Luying Zhou

Efficient multi-layer operational strategies for survivable IP-over-WDM networks

This paper addresses the problem of achieving a balance in satisfying a network service providers requirements: maintaining an acceptable call acceptance rate, satisfying protection requirements of requests, and controlling the signaling overhead in case of a component failure, in IP-over-WDM networks in a dynamic traffic arrival scenario. Satisfying all these aspects is a difficult task especially when the traffic pattern is dynamic in nature and a single layer protection approach is followed. In this work, first we propose a multi-layer protection scheme for achieving a better and acceptable tradeoff between blocking performance and signaling overhead in IP-over-WDM networks. We define various operational settings in the proposed scheme and investigate their impacts on the performance of the scheme. An important feature of this scheme is that, these settings allow a network service provider to select a suitable operational strategy for achieving the desired tradeoff based on networks policy and traffic demand. Then we propose an adaptive protection approach for dynamic traffic in consideration of providing better protection to requests as much as possible while considering blocking performance and signaling overhead. Through simulation experiments we evaluate the performance of the proposals and demonstrate their effectiveness

Best Effort SRLG Failure Protection for Optical WDM Networks

With the increase in the size and number of shared risk link groups (SRLGs) in optical wavelength-division multiplexing (WDM) networks, the capacity efficiency of shared-path protection becomes much poorer due to the SRLG-disjoint constraint, and thus the blocking probability becomes much higher. Furthermore, due to severe traps caused by SRLGs, it becomes more difficult to find an SRLG-disjoint backup path with trap avoidance within reasonable computational complexity. As a result, in a mesh WDM network with a large number of SRLGs or a large SRLG size, 100% SRLG failure protection is no longer a practical protection scheme. To solve this problem, we present a new protection scheme called best effort SRLG failure protection, in which we try to provide an SRLG-disjoint backup path by choosing the backup path sharing the least number of SRLGs with the working path; this is to make the impact of SRLG failures as low as possible and accept as many as possible connection requests. As a result, the proposed best effort SRLG failure protection scheme manages to make a trade-off between blocking probability and survivability. 100% SRLG failure protection becomes a special case of best effort SRLG failure protection when the working path and backup path share zero SRLG. Due to the NP-completeness of this problem, we propose a heuristic to find the optimal result of the best effort SRLG-disjoint backup path under dynamic traffic. We formulate the connection survivability against SRLG failures and analyze the possibility of backup sharing under best effort SRLG failure protection. Analytical and extensive simulation results with various network topology and SRLG parameters demonstrate that, compared with 100% SRLG failure protection, the proposed best effort SRLG failure protection scheme offers much better capacity efficiency and much lower blocking probability while keeping survivability as high as possible. This can be explained by the fact that by slightly loosing the SRLG-disjoint constraint, shared-path protection will become more capacity efficient and more efficient in overcoming traps.

Best Effort Shared Risk Link Group (SRLG) Failure Protection in WDM Networks

With the increase of size and number of shared risk link groups (SRLGs), capacity efficiency of shared-path protection becomes much poorer due to SRLG-disjoint constraints and blocking probability becomes much higher due to severe traps. As a result, 100% SRLG failure protection is no longer a practical protection scheme. To solve this problem, we present a new protection scheme called best effort SRLG failure protection, in which we try to provide SRLG-disjoint backup path by choosing the backup path sharing the least number of SRLGs with the working path, so as to make the impact of SRLG failures as low as possible and accept as many as possible connection requests. 100% SRLG failure protection becomes a special case of best effort SRLG failure protection when the working path and backup path share zero SRLG. We propose a heuristic to find the best effort SRLG-disjoint backup path under dynamic traffic. The best effort SRLG failure protection scheme tries to make a trade-off between blocking probability and survivability. Analytical and simulation results show, compared with 100% SRLG failure protection, the proposed scheme offers much better capacity efficiency and much lower blocking probability while keeping survivability as high as possible.

Providing Differentiated Quality-of-Protection for Surviving Double-Link Failures in WDM Mesh Networks

Providing differentiated quality-of-protection (QoP) for surviving single-link failures in WDM mesh networks has been extensively studied in recent years. This paper investigates the problem of providing differentiated QoP for surviving arbitrary double-link failures by allowing a connection request to choose from several QoP classes. In this paper, we propose to use three classes, i.e., single shared-path protection (SSPP), single dedicated-path protection (SDPP), and double shared-path protection (DSPP) to provide differentiated QoP. We present two differentiated QoP schemes. Scheme 1 (conventional differentiated QoP) is a natural extension of conventional differentiated QoP for surviving single-link failures, which uses SDPP, SSPP, and SDPP separately to satisfy different QoP requirements. Scheme 2 (shared differentiated QoP) tries to share backup resources between SSPP and SDPP. Simulation results show that our proposed architecture of QoP can satisfy different QoP requirements for surviving double-link failures by making a balance between blocking probability and average QoP. Analytical and numerical results indicate that the proposed differentiated QoP scheme 2 are more efficient in improving not only blocking probability but also average QoP.

Backup Reprovisioning After Shared Risk Link Group (SRLG) Failures in WDM Mesh Networks

In this paper, we study the impact of shared risk link group (SRLG) failures on shared-path protection by examining the percentage of connections that are vulnerable after SRLG failures, investigate the benefits of backup reprovisioning after SRLG failures, and evaluate different policies for backup reprovisioning. Compared with single-link failures, SRLG failures leave many more connections unprotected and vulnerable to the next failures and make the network topology much sparser. The major challenge of backup reprovisioning after SRLG failures is how to find SRLG-disjoint backup paths for those unprotected connections with a recovery ratio that is as high as possible within reasonable computational complexity. We are motivated to consider three reprovisioning policies by considering different sequences of reprovisioning according to the degree of SRLG constraints. The first policy is to reprovision backup paths for connections whose working paths traverse more SRLGs first (Policy I), and the second policy is to reprovision backup paths for connections whose working paths traverse fewer SRLGs first (Policy II). The third policy is to do backup reprovisioning randomly, i.e., we pick up an unprotected working path randomly (random reprovisioning). Extensive simulation results show that 1) SRLG failures will leave more connections unprotected compared with single-link failures, and the percentage of connections left vulnerable tends to be proportional to the SRLG size; 2) the network performance based on the first reprovisioning policy always performs best in recovery ratio; and 3) the network performance based on Policy II even underperforms the random reprovisioning. These results can be explained by the fact that connections whose working paths traverse fewer SRLGs are more flexible in finding SRLG-disjoint backup paths, and thus priority given to connections whose working paths traverse more SRLGs in Policy I can significantly improve the recovery ratio.

Stimulate Brillouin Scattering Based Broadband Tunable Slow-Light Conversion in a Highly Nonlinear Photonic Crystal Fiber

An integrated configuration is proposed to convert tunable slow light from signal to another frequency in a wide bandwidth by using a 70 m-long highly nonlinear photonic crystal fiber (HN-PCF). A 10 GHz RZ signal is delayed by a 10 Gbit/s 231-1 pseudo random bit sequence (PRBS) stimulated Brillouin scattering (SBS) pump, and the slow light is converted to another frequency in a broadband by four-wave mixing (FWM). By this way, not only the slow light is converted, but the idler power is enhanced greatly. In our experiment, all-optical controlled 37.5 ps delay time is converted in a 40 nm bandwidth flatly, and 4.7 dB idler power is enhanced simultaneously. The experimental results are in good agreement with those of the theory.

Large-scale WDM passive optical network based on cyclical AWG

A large scale wavelength division multiplexed passive optical network is proposed and experimentally demonstrated. 124 bidirectional optical channels with 10-Gb/s downstream and 1.25-Gb/s upstream transmission are simultaneously distributed by a single 32*32 cyclic AWG. The effect of the extinction ratio and seeding power to BER performance are experimentally investigated. The selection of the subcarrier frequency is also analyzed by simulation.

Provisioning lightpaths and computing resources for location-transparent scheduled grid demands

In this paper, we define a new problem of provisioning lightpaths and computing resources for a set of location- transparent scheduled grid demands in optical grid networks. A location-transparent scheduled grid demand specifies only an amount of computing resources needed in a specified time interval to process input data. The network node generating a demand is called a client node. There are several network nodes which have sufficient resources for a demand. These nodes are called resource nodes. An algorithm is used to choose a resource node to reserve a specified amount of computing resources and provision a lightpath between the resource node and the client node. Given a set of location-transparent scheduled grid demands, it is required to provision the best lightpath (i.e. wavelength resources) as well as computing resources available during the specified time interval for each demand so as to optimize a certain objective function. In our work, we develop integer linear programming (ILP) formulations for 2 objective functions: 1) Given a network capacity, maximize the number of demands accepted; 2) Minimize the total number of wavelength-links to honor a given set of demands. Because the ILP algorithms are computationally expensive, we also develop heuristics to deal with large networks. The simulation results show that our heuristics achieve good performance.

Provisioning Lightpaths and Computing Resources for Scheduled Grid Demands with Location Transparancy

We define a new problem of provisioning resources for a set of scheduled grid demands with location transparency in optical grid networks. We develop an integer linear programming formulation and a heuristic to solve it.

iOPEN testbed for dynamic resource provisioning in metro Ethernet networks

We propose novel iOPEN (integrated OPtical EtherNet) architecture to support dynamic reconfiguration of lightpaths between Ethernet switches and study the network control and operation algorithms and their performance. The iOPEN network maintains the Ethernet frame forwarding features and takes advantage of current available optical network technologies, and extends the Ethernet network technology and services to the metro area. The frame forwarding mechanisms and network topology configurations adapt to changes in traffic conditions for guaranteed QoS and efficient resource utilization. The simulation results from simple network configuration indicate that the iOPEN architecture dynamically reconfigures logical topology of the Ethernet switches in response to traffic changes and utilizes resources more efficiently