Synchronous Optical Network Ring Research Articles

Optimal Algorithms for Near-Hitless Network Restoration via Diversity Coding

Coding-based restoration techniques have proactive restoration which results in time savings over other state-of-the-art restoration techniques. Diversity coding is a coding-based recovery technique which offers near-hitless restoration with a competitive spare capacity requirement with respect to other techniques. In this paper, we show that diversity coding can achieve sub-ms restoration time. In addition, we develop two optimal algorithms for pre-provisioning of the static traffic and one for the dynamic provisioning of the traffic on-demand. There is one algorithm for systematic and one for non-systematic diversity coding in pre-provisioning. An MIP formulation and an ILP formulation are developed for systematic and non-systematic cases, respectively. The MIP formulation of the systematic diversity coding requires much fewer integer variables and constraints than similar optimal coding-based formulations. In dynamic provisioning, an ILP-based algorithm covers both of the systematic and non-systematic diversity coding. In all scenarios, diversity coding results in smaller restoration time, higher transmission integrity, and much reduced signaling complexity than the existing techniques in the literature. Simulation results indicate that diversity coding has significantly higher restoration speed than Shared Path Protection (SPP) and p-cycle techniques from the literature as well as Synchronous Optical Network (SONET) rings, which are commonly deployed by service providers today. In terms of capacity efficiency, it outperforms SONET rings and 1+1 APS, whereas it may require more extra capacity than the p-cycle technique and SPP. Diversity coding offers a preferable tradeoff which offers two orders of magnitude increase in restoration speed at the expense of less than 26% extra spare capacity.

Sonet Network Design Problems

This paper presents a new method and a constraint-based objective function to solve two problemsrelated to the design of optical telecommunication networks, namely the Synchronous Optical Net-work Ring Assignment Problem (SRAP) and the Intra-ring Synchronous Optical Network DesignProblem (IDP). These network topology problems can be represented as a graph partitioning withcapacity constraints as shown in previous works. We present here a new objective function and anew local search algorithm to solve these problems. Experiments conducted in C

A stochastic integer programming approach to solving a synchronous optical network ring design problem

AbstractWe develop stochastic integer programming techniques tailored toward solving a Synchronous Optical Network (SONET) ring design problem with uncertain demands. Our approach is based on an L‐shaped algorithm, whose (integer) master program prescribes a candidate network design, and whose (continuous) subproblems relay information regarding potential shortage penalty costs to the ring design decisions. This naive implementation performs very poorly due to two major problems: (1) the weakness of the master problem relaxations, and (2) the limited information passed to the master problem by the optimality cuts. Accordingly, we enforce certain necessary conditions regarding shortage penalty contributions to the objective function within the master problem, along with a corresponding set of valid inequalities that improves the solvability of the master problem. We also show how a nonlinear reformulation of the model can be used to capture an exponential number of optimality cuts generated by the linear model. We augment these techniques with a powerful upper‐bounding heuristic to further accelerate the convergence of the algorithm, and demonstrate the effectiveness of our methodologies on a test bed of randomly generated stochastic SONET instances. © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 44(1), 12–26 2004

Graph decompositions with application to wavelength add-drop multiplexing for minimizing SONET ADMs

In a synchronous optical network ring, assignment of source-to-destination circuits to wavelengths must respect traffic requirements and minimize both the number of wavelengths and the amount of terminal conversion equipment. When traffic requirements are approximately equal on all source–destination circuits, the assignment can be modeled as a graph decomposition problem. In this setting, techniques from combinatorial design theory can be applied. These techniques are introduced in a simpler form when every source–destination circuit requires one quarter of a wavelength. More sophisticated design-theoretic methods are then developed to produce the required decompositions for all sufficiently large ring sizes, when each source–destination circuit requires one eighth of a wavelength.

A polynomial time approximation scheme for the SONET ring loading problem

A rapidly emerging design paradigm for large-scale optical fiber networks involves connecting clusters of nodes through a synchronous optical network (SONET) ring and building a network over these rings. Although the fiber itself offers virtually unlimited bandwidth, the add/drop multiplexers (ADMs) determine the actual bandwidth available along any edge of the SONET ring. Consequently, there is a cost involved in supporting a high bandwidth along the ring. An important optimization problem arises in this context: Given a set of nodes connected along a bidirectional SONET ring, we must determine a routing scheme that minimizes the bandwidth required to satisfy all the pairwise traffic demands. This problem, known as the ring loading problem, has been studied extensively in recent years. S. Cosares and I. Saniee reported in Telecommunications Systems (Volume 3, 1994) that this problem is NP-hard, which makes it unlikely that a polynomial time algorithm exists to compute an optimal solution. We therefore shift our attention to polynomial time approximation algorithms. Towards this end, Cosares and Saniee presented a polynomial time algorithm that approximates the optimal solution value to within a multiplicative factor of two. More recently, A. Schrijver, P. Seymour, and P. Winkler developed an efficient algorithm (documented in the SIAM Journal of Discrete Mathematics, 1997) that can compute a solution that exceeds the optimum by at most an additive term of 1.5d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> , where d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> is the largest traffic demand between any pair of nodes. While this additive term is relatively small, in many input instances it would represent a significant fraction of the optimal solution value and possibly a significant deviation from it. Is there a polynomial time approximation algorithm that allows us to achieve an error that is an arbitrarily small fraction of the optimal solution value? In this paper, we answer this question in the affirmative. More precisely, building on the work of Schrijver, Seymour, and Winkler, we show that for any fixed ɛ > 0, there exists a polynomial time algorithm that computes a solution that requires bandwidth at most (1 + ɛ) times the optimal bandwidth.

Future WAN architecture driven by services, traffic volume, and technology trends

Wide area networks (WANs) today involve protocol and topological hierarchies. Protocol hierarchy involves Internet protocol (IP), asynchronous transfer mode (ATM), synchronous optical network (SONET), and dense wavelength division multiplexing (DWDM). Self-healing SONET rings provide very fast restoration, and DWDM allows the creation of multiple wavelengths (“virtual fibers”) from a single optical fiber, providing ever-increasing capacity to the SONET layer. Topological hierarchy involves edge nodes and core nodes for IP, ATM, and SONET. It provides traffic aggregation and statistical multiplexing, takes advantage of transport bandwidth and economy of size of packet/cell switches, and allows easier operations. A confluence of factors, however, is driving changes in this network architecture. Explosive growth in traffic volume and emergence of true multiwavelength, multiservice optical networks will make flatter (more heavily meshed) service networks supported by an optical core network more economical in the future. In this paper, we discuss the factors driving this shift in the network architecture, quantify its cost advantage, describe its impact on the requirements for network elements comprising the optical transport network (OTN) and the service network, and discuss new management/control paradigms as well as opportunities for new revenue-generating services resulting from the new architecture.

Topological network design for SONET ring architecture

Service restoration and survivability have become increasingly important in telecommunications network planning with the introduction of fiber-optic high-speed networks. Synchronous optical network (SONET) technology promotes the use of interconnected rings in designing reliable networks. We describe a heuristic approach for designing networks comprised of interconnected rings. Our approach is particularly attractive for relatively sparse networks in which the set of all cycles (constituting the potential rings) can be determined at a reasonable computational effort. Most networks fall into this category. Given a set of nodes, with demand among all possible node-pairs, and a set of available links that connect the nodes, the problem is to select an optimal subset of rings, utilizing only allowable links, such that each node is included in at least one ring and each ring is connected to at least one other ring at two or more nodes. Such a multiple ring network ensures instantaneous restoration of service in case of a single link or node failure. We first generate a large set of candidate rings and approximate the cost of each ring based on the nodes that are served by the ring and based on the demands. We then apply a set covering algorithm that selects a (minimum cost) subset of the candidate rings such that each node is included on at least one ring. Finally, we select a few additional rings in order to achieve the required connectivity among the rings. We present computational results for realistic-size (e.g., 500 nodes) telecommunication networks.

Clustering for the Design of SONET Rings in Interoffice Telecommunications

Optical fiber systems play an essential role in today's telecommunications networks. The recently standardized SONET (Synchronous Optical Network) technology has made rings the preferred architecture for designing survivable networks. The network design problem is very complex in nature, because it involves not only the configuration of rings at the logical level, but also the mapping of this configuration into physical fiber paths. This paper deals with the problem of finding optimal clusters of offices, which can be used as the basis for designing logical rings. A mathematical model of the problem is presented, and a heuristic solution based on the tabu search framework is developed to find optimal or near-optimal solutions.

Survivable SONET networks—design methodology

A prototype software system that implements a methodology for the strategic planning of survivable interoffice networks is presented. The software system determines strategic locations and ring types for synchronous optical network ring placement. Two types of survivable network architectures are considered/spl mdash/1:1 diverse protection and SONET self-healing rings. The software considers three types of SONET self-healing rings/spl mdash/unidirectional, 2-fiber bidirectional, and 4-fiber bidirectional. Hubbing is assumed in all architectures. Inputs include nodes, links, connectivity, facility hierarchy, and multiyear point-to-point demands, together with the costs of fiber material and splicing, route mileage (installation), and multiplexors and regenerators of different rates. The outputs are a set of near-optimal rings based on cost, specifying the ring types and rates, fiber span sizes and counts, regenerator locations and speeds, the topology (set of links to be used), and the network cost. In addition, the software outputs the time in the planning period that each ring and fiber span should be installed. >

SONET implementation

The status of the synchronous optical network (SONET) infrastructure development and deployment are examined to see whether or not they meet original expectations. Issues arising from deployment, such as the use of new features and the necessary support from operations systems, and future directions of SONET are discussed. These future trends include digital cross connect systems (DCSs), SONET ring architectures, and hybrid ring-DCS networks. New SONET services are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Planning and deploying a SONET-based metro network

It is demonstrated that metropolitan networks can be analyzed to develop an architectural strategy that provides both cost-effective bandwidth management and survivability. The planning and deployment considerations, methodologies, and planning tools are discussed. An example of a planned synchronous optical network (SONET) metropolitan network, including the transition from an asynchronous network, is presented. It is shown that the most effective deployment strategy for SONET is built around an infrastructure of survivable SONET rings and automated facility management based on a combination of SONET cross-connects and distributed bandwidth management in SONET ring terminals. This SONET infrastructure will provide the framework for the predicted expansion in communications services, and will meet expanding telecommunication needs. >

SONET ring applications for survivable fiber loop networks

Synchronous optical network (SONET) self-healing rings (SHR) are studied in the loop environment. SONET SHR architectures for loop feeder networks are discussed, focusing on three possible dual central office (CO) architectures for fiber loop networks, using SONET SHRs to reduce network costs and provide network service survivability. These architectures reflect an integrated planning concept for SONET networks that eliminates the boundary between the access network and the inter-office network. It is shown that the use of SONET SHRs makes it easy to evolve to a protected dual CO access architecture. Economic and survivability studies are discussed. The economic studies show that using the ring approach yields significant advantages over the traditional diverse protection approach in terms of cost and survivability, especially for the dual CO architectures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>