Lightpath (wavelength) routing in large WDM networks

In optical burst switching networks, wavelength converters (WCs) of core nodes are used to decrease the burst loss rate. The implementation of the WCs is difficult in the current technology and the cost of WCs is high. So some core nodes may be configured insufficient WCs to reduce the cost in OBS networks. However, many data channel scheduling algorithms do not count the number of WCs and the performance of burst loss rate is not good in the condition of insufficient WCs. To overcome the defect, two novel batch scheduling algorithm with insufficiency of WC are proposed in this paper. The former algorithm improves the WCs’ resource utilization probability to reduce the burst loss rate and the later algorithm saves the WCs’ resource for the incoming bursts to use to improve the burst loss performance. The later algorithm can reduce more burst loss rate with the same number of WCs, compared with the other scheduling algorithms. The simulation results show that the later algorithm is more effective in reducing the burst loss rate with insufficient WCs.

Optical communication, in particular, wavelength-division-multiplexing (WDM) technique, has become a promising networking choice to meet ever-increasing demands on bandwidth from emerging bandwidth-intensive computing/networking applications. A major challenge in designing WDM optical interconnects is how to provide maximum connectivity while keeping minimum hardware cost. The overall hardware cost of a WDM optical interconnect includes not only the cost of switching elements, but also the cost of wavelength conversion. Previous work mainly focused on minimizing hardware cost without taking into consideration the type of wavelength converters used. In this paper, we design WDM optical interconnects with full connectivity by using the low cost limited wavelength converters. We present optimal WDM optical interconnects for both permutation and multicast in single stage and multistage implementations. We also discuss the impact of the relationship between the number of fibers and the number of wavelengths per fiber on the optimal design. As can be seen, the newly designed WDM optical interconnects have minimum hardware cost in terms of the number of crosspoints and wavelength conversion cost.

In this paper, we address the problem of designing wavelength division multiplexing (WDM) optical interconnects with reduced hardware complexity. We propose a new WDM optical interconnect design that reduces both the number of space switches and the cost of wavelength conversion. Wavelength conversion in the proposed design occurs between two pre-defined wavelengths, eliminating the need for expensive wide-range wavelength converters used in most existing designs. In addition, the proposed design follows the recursive structure of the Benes network, and hence, scalability occurs in an orderly fashion. A systematic method for developing interconnects with arbitrary number of wavelengths and fibers is given, and the main properties of the new design are analyzed and compared with existing designs. We show that, the new design requires the minimum number of switching stages and space switches compared to any existing WDM Benes interconnect. Moreover, our design has minimum wavelength conversion cost compared to most existing designs.

The next generation multimedia applications such as video conferencing and HDTV have raised tremendous challenges on the network design, both in bandwidth and service. As wavelength-division-multiplexing (WDM) networks have emerged as a promising candidate for future networks with large bandwidth, supporting efficient multicast in WDM networks becomes eminent. Different from the IP layer, the cost of multicast at the WDM layer involves not only bandwidth (wavelength) cost, but also wavelength conversion cost and light splitting cost. It is well known that the optimal multicast problem in WDM networks is NP-hard. In this paper, we develop an efficient approximation algorithm consisting of two separate but integrated steps: multicast routing and wavelength assignment. We prove that the problem of optimal wavelength assignment on a multicast tree is not NP-hard; in fact, an optimal wavelength assignment algorithm with complexity of O(NW) is presented. Simulation results have revealed that the optimal wavelength assignment beats greedy algorithms by a large margin in networks using many wavelengths on each link such as dense wavelength-division-multiplexing (DWDM) networks. Our proposed heuristic multicast routing algorithm takes into account both the cost of using wavelength on links and the cost of wavelength conversion. The resulting multicast tree is derived from the optimal lightpaths used for unicast.

We address the multicast issue in a wide area WDM network in which a source broadcasts its message to some sites in the network. This problem can be formalized as the following optimal multicast tree problem. Given a directed graph G = (V, E) with a source s and a set S of nodes, assume that every node in S (⊂ V) is reachable from s. Associated with every link e ∈ E, there is a set Λ(e) of available wavelengths on it, |V| = n and |E| = m, find a multicast tree rooted at s including all the nodes in S with minimizing the cost of the tree, in terms of the sum of the cost of wavelength conversion at nodes and the cost of using wavelengths on links in the tree. That is, not only do we need to find a directed tree rooted at s, but also do we need to assign a specific wavelength Λ ∈ Λ(e) to every tree edge e and to set the switches at every node in the tree. Since this problem is NP-complete, it is unlikely that there is a polynomial algorithm to find an exact solution for it. Instead, we first present an approximation algorithm for the problem which runs in time O(k2n + km +kn log(kn) + (kn)1/e|S|), and delivers a solution within O(|S|e) of the optimal, for any fixed 0 > e ≤ 1. We then present a distributed version of the proposed algorithm. The communication and time complexities of the distributed algorithm are O(km) and O(kn) respectively, and the solution delivered is |S| times of the optimal, where k is the number of wavelengths in the network. Finally, we conduct some experiments to verify the applicability of the proposed algorithms. The experimental results matches our algorithmic claims.

This paper proposes the optimal design of lightpath Routing and Wavelength Assignment (RWA) problem in Wavelength Division Multiplexing (WDM) networks without wavelength conversion. We formulate RWA as a mixed Integer Linear Programming (ILP) problem where the objective is to minimize the cost of wavelength assignment to the fiber links in the network. The Lagrangean relaxation technique and the optimization-based heuristics are used to solve this problem. Two sets of computational experiments are performed to test the algorithms for the maximum carried traffic and minimum wavelength requirements in three different network topologies (GTE, ARPA, OCT network). Based on solution quality to the computational experiments, the error gaps between the upper bound and the lower bound are close enough that the near optimal solutions could be obtained. On the other hand, we also show that the solution quality degrade gracefully under more and more heavy traffic network environment. By assessing solution quality and the computational time, we propose the efficient and effective optimization-based algorithms based on the Lagrangean relaxation method for the RWA problem in the WDM networks without wavelength conversion.

Existing methods for handling routing and dimensioning in dynamic WDM networks solve the two problems separately. The main drawback of this approach is that a global minimum cost solution cannot be guaranteed. Given that wavelengths are costly resources, determining the minimum network cost is of fundamental importance. We propose an approach which jointly solves the routing and dimensioning problems in optical burst switching (OBS) networks, guaranteeing a target blocking per connection. The method finds the set of routes and the number of wavelengths per network link that minimise the total network cost. To accomplish this, an integer linear programming problem is solved. The proposed method was applied to ring networks, where the optimal solution achieves a reduction in the network cost of 10–40% (for traffic loads <0.4, compared to solving both problems separately). In the case of mesh topologies, to reduce the computational complexity of the method, we applied a variation of it which achieves a local minimum. Even so, a reduction of 5–20% (for traffic loads <0.4) in the network cost was obtained. This ability to lower network cost could make the proposed method the best choice to date for dynamic network operators.

This paper describes the advantages introduced by wavelength conversion in the design, implementation and management of future WDM optical networks and nodes. We describe the routing and wavelength assignment process in a WDM network and then we will demonstrate the major advantages introduced by wavelength conversion, mainly regarding the dimensioning aspects but also including considerations on the physical and management issues.

Addresses the problem of efficient communication in unreliable multi-hop optical networks supported by wavelength division multiplexing (WDM). We first define a new cost model for routing in (optical) WDM networks that is more general and realistic than the existing models. Our model takes into consideration not only the cost of wavelength access and conversion but also the cost for wavelength switching when several optical channels of the same wavelength arrive at the same node. We then propose a set of efficient algorithms in both reliable and unreliable WDM networks on the new cost model respectively for each of three important communication patterns-multiple point-to-point routing, multicast and multiple multicast.

This paper proposes a new optical path restoration method for wavelength division multiplexing (WDM) networks. In the method, the protection path is established by connecting several sub-lightpaths from the source node to the destination node of the original working lightpath, as opposed to conventional path restoration where a single protection lightpath between the source-destination pair performs restoration. The set of one or more consecutive lightpaths to connect a source-destination pair is called semi-lightpath. The semi-lightpath based restoration provides enhanced flexibility in protection path provisioning and relieves the cost of spare capacity reservation and wavelength conversion at intermediate optical cross-connect nodes. In terms of spare capacity utilization, our method shows substantial reduction of spare capacity overhead compared with dedicated path restoration in all optical networks without wavelength conversion, and shows similar capacity efficiency compared with shared path restoration in opaque networks with full wavelength conversion capability.

Wave length division multiplexing has emerged as a promising technology for backbone networks. The optical layer based on WDM technology provides optical routing services to the upper layers. We consider large optical networks in which nodes employ wavelength-routing switches and wavelength converters which enable the establishment of wavelength-division multiplexed channels called light paths, between node pairs. We propose a algorithm called modified DORA which solves the routing and wavelength assignment of light paths in such networks. We studied the performance of proposed algorithm for a standard NSFNET for 10 nodes and 15 links and analyzed the blocking probability for various cases. We studied the dynamic routing algorithm. We modified the algorithm to suit for WDM networks. We compare it with the exhaust routing in terms of blocking probability, channel utilization and complexity

Multicommodity flow models are commonly used to formulate the logical topology design (LTD) problem and the lightpath routing (LR) problem as mixed integer linear programming (MILP) problems. In general, MILP formulations are intractable even for relatively small networks due to the combinatorial complexity of the problem. In this paper we propose improvements to these models and a method to solve the LTD and the LR problems in a combined manner. The interest is two fold: firstly, by tackling the two problems with separate models, problem instances of realistic size (up to 14 nodes in this paper) can be dealt with. Furthermore, different combinations of optimization models and objective functions can be investigated in a modular manner. Secondly, the mechanisms proposed to combine the problems allow to keep track of the global design problem when solving each individual step.

Translucent optical networks use sparsely located regenerator nodes to increase the optical reach, otherwise limited by the physical layer impairments. Routing in translucent networks often causes the lightpath to traverse a fiber more than once, requiring the use of multiple wavelengths on a fiber for the same lightpath. Most of the routing and wavelength assignment (RWA) algorithms for static demand in translucent networks (termed static RWA) require loop-free routes for shortest path routing and also are agnostic to traffic load. In this paper, we address the problem of static RWA in translucent networks without using physical layer information and show how to route lightpaths on paths with a loop (i.e., not a simple path). We propose integer linear programming formulation to get the exact solutions to the static RWA problem. This work is the first one to optimally solve the static RWA problem for non-simple paths, providing the lower bound on the number of wavelengths and regeneration needed for static lightpath establishment when regeneration facilities are limited. We propose a heuristic algorithm based on the concept of Wardrop equilibrium, to adaptively equalize the mean delay along all the lightpath routes from source to destination. The proposed heuristic can not only accommodate the correlation between feasible lightpath routes but also account for the fact that alternate routes correspond to different levels of choice randomness. Wavelength assignment is done using graph coloring with branch-and-price method. Numerical results demonstrate that the proposed heuristic reduces the number of regenerators and wavelengths required to satisfy a given demand.

This paper outlines an approach, called the optical border gateway protocol (OBGP) of extending the BGP routing protocol to support light path setup and management across an optical network. OBGP is a distributed approach, which gives more control to the edge customer and allows customers to better manage their optical wavelengths. It provides an interdomain routing/signaling solution that integrates heterogeneous domains into an end-to-end optical network and can coexist with most of the existing intradomain solutions. OBGP has the capability of setting up light paths in both networks with wavelength converters as well as in networks without wavelength converters. By combining routing with signaling in OBGP, signaling functions can leverage some features of existing routing functions and thus provide a lightweight solution. The development of OBGP has been discussed by reviewing current BGP behavior and design requirements for OBGP. An implementation of OBGP using simulation tools has been presented, along with initial test results, which have shown that a seamless migration from BGP to OBGP is possible.

The emergence of translucency in WDM networks as a trade-off between the low cost of full transparency and high signal quality provided by full opacity has led to immense interest in translucent network design by the research community in recent years. Efficient translucent network design necessitates the judicious choice of regeneration sites and number of regenerators in order to maintain a predefined quality of transmission and to reduce the overall network cost. In this paper, we explicate a framework that corroborates the offline version of Physical Layer Impairment Aware Routing and Wavelength Assignment (PLI-RWA) problem in translucent networks. The originality of the proposed PLI-Signal Quality Aware RWA (PLI-SQARWA) algorithm lies in finding the routes which use fewest amounts of regenerators and constituting an efficient Regenerator Placement (RP) algorithm to place regenerators before wavelengths are assigned leading to maximal use of regenerators as wavelength converters. Subsequently, in the WA phase, for any further wavelength contention resolutions; we resort to optical wavelength converters. A relevant difference between existing studies and the proposed algorithm is that PLI-SQARWA provisions both, regeneration and wavelength conversion which guarantees zero signal and wavelength blocking. We proceed to the performance comparison of PLI-SQARWA with a heuristic for RWA and RP called COR2P (Cross-Optimization for RWA and RP) and the comparison results reveal that PLI-SQARWA outperforms COR2P in terms of number of network regenerators and time delay while demonstrating similar blocking performance to COR2P at various traffic loads. The results also suggest that to minimize time delay due to Optical-Electrical-Optical (OEO) conversions, using optical wavelength converters for only wavelength contention resolution is a judicious choice rather than resorting to regenerators. Finally, it can be inferred from the study that there exists a trade-off between the overall network cost and the maximum tolerable delay.