Young-Chon Kim

Pre-planned global rerouting for fault management in labeled optical burst-switched WDM networks

Optical burst switching (OBS) is a promising technique for supporting high-capacity bursty data traffic over optical wavelength-division-multiplexed (WDM) networks. A label-switched path can be established to forward a burst control packet (BCP) if each OBS node is augmented with an IP/MPLS controller. Such a network is called a labeled OBS (LOBS) network, and it can exploit the explicit routing and constraint-based routing properties supported in the MPLS framework to perform traffic and resource engineering. However, the burst-loss probability (denoted as BLP) can be large if the traffic is not properly engineered in a LOBS network, especially after a failure occurs. In this paper, we propose to use pre-planned global rerouting to balance network load and to restore bursts after a link fails. We apply optimization techniques to pre-plan explicit backup routes for failure scenarios. Our objective is to achieve optimal load balancing both before and after a failure such that the network state can still remain stable with minimum BLP when failure occurs. We apply the pre-planned global rerouting method in a LOBS network and study the performance of different rerouting schemes on some typical network topologies. Our illustrative numerical examples show that the BLP can be significantly reduced by 25%-99% (when the average link load is less than 0.5) using globally rerouted backup routes, when compared with the scheme without global rerouting. We also observe that the BLP is reduced by 20%-65% (when the average link load is less than 0.5) if the rerouting is done using optimization techniques, when compared with shortest-path routing.

Explicit Routing for Traffic Engineering in Labeled Optical Burst-Switched WDM Networks

Optical burst switching (OBS) is a promising technique for supporting high-capacity bursty data traffic over optical wavelength-division-multiplexed (WDM) networks. A label-switched path can be established to forward a burst control packet (BCP) if each OBS node is augmented with an IP/MPLS controller. Such a network is called a labeled OBS (LOBS) network, and it can exploit the explicit routing and constraint-based routing properties supported in the MPLS framework to perform traffic and resource engineering. In this paper, we consider the traffic-engineering problem in a LOBS network, using explicit routing to balance network load and to reduce the burst-loss probability. We model the traffic-engineering problem in a LOBS network as an optimization problem and propose two new objective functions to minimize network congestion. Our illustrative numerical examples show that the burst-loss probability can be significantly reduced using optimization technique, when compared with shortest-path routing.

A Node-Grade Based AODV Routing Protocol for Wireless Sensor Network

This paper proposes an improved Ad-hoc On-Demand Distance Vector (AODV) routing protocol based on node-grade to reduce the energy consumption of nodes in wireless sensor networks. The improved AODV called Grade-AODV (G-AODV) assigns a grade to each node according to the hop distance of the node to the sink node. The lower grade a node has, the closer it is to the sink. Each node is restricted to receive the route request (RREQ) packet from the nodes which have larger grade than itself. Therefore, the proposed G-AODV can reduce the energy consumption of nodes from two aspects: 1) the useless broadcast of RREQ can be avoided; 2) each packet uses less network resources because the route paths with less hop distance are set up. The performance of G-AODV is evaluated by simulation through OPNET modeler. The simulation results show that the G-AODV has better performance than AODV in view of the utilization and lifetime of network.

Hybrid Protection Architecture against Multipoint Failure in WDM-PON

In this paper, we propose hybrid protection architecture, to protect against multipoint failure in WDM-PON which component failure can potentially lead to an enormous loss of traffic. The proposed architecture is fully configured and the protection fiber can be used to transmit extra traffic under normal states, to increase the survivability and efficiency of the network. If failure is detected, normal traffic is switched to the protection path and extra traffic is preempted. Wavelength assignment and protection methods are also proposed for our protection architecture. The performance of proposed architecture is evaluated in terms of cost, channel utilization and queuing delay.

A novel kind of programmable 3(n) feed-forward optical fiber true delay line based on SOA.

A new kind of 3(n) feed-forward programmable optical fiber true delay line was proposed. Theoretical analysis was presented on its delay performance and expandability. Experimental demonstration was given to show the implementation of such delay lines using SOAs and Farady rotation mirrors. Delay step as small as 0.5 ps with precision of about 0.03 ps was achieved. Measurement was performed to verify the feasibility and results are given.

In-Situ Cure Monitoring of Wind Turbine Blades by Using Fiber Bragg Grating Sensors and Fresnel Reflection Measurement

A fiber-optic cure monitoring system is proposed to measure curing status of composite structure such as a large scale wind turbine blade. The monitoring is based on the measurement of Fresnel reflectivity at the optical fiber/epoxy resin interface. The refractive index of epoxy resin varies throughout curing stages, changing the Fresnel reflectivity. The curing status is decided by monitoring the reflected intensity variation. The usage of fiber Bragg grating (FBG) sensor helps to separate the temperature-induced cross effects. A Gaussian curve fitting algorithm was applied to FBG spectra which were distorted in curing procedure. The substantial measurement errors could be minimized by locating the centroids of the Gaussian curve-fitted spectra. From the experiments performed in various isothermal conditions, the proposed system successfully identified the onset of gelation and the completion of curing of epoxy resins.

Hybrid Communication Network Architectures for Monitoring Large-Scale Wind Turbine

Nowadays, a rapid development in wind power technologies is occurring compared with other renewable energies. This advance in technology has facilitated a new generation of wind turbines with larger capacity and higher efficiency. As the height of the turbines and the distance between turbines increases, the monitoring and control of this new generation wind turbines presents new challenges. This paper presents the architectural design, simulation, and evaluation of hybrid communication networks for a large-scale wind turbine (WT). The communication network of WT is designed based on logical node (LN) concepts of the IEC 61400-25 standard. The proposed hybrid network architectures are modeled and evaluated by OPNET. We also investigate network performance using three different technologies: Ethernet-based, WiFi-based, and ZigBee-based. Our network model is validated by analyzing the simulation results. This work contributes to the design of a reliable communication network for monitoring and controlling a wind power farms (WPF).

A Cross-Layer Duty Cycle MAC Protocol Supporting a Pipeline Feature for Wireless Sensor Networks

Although the conventional duty cycle MAC protocols for Wireless Sensor Networks (WSNs) such as RMAC perform well in terms of saving energy and reducing end-to-end delivery latency, they were designed independently and require an extra routing protocol in the network layer to provide path information for the MAC layer. In this paper, we propose a new cross-layer duty cycle MAC protocol with data forwarding supporting a pipeline feature (P-MAC) for WSNs. P-MAC first divides the whole network into many grades around the sink. Each node identifies its grade according to its logical hop distance to the sink and simultaneously establishes a sleep/wakeup schedule using the grade information. Those nodes in the same grade keep the same schedule, which is staggered with the schedule of the nodes in the adjacent grade. Then a variation of the RTS/CTS handshake mechanism is used to forward data continuously in a pipeline fashion from the higher grade to the lower grade nodes and finally to the sink. No extra routing overhead is needed, thus increasing the network scalability while maintaining the superiority of duty-cycling. The simulation results in OPNET show that P-MAC has better performance than S-MAC and RMAC in terms of packet delivery latency and energy efficiency.

A bandwidth allocation algorithm for improving QoS in EPON with sleep mode

Recently, Ethernet Passive Optical Network (EPON) with sleep mode has been actively investigated to improve energy conservation in the broadband access network. EPON with cyclic sleep mode transmits up/downstream traffic at the same time and put into the sleep mode at idle time in Optical Network Unit (ONU). However, QoS requirement can be violated by the cyclic sleep mode. In this paper, we propose novel bandwidth allocation algorithm to maximize energy efficiency while satisfying QoS requirement. The main idea is to consider up/downstream traffic in order to determine suitable scheduling transmission period on Optical Line Terminal (OLT). To do this, it allocates bandwidth according to request from ONU, usually. However, when downstream traffic in OLT buffer exceeds predefined threshold, the proposed algorithm compares threshold to bandwidth request from ONU for reducing OLT traffic queuing delay. So, our proposed algorithm can satisfy both energy saving and QoS requirement. In order to evaluate the proposed algorithm, we perform simulation in terms of total and average sleep time of ONU, queuing delay of downstream traffic in OLT buffer.

Design of AWG-based WDM-PON architecture with multicast capability

Recently, the triple play service (TPS) has been considered to be a promising business model or application. Thus, the capability for multicast transmission has become a very important requirement for access networks. However, unlike existing passive optical networks (PONs), the arrayed-waveguide grating (AWG) based wavelength-division multiplexing (WDM)-PON does not have multicast capability because it is a P2P network for the downstream direction, from optical line terminal (OLT) to optical network units (ONUs). In this paper, AWG- based WDM-PON architecture with multicast capability is proposed. It provides high scalability and single copy broadcast (SCB) capability by employing multi-stage AWGs at a remote node (RN) and a multi-wavelength converter (MWC) at OLT. The performance of the proposed architecture is evaluated in terms of cost, scalability, link capacity and bandwidth per user, in both upstream and downstream directions, by comparison with other multicasting architectures.