Wavelength assignment in all-optical networks for mesh topologies

All-Optical Networks employing Dense Wavelength Division Multiplexing (DWDM) are believed to be the next generation networks that can meet the ever-increasing demand for bandwidth of the end users. This thesis presents some new heuristics for wavelength assignment and converter placement in mesh topologies. Our heuristics try to assign the wavelengths in an efficient manner that results in very low blocking probability. We propose novel static and dynamic assignment schemes that outperform the assignments reported in the literature even when converters are used. The proposed on-line scheme called Round-Robin assignment outperforms previously proposed strategies such as first-fit and random assignment schemes. The performance improvement obtained with the proposed static assignments is very significant when compared with the dynamic schemes. We designed and developed a simulator in the C language that supports the 2D mesh topology with DWDM. We ran extensive simulations and compared our heuristics with those reported in the literature. We have examined converter placement in mesh topologies and proposed that placing converters at the center yields better results than uniform placement when dimension order routing is employed. We introduced a new concept called wavelength assignment with second trial that results in extremely low blocking probabilities when compared to schemes based on a single trial. Our proposed schemes are simple to implement and do not add to the cost. Thus we conclude that wavelength assignment plays more significant role in affecting the blocking probability than wavelength converters. We further conclude that static schemes without converters could easily outperform dynamic schemes thus resulting in great savings

Efficient communication using multiple cycles and multiple channels

Initially, the use of optical fiber in networks was to create point-to-point links. Optical paths were not altered once they were setup. This limits the ability of the network to respond to changing traffic demands. There were expensive solutions to handle dynamic traffic. One could set up multiple paths for additional traffic. Alternately, traffic that did not have a dedicated optical path needed to be received, the next hop found electronically, and then transmitted again. Current research in optical networking is looking to minimize or even eliminate electronic packet processing in the network. This will reduce the numbers of transmitters, receivers, and processing hardware needed in the network. If a signal can be kept entirely optical, new signal formats can be added to the network by only upgrading systems sending or receiving the new format. Research is currently looking at hardware designs to support electrically changing optical paths, and algorithms to route the optical paths. The topic of this work is the routing algorithms. We wish to keep cost as low as possible, while being able to recover quickly from or completely hide hardware failures. Several strategies exist to meet these expectations that involve a mix of handing routing and failure at the optical or at the electronic layer. This dissertation considers the use of cycles or rings in both establishing optical connections in response to connection requests, and electronic routing on optical cycle\u27s setup when a network is built. Load balancing is an important issue for both approaches. In this dissertation we provide heuristics and integer linear program (ILP) that can be used to find cycles in a network. We report on experiments showing the effectiveness of the heuristics. Simulations show the importance of load balancing. In the case of electronic routing, we setup cycles in the network which allow nodes on the cycle to communicate with each other. We select cycles so that they have two properties. One property is that all node pairs appear on at least one cycle. The other property is that each cycle contains a cyclical quorum. The first property allows for a network to support all-to-all communication entirely in the optical domain. The second property allows for quorum based distributed systems to send a message to an entire quorum in an all optical one-to-many connection. The use of quorums makes distributed systems efficient at tasks such as coordinating mutual exclusion or database replication. There is a need for the optical layer of the network to provide support for keeping latency of this type of communication low because as designers have scarified the benefits of using quorums in higher latency networks. Combined with light trails, cycles based on quorums requires fewer transmitter and receivers than light-paths to support all-to-all traffic

Design and provisioning of WDM networks for traffic grooming

Wavelength Division Multiplexing (WDM) is the most viable technique for utilizing the enormous amounts of bandwidth inherently available in optical fibers. However, the bandwidth offered by a single wavelength in WDM networks is on the order of tens of Gigabits per second, while most of the applications\u27 bandwidth requirements are still subwavelength. Therefore, cost-effective design and provisioning of WDM networks require that traffic from different sessions share bandwidth of a single wavelength by employing electronic multiplexing at higher layers. This is known as traffic grooming. Optical networks supporting traffic grooming are usually designed in a way such that the cost of the higher layer equipment used to support a given traffic matrix is reduced. In this thesis, we propose a number of optimal and heuristic solutions for the design and provisioning of optical networks for traffic grooming with an objective of network cost reduction. In doing so, we address several practical issues. Specifically, we address the design and provisioning of WDM networks on unidirectional and bidirectional rings for arbitrary unicast traffic grooming, and on mesh topologies for arbitrary multipoint traffic grooming. In multipoint traffic grooming, we address both multicast and many-to-one traffic grooming problems. We provide a unified frame work for optimal and approximate network dimensioning and channel provisioning for the generic multicast traffic grooming problem, as well as some variants of the problem. For many-to-one traffic grooming we propose optimal as well as heuristic solutions. Optimal formulations which are inherently non-linear are mapped to an optimal linear formulation. In the heuristic solutions, we employ different problem specific search strategies to explore the solution space. We provide a number of experimental results to show the efficacy of our proposed techniques for the traffic grooming problem in WDM networks

Approximable 1-Turn Routing Problems in All-Optical Mesh Networks

In all-optical networks, several communications can be transmitted through the same fiber link provided that they use different wavelengths. The MINIMUM ALL-OPTICAL ROUTING problem (given a list of pairs of nodes standing for as many point to point communication requests, assign to each request a route along with a wavelength so as to minimize the overall number of assigned wavelengths) has been paid a lot of attention and is known to be N P–hard. Rings, trees and meshes have thus been investigated as specific networks, but leading to just as many N P–hard problems. This paper investigates 1-turn routings in meshes (paths are allowed one turn only). We first show the MINIMUM LOAD 1-TURN ROUTING problem to be N P–hard but 2-APX (more generally, the MINIMUM LOAD k-CHOICES ROUTING problem is N P–hard but k-APX), then that the MINIMUM 1-TURN PATHS COLOURING problem is 4-APX (more generally, any d-segmentable routing of load L in a hypermesh of dimension d can be coloured with 2d(L−1)+1 colours at most). >From there, we prove the MINIMUM ALL-OPTICAL 1-TURN ROUTING problem to be APX

Traffic grooming and wavelength conversion in optical networks

Wavelength Division Multiplexing (WDM) using wavelength routing has emerged as the dominant technology for use in wide area and metropolitan area networks. Traffic demands in networks today are characterized by dynamic, heterogeneous flows. While each wavelength has transmission capacity at gigabit per second rates, users require connections at rates that are lower than the full wavelength capacity. In this thesis, we explore network design and operation methodologies to improve the network utilization and blocking performance of wavelength routing networks which employ a layered architecture with electronic and optical switching. First we provide an introduction to first generation SONET/SDH networks and wavelength routing networks, which employ optical crossconnects. We explain the need and role of wavelength conversion in optical networks and present an algorithm to optimally place wavelength conversion devices at the network nodes so as to optimize blocking performance. Our algorithm offers significant savings in computation time when compared to the exhaustive method.;To make the network viable and cost-effective, it must be able to offer sub-wavelength services and be able to pack these services efficiently onto wavelengths. The act of multiplexing, demultiplexing and switching of sub-wavelength services onto wavelengths is defined as traffic grooming. Constrained grooming networks perform grooming only at the network edge. Sparse grooming networks perform grooming at the network edge and the core. We study and compare the effect of traffic grooming on blocking performance in such networks through simulations and analyses. We also study the issue of capacity fairness in such networks and develop a connection admission control (CAC) algorithm to improve the fairness among connections with different capacities. We finally address the issues involved in dynamic routing and wavelength assignment in survivable WDM grooming networks. We develop two schemes for grooming primary and backup traffic streams onto wavelengths: Mixed Primary-Backup Grooming Policy (MGP) and Segregated Primary-Backup Grooming Policy (SGP). MGP is useful in topologies such as ring, characterized by low connectivity and high load correlation and SGP is useful in topologies, such as mesh-torus, with good connectivity and a significant amount of traffic switching and mixing at the nodes

Optical control plane: theory and algorithms

In this thesis we propose a novel way to achieve global network information dissemination in which some wavelengths are reserved exclusively for global control information exchange. We study the routing and wavelength assignment problem for the special communication pattern of non-blocking all-to-all broadcast in WDM optical networks. We provide efficient solutions to reduce the number of wavelengths needed for non-blocking all-to-all broadcast, in the absence of wavelength converters, for network information dissemination. We adopt an approach in which we consider all nodes to be tap-and-continue capable thus studying lighttrees rather than lightpaths. To the best of our knowledge, this thesis is the first to consider “tap-and-continue” capable nodes in the context of conflict-free all-to-all broadcast. The problem of all to-all broadcast using individual lightpaths has been proven to be an NP-complete problem [6]. We provide optimal RWA solutions for conflict-free all-to-all broadcast for some particular cases of regular topologies, namely the ring, the torus and the hypercube. We make an important contribution on hypercube decomposition into edge-disjoint structures. We also present near-optimal polynomial-time solutions for the general case of arbitrary topologies. Furthermore, we apply for the first time the “cactus” representation of all minimum edge-cuts of graphs with arbitrary topologies to the problem of all-to-all broadcast in optical networks. Using this representation recursively we obtain near-optimal results for the number of wavelengths needed by the non-blocking all-to-all broadcast. The second part of this thesis focuses on the more practical case of multi-hop RWA for non- blocking all-to-all broadcast in the presence of Optical-Electrical-Optical conversion. We propose two simple but efficient multi-hop RWA models. In addition to reducing the number of wavelengths we also concentrate on reducing the number of optical receivers, another important optical resource. We analyze these models on the ring and the hypercube, as special cases of regular topologies. Lastly, we develop a good upper-bound on the number of wavelengths in the case of non-blocking multi-hop all-to-all broadcast on networks with arbitrary topologies and offer a heuristic algorithm to achieve it. We propose a novel network partitioning method based on “virtual perfect matching” for use in the RWA heuristic algorithm

Architecture and sparse placement of limited-wavelength converters for optical networks

Equipping all nodes of a large optical network with full conversion capability is prohibitively costly. To improve performance at reduced cost, sparse converter placement algorithms are used to select a subset of nodes for full-conversion deployment. Further cost reduction can be obtained by deploying only limited conversion capability in the selected nodes. We present a limited wavelength converter placement algorithm based on the k-minimum dominating set (k-MDS) concept. We propose three different cost-effective optical switch designs using the technologically feasible nontunable optical multiplexers. These three switch designs are flexible node sharing, strict node sharing, and static mapping. Compared to the full search heuristic of O(N-3) complexity based on ranking nodes by blocking percentages, our algorithm not only has a better time complexity O(RN2), where R is the number of disjoint sets provided by k-MIDS, but also avoids the local minimum problem. The performance benefit of our algorithm is demonstrated by network simulation with the U.S Long Haul topology having 28 nodes (91 is 5) and the National Science Foundation (NSF) network having 16 nodes (91 is 4). Our simulation considers the case when the traffic is not uniformly distributed between node pairs in the network using a weighted placement approach, referred to as k-WMDS. From the optical network management point of view, our results also show that the limited conversion capability can achieve performance very close to that of the full conversion capability, while not only decreasing the optical switch cost but also enhancing its fault tolerance

End-to-End Provisioning of Latency and Availability Constrained 5G Services

We address a key challenge of 5G networks by proposing a strategy for the resource-efficient and end-to-end allocation of compute and connectivity resources in a dynamic 5G service provisioning scenario, such that the service latency and availability requirements are guaranteed. Our heuristic algorithm shows that resource efficiency is significantly improved by processing services in the large core data centers (DCs) with a rich amount of compute resources and exploiting the benefits of traffic grooming over the metro and core fiber links. Moreover, our resource-efficient provisioning algorithm avoids possible violation of the service availability requirements caused by reaching the central DC locations by adding backup connectivity resources. Our simulation results demonstrate a resource efficiency improvement reflected by lowering the service blocking probability by up to four orders of magnitude compared to the conventional service provisioning methods utilizing distributed small DCs