobile host changes, the new location information is stored in the next frame of databases. Thus, the proposed strategy is referred to as the sliding-frame strategy. The average communication cost and average database response time of the proposed sliding-frame strategy are analyzed and shown to be always lower than or equal to those of the strategy proposed by Krishnamurthi et al.
    IEEE Transactions on Vehicular Technology 10/2008; · 2.06 Impact Factor
  • Hwa-Chun Lin, Sheng-Wei Wang, Meng-Lin Hung
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    ABSTRACT: An alternate routing algorithm requires a set of predetermined routing paths between each source-destination pair. To reduce the connection blocking probability, it is desirable that the predetermined routing paths between each source-destination pair be link-disjoint. The predetermined routing paths used in previous works on alternate routing are the -shortest link-disjoint paths in terms of hop count. The shared links among the -shortest link-disjoint paths between different source-destination pairs may cause high connection blocking probability. Thus, depending on the traffic requirements of all source-destination pairs, hop-count based -shortest link-disjoint paths may not be the best choice for the predetermined routing paths. This paper proposes a method to find a set of link-disjoint routing paths between each source-destination pair to be used by an alternate routing algorithm in order to reduce the connection blocking probability. The key idea is to find a set of link-disjoint routing paths based on the routing paths that are utilized by the optimal traffic pattern in the network. Then, for each source-destination pair, we select a set of link-disjoint routing paths from the routing paths that are utilized by the optimal traffic pattern such that the selected set of link-disjoint routing paths carries the most of the traffic between the source-destination pair. Simulations are performed to compare the performance of using the link-disjoint routing paths found by the proposed method as the predetermined routing paths and those of using the hop-count based -shortest link-disjoint paths and employing the routing paths found by the capacity-balanced alternate routing method proposed method by Ho and Mouftah (in 2002) as the predetermined routing paths. Our simulation results show that using the link-disjoint routing paths found by the proposed method yields significantly lower connection blocking probability than employing the hop-count based -shortest link-dis- joint paths and using the routing paths found by the capacity-balanced alternate routing method (Ho and Mouftah, 2002).
    Journal of Lightwave Technology 07/2008; 26(11):1432-1444. · 2.56 Impact Factor
  • Hwa-Chun Lin, Pei-Shin Liu
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    ABSTRACT: This paper considers transceiver array-based single-hop wavelength division multiplexing (WDM) networks with reservation-based packet scheduling algorithms. In reservation-based packet scheduling algorithms for single-hop WDM networks, one or more of the wavelengths are used as control channels for transmitting reservation information. Time on a control channel is divided into control frames and each control frame is further divided into control slots. Each node is usually assigned a dedicated control slot in each control frame. Before transmitting a data packet, a node sends a control packet in a control slot to all other nodes to reserve a data slot. This paper proposes to adjust the lengths of the control frames dynamically according to the loads of the nodes by removing unused control slots. A dynamic control frame structure with variable number of control slots is proposed. A method is devised to enable the nodes in the network to dynamically acquire and release control slots depending on their loads such that the control frames include only necessary control slots for those nodes that have or potentially have data packets to send. Therefore, the delays for transmitting control packets and data packets can be reduced. Dynamically adjusting the lengths of the control frames is able to reduce the delays for transmitting control packets and data packets when the network load is light to medium or the traffic pattern is moderately or highly nonuniform; however, it introduces extra overhead in each control frame such that the length of the control frame may become larger than the size of the control frame in the fixed control frame structure resulting in higher mean packet delay when the load of the network is heavy and the traffic pattern is uniform or nearly uniform. Therefore, this paper further proposes a hybrid fixed and dynamic scheme that dynamically employs the fixed control frame scheme or the dynamic control frame scheme depending on the loads of the nodes- . The performance of the proposed hybrid scheme is studied via simulations. Our simulation results show that the hybrid scheme is able to dynamically choose the better of the fixed and dynamic control frame schemes such that it yields the lowest mean packet delay for the entire range of network loads and traffic patterns.
    Journal of Lightwave Technology 05/2008; 26(7):742-755. · 2.56 Impact Factor
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    Hwa-chun Lin, show-shiow Tzeng
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    ABSTRACT: In this paper, we consider cluster-based micro/picocellular networks with overlapped cell-clusters. Channel assignment and hand-off policies are essential and important policies in cellular wireless networks. The issue of how different channel assignment and hand-off policies in the overlapped areas affect the overall system performance has not yet been studied in the literature. This paper provides a thorough study and understanding of this issue. We propose two cluster channel assignment policies, namely, partitioned and shared cluster channel assignment policies, and two hand-off policies, namely, boundary and early hand-off policies. The proposed cluster channel assignment policies and hand-off policies are combined to obtain three different strategies, namely, partitioned-boundary, partitioned-early, and shared-boundary strategies. Extensive simulations are used to study the performance of the strategies. Our results show that the partitioned-early and shared-boundary strategies produce significantly lower hand-off dropping and forced termination probabilities than the partitioned-boundary strategy. The partitioned-early and shared-boundary strategies yield similar performance.
    Wireless Personal Communications 09/2007; 43(2):449-465. · 0.43 Impact Factor
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    ABSTRACT: This paper proposes a new fixed-alternate routing algorithm for all-optical WDM networks without wavelength conversion in order to reduce the connection blocking probability. The key idea in the proposed fixed-alternate routing algorithm is to try to route the traffics in approximately the optimal way. The multiple routing paths between each source-destination pair are arranged and used in descending order according to the traffic intensities obtained by solving a nonlinear multicommodity flow optimization problem. It is well known that finding the connection blocking probability is a very difficult task. Therefore, an objective function closely related to the connection probability is devised and used to formulate a nonlinear multicommodity flow optimization problem. Simulations are performed to study the performance of the proposed fixed-alternate routing algorithm. Our simulation results show that sorting the routing paths according to the optimally assigned traffic intensities in the proposed fixed-alternate routing algorithm can effectively reduce the connection blocking probability compared with sorting the routing paths according to hop counts in a typical fixed-alternate routing algorithm. In general, in all-optical WDM networks, a connection request that goes through a longer path experiences higher connection blocking probability than a connection request that goes through a shorter path. This is known as the fairness problem. Our simulation results show that the proposed algorithm yields better fairness than a typical fixed-alternate routing algorithm.
    Communications, 2006. ICC '06. IEEE International Conference on; 07/2006
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    ABSTRACT: Link failure is one of the most critical network fault conditions. Relying solely on SNMP traps to detect and identify link failures is not a complete solution. To supplement the SNMP-trap mechanism, one or more detectors can be placed in the network to periodically poll the devices using the ping or traceroute utilities such that all links are under the surveillance of the detectors. The goal is to place the smallest number of detectors to have all of the links under surveillance such that the cost of placing detectors in the network is reduced. In this paper, this problem is formulated as a minimum set covering problem. A new heuristic algorithm is proposed for this problem. Simulations are performed to study the performance of the proposed heuristic algorithm.
    Communications, 2005. ICC 2005. 2005 IEEE International Conference on; 06/2005
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    ABSTRACT: Efficient utilization of radio resource is one of the most important issues in wireless systems. In existing TDD based PRMA protocol and its variations, a mobile terminal is assigned on one of the frequency carriers after completing a registration procedure. Since mobile terminals enter and leave the system in an unpredictable fashion, some of the frequency carriers may become heavily loaded while other frequency carriers are underutilized. The frequency carriers can be utilized more efficiently by allowing the mobile terminals to switch among the frequency carriers. To enable the mobile terminals to switch among the frequency carriers efficiently, this paper proposes to arrange the frame boundaries on the frequency carriers in a slanted fashion. A scheme is proposed to enable a mobile terminal to switch among different frequency carriers such that shorter time is required to obtain a slot at the beginning of a talk spurt or a burst of data. Simulations are performed to compare the performance of the proposed scheme with a scheme that does not allow mobile terminals to switch among frequency carriers. Our simulation results show that the proposed slanted frame arrangement scheme yields significantly lower mean request waiting time and packet dropping ratio.
    International Journal of Wireless Information Networks 01/2005; 12:101-108.
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    Hwa-Chun Lin, Pei-Shin Liu
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    ABSTRACT: In reservation-based packet scheduling algorithms for single-hop WDM networks, one of the wavelengths is used as a control channel which is shared by all of the nodes for transmitting reservation information. Time on the control channel is divided into control frames of fixed length. Each of the control frames is further divided into a number of control slots. Before transmitting a data packet, a node sends a control packet in a control slot to inform all other nodes of its intention to send a data packet. The data packet can then be scheduled for transmission. Each of the nodes in the system is assigned a dedicated control slot. Free control slots in the control frames cannot be used by other nodes. The control packets generated by those nodes that have more data packets to send must be transmitted in the next or later control frames although there are a number of free control slots. The result of delaying the transmissions of control packets is increased packet delays. This effect has significant impact on packet delays under nonuniform traffics. To increase the utilization of the control slots and reduce the packet delays, we propose to adjust the lengths of the control frames dynamically according to the traffic patterns of the nodes. We propose a dynamic control frame structure with variable number of control slots. A scheme is devised to enable the nodes in the network to dynamically acquire and release control slots depending on their loads. Thus, the control frames will include only necessary control slots for those nodes that have or potentially have data packets to send. Therefore, the control slots on the control channel can be used efficiently and the packet delays can be reduced. Simulations are performed to study the performance of the proposed dynamic control frame structure. Our simulation results show that dynamically adjusting the lengths of the control frames can effectively increase the utilization of the control slots and reduce the mean packet - delay under nonuniform traffic compared with using fixed-length control frames
    Parallel Processing, 2003. Proceedings. 2003 International Conference on; 11/2003
  • Hwa-Chun Lin, Yung-Hua Chu
    Proceedings of the International Conference on Wireless Networks, ICWN '03, June 23 - 26, 2003, Las Vegas, Nevada, USA; 01/2003
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    ABSTRACT: This paper studies the different arrangements of frames in the time division duplexing (TDD)-based packet reservation multiple access (PRMA) protocol on multiple frequency carriers. Two frame arrangements, namely, aligned and slanted arrangement, are investigated. In the aligned arrangement, frame boundaries are aligned on all frequency carriers, in the slanted arrangement, the frame boundaries are shifted by one slot from one frequency carrier to the next. With slanted frame arrangement, a scheme is proposed to enable a mobile terminal to switch among different frequency carriers such that shorter time is required to obtain a slot at the beginning of a talk spurt. Extensive simulations are performed to compare the performance of the two arrangements of frames. Simulation results show that the slanted frame arrangement yields significantly lower mean request waiting time and packet dropping ratio than the aligned frame arrangement.
    Telecommunications, 2003. ICT 2003. 10th International Conference on; 01/2003
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    Hwa-Chun Lin, Zhe-Hong Lin
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    ABSTRACT: A core based tree established by the core based tree multicast routing architecture (CBT), the protocol independent multicast-sparse mode (PIM-SM), or the core-manager based multicast routing (CMMR) is rooted at a center node called core or rendezvous point (RP). The routes from the core (or RP) to the members of the multicast group are shortest paths. The costs of the trees constructed based on the core and the packet delays are dependent on the location of the core. In existing core based multicast routing architectures (CBT, PIM-SM, and CMMR), the core for a multicast group is selected from a set of candidate cores. However, none of them suggests a method for selecting the set of candidate cores. We propose three methods for selecting the set of candidate cores. The three proposed methods are compared with a method which select the candidate cores randomly. Three performance measures, namely, tree cost, mean packet delay, and maximum packet delay are considered. Our results show that the three proposed methods produce lower tree cost and significantly lower mean packet delay and maximum packet delay than the method which selects the candidate cores randomly. One of the three proposed methods, namely, k-maximum path count method.
    Communications, 2002. ICC 2002. IEEE International Conference on; 02/2002
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    Hwa-Chun Lin, Chun-Hsin Wang
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    ABSTRACT: The problem of minimizing the number of transmissions for a multicast transmission under the condition that the packet delay is minimum in single-hop wavelength division multiplexing (WDM) networks is studied in this paper. This problem is proved to be NP-complete. A heuristic multicast scheduling algorithm is proposed for this problem. Extensive simulations are performed to compare the performance of the proposed heuristic algorithm with two other multicast scheduling algorithms, namely, the greedy and no-partition scheduling algorithms. The greedy algorithm schedules as many destination nodes as possible in the earliest data slot. The no-partition algorithm schedules the destination nodes of a multicast packet to receive the packet in the same data slot without partitioning the multicast transmission into multiple unicast or multicast transmissions. Our simulation results show that (i) an algorithm which partitions a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than the no-partition algorithm when the number of data channels in the system is limited and (ii) the proposed heuristic algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.
    Photonic Network Communication 01/2002; 4(2):191-203. · 0.45 Impact Factor
  • Hwa-Chun Lin, Chun-Hsin Wang
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    ABSTRACT: This paper shows that, for single-hop wavelength division multiplexing (WDM) networks, a multicast scheduling algorithm which always tries to partition a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than a multicast scheduling algorithm that does not partition multicast transmissions. The performance of a multicast scheduling algorithm may depend on the traffic conditions and the availability of the channel resource in the network. A hybrid multicast scheduling algorithm that can be used in single-hop WDM networks
    Journal of Lightwave Technology 12/2001; 19(11):1654-1664. · 2.56 Impact Factor
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    Hwa-Chun Lin, Chun-Hsin Wang
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    ABSTRACT: This paper shows that, for single-hop WDM networks, a multicast scheduling algorithm which always tries to partition a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than a multicast scheduling algorithm which does not partition multicast transmissions. The performance of a multicast scheduling algorithm may depend on the traffic conditions and the availability of the channel resource in the network. A hybrid multicast scheduling algorithm that can produce good performance for wide ranges of the traffic conditions and the availability of the channel resource in the network is proposed. Depending on the average utilizations of the data channels and the receivers, the proposed hybrid multicast scheduling algorithm dynamically chooses to employ a multicast scheduling algorithm which always tries to partition multicast transmissions or a multicast scheduling algorithm which does not partition multicast transmissions. Extensive simulations are performed to study the performance of the proposed hybrid algorithm. Our simulation results show that the proposed hybrid algorithm produces lower mean packet delay for wide ranges of the load, the maximum multicast group size, the percentage of unicast traffic, and the number of data channels in the network compared with a multicast scheduling algorithm which always tries to partition multicast transmissions and a multicast scheduling which does not partition multicast transmissions
    INFOCOM 2001. Twentieth Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings. IEEE; 02/2001 · 2.56 Impact Factor
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    ABSTRACT: For the purpose of distributed network management, this paper employs a Web-based distributed network management architecture which uses the same HTTP protocol to download Java applets, to access management applications, and to communicate between management applications located at different sites. The advantage of using a single protocol (HTTP) at the transport layer is that it does not require an additional process in a network management server to handle a different protocol. A Web-based distributed topology discovery scheme is developed based on the Web-based distributed network management architecture. The Web-based distributed network management architecture and the distributed topology discovery scheme are implemented using the Java servlet technique. Our experimental results show that the average delay for discovering the topology using a distributed manner yields significantly lower delay than using a centralized manner
    Information Networking, 2001. Proceedings. 15th International Conference on; 02/2001
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    Hwa-Chun Lin, Kuen-Feng Yang
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    ABSTRACT: To support server-based reliable multicast, repair servers are used to store packets from sender(s) such that lost packets can be retransmitted to receivers from the repair servers. A repair server can be a specially designed host co-located with a router or a router with the functions of a repair server integrated in it. It may not be practical to place a repair server at each of the routers in the network if the size of the network is large. It is more economical to place repair servers at a subset of the nodes in the network such that the placement is cost-effective. Improper placement of repair servers may result in low utilization of the repair servers. It is desirable to place repair servers in the network such that they can be used effectively. Given a number of repair servers, we want to find a subset of the nodes in the network to place the repair servers such that the repair servers can be used effectively. To our knowledge, this problem has not been studied in previous researches. We propose three methods for the placement of repair servers. The performance of the three proposed methods are compared with that of a method which place the repair servers randomly in the network. Our simulation results show that the three proposed methods yield significant better performance than the random placement method. One of the three proposed methods, namely, k-maximum path count method, produces the best performance among the three proposed methods
    Communications, 2001. ICC 2001. IEEE International Conference on; 02/2001
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    Hwa-Chun Lin, Chien-Yi Ho
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    ABSTRACT: This paper proposes a new strategy for storing location information of mobile hosts in distributed location information databases along with a scheme for retrieving the location information of mobile hosts. A number of consecutively numbered databases are arranged into a frame of databases. A frame of databases overlaps with the next frame except one database. The location information of a mobile host is replicated and stored in the databases in the same frame. When the location area of a mobile host changes, the new location information is stored in the next frame of databases. This strategy is referred to as the sliding-frame strategy. We show that the proposed sliding-frame strategy yields significantly lower cost for updating and querying the location information databases than the strategies proposed by G. Krishnamurthi et al. (see Proc. 4th Annual ACM/IEEE International Conference on Mobile Computing and Networking, 1998; Proc. IEEE ICC'99, p.1768-72, 1999)
    Vehicular Technology Conference, 2001. VTC 2001 Spring. IEEE VTS 53rd; 02/2001
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    Hwa-Chun Lin, Shou-Chuan Lai
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    ABSTRACT: The Core Base Tree (CBT) multicast routing architecture is a multicast routing protocol for the Internet. The CBT establishes a single shared tree for a multicast connection. The shared tree is rooted at a center node called core. The location of the core may affect the cost and performance of the CBT The core placement method proposed in Lin and Lai (1998) requires the knowledge of the network topology. In this paper we propose a simple and effective method for selecting the core. This method requires only the distance vector information. The performance of this method is compared with several other methods including the one proposed in Lin and Lai (1998) by extensive simulations. Our results show that this simple core placement method for the CBT is very effective. It produces the lowest mean delay, maximum delay, and total cost among the methods studied in this paper
    Performance, Computing, and Communications Conference, 2000. IPCCC '00. Conference Proceeding of the IEEE International; 03/2000