Weiyi Zhang

A biased random-key genetic algorithm for wireless backhaul network design

Graphical abstractDisplay Omitted HighlightsWe propose a novel network design problem for wireless backhaul networks.Its objective function is computed using the value of the maximum flow and network costs.We propose a BRKGA and a mixed integer linear programming model (MIP) to solve it.We assess the great performance of BRKGA over 30 large real-world instances. This paper describes a biased random-key genetic algorithm for a real-world wireless backhaul network design problem. This is a novel problem, closely related to variants of the Steiner tree problem and the facility location problem. Given a parameter h, we want to build a forest where each tree has at most h hops from the demand nodes, where traffic originates, to the root nodes where each tree is rooted. Candidate Steiner nodes do not have any demand but represent locations where we can install cellsites to cover the traffic and equipment to backhaul the traffic to the cellular core network. Each Steiner node can cover demand nodes within a given distance, subject to a capacity constraint. The aggregate set of constraints may make it impossible to cover or backhaul all demands. A revenue function computes the revenue associated with the total amount of traffic covered and backhauled to the root nodes. The objective of the problem is to build a forest that maximizes the difference between the total revenue and the cost associated with the installed equipment. Although we will have a forest when we consider only the backhaul links and root nodes, the addition of demand vertices can induce undirected cycles, resulting in a directed acyclic graph. We consider instances of this problem with several additional constraints that are motivated by the requirements of real-world telecommunication networks.

Asymmetric optical connections for improved network efficiency

Links in an IP network are unidirectional but currently are routed over bidirectional optical circuits with identical A → Z and Z → A capacities. Potentially there could be savings if the two directions of an optical circuit could be treated independently. In this study of possible savings, we have quantified the asymmetry of traffic on a current large IP backbone. A theoretical greenfield network with similarly asymmetric traffic is modeled, and it is shown that the use of unidirectional circuits to satisfy traffic demands provides significant equipment savings. We consider this study of the benefits of this approach to be a first step in deciding whether it makes economic sense to tackle the hurdles that would face such a major change in network design and operations.

On concentrating regenerator sites in ROADM networks

Concentrating optical regenerators in a subset of nodes provides significant savings. We present a heuristic for choosing this subset. In the studied cases our results have 1 or 2 more sites than the minimum.

Constraint routing and regenerator site concentration in ROADM networks

Advances in the development of colorless and nondirectional reconfigurable optical add-drop multiplexers (ROADMs) enable flexible predeployment of optoelectronic regenerators (reshaping, retiming, and reamplifying known as 3R) in future optical networks. Compared to the current practice of installing a regenerator only when a circuit needs them, predeployment of regenerators in specific sites will allow service providers to achieve rapid provisioning such as bandwidth-on-demand service and fast restoration. Concentrating the predeployment of regenerators in a subset of ROADM sites will achieve high utilization and reduces the network operational costs. We prove the resulting optimization problem is NP-hard and provide the proof. We present an efficient heuristic for this problem that takes into account both the cost of individual circuits (regenerator cost and transmission line system cost) and the number of regenerator sites. We validate our heuristic approach with integer linear programming (ILP) formulations for a small network. Using specific network examples, we show that our heuristic has near-optimal performance under most studied scenarios and cost models. We further enhance the heuristic to incorporate the probability of demand for each circuit. This enables a reduction in the number of regenerator sites by allowing circuits to use costlier paths if they have lower probability of being needed. We also evaluate the heuristic to determine the extra regenerator sites required to support diverse routing. In this paper, we provide detailed analysis, pseudocodes, and proofs for the models presented in our previous work [Nat. Fiber Optic Engineers Conf., 2012, NW3F.6; 9th Int. Conf. on Design of Reliable Communication Networks (DRCN), 2013, 139] and compare the heuristic results with ILP for a small-scale network topology.

Leveraging SDN to streamline metro network operations

The confluence of two recent technological trends - the maturation of ROADM technology and the rise of SDN - has produced the perfect opportunity to streamline carrier metro network operations through the use of automation. This article introduces readers to the carrier metro network and describes the challenges of automating carrier metro network operations. To this end, we illustrate both the inherent complexity of todays metro network and the legacy processes that have been put in place to manage this complexity. Our discussion covers the essential details regarding current practices in metro network operation, and touches on the economic and technical factors that have contributed to these processes remaining in place for so long. We explain how the application of lean methodology can streamline and automate metro network processes - enabling carriers to reduce work in progress, thereby simultaneously decreasing both operational expenditures and time to market.

Evolution of the IP-over-Optical Core network

We explore alternative architectures to reduce cost of IP-over-Optical Core networks. We conducted a detailed cost study of three architectures. We start with a Baseline architecture that captures present mode of operations (PMO) with future traffic projections and utilizes technologies such as Ethernet line-cards (LCs) and OTN sub-wavelength switching. The next architecture, Streamlined, replaces the hub-and-spoke topology of Baseline with a flat topology and is also more judicious in its restoration design. Our detailed study shows significant cost savings for the Streamlined architecture compared to the Baseline. We reduce the cost further in our third proposed architecture: Ethernet Enabled IP core (EEIPC) consisting of OTN switches (with and without packet switching) and without any backbone routers or MPLS switches. Our results also demonstrate that we can achieve significant reduction in switching costs but reducing cost of transport remains a significant challenge.

Cost Comparison of Alternative Architectures for IP-over-Optical Core Networks

AbstractWe explore alternative architectures to reduce cost of IP-over-optical core networks. We conducted a detailed cost study of three architectures. We start with a Baseline architecture that captures present mode of operations with future traffic projections and utilizes technologies nsuch as Ethernet line-cards and OTN sub-wavelength switching. nThe next architecture, Streamlined, replaces the hub-and-spoke topology of Baseline with a flat topology and is also more judicious in its restoration design. Our detailed study shows significant cost savings for the Streamlined architecture compared to the Baseline. nWe reduce the cost further in our third proposed architecture: Ethernet enabled IP core consisting of OTN switches (with and without packet switching) and without any backbone routers or MPLS switches. Our results also demonstrate that we can achieve significant reduction in switching costs but reducing cost of transport remains a significant challenge. This paper is an extended version of our previous work published in (11th international conference on the design of reliable communication networks (DRCN), pp 227–234, 2015).

Asymmetric optical connections for improved network efficiency: Erratum

An error in a recent paper is corrected. Elements in a figure were improperly labeled; a revised figure is provided.