Tianjian Li

On service provisioning under a scheduled traffic model in reconfigurable WDM optical networks

In this paper, we propose a general scheduled traffic model, sliding scheduled traffic model. In this model, the setup time t/sub s/ of a demand whose holding time is T time units is not known in advance. Rather t/sub s/ is allowed to begin in a pre-specified time window [l,T] subject to the constraint that l/spl les/t/sub s//spl les/r-T. We then consider two problems: (1) how to properly place a demand within its associated time window to reduce overlapping in time among a set of demands; and (2) route and assign wavelengths (RWA) to a set of demands under the proposed sliding scheduled traffic model in mesh reconfigurable WDM optical networks without wavelength conversion. In addition, we consider how to rearrange a demand by negotiating a new setup time that minimizes the demand schedule change in case that the demand is blocked. To maximize temporal resource reuse, we propose a demand time conflict reduction algorithm to solve the first problem. Two algorithms, window based RWA algorithm and traffic matrix based RWA algorithm, are then proposed for the second problem. We compare the proposed RWA algorithms against a customized tabu search scheme. Simulation results show that the proposed demand time conflict reduction algorithm can resolve well over 50% of time conflicts and the space-time RWA algorithms are effective in satisfying demand requirements and minimizing total network resources used, d.

On survivable service provisioning in WDM optical networks under a scheduled traffic model

We study survivable service provisioning under a scheduled traffic model in wavelength convertible WDM optical mesh networks. In this model, a set of demands is given, and the setup time and teardown time of each demand are known in advance. We formulate the problem as integer linear programs that maximally exploit network resource reuse in both space and time. The objective is to minimize the total number of wavelength-links used by working paths and protection paths of all traffic demands while 100% restorability is guaranteed against any single failures. Our simulation results indicate that joint 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

On optimal survivability design in WDM optical networks under a scheduled traffic model

We 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 time and teardown time of a demand are known in advance. We formulate the joint routing and wavelength assignment problems into integer linear programs that maximally exploit network resource reuse in both space and time. To solve large problems, the joint RWA problems are divided to a routing subproblem and wavelength assignment subproblems which are then solved individually. The overall objective is to minimize the total number of wavelength-links used by working paths and protection paths of all traffic demands while 100% restorability is guaranteed against any single failures. 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.

Survivable scheduled service provisioning in WDM optical networks with iterative routing

Survivable service provisioning design has emerged as one of the most important issues in communication networks in recent years. In this work, we study survivable service provisioning with shared protection under a scheduled traffic model in wavelength convertible WDM optical mesh networks. In this model, a set of demands is given, and the setup time and teardown time of a demand are known in advance. Based on different protection schemes used, this problem has been formulated as integer linear programs with different optimization objectives and constraints in our previous work. The problem is NP-hard. We therefore study time efficient heuristic solutions to the problem. Our approach is based on an iterative survivable routing (ISR) scheme that utilizes a capacity provision matrix and processes demands sequentially using different demand scheduling policies. The objective is to minimize the total network resources (e.g., number of wavelength-links) used by working paths and protection paths of a given set of demands while 100% restorability is guaranteed against any single failure. The proposed algorithm is evaluated against solutions obtained by integer linear programming. Our simulation results indicate that the proposed ISR algorithm is extremely time efficient while achieving excellent performance in terms of total network resources used. The impact of demand scheduling policies on the ISR algorithm is also studied.

On optimal survivability design under a scheduled traffic model in wavelength-routed optical mesh networks

We 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 time and teardown time of a demand are known in advance. We formulate the joint routing and wavelength assignment problems as integer linear programs that maximally exploit network resource reuse in both space and time. Moreover, we propose efficient heuristic algorithms 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

Approximating Optimal Survivable Scheduled Service Provisioning in WDM Optical Networks with Iterative Survivable Routing

Survivable service provisioning design has emerged as one of the most important issues in communication networks in recent years. In this work, we study survivable service provisioning with shared protection under a scheduled traffic model in wavelength convertible WDM optical mesh networks. In this model, a set of demands is given, and the setup time and teardown time of a demand are known in advance. Based on different protection schemes used, this problem has been formulated as integer linear programs with different optimization objectives and constraints in our previous work [8, 9]. The problem is shown to be NP- hard. We therefore study time efficient approaches to approximating the optimal solution to the problem. Our proposed approach is based on an iterative survivable routing (ISR) scheme that utilizes a capacity provision matrix and processes demands sequentially using different demand scheduling policies. The objective is to minimize the total network resources (e.g., number of wavelength-links) used by working paths and protection paths of a given set of demands while 100% restorability is guaranteed against any single failure. The proposed algorithm is evaluated against solutions obtained by integer linear programming. Our simulation results indicate that the proposed ISR algorithm is extremely time efficient while achieving excellent performance in terms of total network resources used. The impact of demand scheduling policies on the ISR algorithm is also studied.

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 Dijkstras 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.

Approximating optimal survivable scheduled service provisioning in WDM optical networks with Shared Risk Link Groups

Survivable service provisioning design has been an important issue in communication networks. In this work, we study survivable service provisioning using shared path based protection under a scheduled traffic model in wavelength convertible WDM optical mesh networks with Shared Risk Link Groups (SRLGs). In the scheduled traffic model, a set of demands is given, and the setup time and teardown time of a demand are known in advance. The objective is to minimize the total network resources (e.g., the number of wavelength-links) used by working paths and protection paths of the given set of demands while 100% restorability is guaranteed against any single SRLG failure. This problem is known to be NP-hard. We therefore study a time efficient approach to approximating the optimal solution to the problem. Our proposed approach is based on an iterative survivable routing scheme that utilizes a capacity provision matrix and processes demands sequentially. Our simulation results indicate that the proposed ISR-SRLG algorithm achieves excellent performance in terms of the total network resources used.

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.

Optimal configuration of p-cycles in WDM optical networks with sparse wavelength conversion

In this paper, we study the optimal configuration of p-cycles in survivable WDM optical mesh networks with sparse wavelength conversion while 100% restorability is guaranteed against any single failures. We formulate the problem as an integer linear program. In our optimization model, working paths are known before protection configuration is done. p-cycles and wavelength converters are then optimally determined subject to the constraint that only a given number of nodes have wavelength conversion capability. The objective is to minimize the cost of link capacity used by all p-cycles to accommodate a set of traffic demands. In the proposed p-cycle configuration architecture, we take into account converter sharing: (a) when converters are used for accessing p-cycles and for wavelength conversion between two adjacent on-cycle spans; (b) when converters are used among disjoint straddling spans incident to the same node for accessing p-cycles. Converter sharing enables the network to require as few converters as possible to attain a satisfactory level of performance. Our simulation results indicate that the proposed approach significantly outperforms the approach for WP networks in terms of protection cost and can obtain the optimal performance as achieved by the approach for VWP networks, but requires fewer wavelength conversion sites and fewer wavelength converters.