Optical Mesh Research Articles

Lightpath routing for maximum reliability in optical mesh networks

We consider the problem of maximizing the reliability of connections in optical mesh networks against simultaneous failures of multiple fiber links that belong to a shared-risk link group (SRLG). We study the single-lightpath, parallel-lightpaths, and lightpath protection problems for connections between two end nodes, as well as the lightpath-ring problems for connections of three or more end nodes. We first study the special problems where all SRLGs have the same failure probability. In these problems, every SRLG is represented by a distinct color and every fiber link is associated with one or more colors, depending on the SRLGs to which the link belongs. We formulate the problems as minimum-color lightpath problems. By minimizing the number of colors on the lightpaths, the failure probability of the lightpaths can be minimized. We prove the problems to be NP-hard. We then extend the results to the general problems where the failure probabilities of the SRLGs may differ. Heuristic algorithms are proposed for larger instances of the problems, and the heuristics are evaluated through simulations.

Improved reliability of free-space optical mesh networks through topology design

We propose a method for the topology design of free-space optical (FSO) mesh networks in order to enhance network reliability under a defined degree constraint of each FSO node. The methodology presented enlarges the minimum angle between adjacent links at each node. Simulation results show that, compared to other methods, the proposed algorithm not only provides a higher connectivity and lower delay for FSO networks but also makes the constructed FSO networks more tolerant in a dynamic environment.

Design of grooming architectures for optical WDM mesh networks: limited grooming with electronic wavelength conversion

In this article, we consider the problem of traffic grooming in optical wavelength division multiplexed (WDM) mesh networks under static traffic conditions. The objective of this work is to minimize the network cost and in particular, the electronic port costs incurred for meeting a given performance objective. In earlier work, we have shown the benefits of limited grooming switch architectures, where only a subset of wavelengths in a network are equipped with expensive SONET Add Drop Multiplexers (SADM) that provide the grooming functionality. In this work, we also consider the wavelength conversion capability of such groomers. This can be achieved using a digital cross-connect (DCS) in the grooming switch to switch low-speed connections between the SADMs (and hence, between wavelengths). The grooming switch thus avoids the need for expensive optical wavelength converters. Based on these observations, we propose a limited conversion-based grooming architecture for optical WDM mesh networks. The local ports at every node in this architecture can be one of three types: an add-drop port, a grooming port that allows wavelength conversion or a grooming port that does not allow wavelength conversion. The problem studied is: given a static traffic model, where should the different ports be placed in a network? We formulate this as an optimization problem using an Integer Linear Programing (ILP) and present numerical results for the same. We also present a heuristic-based approach to solve the problem for larger networks.

Holding-Time-Aware Dynamic Traffic Grooming

Progress in network technologies and protocols is paving the road towards flexible optical transport networks, in which dynamic leasable circuits could be set up and released on a short-term basis according to customers requirements. Recently, new solutions for automated network management promise to allow customers to dinamically specify the terms of the Service Level Agreement (SLA) to be guaranteed by the service provider. Since this new information is made available, we propose to exploit the knowledge of connection holding time, among the other Service Level Specifications (SLS), to improve the routing efficiency. In this work, we consider that a typical electronic-layer (e.g., SDH or MPLS) demand requires only a fraction of the capacity of the single wavelength bandwidth and we investigate a new algorithm for traffic grooming of sub-wavelength connections in an optical mesh network. We rely on the knowledge of the holding time of connection requests to exploit lightpath capacity and hence to achieve significant reduction in blocking probability for the traffic grooming problem. Our new methodology is applied on a typical US nation-wide network and results are compared with those given by previous known approaches.

Survivable wavelength‐routed optical network design using genetic algorithms

AbstractThe provision of acceptable service in the presence of failures and attacks is a major issue in the design of next generation dense wavelength division multiplexing (DWDM) networks. Survivability is provided by the establishment of spare lightpaths for each connection request to protect the working lightpaths. This paper presents a genetic algorithm (GA) solver for the routing and wavelength assignment problem with working and spare lightpaths to design survivable optical networks in the presence of a single link failure. Lightpaths are encoded into chromosomes made up of a fixed number of genes equal to the number of entries in the traffic demand matrix. Each gene represents one valid path and is thus coded as a variable length binary string. After crossover and mutation, each member of the population represents a set of valid but possibly incompatible paths and those that do not satisfy the problem constraints are discarded. The best paths are then found by use of a fitness function and these are assigned the minimum number of wavelengths according to the problem constraints. The proposed approach has been evaluated on dedicated path protection and shared path protection. Simulation results show that the GA method is efficient and able to design DWDM survivable real‐world optical mesh networks. Copyright © 2007 John Wiley & Sons, Ltd.

A novel ring-tree-based routing and wavelength assignment algorithm for multicasting in DWDM optical mesh networks

Multicast session communications, such as video-conferencing and video-broadcasting, in DWDM mesh networks require the efficient multipoint-to-multipoint multicast algorithms. Several heuristics have approximate solutions using lightpath or light-tree for one-to-multipoint multicast communications, but few papers have discussed the multipoint-to-multipoint multicast problems in DWDM mesh networks. This paper proposes a ring-tree-based routing and wavelength assignment (RTRWA) solution in DWDM mesh networks. It proceeds to multipoint-to-multipoint multicast transmission by reserving links and wavelengths assigned by the Least Converter Count algorithm. The RTRWA algorithm tries to find an optimal ring path that connects all multicast session members with unidirectional links and connects the remaining nodes to the ring path with the light-tree. The RTRWA algorithm outperforms the Steiner minimal tree (SMT) algorithm in terms of the call blocking probability, difference in user capacity and the mean maximum transmission time.

A Routing Algorithm Framework for Survivable Optical Networks Based on Resource Consumption Minimization

In this paper, we consider the problem of determining primary and backup paths for survivable optical wavelength-division multiplexed mesh networks. We propose a distributed routing mechanism, which is called Least Resource Consumption Routing, that tries to minimize the combined cost of the primary and the backup paths. The proposed cost model includes the effect of various factors such as mean load, variance of the load on the route, number of converters required by the route, and the length of the route. Further, we model the route cost in such a way that it is extensible to include any new parameters and vary their relative importance. The performance studies conducted for the 14-node National Science Foundation Network and a 30-node topology show that the proposed scheme leads to significant improvements in blocking probability at low and moderate loads. Further, the proposed cost model also reduces the number of converters required to obtain a target blocking performance as compared to some other techniques proposed in the literature.

Integrated topology control and routing in wireless optical mesh networks

We study the problem of integrated topology control and routing in Free Space Optical (FSO) mesh backbone networks. FSO links are high-bandwidth, low interference links that can be set-up very fast, making them suitable for mesh networking. FSO networks are highly constrained by interface constraints, i.e., constraints on the number of FSO links a node can establish. We prove the problem to be NP-Hard and propose efficient algorithms for integrated topology control and single-path or multi-path routing.

A Novel Survivable Routing Algorithm With Partial Shared-Risk Link Groups (SRLG)-Disjoint Protection Based on Differentiated Reliability Constraints in WDM Optical Mesh Networks

Previous research on survivability with differentiated reliability in wavelength-division-multiplexing (WDM) optical mesh networks mostly considered the failure probability of a fiber link with the link length that may not be a good solution for consideration of shared-risk link groups (SRLGs). In this paper, we propose a new model of failure probability with the SRLG constraints in WDM optical mesh networks. Based on this model, we present the backup resources assignment and the routing selection method with the differentiated reliable requirements of users. To evaluate the performances of this model, we propose a novel survivable routing algorithm called partial SRLG-disjoint protection (PSDP) to tolerate the single-SRLG failure. Compared with the previous algorithm, PSDP can obtain a better resource utilization ratio and lower blocking probability. Simulation results are shown to be promising.

Analysis of Connection Availability in an All-Optical Mesh Network

This paper presents the method of an availability performance analysis that can be used for all-optical networks. We compare different schemes of protection and restoration in a fully connected mesh network based on optical cross-connects, optical fibers, and fiber amplifiers. Specifically treated is an optical mesh network physically mapped onto a Scandinavian backbone. In order to compare different survivability strategies, we selected two nodes located roughly 420 km apart. The goal of this work is to point out possible ways to improve connection availability. A number of survivability schemes are compared, for which the availability model of logical connection is derived and a calculation procedure is described. Our results show that unprotected schemes cannot ascertain reasonably high requirements on connection availability in the backbone network. Thus, if a redundant structure of logical connection is considered, the particular survivability scheme should be evaluated in order to maximize connection availability.

LSSP: A novel local segment-shared protection for multi-domain optical mesh networks

This paper investigates the survivability in multi-domain optical mesh networks and presents a new model of multiple failures that is defined that there is one failed link in each single-domain and are multiple failed links in the whole multi-domains. Since the conventional Extended-Path-Shared Protection (EPSP) approach cannot provide 100% protection ability for this model, we propose a novel approach called Local Segment-Shared Protection (LSSP) to provide efficient survivability for this model. In our approach, LSPP first computes one inter-domain primary path for each connection request and follows to compute one intra-domain link-disjoint local segment-backup path for each primary-segment path in each single-domain, respectively, where the backup resources can be shared by different segment-backup paths if the corresponding primary-segment paths are link-disjoint. Compared with the conventional EPSP, although LSSP increases moderate backup resources consumption, it not only can provide 100% protection ability for multiple failures but also can perform much faster recovery time and easier survivable operation and management. The simulation results are shown to be promising.

A Zone-Based Approach for Scalable Dynamic Traffic Grooming in Large WDM Mesh Networks

Dynamic traffic grooming in optical mesh networks is one of the most important and practical problems for designing wavelength-division-multiplexing networks. Most of the previous work solves this problem by applying the Dijsktra's algorithm on an auxiliary graph. Although those algorithms may give a good performance since they have a global view of the whole network, they are very time consuming and thus cannot be applied in large networks. Therefore, to the best of our knowledge, for the first time, we propose a heuristic algorithm to reduce the required computations by minimizing the size of the graph. We compare our algorithm with existing algorithms by extensive simulations in a typical 24-node mesh networks. The results demonstrate that our algorithm can significantly reduce the computational complexity, typically by a few tens times. Despite its simplification, our algorithm outperforms existing algorithms by large margins since it can easily avoid lightpaths that consume a large amount of network resources

Performance study of IP and SONET grooming in optical WDM mesh networks

We study the problem of IP traffic grooming in optical wavelength-division-multiplexed (WDM) mesh networks. Two different grooming architectures are considered: (i) IP/MPLS grooming, and (ii) SONET grooming. The IP/MPLS grooming approach provides a fine level of grooming granularity realized via software-based implementations but has router-processing-related bottlenecks. The SONET grooming approach is realized in dedicated hardware, but it is more expensive and typically offers limited grooming granularity choices. We also consider multipath routing as used in SONET virtual concatenation techniques, and we study the impact of the differential delay constraint. A detailed comparison of the different grooming options in terms of blocking probability, lightpath utilization, and survivability issues is presented. The simulation analysis helps quantify the improved performance of finer granularity grooming approaches over the coarser SONET-based approaches.

Optimal design for survivable backbones with end-to-end and subpath wavebanding

We deal with the optimal design of a survivable optical mesh network supporting end-to-end and subpath waveband switching (WBS) in order to compare various WBS schemes according to a given cost function. An integer linear programming formulation is proposed to minimize the global network cost, which is expressed in terms of port cost, fiber cost, and propagation delay cost. We assume a single-layer multigranularity optical cross-connect (MG-OXC) node with a variable number of incoming fibers and a fixed number of wavelengths per waveband. The results show that on our case-study networks WBS with joint end-to-end and subpath wavebanding guarantees a gain of up to 22% and 85% in port number and global network costs, respectively. © 2006 Optical Society of America OCIS codes: 000.1200, 060.0060.

Performance evaluation of an intelligent routed WDM mesh network: An analytical approach

This paper presents an analytical model of an optical mesh network capable of handling WDM traffic intelligently. The router is modeled as a processor to read the instructions in the header of the packet to implement the required algorithm adopting standard queuing concepts. Packet stacking, switching, or routing performance deliberately depends on packet size, node architecture and network parameters. The numerical result shows a huge data transmission through the router with a least dependence on the routing time up to a significant data rate and thus provides a significant improvement in call connection probability.

Multicast protection scheme in survivable WDM optical networks

The protection design is a key issue in survivable wavelength division multiplexing (WDM) optical networks. Most researches focused on protecting unicast traffic against the failure of a single network component such as a link or a node. In this paper, we investigate the protection scheme for multicast traffic in meshed WDM optical networks under dual-link failure consideration, and propose a novel protection algorithm called shared segment protection with reprovisioning (SSPR). Through dynamically adjusting link-cost according to the current network state, SSPR establishes a primary light-tree and corresponding link-disjoint backup segments for each multicast connection request. A backup segment can efficiently share wavelength capacity of its working tree or the common resource of other backup segments. Capacity reprovisioning establishes new segments for the vulnerable connections after a link failure and tolerates following link failures. The simulation results show that SSPR not only can make good use of wavelength resources and protect multicast sessions against any single-link failure, but also can greatly improve the traffic restorability in the event of dual-link breakdown.

A novel backup multiplexing scheme for surviving double-link failures in mesh optical networks without wavelength conversion capability

We consider the problem of recovery from any double-link failure by exploiting shared path protection in wavelength-division multiplexing (WDM) mesh networks. We for the first time discover the phenomenon of sharing contradiction, which results in the violation of 100% recovery guarantee. To completely eliminate the sharing contradiction, we introduce the so-called preference policy, which implies that one of two backup paths (BPs) for each connection is given priority over the other to recover the failed active path (AP). Based on this policy, we propose a backup-multiplexing scheme with 100% recovery guarantee. Further, we transform the problem of minimizing the total number of wavelength-links under the wavelength continuity constraint while recovering from any dual-link failure to integer linear programming (ILP) formulations. Additionally, we investigate three preference policies, i.e., the first backup path preference policy (FBPPP), the second backup path preference policy (SBPPP), and the optimal preference policy (OPP). The numerical results show that our proposed backup multiplexing scheme can reduce about 30% wavelength-link consumption, compared to dedicated protection. Also, the results show that the policy, which specifies that the shorter one of two backup paths is preferred, generally outperforms the policy, which specifies that the longer one of two backup paths is preferred. Furthermore, the results show that OPP has a better performance when two BPs for each connection are more comparable in their lengths.

Optimal capacity assignment for p-cycle in survivable optical mesh networks

The preconfiguration cycle (p-cycle) is an excellent protection scheme that benefits both the fast recovery time and the efficient resource utilization in wavelength-division-multiplexing (WDM) mesh networks. Before providing protection for any link whose end nodes are both on the p-cycle, the spare capacity assignment for the p-cycles is a very important step for p-cycle design in WDM networks. We present a heuristic scheme, called the p-Cycle Capacity Assignment Algorithm (CCAA), to achieve an optimal capacity assignment of p-cycles in WDM networks without using Integer Linear Programming (ILP). CCAA can configure the p-cycles with good actual efficiency because it first consumes the spare capacity of the links where more spare capacity exists. This scheme is more suitable for the design of maximum p-cycle restorability with a given spare capacity distribution. When allocating the spare capacity for the p-cycles in WDM mesh networks, this scheme considers the actual distribution of the working capacity and the spare capacity of a certain traffic pattern. The performance of CCAA is evaluated by computer simulations on the real-world network topology.

A novel algorithm for node‐encircling and link candidate p‐cycles design in WDM mesh network

A fault recovery system that is fast and reliable is essential in survivability design in wavelength‐division‐multiplexing (WDM) mesh networks. The Pre‐configuration Cycle (p‐cycle) is a promising approach for protecting working capacities in optical mesh networks. Finding good candidate cycles is the first and a very important step in p‐cycle design. We first introduce the definition of the local‐map and several algorithms for finding cycles. A novel heuristic algorithm, called Local‐map Cycles Mining Algorithm (LCMA), for finding simple node‐encircling and link candidate p‐cycles based on the local‐map is proposed in this paper. We perform the expanding algorithms on the cycle generated by LCMA to get more efficient candidate p‐cycles. Comparisons are made between this algorithm and the Depth First Search (DFS) algorithm and the result shows that the LCMA can find more candidate p‐cycles with good efficiency in optical mesh networks without enumerating all cycles.

On Optimal<tex>$p$</tex>-Cycle-Based Protection in WDM Optical Networks With Sparse-Partial Wavelength Conversion

We study the optimal configuration of p-cycles in survivable wavelength division multiplexing (WDM) optical mesh networks with sparse-partial wavelength conversion while 100% restorability is guaranteed against any single failures. We formulate the problem as two integer linear programs (Optimization Models I, and II) which have the same constraints, but different objective functions. p-cycles and wavelength converters are optimally determined subject to the constraint that only a given number of nodes have wavelength conversion capability, and the maximum number of wavelength converters that can be placed at such nodes is limited. Optimization Model I has a composite sequential objective function that first (G1) minimizes the cost of link capacity used by all p-cycles in order to accommodate a set of traffic demands; and then (G2) minimizes the total number of wavelength converters used in the entire network. In Optimization Model II, the cost of one wavelength converter is measured as the cost of a deployed wavelength link with a length of alpha units; and the objective is to minimize the total cost of link capacity & wavelength converters required by p-cycle configuration. During p-cycle configuration, our schemes fully takes into account wavelength converter sharing, which reduces the number of converters required while attaining a satisfactory level of performance. Our simulation results indicate that the proposed schemes significantly outperform existing approaches in terms of protection cost, number of wavelength conversion sites, and number of wavelength converters needed