Browsing by Author "Chen, Chien"

Now showing 1 - 20 of 53

A blocking probability model in multigranularity cross-connect optical networks
(2007)
Kuo, Xiu-Jia
;
Chen, Chien
;
資訊工程學系
;
Department of Computer Science
This study analyzes the blocking rate in an optical network with multi-granularity optical cross connect (MG-OXC). The MG-OXC architecture is composed of three kinds of granularity (fiber, waveband, and wavelength) in order to resolve the scalability problem due to the exponentially increasing traffic in traditional OXC. Based on the MG-OXC optical networks, a fundamental issue is to develop the algorithms for the routing and wavelength assignment (RWA) with tunnel allocation. In this paper, we have worked from a slightly different angle. We propose a blocking probability model using Erlang loss formula to estimate the performance of tunnel allocation with a different tunnel length constraint. Finally the analytical results, which have proved to be very close to the simulation results, obtained from various kinds of network topologies are shown.
A distance-aware counter-based broadcast scheme for wireless ad hoc networks
(2005)
Chen, Chien
;
Hsu, Chin-Kai
;
Wang, Hsien-Kang
;
資訊工程學系
;
Department of Computer Science
In mobile ad hoc networks (MANETs), broadcasting is a common operation for providing network functions, such as route discovery and source paging. However, an uncontrolled broadcast, which is also called blind flooding, is inefficient and may lead to heavy redundancies, contentions and collisions, and is commonly referred to as a "broadcast storm" problem [1]. Although this problem has been addressed extensively, most studies suffer with respect to balance between coverage performance and rebroadcasting efficiency. This investigation proposes an efficient algorithm called "DIS_RAD", which introduces the concept of distance into the counter-based broadcast scheme. The proposed approach gives nodes closer to the border a higher rebroadcast probability since they create better Expected Additional Coverage (EAC) [1]. Here, a distance threshold is adopted to distinguish between interior and border nodes. Two distinct Random Assessment Delays (RADs) are applied to the border and interior nodes, with the border nodes having shorter RADs than the interior nodes. The analytical results indicate that the proposed scheme indeed provides a higher rebroadcast probability for border nodes and a lower rebroadcast probability for interior nodes. The simulation results demonstrate that the proposed "DIS_RAD" scheme works much better than other schemes. The probability analysis model also confirms the validity of the simulation results. Most important, the proposed scheme can keep, good balance between reachability and rebroadcast efficiency in various network densities. Therefore, the dynamic adjust counter threshold according to network densities is not necessary.
A Low-Latency Multipath Routing Without Elephant Flow Detection for Data Centers
(2016)
Chakraborty, Suchandra
;
Chen, Chien
;
資訊工程學系
;
Department of Computer Science
Multipath routing in data center has been studied intensively in recent years in order to minimize the finish time of data transfer or the latency of message sending. Existing scheme of splitting traffic at the granularity of packets can cause reordered packets within a TCP flow. Another alternative scheme of splitting traffic at the granularity of a flow avoids packet reordering but may increase latency as it does not differentiate between elephant and mice flows. A newer efficient approach is to split elephants down into many mice flows, and distribute them uniformly at random over all paths. However, elephant detection is mandatory and the performance is largely depends on accuracy of the elephant detection. We propose, a simple yet effective multipath routing that leverage the same idea of splitting elephants down into many mice flows but without any farther requirement of elephant flow detection by using the hard time-out based flow removal feature of OpenFlow switches. Furthermore, we integrate a VLAN based routing scheme to addresses the challenges of cost-effective scalability. As per our simulation using mininet, we found a 44% reduction in overall flow completion time (FCT) compared to TinyFlow and 32% reduction in the consumption of flow table entry resources inside of aggregate switches in datacenter.
A new model for optimal routing and wavelength assignment with fixed-length tunnel allocation in multi granularity cross-connect WDM networks
(2005)
Chen, Chien
;
Kuo, Xiu-Jia
;
Chen, Ying-Yu
;
Lo, Tse-Yu
;
資訊工程學系
Multi-granularity Optical Cross-Connect (MG-OXC) has been proposed to provide a cost-efficient way to support the growing demand for bandwidth. In the MG-OXC networks, consecutive wavelengths are bundled to form a tunnel and then switched as a single unit. Network resources at the intermediate nodes on the route of a tunnel, including switching fabrics and multiplexers, can thus be reduced. In this paper we consider the problem of routing and wavelength assignment (RWA) with tunnel allocation in MG-OXC networks. Given a set of static lightpath requests, our problem is to (a) allocate a set of fixed-length tunnels (b) find routes from the source nodes to their respective destination nodes, and (c) assign wavelengths to theses route. The objective here is to minimize the blocking probability. Furthermore, we extend our work for the dynamic RWA problem. Given a historical traffic matrix, the dynamic RWA problem is how to build a set of tunnels offline to accommodate the future dynamic lightpath requests in such a way that the blocking probability can be minimized. In order to utilize the wavelength ports and fibers efficiently, each tunnel established should follow a tunnel length constraint which could be equal to the average network hop distance. Based on this criterion, a novel graph model is proposed [7] in which edges are added only for the node pairs whose hop distance follow the tunnel length constraint to form an auxiliary graph. In this paper, we suggest a 0/1 Integer Linear Programming (ILP) formulaion for RWA with tunnel allocation in MG-OXC networks under the tunnel length constraint. The previous auxiliary graph model is extended to a layered auxiliary graph model to facilitate the formulation. We compare the performance of different heuristics, including CB-STA [1], WTA and PCWTA [7], to the ILP solution. The simulation results show that PC-WTA and WTA outperforms CB-STA in all switching type combinations and network topologies, and they are very close to the optimal value calculated from our ILP formulation.
A Software Defined Network Architecture for GeoBroadcast in VANETs
(2015)
Liu, Yu-Chun
;
Chen, Chien
;
Chakraborty, Suchandra
;
資訊工程學系
;
資訊技術服務中心
This paper proposes a Software Defined Network (SDN) architecture for GeoBroadcast in VANETs. We have implemented a component to automatically manage the geographical location of Road Side Units (RSUs), which are used as a basis for our GeoBroadcast routing. GeoBroadcast in a vehicular network supports periodic broadcast messages from a source vehicle to the destination vehicles that are located in a specific geographical region. In existing Intelligent Transport Systems (ITS), the GeoBroadcast mechanism can be implemented using traditional IP networking. Typically, every periodic warning messages received at nearest RSU from the source must be routed to the control center in ITS, where it is redirected to every other RSUs, that are located in the destination geographical region for broadcasting. As a result, huge overhead in the control center is produced and higher network bandwidth is consumed. However, in our SDN based GeoBroadcast mechanism, the first warning message received by the source RSU is sent to the SDN controller as a packet-in message. The SDN controller will decode the packet-in message and use topological and geographical information to set up the routing paths to the destination RSUs, by installing appropriate flow entries on the corresponding RSUs and intermediate switches, for the following periodic warning messages that are to be broadcasted. As per our simulation with OpenNet a significant reduction by 84% in controller overhead, 60% in network bandwidth consumption, and 81% in latency are achieved.
A Weighted ECMP Load Balancing Scheme for Data Centers Using P4 Switches
(2018-01-01)
Ye, Jin-Li
;
Chen, Chien
;
Chu, Yu Huang
;
資訊工程學系
;
資訊技術服務中心
This paper proposes a weighted Equal-cost multipath (W-ECMP) scheme in datacenters using a Programmable Data plane. Nowadays, data center networks face ongoing challenges for higher performance and greater efficiency. Equal-cost multi-path (ECMP) routing, the most common load-balancing scheme used on data center networks, tries to balance the traffic without awareness of the network congestion. To overcome this problem, CONGA and HULA are proposed successively. CONGA has implemented customized ASIC as a part of the switch fabric to collect congestion information distributively. Nevertheless, ASICs solution shows a lack of scalability and flexibility. However, although HULA solves some problems of CONGA by using p4 switch, best path selection strategy in HULA only selects and records the best path, which makes it easy to congest the best path, and HULA uses probes that waste bandwidth and deteriorate the performance. To solve the problems of HULA, W-ECMP chooses a path with a weighted probability to avoid congesting a path quickly. W-ECMP encapsulates the path congestion information into the normal traffic similar to the concept of Inband Network Telemetry (INT) in P4, which increases updating speed as the network loading increases. From experimental results, W-ECMP performs better than HULA does in average flow completion time (FCT).
A Zero Flow Entry Expiration Timeout P4 Switch
(2018-01-01)
He, Cheng-Hung
;
Chang, Brian Y.
;
Chakraborty, Suchandra
;
Chen, Chien
;
Wang, Li Chun
Existing OpenFlow based flow expiry mechanisms rely on a fixed timeout after which the switch proactively removes the flow entries from its flow table. Assigning an appropriate value to this timeout presents a tradeoff between efficient flow table utilization and controller overhead.We propose a simple addition of a zero flow entry expiration timeout scheme to idle timeout mechanism on a P4 based switch that identifies the last packet of a TCP flow, and removes the corresponding flow entry from the flow table. It enables connections to be deleted from the flow table right after it finishes, instead of waiting to expire after it reaches the timeout threshold and causing unnecessary flow table occupation.
Adaptive Urban Traffic Signal Control System with Bus Priority
(2013-01-01)
Jeng, Andy An-Kai
;
Jan, Rong-Hong
;
Chen, Chien
;
Chang, Tzu-Lin
;
資訊工程學系
In recent years, with the economic development and urbanization, traffic congestion has become a serious problem in urban environments. Traffic signal control plays a key role in Intelligent Transportation System (ITS). Particularly, bus system can carry a higher capacity of passengers, which help to relief traffic jam in cities. However, different from ordinary vehicles, bus system has several unique features, including higher capacity of passengers, fixed routes and specific requirements on arrival time and headway. In this paper, we propose an adaptive traffic signal control approach with bus Priority that determines the phase sequence and time in non-fixed order based on synergic information to improve the performance of bus system with a very small cost to ordinary vehicles. Simulation results show that our approach can significantly reduce the waiting time of buses, keep bus schedules on time, and regular bus headway.
An Energy-Efficient Scheduling for Multiple MSSs in IEEE 802.16e Broadband Wireless
(2008)
Huang, Shih-Chang
;
Chen, Chien
;
Jan, Rong-Hong
;
Hsieh, Cheng-Chung
;
資訊工程學系
This paper proposes an energy-efficient traffic scheduling approach for 802.16e broadband wireless networks. Instead of considering a single Mobile Subscriber Station (MSS) as most of the current researchers do, multiple MSSs are considered in our work. The constant bit rate traffic with QoS delay constraint is considered in this paper. The proposed approach considers both energy efficiency and bandwidth utilization. First, we derive a minimum wakeup time for each MSS to achieve the maximum power saving by waking up the minimum number of time slots. After then, we interleave the traffic of multiple MSSs by taking advantage of feasible slot allocation. In order to support the maximum number of MSSs, our scheduling problem can be transformed into a maximum bipartite matching problem. We use the Ford-Fulkerson maximum flow algorithm to obtain a feasible schedule for multiple MSSs. Simulation results show that our proposed approach has better bandwidth utilization and achieves maximum energy saving.
Channel Assignment and Routing for Multi-Channel Wireless Mesh Networks Using Simulated Annealing
(2006)
Chen, Ying-Yu
;
Liu, Shang-Chun
;
Chen, Chien
;
資訊工程學系
;
Department of Computer Science
Wireless mesh networks (WMNs) are emerging as a favorable technology for last-mile Internet access. Nodes in WMNs can be equipped with multiple interfaces which work in different channels to increase the available bandwidth. However, efficient channel assignment schemes are still needed due to the interference effect and the limited number of orthogonal channels. In this paper, we consider the channel assignment and routing for dynamic traffic in WMNs. We adopt the static channel assignment strategy to the network interfaces. The problem is simplified into two sequential stages. The first is to assign channels to interfaces while the second is to determine the route for each coming traffic demand. We propose a Mixed Integer Linear Programming (MILP) formulation to the problem and develop a simulated annealing based channel assignment algorithm for the channel assignment. The shortest path routing is adopted for the dynamic traffic. Simulation results show the network throughput and blocking probability under different network scenarios.
CROP: Community-Relevance-Based Opportunistic Routing in Delay Tolerant Networks
(2014-09-01)
Chang, Je-Wei
;
Chen, Chien
;
交大名義發表
;
資訊工程學系
;
資訊技術服務中心
Researchers have developed several social-based routing protocols for delay tolerant networks (DTNs) over the past few years. Two main routing metrics to support social-based routing in DTNs are centrality and similarity metrics. These two metrics help packets decide how to travel through the network to achieve short delay or low drop rate. This study presents a new routing scheme called Community-Relevance based Opportunistic routing (CROP). CROP uses a different message forwarding approach in DTNs by combining community structure with a new centrality metric called community relevance. One fundamental change in this approach is that community relevance values do not represent the importance of communities themselves. Instead, they are computed for each community-community relationship individually, which means that the level of importance of one community depends on the packet\'s destination community. The study also compares CROP with other routing algorithms such as BubbleRap and SimBet. Simulation results show that CROP achieves an average delivery ratio improvement of at least 30% and can distribute packets more fairly within the network.
CROP: Community-Relevance-Based Opportunistic Routing in Delay Tolerant Networks
(2013)
Chang, Je-Wei
;
Chen, Chien
;
資訊工程學系
;
Department of Computer Science
Researchers have developed several social-based routing protocols for delay tolerant networks (DTNs) over the past few years. Two main routing metrics to support a social-based routing in DTNs are centrality and similarity metrics. These two metrics help packets decide how to travel through the network to achieve a low delay or low drop rate. This study presents a new routing scheme called Community-Relevance based OPportunistic routing (CROP). CROP uses a different message forwarding approach in DTNs by combining community structure with a new centrality metric called community relevance. One fundamental change in this approach is that community relevance values do not represent the importance of communities themselves. Instead, they are computed for each community-community relationship individually which means that the level of importance of one community varies depending on the packet's destination community. This study compares CROP with other routing algorithms such as BubbleRap and SimBet. Simulation results show that CROP achieves an average delivery ratio improvement of at least 30% and can distribute packets more fairly within the network.
Design of Tunnel-based Protection Schemes in Multigranularity Optical Cross-connect Networks
(2005)
Lo, Tse Yu
;
Chen, Chien
;
Chen, Ying Yu
;
資訊工程學系
;
Department of Computer Science
As the technology advances to increase the number of wavelengths in fiber links, multigranularity optical cross-connects (MG-OXCs) have emerged as a solution to reduce the manufacturing cost of the traditional optical cross-connects (OXCs). In this paper, we aim to provide an efficient fault-recovery protection scheme for the lightpaths in the MG-OXC networks. A segment-based protection scheme, called Tunnel Based Segment Protection (TSP) is proposed to recover the communications interrupted by a fiber cut. TSP first allocates all the tunnels off-line according to the historical traffic matrix and then starts to serve the incoming requests. When allocating a tunnel, a backup tunnel is always allocated as well. Consequently, a lightpath is naturally divided into segments according to the switching types along the path. Therefore, after a working path is found for a connection request, only a shared backup path for those segments in the corresponding wavelength-switching layers need to be found. In addition, TSP utilizes wavelength-switching ports efficiently since working and backup tunnels can share the same wavelength-switching ports at two ends of the tunnel. Simulation results show that the network performance is improved comparing to adapt a straightforward path protection scheme for MG-OXC networks.
Distortion-based Video Streaming over Vehicular Ad Hoc Networks in Highway
(2014-01-01)
Chang, Je-Wei
;
Sun, Kuan-Yu
;
Chen, Chien
;
Jeng, Andy An-Kai
;
資訊工程學系
There are already many routing protocols tailored for Vehicular Ad Hoc Networks (VANET). However, few of them are suitable for real-time video streaming delivery. The network partition nature and dynamic changing network topology of VANET make it hard for existing protocols to satisfy the stringent delay requirements of video streaming or other multimedia applications. To address this issue, this study first develops a rate distortion model based on a shadowing model and 802.11 DCF with RTS/CTS scheme over a highway road segment. Based on the proposed rate distortion model and traffic statistic information (vehicle density over a road), we can decide the best next-hop forwarding distance. Since a vehicle may not have a neighbor vehicle at the best forwarding distance, this study proposes a cell based packet forwarding scheme based on the derived best forwarding distance to prioritize the neighboring vehicles of a sender We set up the simulations using NS2 to validate the performance of the proposed protocol. The results show that the proposed protocol can yield a 30% PSNR improvement.
Dynamic Reordering Bloom Filter
(2017-01-01)
Chang, Da-Chung
;
Chen, Chien
;
Thanavel, Mahadevan
;
資訊工程學系
;
資訊技術服務中心
In order to check a membership in multiple sets of bloom filter in a dynamic bloom filter, a sequential search is usually used. Since the distribution of queried data is unpredictable because the distribution has a feature of temporal locality. Therefore more search cost is incurred if queried data is stored in the peer which is corresponded to the Bloom Filter has lower query priority. In this paper, we introduce Dynamic Reordering Bloom Filter that can save the cost of searching Bloom Filter by dynamically reorder the searching sequence of multiple bloom filters in a dynamic bloom filter with One Memory Access Bloom Filter (OMABF) and checked in the order saved in Query Index (QI). The performance of the system is evaluated by Markov Chain. Simulation results show that our scheme on average has 43% better in searching performance comparing with the sequential methods, which is verified via three different trace log files.
Early recovery of interhemispheric functional connectivity after corpus callosotomy
(2019-06-01)
Hung, Sheng-Che
;
Lee, Cheng-Chia
;
Chen, Hsin-Hung
;
Chen, Chien
;
Wu, Hsiu-Mei
Objective To investigate whether interhemispheric functional connectivity (FC) recovers in the first year after total callosotomy. Methods Eight epilepsy patients undergoing total callosotomy were recruited. Resting-state functional magnetic resonance imaging was acquired before and after surgery. The precallosotomy and postcallosotomy interhemispheric and intrahemispheric FC was analyzed by using graph theory and voxel-mirrored homotopic connectivity (VMHC). The seizure outcome was scored using the Engel surgical outcome scale. Results After callosotomy (mean postoperative interval = 4 months), the network density, average node degree, characteristic path length, and global efficiency of the whole interhemispheric networks were significantly decreased, compared to those in the precallosotomy networks. However, postcallosotomy interhemispheric FC and homotopic VMHC were not significantly reduced in bilateral frontal and temporal lobes. The network density and average node degree of the intrahemispheric networks were significantly increased. The characteristic path length and global efficiency of intrahemispheric networks were unchanged. Significance The interhemispheric FC may be preserved or recover early within the first postoperative year after total callosotomy, particularly in the frontal and anterior temporal lobes.
Efficient Broadcast Mechanism for Cooperative Collision Avoidance Using Power Control
(2009)
Jeng, Andy An-Kai
;
Jan, Rong-Hong
;
Chen, Chien
;
Chiang, Tsun-Chieh
;
資訊工程學系
Improving driver's safety has been an active research area in wireless communication. In particular, the vehicle cooperative collision avoidance (CCA) is one of the most important issues in safety applications. A variety of broadcast protocols has been proposed for vehicular network. However, there is only a few of them dedicatedly designed for the CCA system. In this paper, we propose a novel broadcast mechanism for CCA using the power control technique. The power control rule is based on the safe distance between vehicles. Simulation results show that our approach can significantly reduce the delivery delay and avoid car collision.
Efficient Failover and Load Balancing for Dependable SIP Proxy Servers
(2008)
Cheng, Yun-Jung
;
Wang, Kuochen
;
Jan, Rong-Hong
;
Chen, Chien
;
Huang, Chia-Yuan
In this paper, we designed and implemented a dependable SIP-based clustered architecture for VoIP and multimedia applications, and also proposed an efficient OpenAIS-based SIP Load Balancing strategy (OSLB) that can balance proxy servers' load and achieve fast failover by reducing the number of failed calls when one of the dispatchers or one of the SIP proxy servers crashes. Experimental results show that our OSLB is comparable to an existing work, SIP load balancer, in terms of load balance metric (1.05 vs. 1.04). However, our OSLB reduces the number of failed calls by 86% when a proxy server failed compared to the SIP load balancer. This work, which is part of an EPON project, has been realized in an industry standard ATCA-based platform to provide high availability carrier-grade services, and is currently under a field trial In an ISP.
Elephant Flow Detection in Datacenters Using OpenFlow-based Hierarchical Statistics Pulling
(2014)
Lin, Chun-Yu
;
Chen, Chien
;
Chang, Je-Wei
;
Chu, Yu Huang
;
資訊工程學系
This paper proposes an effective elephant flow detection in datacenters. Equal Cost MultiPath (ECMP) is a popular routing mechanism to achieve load balancing in datacenter networks. However, ECMP only considers equally distributing the flows over equal-length paths, but does not take the size of the flows into account. Previous studies show that detecting and rerouting elephant flows (flows that transfer significant amount of data) effectively can lead to a 113% improvement in aggregate throughput compared with the simple use of ECMP. A naive way to detect the elephant flows is to pull statistics from each flow independently. Since "the elephant and mouse phenomenon" suggests that there are only very few elephant flows in a datacenter network, it\'s not efficient to collect information from each flow. Therefore, we propose a Hierarchical Statistics Pulling (HSP) mechanism using OpenFlow protocol to save bandwidth consumption and processing time. In order to further improve the performance of HSP, two supplement functions called elephant store and range splitting are developed. Our approaches can detect elephant flows with only a small amount of network bandwidth consumption. We use Mininet emulator and mathematical analysis to verify our methods. Both of them confirm the benefits of our approaches.
Enhancing Application Performance through OpenFlow Enabled Multi-homed Devices
(2014)
Tamba, Bully
;
Tseng, Kuo-Chun
;
Chen, Chien
;
Tseng, Chien-Chao
;
資訊工程學系
The increasing demand for mobile data usage is overwhelming our wireless network. However, most of these devices are equipped with multiple network interfaces (multi-homed) which when properly exploited have the potential to increase bandwidth capacity and ensure reliable connectivity. But some technical challenges are restricting our multimode devices to using one single interface at a time. In this paper, we advocate for the use of multiple interfaces simultaneously, which can achieve reliable network connectivity, allow applications to distribute their traffic over multiple interfaces, and aggregate the capacity of different paths. We proposed an OpenFlow-based Multiple WLAN Interface (OpenMWF) prototype, designed by embedding OpenFlow network resource controller and a data forwarding open virtual switch (OVS) in the network stack of the device operating system. A proof of concept implementation and evaluation was carried out using Web-based Real-Time Communication (WebRTC) interactive video conferencing and multi-source downloading utility (Aria2c) applications use cases. The result showed the approach yielded benefits for applications performance, over single interface usage.