Ajmal Muhammad

Energy-Efficient WDM Network Planning with Dedicated Protection Resources in Sleep Mode

Energy-efficient optical networks are gaining momentum as environmental-friendly solutions with reduced operational costs. Energy-efficiency can be achieved by using devices in sleep mode, i.e., a low-power, inactive state in which devices can be suddenly waken-up upon occurrence of triggering events. This paper advocates a sleep mode option for the optical devices (e.g., amplifiers, optical switches) installed for protection purposes only. These devices can be put in sleep mode to reduce the network power consumption, but they can be promptly waken up (if necessary) upon a failure occurrence. This principle is proposed and applied in Wavelength Division Multiplexing (WDM) networks with dedicated-path protection to ensure survivability against single-link failures. The main contribution of the paper is the definition of the energy-efficient network planning problem for resilient WDM networks where optical devices can be configured in sleep mode. Optimal results of the integer linear programming (ILP) problem show savings of up to 25% in the overall power consumption.

Energy-efficient lightpath provisioning in a static WDM network with dedicated path protection

The interest in the energy consumption of communication networks has risen in the recent years. In an effort to tackle this problem, several approaches have been presented to reduce the power consumed by the entire network infrastructure, including optical transport. Most of the solutions studied and proposed in the literature, however, pay little or no attention to the power consumed to ensure the resiliency of the overall network.

Resource Allocation for Space-Division Multiplexing: Optical White Box Versus Optical Black Box Networking

Elastic optical networking (EON) with space-division multiplexing (SDM) is the only evident long-term solution to the capacity needs of the future networks. The introduction of space via spatial fibers, such as multicore fibers (MCF) to EON provides an additional dimension as well as challenges to the network planning and resource optimization problem. There are various types of technologies for SDM transmission medium, switching, and amplification; each of them induces different capabilities and constraints on the network. For example, employing MCF as the transmission medium for SDM mitigates the spectrum continuity constraint of the routing and spectrum allocation problem for EON. In fact, cores can be switched freely on different links during routing of the network traffic. On the other hand, intercore crosstalk should be taken into account while solving the resource allocation problem. In the framework of switching for elastic SDM network, the programmable architecture on demand (AoD) node (optical white box) can provide a more scalable solution with respect to the hard-wired reconfigurable optical add/drop multiplexers (ROADMs) (optical black box). This study looks into the routing, modulation, spectrum, and core allocation (RMSCA) problem for weakly-coupled MCF-based elastic SDM networks implemented through AoDs and static ROADMs. The proposed RMSCA strategies integrate the spectrum resource allocation, switching resource deployment, and physical layer impairment in terms of intercore crosstalk through a multiobjective cost function. The presented strategies perform a cross-layer optimization between the network and physical layers to compute the actual intercore crosstalk for the candidate resource solutions and are specifically tailored to fit the type of optical node deployed in the network. The aim of all these strategies is to jointly optimize the switching and spectrum resource efficiency when provisioning demands with diverse capacity requirements. Extensive simulation results demonstrate that 1) by exploiting the dense intranodal connectivity of the ROADM-based SDM network, resource efficiency and provisioned traffic volume improve significantly related to the AoD-based solution, 2) the intercore crosstalk aware strategies improve substantially the provisioned traffic volume for the AoD-based SDM network, and 3) the switching modules grows very gently for the network designed with AoD nodes related to the one with ROADMs as the traffic increases, qualifying AoD as a scalable and cost-efficient choice for future SDM networks.

Introducing flexible and synthetic optical networking: planning and operation based on network function programmable ROADMs

Elastic optical networks are envisaged as promising solutions to fulfill the diverse bandwidth requirements for the emerging heterogeneous network applications. To support flexible allocation of spectrum resources the optical network nodes need to be agile. Among the different proposed solutions for elastic nodes, the one based on architecture of demand (AoD) exhibits considerable flexibility against the other alternatives. The node modules in the case of AoD are not hard-wired, but can be connected/disconnected to any input/output port according to the requirements. Thus, each AoD node and the network (fabricated with AoD nodes) as a whole acts like an optical field-programmable gate array. This flexibility inherent in AoD can be exploited for different purposes, such as for cost-efficient and energy-efficient design of the networks. This study looks into the cost-efficient network planning issue for synthetic networks implemented through AoD nodes. The problem is formalized as an integer linear programming formulation for presenting the optimal solution. Furthermore, a scalable and effective heuristic algorithm is proposed for cost-efficient design, and its performance is compared with the optimal solution. The designed networks with AoD nodes are further investigated for a dynamic scenario, and their blocking probability due to limited switching resources in the nodes is examined. To alleviate the blocking performance for the dynamic case, an efficient synthesis strategy along with a scheme for optimal placement of switching resources within the network nodes is presented. Extensive results show that 1) even at high loads, the network with AoD nodes achieves saving of switching modules up to 40% compared to the one with static reconfigurable optical add- drop multiplexers (ROADMs) through a proper network design, 2) by diminishing the spectrum selective switches the overall power consumption of the network decreases by more than 25% for high loads, and 3) for the dynamic scenario the blocking owing to the node modules constraint is alleviated significantly by slightly augmenting the switching devices and optimally deploying them within the network nodes.

Flexible and Synthetic SDM Networks with Multi-core-Fibers Implemented by Programmable ROADMs

This study looks into network planning issues for synthetic MCF-based SDM networks implemented through programmable ROADMs. The results show that significant savings in switching modules and energy can be attained by exploiting the flexibility inherent in programmable ROADM through a proper network design.

Routing and Spectrum Assignment in Elastic Filterless Optical Networks

Elastic optical networking is considered a promising candidate to improve the spectral efficiency of optical networks. One of the most important planning challenges of elastic optical networks is the NP-hard routing and spectrum assignment (RSA) problem. In this paper, we investigate offline RSA in elastic filterless optical networks, which use a passive broadcast-and-select architecture to offer network agility. Here, an elastic optical network is referred to as the optical network that can adapt the channel bandwidth, data rate, and transmission format for each traffic demand in order to offer maximum throughput. In elastic filterless networks, the presence of unfiltered signals resulting from the drop-and-continue node architecture must be considered as an additional constraint in the RSA problem. In this paper, first, the RSA problem in elastic filterless networks is formulated by using an integer linear program to obtain optimal solutions for small networks. Due to the problem complexity, two efficient RSA heuristics are also proposed to achieve suboptimal solutions for larger networks in reasonable time. Simulation results show that significant bandwidth savings in elastic filterless networks can be achieved compared with the fixed-grid filterless solutions. The proposed approach is further tested in multi-period traffic scenarios and combined with periodical spectrum defragmentation, leading to additional improvement in spectrum utilization of elastic filterless optical networks.

Effect of delay tolerance in WDM networks with differentiated services

We study a dynamic WDM network supporting different service classes (SC) containing applications having similar setup delay tolerance. By utilizing delay tolerance we propose scheduling strategies able to significantly reduce blocking probability of each SC.

Impairment-aware dynamic provisioning in WDM networks with set-up delay tolerance and holding-time awareness

We study a dynamic WDM network with nonideal components in the physical layer which uses an impairment-aware routing and wavelength (RWA) algorithm for connection provisioning. We investigate the reduction in blocking probability (BP) by utilizing service Level Agreement (SLA) metric i.e. setup delay tolerance during connection provisioning. Furthermore, we explore the improvement in the network performance by efficiently utilizing the knowledge of the connections holding-time, another metric of SLA. Keeping in mind that BP reduction can be obtained by set-up delay tolerance [1] our focus is to investigate how set-up delay tolerance combined with holding-time awareness can improve BP performance caused by physical impairment. Our simulation results confirm that significant improvement can be achieved by holding-time aware connection provisioning compared to the unaware holding-time case. Moreover as expected, set-up delay tolerance can reduce BP even without knowledge of connections holding-time.

Reliability differentiation in energy efficient optical networks with shared path protection

Energy and resource efficiency are two contrasting objectives to optimize in dynamic and survivable optical networks. Known solutions for improving the energy efficiency include the use of the shared path-protection (SPP) mechanism and of a low power consuming mode (i.e., sleep) for protection resources. On the other hand, resource efficiency can be improved by introducing the concept of Differentiated Reliability (DiR) which can be combined with SPP in order to match the level of provisioned protection resources to the reliability requirements for each specific demand. This paper assesses the energy efficiency of the DiR concept combined with SPP and sleep mode support. A multi-objective optimization algorithm is proposed with the intent of jointly optimizing the energy and resource efficiency when dynamically establishing lightpaths with specific reliability levels. Simulation results show that when the proposed multi-objective cost function is properly tuned, not only the SPP-based DiR approach reduces the blocking probability but it is also able to save power for any network load. By enabling sleep mode additional power savings can be achieved at low loads, leading to an overall saving of up to 25%.

Service differentiated provisioning in dynamic WDM networks based on set-up delay tolerance

Optical networks are expected to provide a unified platform for a diverse set of emerging applications (three-dimensional TV, digital cinema, e-health, grid computing, etc). The service differentiation will be an essential feature of these networks. Considering the fact that users have different levels of patience for different network applications, referred to as set-up delay tolerance, it will be one of the key parameters for service differentiation. Service differentiation based on set-up delay tolerance will not only enable network users to select an appropriate service class (SC) in compliance with their requirements, but will also provide an opportunity to optimize the network resource provisioning by exploiting this information, resulting in an improvement in the overall performance. Improvement in network performance can be further enhanced by exploiting the connection holding-time awareness. However, when multiple classes of service with different set-up delay tolerances are competing for network resources, the connection requests belonging to SCs with higher set-up delay tolerance have better chances to grab the resources and leave less room for the others, resulting in degradation in the blocking performance of less patient customers. This study proposes different scheduling strategies for promoting the requests belonging to smaller set-up delay tolerance SCs, such as giving priority, reserving some fraction of available resources, and augmenting the research space by providing some extra paths. Extensive simulation results show that 1) priority in the rescheduling queue is not always sufficient for eradicating the degradation effect of high delay tolerant SCs on the provisioning rate of the most stringent SC, and 2) by utilizing the proposed strategies, resource efficiency and overall network blocking performance improve significantly in all SCs.