Optical WDM Mesh Networks Research Articles

Rerouting schemes for dynamic traffic grooming in optical WDM networks

Traffic grooming in optical WDM mesh networks is a two-layer routing problem to effectively pack low-rate connections onto high-rate lightpaths, which, in turn, are established on wavelength links. The objective of traffic grooming is to improve resource efficiency. However, resource contention between lightpaths and connections may result in inefficient resource usage or even the blocking of some connections. In this work, we employ a rerouting approach to alleviate resource inefficiency and improve the network throughput under a dynamic traffic model. We propose two rerouting schemes, rerouting at lightpath level (RRLP) and rerouting at connection level (RRCON) and a qualitative comparison is made between the two. We also propose two heuristic rerouting algorithms, namely the critical-wavelength-avoiding one-lightpath-limited (CWA-1L) rerouting algorithm and the critical-lightpath-avoiding one-connection-limited (CLA-1C) rerouting algorithm, which are based on the two rerouting schemes. Simulation results show that rerouting reduces the blocking probability of connections significantly.

Availability-Aware Provisioning Strategies for Differentiated Protection Services in Wavelength-Convertible WDM Mesh Networks

In an optical WDM mesh network, different protection schemes (such as dedicated or shared protection) can be used to improve the service availability against network failures. However, in order to satisfy a connections service-availability requirement in a cost-effective and resource-efficient manner, we need a systematic mechanism to select a proper protection scheme for each connection request while provisioning the connection. In this paper, we propose to use connection availability as a metric to provide differentiated protection services in a wavelength-convertible WDM mesh network. We develop a mathematical model to analyze the availabilities of connections with different protection modes (i.e., unprotected, dedicated protected, or shared protected). In the shared-protection case, we investigate how a connection's availability is affected by backup resource sharing. The sharing might cause backup resource contention between several connections when multiple simultaneous (or overlapping) failures occur in the network. Using a continuous-time Markov model, we derive the conditional probability for a connection to acquire backup resources in the presence of backup resource contention. Through this model, we show how the availability of a shared-protected connection can be quantitatively computed. Based on the analytical model, we develop provisioning strategies for a given set of connection demands in which an appropriate, possibly different, level of protection is provided to each connection according to its predefined availability requirement, e.g., 0.999, 0.997. We propose integer linear programming (ILP) and heuristic approaches to provision the connections cost effectively while satisfying the connections' availability requirements. The effectiveness of our provisioning approaches is demonstrated through numerical examples. The proposed provisioning strategies inherently facilitate the service differentiation in optical WDM mesh networks.

Path-protection-based routing and wavelength assignment in wavelength-division multiplexing optical networks under a scheduled traffic model

Feature Issue on High Availability in Optical NetworksWe study the optimal survivability design problem under a scheduled traffic model in wavelength-convertible WDM optical mesh networks. In this model, a set of demands is given, and the setup and tear-down time of a demand are known in advance. We formulate the joint routing and wavelength assignment problems as integer linear problems that maximally exploit network resource reuse in both space and time. Moreover, we propose efficient heuristic algorithms with different demand-ordering policies to solve large survivable routing and wavelength assignment problems under the scheduled traffic model. Our simulation results indicate that the optimization of resource sharing in space and time enabled by our connection-holding-time-aware protection schemes can achieve significantly better resource utilization than schemes that are holding-time unaware. In addition, the proposed heuristic algorithms are shown to be indeed very effective.

다중 링 구조를 이용한 WDM 통신망 복구 및 자원 예약 기법

본 논문에서는 대용량 WDM 광통신망에서 장애가 발생하였을 경우 이를 효율적으로 복구할 수 있는 기법에 대해 연구하며, 특히 보다 적은 통신망 자원을 이용해 높은 복구율을 얻을 수 있도록 복구 기술의 효율성을 극대화하는 것을 연구의 중점 목표로 한다. 복구 방법의 효율성은 목표로 하는 복구율을 얻기위해 필요한 예비 자원의 양에 의해 결정되며, 효율성을 높이기 위한 기본적인 방법은 예비 자원의 공유이다. 이를 위해서 복구용 대역폭의 공유뿐만 아니라 복구 경로의 공유를 통해 자원 이응의 효율성을 증가시킬 수 있는 기법을 제안한다. 제안된 기법은 논리적인 다중 링 구조에 의한 통신망 복구 기법으로 링 토폴로지의 특성을 이용해 빠르고 간단한 복구 동작을 제공하며, 동시에 다중 링 구성을 통하여 대체 경로의 분산과 공유 정도를 높이고 단위 링크당 예약되어야 하는 예비 광파장의 수를 줄임으로써 전체 통신망 자원 이용의 효율성을 높일 수 있다. 성능 분석 결과 제안된 기법은 목표로 하는 복구율을 보장하는 동시에 통신망 자원 이용의 효율성을 크게 증가시킴을 확인할 수 있었다. This paper studies network recovery methods for WDM optical mesh networks, concentrating on improving spare resource utilization. The resource efficiency can be obtained by sharing spare resources needed for network recovery. To improve the sharability of spare resources in WDM networks, methods to share backup paths us well as spare capacity should be studied. The proposed method in this paper uses multiple ring-covers and this method provides fast and simple recovery operation by exploiting the characteristics of logical ring topology, and also provides efficient resource utilization by using multiple distributed backup paths to improve the sharability of overall spare resources in the networks. This method can provide layered reliability to network service by enabling hierarchical robustness against multiple failures. The performance results show that the proposed method provide improved resource efficiency for single failure and enhanced robustness for multiple failures.

A Novel Heuristic Algorithm for Highly Utilizable Shared Protection in Optical WDM Mesh Networks

Network survivability is one of the most pivotal issues in optical WDM networks. In particular, if a conduit is cut, approximately 16 terabits per millisecond can be lost in recent technology. A huge loss even by a single conduit failure fatally damages the performance and operation of the whole network. In this paper, we propose a new heuristic algorithm, called the Generalized Minimum-Cost (GMC) selection algorithm, to choose a pair of working and backup path which firstly minimizes total number of required wavelengths of working and backup path and secondly distributes lightpath request traffic into whole network links, if there are several pairs to require the same number of minimum wavelengths, in order to achieve load-balancing effect. GMC selection algorithm contains several formulas to get Working and Backup path Reservation Cost (WBRC) which can be obtained through heuristic GMC function. By using WBRC, our GMC selection algorithm achieves superior performance compared to the current Combined Min-Cost (CMC) selection algorithm and random selection algorithm in terms of the amount of wavelength consumption and blocked lightpath requests, especially on the relatively less-connected New Jersey LATA and 28-node US networks. Furthermore, we suggest a maximum number of non-blocked lightpath requests against single link failure in simulated networks for network operators to consider acceptable maximum traffic on their networks, so that they can provide 100% restoration capability in a single link failure without lightpath request blocking. We also analyze the complexity of the GMC selection algorithm and verify that the complexity of the GMC selection algorithm is lower than that of the CMC selection algorithm if the number of lightpath requests is sufficiently large.

Efficient Online Algorithms for Dynamic Shared Path Protection in WDM Optical Networks

In this work, we have proposed and studied efficient online algorithms for shared path protection under dynamic traffic conditions in survivable WDM optical mesh networks. Given a connection request, routing and wavelength assignment of a working path and a protection path for the request is formulated as two integer linear programs based on shared and dedicated path protection, respectively. The objective is to minimize the total cost of additional resources used by the working path as well as the protection path to accommodate a new connection request. We then devise two resource efficient online algorithms using pre-computed candidate routes. The first algorithm uses one candidate working path and one candidate protection path for each newly arrived connection request while the second algorithm may use multiple candidate working paths and/or multiple candidate protection paths. The selection of a pair of paths from candidate routes as well as the assignment of appropriate wavelengths to accommodate a connection request is then jointly considered to minimize the total cost of additional resources. The solutions to the ILP formulations serve as the baseline for evaluating the performance of the proposed algorithms. We have evaluated the effectiveness of the proposed online algorithms via extensive simulations in terms of the connection blocking probability and the revenue earnings improved over the dedicated path protection approach. Our simulations indicate that our proposed computationally efficient online algorithms are able to provide 100% restorability against single failures with a resource efficiency comparable to that of the optimal shared path protection. The results also show that a small increase in the number of candidate working paths or protection paths (from 1 to 3) provides better performance, but a further increase does not improve the performance significantly. Therefore, a proper balance can be struck to achieve both satisfactory performance and efficient computation.

Cost Effective Shared Path Protection for WDM Optical Mesh Networks with Partial Wavelength Conversion

In this paper, we study routing and wavelength assignment of connection requests in survivable WDM optical mesh networks employing shared path protection with partial wavelength conversion while 100% restorability is guaranteed against any single failures. We formulate the problem as a linear integer program under a static traffic model. The objective is to minimize the total cost of wavelength-links and wavelength converters used by working paths and protection paths of all connections. A weight factor is used which is defined as the cost ratio of a wavelength converter and a wavelength-link. Depending on the relative cost of bandwidth and wavelength conversion, the optimization objective allows a proper tradeoff between the two. The proposed algorithm, the shortest-widest-path-first (SWPF) algorithm, uses a modified Dijkstra's algorithm to find a working path and a protection path for each connection request in the wavelength graph transformed from the original network topology. When there are multiple candidate paths that have the same minimum total cost, the path along which the maximum number of converters used at each node is minimized is chosen by the SWPF algorithm. We have evaluated the effectiveness of the proposed algorithm via extensive simulation. The results indicate that the performance of the proposed algorithm is very close to that of the optimal solutions obtained by solving the ILP formulation and outperforms existing heuristic algorithms in terms of total number of converters used and the maximum number of converters required at each node in the network. The proposed algorithm also achieves slightly better performance in terms of total cost of wavelength-links and converters used by all connections. We also investigated shared path protection employing converter sharing. The results show that the technique can reduce not only the total number of converters used in the network but also the maximum number of converters required at each node, especially when a large number of converters are needed in the network. In this study, although the ILP formulation is based on static traffic, the proposed algorithm is also applicable to routing dynamic connection requests.

Minimizing wavelength-conversion costs in WDM optical networks with p-cycle-based protection

We study the configuration of preconfigured protection cycles (p-cycles) in survivable WDM optical mesh networks with partial wavelength conversion with 100% restorability guaranteed against any single failures. We consider the general case in which a p-cycle is allowed to use converters partially on the path. We formulate the problem as two integer linear programs, one for nonjoint and one for joint optimization. In the nonjoint optimization case, working paths are known before the protection configuration is processed. Then, p-cycles and wavelength converters are optimally determined. In the joint optimization case, working paths, p-cycles, and wavelength converters are jointly determined. The objective in both cases is to minimize the total cost of link capacity used by the working paths and the p-cycles as well as the cost of wavelength converters required for accommodation of a set of traffic demands. The proposed p-cycle configuration architectures take full advantage of converter sharing that reduces the network cost by requiring as few converters as possible. Our numerical results indicate that the proposed approaches outperform existing ones in terms of total network cost, total number of converters required, and maximum number of converters required at a node.

Traffic engineering in multigranularity heterogeneous optical WDM mesh networks through dynamic traffic grooming

In this article we investigate the problem of efficiently provisioning connections of different bandwidth granularities in a heterogeneous WDM mesh network through dynamic traffic grooming schemes under traffic engineering principles. Due to the huge amount of traffic a WDM backbone network can support and the large geographic area it can cover, constructing and upgrading such an optical WDM network can be costly. Hence, it is extremely important for network operators to apply traffic engineering strategies to cost-effectively support different bandwidth granularity services using only the appropriate amount of network resources. This requires an optical WDM network to have multigranularity switching capability, and such a network tends to be a multivendor heterogeneous network. However, WDM network heterogeneity increases the difficulty and challenge of efficient traffic provisioning. In this article we present different TE issues that need to be carefully considered in such an optical WDM network, and propose possible solutions and extensions for the generalized multiprotocol label switching optical network control plane. We extend an existing generic graph model to perform efficient traffic grooming and achieve different TE objectives through simple shortest path computation algorithms. We show that our approach is very practical and very suitable for traffic engineering in a heterogeneous multigranularity optical WDM mesh network.