Avishek Nag

Optical Network Design With Mixed Line Rates and Multiple Modulation Formats

With the growth of traffic volume and the emergence of various new applications, future telecom networks are expected to be increasingly heterogeneous with respect to applications supported and underlying technologies employed. To address this heterogeneity, it may be most cost effective to set up different lightpaths at different bit rates in such a backbone telecom mesh network employing optical wavelength-division multiplexing. This approach can be cost effective because low-bit-rate services will need less grooming (i.e., less multiplexing with other low-bit-rate services onto high-capacity wavelengths), while a high-bit-rate service can be accommodated directly on a wavelength itself. Optical networks with mixed line rates (MLRs), e.g., 10/40/100 Gb/s over different wavelength channels, are a new networking paradigm. The unregenerated reach of a lightpath depends on its line rate. So, the assignment of a line rate to a lightpath is a tradeoff between its capacity and transparent reach. Thus, based on their signal-quality constraints (threshold bit error rate), intelligent assignment of line rates to lightpaths can minimize the need for signal regeneration. This constraint on the transparent reach based on threshold signal quality can be relaxed by employing more advanced modulation formats, but with more investment. We propose a design method for MLR optical networks with transceivers employing different modulation formats. Our results demonstrate the tradeoff between a transceivers cost and its optical reach in overall network design.

On the Design of Energy-Efficient Mixed-Line-Rate (MLR) Optical Networks

With increasing energy consumption of the Internet, it is now imperative to design energy-efficient network architectures and protocols. Optical technologies have significant promise in improving the energy efficiency of network infrastructures. Future optical backbone networks will be heterogeneous in nature where a single link may carry various line-rate signals. This mixed-line-rate (MLR) network architecture is shown to be cost effective in satisfying heterogeneous traffic demands. In this study, we present mathematical models that can act as references for designing energy- and cost-efficient MLR optical networks. We also perform a comparative study of the energy efficiency of MLR and special cases of MLR design, named as single-line-rate networks (where all the links have same line rates). We explore the scenarios where the MLR networks minimize energy consumption. Finally, we investigate the relationship between energy-minimized and cost-minimized MLR network design.

Computing for rural empowerment: enabled by last-mile telecommunications

Increasing economic and educational exposure, and promotion of global health and wellness can be achieved through the power of sharing knowledge, technology, and resources. ICT can play a key role in disseminating such knowledge across the world. But a digital divide exists between urban and rural/remote areas, which results in economic and social disparities across regions. Developing last-mile telecommunication technologies for rural/remote areas is a crucial aspect in providing computing and ICT services that can integrate millions of stakeholders in rural/remote areas globally into the digital age, particularly with the advent of cloud computing. This article focuses on the different aspects of providing last-mile rural telecommunication access such as interfering factors, technology options, and deployment trends. This article aims to guide service providers, industry practitioners, and local entrepreneurs with a technology-and-deployment-trend analysis to choose, deploy, and operate suitable telecommunication networks depending on the unique features of the rural/remote area. Our goal is to bring attention to accessible and affordable technologies with practical considerations.

Optical network design with mixed line rates and multiple modulation formats

We propose a design method for mixed-line-rate (MLR) optical networks with transceivers employing different modulation formats. Our results demonstrate the tradeoff between a transceivers cost and its optical reach in overall network design.

Transparent optical network design with mixed line rates

Future telecommunication networks are expected to be increasingly heterogeneous and support a wide variety of traffic demands. Based on the nature of the demands, it may be convenient to set up lightpaths with different bit rates. Then, the network design cost could be reduced because low-bit-rate services will need less grooming (i.e., less multiplexing with other low-bit-rate services onto high-capacity wavelengths) while high-bit-rate services can be accommodated on a wavelength itself. Future optical networks may support mixed line rates (say over 10/40/100 Gbps). Since a lightpath may travel a long distance, for high bit rates, the effect of the physical impairments along a lightpath may become very significant (leading to high bit-error rate (BER)); and the signals maximum transmission range, which depends on the bit rate, will become limited. In this study, we propose a novel, cost-effective approach to design a mixed-line-rate (MLR) network with transmission-range (TR) constraint. By intelligent assignment of channel rates to lightpaths, based on their TR constraint, the need for signal regeneration can be minimized, and a ldquotransparentrdquo optical network can be designed to support all-optical end-to-end lightpaths. The design problem is formulated as an integer linear program (ILP). Our results show that, with mixed line rates and maximum transmission range constraints, one can design a cost-effective network.

Energy-efficient and cost-efficient capacity upgrade in mixed-line-rate optical networks

Traffic in telecom networks is increasing rapidly, and it has been a challenging task to plan and upgrade network capacities for this increasing traffic, keeping the cost of resources within a targeted budget. Besides handling this drastic growth in traffic, future optical networks are also expected to be increasingly heterogeneous with respect to services supported and underlying technologies employed. To support this heterogeneous volume of traffic, mixed-line-rate (MLR) optical networks with line rates of 10, 40, and 100 Gbps have been shown to be effective. In the case of a greenfield network design, i.e., when planning capacities for a new network, MLR networks have been shown to be cost efficient as well as energy efficient in some recent studies. The concept of an MLR network is evolutionary, starting from a 10G single-line-rate network to a coexistence of multiple line rates in the same network as capacities on some links are periodically upgraded from 10G per wavelength to 40G and 100G per wavelength with traffic growth. Therefore, from a network-upgrade perspective, an important issue is to devise a cost-optimized migration strategy from 10G to 40G to 100G and beyond, given a traffic growth model. However, energy consumption in different elements in the network, especially in those elements whose energy consumption depends on the bandwidth of the traffic that they are handling, is also an important parameter to consider. Therefore, the ultimate question is: Can an MLR be a good candidate for energy-efficient and cost-efficient upgrade? In this study, we investigate the energy-efficient and cost-efficient MLR network-upgrade problem. In this context, we also study the effect of network connection disruption on energy-efficient and cost-efficient MLR network upgrade. In general, the service providers aim would be to have as few disruptions as possible during capacity upgrade, as disruptions may induce service degradation. Our results show that the amount of disruptions has a conflicting effect on energy-efficient and cost-efficient upgrade in MLR networks, and we develop an optimized upgrade strategy so that both cost and energy are kept within a certain limit.

Transparent vs. translucent optical network design with mixed line rates

We propose new design models for mixed-line-rate (MLR) optical networks with no regeneration (transparent) and selective regeneration (translucent). Our results show the interplay between transponder cost and regenerator card cost using mixed line rates.

Robust Design of Spectrum-Efficient Green Optical Backbone Networks

We propose an orthogonal frequency division multiplexing (OFDM) based optical network design focussing on minimizing the total power consumption of the network to make the network green. OFDM is a promising technology for next-generation optical networks to support high capacity and heterogeneity in network traffic by having flexible bandwidth allocation per wavelength. Another paradigm for supporting traffic heterogeneity and high bandwidth demands is mixed-line-rate (MLR) networks where wavelengths can have discrete capacities of 10/40/100 Gbps which are single carrier based. In this study, we compare the energy efficiency of an OFDM-based network versus a MLR network. We formulate mixed integer linear program (MILP) models to design energy-efficient MLR and OFDM-based networks with two scenarios: (1) with fixed average traffic per source-destination pair of the network, and (2) with uncertainties in the traffic that an actual network may have. For scenario (2), we employ a robust optimization technique which is called τ-robust optimization. Our results show that OFDM outperforms MLR in terms of energy efficiency especially when the traffic in the network takes random peaks in some of the links.

Mixed-line-rate optical network design with wavebanding

Abstract To cope with ever increasing and more heterogeneous traffic demands, today’s optical backbone networks are expected to support mixed line rates (MLR) over different wavelength channels. MLR networks can be designed to provide flexible rate assignments to low-bit-rate services and high-bit-rate services in a cost-effective manner. But with increasing number of wavelengths in the network, aggregating wavelengths into wavebands can further reduce the network cost. In this study, we incorporate the idea of waveband switching in MLR network design. Wavebanding or grouping of optical paths reduces the optical switch size at the optical cross-connects (OXCs). When several lightpaths share several common links, they can be grouped together and routed as a single waveband. For optical bypass at a transit node, only two optical ports are required for each waveband, hence reducing the port cost. It can be a challenge for an MLR network to waveband wavelengths of different line rates that have different transmission reaches. In our design, we present a suitable switching architecture and propose an efficient and cost-effective approach for wavebanding in an MLR network. The design problem is formulated as a mixed integer linear program (MILP) where the objective is to minimize transponder cost and port cost. A heuristic algorithm for wavebanding in MLR networks is provided. To further optimize our solution, we also present a Simulated Annealing algorithm for wavebanding. Our results show a significant improvement in cost savings compared to single-line-rate (SLR) networks with wavebanding and an MLR network employing only wavelength switching.

On Spectrum-Efficient Green Optical Backbone Networks

We propose an orthogonal frequency division multiplexing (OFDM) based backbone optical network design. We focus on minimizing the total energy consumption of the network i.e., to make the network green. OFDM is a promising technology for next- generation optical networks with per-wavelength capacities higher than or equal to 100 Gbps. In addition, it can support heterogeneity in network traffic by having flexible bandwidth allocation per wavelength. The flexibility comes through the multiple subcarriers in an OFDM signal which can be modulated with the client data signals. Another paradigm for supporting traffic heterogeneity and high bandwidth demands is mixed-line-rate (MLR) networks where wavelengths can have discrete capacities of 10/40/100 Gbps which are single carrier based. In this study, we compare the energy efficiency of an OFDM-based network versus a MLR network. Our results show that OFDM outperforms MLR in terms of energy efficiency.