Limited Wavelength Conversion Capability Research Articles

Fast Service Recovery Under Shared Protection in WDM Networks

In this paper, we investigate the problem of survivable routing of static demands in connection-oriented WDM networks with shared protection. We first discuss conditions and characteristics of a typical backup path sharing approach with respect to the average length of backup paths, and the values of connection restoration time. Next we propose a new method of sharing the backup paths, called SPGC, which is the first one that does not increase the length of backup paths (thus providing fast restoration of broken connections). The respective ILP model has been introduced. Owing to the complexity of the SPGC problem, an efficient heuristic algorithm designed for the general case of limited wavelength conversion capability has been also proposed. Extensive numerical experiments have shown that the proposed backup path sharing approach provides values of service recovery time which are up to 50% shorter on average, compared to the typical sharing technique. These results were achieved together with a significant reduction of the total link capacity utilization ratio of up to 40%.

A wavelength assignment algorithm for de Bruijn WDM networks

This paper proposes an offline wavelength assignment technique for de Bruijn (d, k) optical wavelength division multiplexing (WDM) networks having nodal degree d and diameter k that can support lightpaths between pair of nodes. Each lightpath uses a channel (wavelength) along each link in its route. An efficient algorithm is proposed that can be used to assign wavelengths to lightpath requests in O(k|V|) time, where |V| represents the number of nodes of the de Bruijn network and V represents the set of nodes. The proposed algorithm can be efficiently used for wavelength assignment in de Bruijn WDM networks having limited wavelength conversion capabilities. This work shows that de Bruijn graph can be expressed as union of edge-disjoint rings. Wavelengths are assigned for the individual rings in the graph thus resulting in the assignment for the graph itself. Results are shown for a given de Bruijn graph and for an arbitrary request. The proposed algorithm is compared with two other algorithms, which use two other known works of wavelength assignment on ring topology. Comparisons of the time complexity and the type of wavelength conversion required for these algorithms clearly show that the proposed algorithm is a faster and more efficient way of assigning wavelengths.

Performance analysis of optical burst switching node with limited wavelength conversion capabilities

The systematical and scalable frameworks were provided for estimating the blocking probabilities under asynchronous traffic in optical burst switching (OBS) nodes with limited wavelength conversion capability (LWCC). The relevant system architectures of limited range and limited number of wavelength converters (WCs) deployed by a share-per-fiber (SPF) mode were developed, and the novel theoretical analysis of node blocking probability was derived by combining the calculation of discouraged arrival rate in a birth-death process and two-dimensional Markov chain model of SPF. The simulation results on single node performance verify the accuracy and effectiveness of the analysis models. Under most scenarios, it is difficult to distinguish the plots generated by the analysis and simulation. As the conversion degree increases, the accuracy of the analysis model worsens slightly. However, the utmost error on burst loss probability is far less than one order of magnitude and hence, still allows for an accurate estimate. Some results are of actual significance to the construction of next-generation commercial OBS backbones.

Reservation signalling mechanism for reducing blocking probability in optical burst switching networks with limited wavelength conversion capabilities

First, the optical burst switching (OBS) network with limited wavelength conversion capability (LWCC) is decomposed into multiple wavelength continuous segments according to the position of wavelength converters. Based on the decomposed network model, two reservation signalling mechanisms for OBS-LWCC networks, namely wavelength-amend-on-demand (WAoD) and contention-based limited signalling protocol (CLSP), are proposed to reduce the blocking probability in the OBS-LWCC networks. In WAoD, the congested node sends a feedback message to the closest upstream switch with wavelength conversion capability. The notified switch will change the burst wavelength to the one assigned by the congested node to avoid collision in advance. Extensive simulation results indicate that by applying the wavelength reconfiguration method to the core nodes without wavelength conversion capability, the proposed WAoD scheme can improve the blocking performance in the OBS-LWCC networks significantly. Furthermore, CLSP, which combines the burst time-slot reconfiguration with the wavelength reconfiguration of WAoD, always has the lowest burst loss probability when compared with both the conventional and the proposed reservation mechanisms.

Multicasting for all-optical multifiber networks

All-optical wavelength-routed WDM WANs can support the high bandwidth and the long session duration requirements of the application scenarios such as interactive distance learning or on-line diagnosis of patients simultaneously in different hospitals. However, multifiber and limited sparse light splitting and wavelength conversion capabilities of switches result in a difficult optimization problem. We attack this problem using a layered graph model. The problem is defined as a k-edge-disjoint degree-constrained Steiner tree problem for routing and fiber and wavelength assignment of k multicasts. A mixed integer linear programming formulation for the problem is given, and a solution using CPLEX is provided. However, the complexity of the problem grows quickly with respect to the number of edges in the layered graph, which depends on the number of nodes, fibers, wavelengths, and multicast sessions. Hence, we propose two heuristics layered all-optical multicast algorithm [(LAMA) and conservative fiber and wavelength assignment (C-FWA)] to compare with CPLEX, existing work, and unicasting. Extensive computational experiments show that LAMA's performance is very close to CPLEX, and it is significantly better than existing work and C-FWA for nearly all metrics, since LAMA jointly optimizes routing and fiber-wavelength assignment phases compared with the other candidates, which attack the problem by decomposing two phases. Experiments also show that important metrics (e.g., session and group blocking probability, transmitter wavelength, and fiber conversion resources) are adversely affected by the separation of two phases. Finally, the fiber-wavelength assignment strategy of C-FWA (Ex-Fit) uses wavelength and fiber conversion resources more effectively than the First Fit.

Optimal scheduling in buffered WDM interconnects with limited range wavelength conversion capability

All optical networking is a promising candidate for supporting high-speed communications because of the huge bandwidth of optics. In this paper, we study optimal scheduling in buffered WDM interconnects with limited range wavelength conversion capability. We formalize the problem of maximizing network throughput and minimizing total delay as a problem of finding an optimal matching in a weighted bipartite graph. We then give a simple algorithm, called the Scan and Swap Algorithm, that finds the optimal matching in O(kB) time, where k is the number of wavelengths per fiber and B is the buffer length, as compared to directly adopting other existing algorithms that need at least O(k/sup 2/N/sup 2/ + k/sup 2/BN) time, where N is the number of input fibers.

Optimal scheduling algorithms in WDM optical interconnects with limited range wavelength conversion capability

Optical communication is a promising candidate for many emerging networking and parallel/distributed computing applications because of its huge bandwidth. Wavelength division multiplexing (WDM) is a technique that can better utilize the optical bandwidth by dividing the bandwidth of a fiber into multiple wavelength channels. In this paper, we study optimal scheduling algorithms to resolve output contentions in bufferless time slotted WDM optical interconnects with wavelength conversion ability. We consider the general case of limited range wavelength conversion with arbitrary conversion capability, as limited range wavelength conversion is easier to implement and more cost effective than full range wavelength conversion, and it also includes full range wavelength conversion as a special case. We first consider the conversion scheme in which each wavelength can be converted to multiple wavelengths in an interval of wavelengths and the intervals for different wavelengths are ordered. We show that the problem of maximizing network throughput can be formalized as finding a maximum matching in a bipartite graph. We then give an optimal scheduling algorithm called the first available algorithm that runs in O(k) time, where k is the number of wavelengths per fiber. We also study the case where the connection requests have different priorities. We formalize the problem as finding an optimal matching in a weighted bipartite graph and give a scheduling algorithm called the downwards expanding algorithm that runs in O(kD + Nklog(Nk)) time where N is the number of input fibers of the interconnect and D is the conversion degree. Finally, we consider the circular symmetrical wavelength conversion scheme and give optimal scheduling algorithms for nonprioritized scheduling in O(Dk) time and prioritized scheduling in O(k/sup 2/+Nklog(Nk)) time.

Operation of WDM networks with different wavelength conversion capabilities

We study the impact of wavelength conversion capability on wavelength routing WDM networks with fixed shortest-path routing. We propose a method for implementing wavelength routing in a WDM network with partial wavelength conversion capability. Simulation results show that such partial wavelength conversion networks provide a performance in between that of wavelength continuous networks and those with full conversion capability. In addition, it can be seen that only limited wavelength conversion capability is enough to provide a performance close to that of a network with full conversion. Analytical and simulation bounding results for the full and no conversion cases have also been provided.

Multiwavelength optical networks with limited wavelength conversion

This paper proposes optical wavelength division multiplexed (WDM) networks with limited wavelength conversion that can efficiently support lightpaths (connections) between nodes. Each lightpath follows a route in a network and must be assigned a channel on each link along the route. The load /spl lambda//sub max/ of a set of lightpaths is the maximum over all links of the number of lightpaths that use the link. At least /spl lambda//sub max/ wavelengths will be needed to assign channels to the lightpaths. If the network has full wavelength conversion capabilities, then /spl lambda//sub max/ wavelengths are sufficient to perform the channel assignment. Ring networks with fixed wavelength conversion capability within the nodes are proposed that can support all lightpath sets with load /spl lambda//sub max/ at most W-1, where W is the number of wavelengths in each link. Ring networks with a small additional amount of wavelength conversion capability within the nodes are also proposed that allow the support of any set of lightpaths with load /spl lambda//sub max/ at most W. A star network is also proposed with fixed wavelength conversion capability at its hub node that can support all lightpath sets with load /spl lambda//sub max/ at most W. These results are extended to tree networks and networks with arbitrary topologies. This provides evidence that significant improvements in traffic-carrying capacity can be obtained in WDM networks by providing very limited wavelength conversion capability within the network.