Ming Xia

Green Provisioning for Optical WDM Networks

Since the Internet consumes a large (and increasing) amount of energy, “green” strategies are desirable to help service providers (SP) operate their networks and provision services more energy efficiently. We focus on green provisioning strategies for optical wavelength-division multiplexing networks. A number of approaches from component layer to network layer are discussed, which should help improve the energy efficiency of the networks. Then, we consider a typical optical backbone network architecture, and minimize the operational power for provisioning. Typically, operational power depends on strategy (e.g., optical bypass versus traffic grooming), operations (e.g., electronic domain versus optical domain), and route. We analyze the constituents of operational power in various scenarios, and discuss the opportunities for energy savings. We propose a novel auxiliary graph, which can capture the power consumption of each provisioning operation. Based on the auxiliary graph, we develop a power-aware provisioning scheme to minimize the total operational power. Performance evaluation shows that our scheme always needs the least operational power, with comparison to a direct-lightpath approach and a traffic-grooming approach. The result also suggests proportional power consumption by operations (network equipment) and end-node traffic grooming to fully exploit the power-saving potential of optical networks.

Greening the Optical Backbone Network: A Traffic Engineering Approach

Since telecom networks consume a large (and increasing) amount of energy, green strategies are desirable to help Service Providers (SP) operate their networks and provision services more energy-efficiently. In this study, we focus on operating optical backbone networks with green strategies. We consider a typical optical backbone network architecture, and minimize the Operational Power for service provisioning following a Traffic Engineering (TE) approach. Service provisioning is schematically decomposed as multiple serial operations, and power efficiency is analyzed for both optical bypass and traffic grooming. We propose a novel auxiliary graph, which can capture the flow of operations and their associated power. Based on the auxiliary graph, we present a Power-Aware scheme that minimizes the Operational Power. Simulation results show reduced power consumption by our scheme, in comparison to a generic traffic grooming approach.

Risk-aware provisioning for optical WDM mesh networks

A service-level agreement (SLA) typically specifies, among other metrics, the availability a service provider (SP) promises to a customer. In an optical wavelength division multiplexing (WDM) network, connection-oriented provisioning is commonly based on whether the paths statistical availability complies with the SLA-requested availability. Because of the stochastic nature of network failures, the actually provisioned availability over a specific time period is subject to uncertainty, and hence the SLA is usually at risk. We consider this uncertainty and study provisioning to minimize SLA violations. We show that the SLA Violation Risk is affected by a number of factors (e.g., failure profiles, availability target, and penalty period), and hence cannot simply be characterized by statistical path availability. We formulate the problem of risk-aware provisioning in WDM mesh networks, where path selection is dictated by SLA Violation Risk. In particular, we focus on devising an efficient scheme capable of computing path(s) that are likely to successfully accommodate the SLA-requested availability. A novel technique is applied to convert links with heterogeneous failure profiles to reference links that capture the main risk features in a relative manner. Based on the “reference link” concept, our Risk-Aware Provisioning scheme uses only limited failure information. We also extend our Risk-Aware Provisioning to use shared-path protection (SPP) for connections with strict availability requirements. We evaluate the performance and demonstrate the effectiveness of our schemes in terms of SLA violation ratio compared to the generic availability-aware approaches.

Service-Centric Provisioning in WDM Backbone Networks for the Future Internet

A service level agreement (SLA) is a formal contract between the service provider (SP) and the customer. Among various specifications, the SLA states an availability requirement and a penalty the SP pays if this requirement is violated. Traditional approaches to protection use a fixed deployment of backup resources, or do not consider the status of a service. As more heterogeneous applications use optical wavelength-division multiplexing (WDM) backbone network services of the future internet, these service-agnostic approaches are unable to accommodate the differentiated availability requirements. This results in substantial revenue loss either by refusing requests, or by accepting them and then violating their SLAs. In this paper, we propose and investigate the characteristics of a centralized control and management framework for service-aware, admission, and re-provisioning (SAR) in WDM backbone networks of the future internet. Our framework aggressively admits service requests, and dynamically reprovisions existing services by exploiting knowledge of their status. We first propose a GMPLS-based architecture and a revenue model for our analysis. Then we introduce a priority index, called urgency level (UL). An UL is assigned to an existing service indicating its status and relative importance, technically and economically. We reprovision resources by shifting them from low-UL services to provide backups for higher-UL services, which are more at risk of violating their SLAs or which have higher penalties. Our framework increases the revenue for the SP by creating more sales revenue and reducing potential penalties. Numerical results show improved performance in terms of 1) lower resource overbuild; 2) lower bandwidth blocking ratio; 3) higher SLA satisfaction ratio; 4) more balanced SLA violations; and 5) higher overall net revenue. Our framework is also shown to be effective for a range of failure models and penalty strategies.

Survivable Multipath Traffic Grooming in Telecom Mesh Networks With Inverse Multiplexing

We investigate the survivable traffic grooming problem with inverse multiplexing in telecommunication mesh networks employing next-generation SONET/SDH and WDM. With the support of virtual concatenation, a connection of any bandwidth can be provisioned as several subconnections (i.e., inverse multiplexed) over diverse paths. Therefore, it is important to efficiently groom and protect these low-speed subconnections onto high-capacity wavelength channels, considering the typical constraints. We propose and investigate the characteristics of survivable multipath traffic grooming with protection-at-connection and protection-at-lightpath levels for grooming connections with shared protection, subject to the constraints of the inverse-multiplexing factor, differential-delay constraint, and grooming ports. Since this problem is NP-complete, we propose effective heuristics using a novel analytical model. Our results show that (1) the network performance, in metrics of bandwidth blocking ratio and resource overbuild, can be notably improved by exploiting the inverse-multiplexing capability, (2) tight constraints have negative impact on performance, (3) protection-at-connection performs better in most cases of multipath provisioning when the constraints are not too tight, and (4) protection-at-lightpath achieves better performance when the number of grooming ports is moderate or small.

Migration from fixed grid to flexible grid in optical networks

Optical WDM backbone networks based on fixed spectrum grid have limitations such as low spectrum utilization and rigidity in provisioning for heterogeneous rates. Flexible-grid technologies can alleviate these limitations for on-demand provisioning. These technologies represent promising candidates for future optical networks supporting beyond-100-Gb/s signals. However, a one-time green-field deployment of flexible-grid technologies may not be practical, as the already-made investment in existing fixed-grid WDM networks needs to be preserved, and interruptions to ongoing services need to be minimized. Therefore, we envision that fixed-and flexible-grid technologies will coexist, which will bring the challenge of interoperating fixed-and flexible-grid equipment. It is also important to design the optimum migration strategy to maximize cost effectiveness and minimize service interruption. In this article, we discuss the key aspects of network architectures supporting coexistence of fixed and flexible grid technologies, and outline the challenges of network operations. We also propose and evaluate different migration strategies from fixed grid to flexible grid under different network scenarios.

A Multistate Multipath Provisioning Scheme for Differentiated Failures in Telecom Mesh Networks

Telecommunication networks spanning large areas are subject to various failures, such as natural disasters, operation errors, and malicious attacks. Disaster failures (DFs) are those, which can lead to a large-area malfunction and degrade the performance of a backbone telecom mesh network. A survivable network provisioning scheme that can recognize and address multiple levels of network failures, including DFs, is desirable for the future Internet. We study the characteristics of multiple failures in telecom mesh networks, such as optical wavelength-division-multiplexed (WDM) networks. In particular, we devise a novel provisioning scheme for telecom mesh networks, which can efficiently exploit the network connectivity using multiple paths. Three provisioning states are defined, in response to single-link failure (SF), multiple-link failure (MF), and DF. We integrate the conventional primary-backup method with reprovisioning and degraded service (i.e., a reduced level of service versus no service at all) into a state-transition model to handle different levels of failures. A predefined level of service is guaranteed for premium customers even if the service cannot be fully recovered. Multinode failures within the same shared risk group (SRG) and failures on destination node are also considered in our study. Our results show that: 1) connection-dropping probability due to a node failure can be significantly reduced with a small extra cost in SF protection; 2) for single-node failure, our algorithm achieves better performance than the shortest vertex-disjoint algorithm; and 3) remote-site data replication is effective to protect against destination-node failures.

A Novel SLA Framework for Time-Differentiated Resilience in Optical Mesh Networks

Telecom customers may have specific time periods during which they require extra resilience. However, these time-differentiated resilience requirements are not effectively addressed by current service level agreement (SLA) frameworks. To satisfy these high priority periods, a generic SLA framework typically provides upgraded protection over the entire service duration, which is unnecessary and expensive. In this study, we propose a novel SLA framework that allows customers to specify critical windows (CWs) to address their time-differentiated demands for resilience. CWs correspond to the resilience-sensitive periods, and connections are backed up during CWs using pre-cross-connected protection. To achieve high resource efficiency, we identify opportunities for backup resource sharing in a time-domain multiplexing manner. Two heuristic schemes are proposed, namely, Locally and Globally CW-Aware connection assignments. Our study on a sample optical mesh network shows that, by applying our SLA framework, 1) resource efficiency can be significantly improved, 2) CWs are effectively protected with high resilience (in terms of availability), 3) the availability of CWs can be increased almost linearly with used backup resources, and (4) our framework (approach) requires low operational complexity.

Risk-Aware Routing for Optical Transport Networks

A Service Level Agreement (SLA) typically specifies the availability a Service Provider (SP) promises to a customer. In an Optical Transport Network, finding a lightpath for a connection is commonly based on whether the availability of a lightpath availability complies with the connections SLA-requested availability. Because of the stochastic nature of network failures, the actual availability of a lightpath over a specific time period is subject to uncertainty, and the SLA is usually at risk. We consider the network uncertainty, and study routing to minimize the probability of SLA violation. First, we use a single-link model to study SLA Violation Risk (i.e., the probability of SLA violation) under different settings. We show that SLA Violation Risk may vary by paths and is affected by other factors (e.g., failure rate, connection holding time, etc.), and hence cannot be simply described by path availability. We then formulate the problem of risk-aware routing in mesh networks, in which routing decisions are dictated by SLA Violation Risk. In particular, we focus on devising a scheme capable of computing lightpath(s) that are likely to successfully accommodate a connections SLA-requested availability. A novel technique is applied to convert links with heterogeneous failure profiles to reference links which capture the main risk features in a relative manner. Based on the reference link concept, we present a polynomial Risk-Aware Routing scheme using only limited failure information. In addition, we extend our Risk-Aware Routing scheme to incorporate shared path protection (SPP) when protection is needed. We evaluate the performance and demonstrate the effectiveness of our schemes in terms of SLA violation ratio and, more generally, contrast them with the generic availability-aware approaches.

SLA-Aware Provisioning for Revenue Maximization in Telecom Mesh Networks

Service level agreement (SLA) is a contract between the service provider (SP) and the customer. Among various parameters, SLA imposes penalties on the SP when the customers quality-of-service (QoS) requirements are violated. Hence, it is desirable to avoid SLA violations and such penalties. SLA also states the maximum amount of downtime a connection may tolerate during its lifetime. In this study, we present a dynamic provisioning scheme called Preemption-Oriented SLA-Aware Provisioning (POSAP) for telecom mesh networks, which considers a connections (1) availability requirements, (2) penalty, and (3) state. In addition to the connections various parameters (availability, penalty, etc.), the amount of affordable downtime is used as a metric to determine the risk of violating the connections SLA, and hence, its priority. Connections priority is denoted by urgency level. Our scheme allows resource preemption among connections, i.e., high-priority connections may preempt backup resources from low-priority connections. Also, new connection requests may preempt resources from existing connections. Urgency level determines how resources can be preempted. Our scheme is applied to a US-wide network. Our results show the improved performance in terms of (1) reduced SLA violations, (2) increased network utilization, and (3) increased network revenue, compared to a dedicated primary-backup (P-B) scheme.