Optical Mesh Research Articles

Network control and management challenges in opaque networks utilizing transparent optical switches

There is a potential for significant cost, footprint, and power savings by eliminating unnecessary opto-electronic conversions on a signal path in a core optical mesh network. The article addresses and clarifies some fundamental issues surrounding all-optical networking and all-optical switching, and analyzes the trade-offs between transparent and opaque networking. It investigates a number of networking and interface compatibility issues that arise for an opaque network with transparent switches, and presents a number of ways to address these issues.

Efficient capacity sharing for path protection in meshed optical networks

Feature Issue on Next-Generation WDM Network Design and Routing (WDMN). Efficient resource management in meshed optical networks is critical for supporting differentiated services, such as network restoration, in a cost-competitive manner. We propose and study several alternatives for dynamic and distributed selection of primary and protection paths. The focus is on algorithms where the bandwidth can be shared efficiently among protection paths, although other alternatives are considered as well. The routing algorithm and link cost function are based on a Markov decision-process framework. In particular, we use this framework to justify the link cost structure for primary and shared bandwidth. We also propose and study several options for describing the link state, which in turn determines the link cost, with the objective of minimizing the amount of data to be advertised without sacrificing performance. The proposed solutions can be implemented without changing the existing set of protocols. The numerical results show performance and cost savings for the different algorithm options.

Inter-domain routing based on simulated annealing algorithm in optical mesh networks

For the first time a real-time and distributed routing algorithm based on Simulated Annealing (SA) algorithm is proposed to promote the intelligence, survivability, and interworking in optical mesh networks. Further, a SA-based Two-steps Optimization Routing Algorithm (SATORA) is proposed to obtain the inter-domain routing of global optimization. Compared with the previous approaches, this SA-based routing algorithm can achieve the routing optimization under multi-constraint condition, and can acquire the working and backup paths at one time for network survivability as well. Two crucial factors, the path hop count and the network congestion degree, are considered evaluating the cost of the path. Simulation experiments on different networks indicate that the SATORA can reduce the congestion degree of the networks and enhance the blocking performance of routing calculation for traffic requests when the inter-domain path protection is required.

Improving bandwidth efficiency in fault‐tolerant opaque IP over optical mesh networks

AbstractAdequately providing fault tolerance while using network capacity efficiently is a major topic of research in optical networks. In order to improve the network utilization, grooming of low‐rate connections in optical networks has been usually performed at the edge of the network. However, in all‐optical networks once a channel is assigned, its entire capacity is dedicated to the users independently of its grooming capabilities. As current users don't usually require such big capacities, bandwidth inefficiencies still occur. In this paper we address this issue introducing unlimited grooming per link (UGPL), a new restoration mechanism for opaque mesh optical networks that grooms connections on a per‐link basis. Simulation results show that UGPL provides the best bandwidth efficiency and the best blocking probability compared to traditional 1 + 1 protection and 1 : N end‐to‐end sharing schemes. Furthermore, we show that the 1 : N end‐to‐end restoration scheme provides no benefits over the simpler and faster 1 + 1 protection scheme. Copyright © 2004 John Wiley & Sons, Ltd.

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 grooming for survivable WDM networks: dedicated protection [Invited

We investigate the survivable traffic-grooming problem for optical mesh networks employing wavelength-division multiplexing (WDM) and dedicated protection. We consider the dynamic-provisioning environment in which a connection arrives at random, holds for a random amount of time, and then departs. A typical connection request may require bandwidth less than that of a wavelength, and it may also require protection from network failures, typically fiber cuts. On the basis of generic grooming-node architecture, we propose two approaches--protection-at-lightpath (PAL) level and protection-at-connection (PAC) level--for grooming a connection request. Here we investigate dedicated protection. In a companion paper [IEEE J. Sel. Areas Commun. 21, 1367 (2003)], we investigate shared protection, which leads to a substantially different treatment. For dedicated protection, we prove that the problem of provisioning a connection under PAC is NP-complete, propose effective heuristics for both schemes, and define comprehensive performance metrics to compare PAL with PAC with respect to wavelength or grooming-port efficiency. Our findings are as follows. Under today's typical connection-bandwidth distribution in which lower-bandwidth connections outnumber higher-bandwidth connections, PAC outperforms PAL (in terms of bandwidth-blocking ratio, lightpath use, and wavelength use) if the number of grooming ports is large; however, PAL outperforms PAC (in terms of bandwidth-blocking ratio and grooming-port use) when the number of grooming ports is moderate or small.

Control and management protocols for survivable optical mesh networks

This paper considers the problem of online provisioning and restoration of sharable, restorable connections in a mesh-based optical network. First, we propose a new framework called distributed path selection with local information (DPLI) and discuss in detail a control and management protocol to set up and tear down connections and determine restoration capacity sharability in a distributed manner. Since only local information is maintained at each node, protocol scalability is not a big concern. Second, we discuss the important problem of the network's ability to quickly recover from element failures. We propose a new rapid restoration signaling that minimizes the service interruption time upon the occurrence of a failure in a network with preplanned restoration paths. The significant contribution of this new algorithm is that the connection restoration time is found to be independent of the restoration path length (i.e., eliminating the effect of the propagation delay), of the accumulation of the switch configuration time along the restoration path, and of the switch configuration waiting time at any particular node when multiple configuration requests arrive simultaneously. We evaluate through simulation experiments the effectiveness of the proposed protocols.

Traffic grooming for survivable WDM networks-shared protection

We investigate the survivable traffic-grooming problem for optical mesh networks employing wavelength-division multiplexing (WDM). In the dynamic provisioning context, a typical connection request may require bandwidth less than that of a wavelength channel, and it may also require protection from network failures, typically fiber cuts. Based on a generic grooming-node architecture, we propose three approaches for grooming a connection request with shared protection: protection-at-lightpath level (PAL); mixed protection-at-connection level (MPAC); separate protection-at-connection level (SPAC). In shared-mesh protection, backup paths can share resources as long as their corresponding working paths are unlikely to fail simultaneously. These three schemes explore different ways of backup sharing, and they trade-off between wavelengths and grooming ports. Since the existing version of the problem for provisioning one connection request with shared protection is NP-complete, we propose effective heuristics. Under today's typical connection-bandwidth distribution where lower bandwidth connections outnumber higher bandwidth connections, we find the following: 1) it is beneficial to groom working paths and backup paths separately, as in PAL and SPAC; 2) separately protecting each individual connection, i.e., SPAC, yields the best performance when the number of grooming ports is sufficient; 3) protecting each specific lightpath, i.e., PAL, achieves the best performance when the number of grooming ports is moderate or small.

Disinfecting E.coli Bacteria In Drinking Water Using A Novel Fluidized Bed Reactor.

Disinfecting microorganisms such as E.coli is a great concern in drinking water supply facilities around the world. Photocatalysis became an attractive technology to disinfect microorganisms due to its ability to degrade very low concentration of microorganisms without producing any harmful by-products. The use of optical fibre mesh reactors and slurry type photocatalytic reactors has been investigated by researchers around the world. It was shown that such reactors have low potential to be scaled up. An annular type fluidized bed reactor has been constructed and tested to disinfect E.coli bacteria. A specially prepared catalyst (TiO2 + Glass Bead + Zeolite) was used for this purpose. The proposed catalyst offered better degradation of E.coli compared to existing technology. Fluidization enhances the degradation of E-coli by moving the catalyst particles to the illuminated zone. E.coli degradation is tested in a similar arrangement in small scale with 100cm3 of contaminated water with the 106 E-coli/cm3. Repeated experiments were done with/without the presence of catalyst along with UV irradiation. With the presence of catalyst in the fluidized condition, the E-coli count is reduced to only 100/cm3 whereas the E-coli count after 30 minutes of UV irradiation only became 1800/cm3. The efficiency of E.coli removal is increased to 99.99% from 99.82% by using the proposed technology. Results of small scale prompted a construction of a pilot plant scale reactor and effectiveness of this reactor is being tested. Use of supported catalyst and the effective illumination of catalyst by fluidization help faster disinfection of microorganisms by this reactor. It has been found that the pilot scale is capable of degrading 84% of E.coli within 80minutes compared with 77.3% by using UV only which has capacity of handling 46 litre/min. E.coli degradation in larger scale is being tested for the first time and its result compared with only UV destruction is promising. The potential to use this method on a continuous reactor increases the potential for scale up.

Optimal design of survivable mesh networks based on line switched WDM self-healing rings

Network survivability provided at the optical layer is a desirable feature in modern high-speed networks. For example, the wavelength division multiplexed (WDM) self-healing ring (or SHR/WDM) provides a simple and fast optically transparent protection mechanism against any single fault in the ring. Multiple self-healing rings may be deployed to design a survivable optical mesh network by superposing a set of rings on the arbitrary topology. However, the optimum design of such a network requires the joint solution of three subproblems: the ring cover of the arbitrary topology (the RC subproblem); the routing of the working lightpaths between end node pairs to carry the offered traffic demands (the WL subproblem); and the provisioning of the SHR/WDM spare wavelengths to protect every line that carries working lightpaths (the SW subproblem). The complexity of the problem is exacerbated when software and hardware requirements pose additional design constraints on the optimization process. The paper presents an approach to optimizing the design of a network with arbitrary topology protected by multiple SHRs/WDM. Three design constraints are taken into account, namely, the maximum number of rings acceptable on the same line, the maximum number of rings acceptable at the same node, and the maximum ring size. The first objective is to minimize the total wavelength mileage (working and protection) required in the given topology to carry a set of traffic demands. The exact definition of the problem is given based on an integer linear programming (ILP) formulation that takes into account the design subproblems and constraints and assumes ubiquitous wavelength conversion availability. To circumvent the computational complexity of the exact problem formulation, a suboptimal solution is proposed based on an efficient pruning of the solution space. By jointly solving the three design subproblems, it is numerically demonstrated that the proposed optimization technique yields up to 12% reduction of the total wavelength mileage when compared to solutions obtained by sequentially and independently solving the subproblems. The second objective is to reduce the number of wavelength converters required in the solution produced by the ILP formulation. Two approaches are proposed in this case that trade the required wavelength mileage for the number of wavelength converters.

Path-protection routing and wavelength assignment (RWA) in WDM mesh networks under duct-layer constraints

This study investigates the problem of fault management in a wavelength-division multiplexing (WDM)-based optical mesh network in which failures occur due to fiber cuts. In reality, bundles of fibers often get cut at the same time due to construction or destructive natural events, such as earthquakes. Fibers laid down in the same duct have a significant probability to fail at the same time. When path protection is employed, we require the primary path and the backup path to be duct-disjoint, so that the network is survivable under single-duct failures. Moreover, if two primary paths go through any common duct, their backup paths cannot share wavelengths on common links. This study addresses the routing and wavelength-assignment problem in a network with path protection under duct-layer constraints. Off-line algorithms for static traffic is developed to combat single-duct failures. The objective is to minimize total number of wavelengths used on all the links in the network. Both integer linear programs and a heuristic algorithm are presented and their performance is compared through numerical examples.

Diverse routing in optical mesh networks

We study the diverse routing problem in optical mesh networks. We use a general framework based on shared risk link groups to model the problem. We prove that the diverse routing problem is indeed NP-complete, a result that has been conjectured by several researchers previously. In fact, we show that even the fiber-span-disjoint paths problem, a special case of the diverse routing problem, is also NP-complete. We then develop an integer linear programming formulation and show through numerical results that it is a very viable method to solve the diverse routing problem for most optical networks found in many applications which typically have no more than a few hundred nodes and fiber spans.

Improving restoration success in mesh optical networks [Invited

In shared mesh restoration, a distributed signaling protocol is used to reroute connections from failed service paths to restoration paths upon failure events. However, even when the network contains sufficient capacity, the restoration paths could be blocked for two different reasons: (1) with distributed restoration-path selection schemes, multiple restoration paths may compete for the capacity of the same logical links, even when other logical links have sufficient capacity; (2) multiple restoration-path setup attempts may compete for the same channels within the logical link (the glare problem), even when sufficient capacity is available within the logical link. We propose a hybrid distributed-centralized restoration mechanism for restoration-path selection and a channel-selection scheme that eliminates almost all glares. As shown from simulation in a typical intercity backbone network, our proposed hybrid mechanism improves the first restoration attempt success ratio by 40% compared with a pure distributed restoration approach. In addition, the proposed restoration-path selection algorithm saves up to 50% of restoration capacity compared with the disjoint shortest-path algorithm and 15% compared with a previously published greedy algorithm.

Performance evaluation of optical mesh restoration schemes

This paper investigates the performance of various schemes for restoration of lightpaths in an optical mesh network. We consider schemes in which backup paths for links or paths are pro-computed, but wavelength assignment is either pro-computed (static) or done dynamically upon failure (dynamic). In static restoration we compare the performance of link and path restoration in terms of capacity requirement and restoration time. For the dynamic restoration, we consider several dynamic wavelength reservation schemes such as backward and forward reservation with different portion of wavelength to be reserved in both directions. Their performance is evaluated in terms of restoration speed and restorability. Simulation results indicate that path protection requires less capacity than link protection for 100% restorability, and dynamic restoration with backward wavelength reservation shows better restorability than static restoration schemes, when the extra capacity is relatively small. Forward wavelength reservation shows faster restoration speed with lower restorability than the backward wavelength reservation. In general, the optimal restoration scheme depends on extra capacity available and restoration time limit.

On the fault-tolerant embeddings of complete binary trees in the mesh interconnection networks

In this article, several schemes are proposed for embedding complete binary trees (CBT) into meshes. All of the proposed methods outperform those in the previous studies. First, a link congestion 1 embedding is achieved. Its expansion ratio is at the lowest level as we know now. Except for this superiority, it also provides another capability for fault tolerance to resist abnormal system faults, thus the embedding structure can be more guaranteed and the node utilization is raised further. Second, a link congestion 1 embedding with no-bending constraint is obtained. This scheme provides efficient CBT embedding for both the optical mesh and general mesh at the same time while keeping those good properties as the previous scheme. The last one is an optimal embedding which is applied to a 3D cubic mesh, where the node is almost fully utilized and its link congestion is 2.

A series of Hamiltonian cycle-based solutions to provide simple and scalable mesh optical network resilience

A mesh optical resilience solution has many requirements, some of which conflict with others. This article highlights the issues relevant to mesh optical resilience and the challenges of meeting the myriad requirements. A series of Hamiltonian cycle-based solutions with different efficiency, complexity, and scalability trade-offs are introduced. Solutions for moderate-sized and large networks are differentiated with the former emphasizing simplicity and efficiency, and the latter stressing resilience from multiple simultaneous failures and isolation of failure events.

Electrical ingress buffering and traffic aggregation for optical packet switching and their effect on TCP-level performance in optical mesh networks

The wide deployment of wavelength-division multiplexing technology and new transmission techniques have resulted in significant increases in the transmission capacity in optical fibers, both in the number of wavelengths and the bandwidth of each wavelength channel. Meanwhile, the fast growth of the Internet demands more data switching capacity in the network in order to deliver high bandwidth to end users. Although the capacity of electronic routers has been increasing consistently in the past, optical switching appears to be a more cost-effective way to switch individual wavelengths. As the bit rate per wavelength channel continues to grow, optical subwavelength switching emerges as a new paradigm capable of dynamically delivering the vast bandwidth WDM offers. This article discusses one of such techniques, namely optical packet switching, and its performance perceived by end users in optical mesh networks. Specifically, our investigation reveals the benefit of using electrical ingress buffering and traffic aggregation to reduce packet-loss rate of optical packet-switched networks. Through simulation experiments, we present an evaluation of the network's TCP-level performance based on the proposed architecture.

Fast, scalable, and distributed restoration in general mesh optical networks

Service providers are demanding transport network solutions that can accommodate exponential traffic growth and, at the same time, provide novel services such as point-and-click provisioning of very high bandwidth circuits, optical bandwidth service management, fast protection and restoration, and bandwidth on demand. It is becoming increasingly clear that the required scalability (terabits/s to petabits/s) and cost structure can only be provided by transparent optical cross connects (OXCs). The challenge, then, is to make the optical network consisting of OXCs, dense wavelength division multiplexers (DWDMs), and optical add/drop multiplexers (OADMs) dynamic and intelligent. A major aspect of this intelligence is fast provisioning and restoration. In this paper, we present a fast, scalable, and distributed solution for optical layer restoration in general mesh-type optical networks, which is being implemented as part of the Optical Navigator System (ONS) residing in Lucent's LambdaRouter product. The key ingredients to our solution are a fast and scalable restoration strategy, a fast and scalable connection setup strategy, a contention-free wavelength assignment strategy, and a fast and reliable data communications network to exchange signaling messages. We also introduce novel concepts of demand bundling and optical virtual paths that ensure that restoration performance scales with network and traffic volumes. Together these components provide an intelligent optical networking solution that not only guarantees restoration times within few hundreds of milliseconds, but also achieves scalability.

A network management architecture for robust packet routing in mesh optical access networks

We describe an architecture for an optical local area network (LAN) or metropolitan area network (MAN) access. The architecture allows for bandwidth sharing within a wavelength and is robust to both link and node failures. The architecture can be utilized with an arbitrary, link-redundant mesh network (node-redundancy is necessary only to handle all node failures), and assumes neither the use of a star topology nor the ability to embed such a topology within the physical mesh. Reservation of, bandwidth is performed in a centralized fashion at a (replicated) head end node, simplifying the implementation of complex sharing policies relative to implementation on a distributed set of routers. Unlike a router, however, the head end does not take any action on individual packets and, in particular, does not buffer packets. The architecture thus avoids the difficulties of processing packets in the optical domain while allowing for packetized shared access of wavelengths. We describe the route construction scheme and prove its ability to recover from single link and single node failures, outline a flexible medium access protocol and discuss the implications for implementing specific policies, and propose a simple implementation of the recovery protocol in terms of state machines for per-link devices.

Generalized loop-back recovery in optical mesh networks

Current means of providing loop-back recovery, which is widely used in SONET, rely on ring topologies, or on overlaying logical ring topologies upon physical meshes. Loop-back is desirable to provide rapid preplanned recovery of link or node failures in a bandwidth-efficient distributed manner. We introduce generalized loop-back, a novel scheme for performing loop-back in optical mesh networks. We present an algorithm to perform recovery for link failure and one to perform generalized loop-back recovery for node failure. We illustrate the operation of both algorithms, prove their validity, and present a network management protocol algorithm, which enables distributed operation for link or node failure. We present three different applications of generalized loop-back. First, we present heuristic algorithms for selecting recovery graphs, which maintain short maximum and average lengths of recovery paths. Second, we present WDM-based loop-back recovery for optical networks where wavelengths are used to back up other wavelengths. We compare, for WDM-based loop-back, the operation of generalized loop-back operation with known ring-based ways of providing loop-back recovery over mesh networks. Finally, we introduce the use of generalized loop-back to provide recovery in a way that allows dynamic choice of routes over preplanned directions.