Mixed Line Rate Research Articles

Investigation of launch power and regenerator placement effect on the design of mixed-line-rate (MLR) optical WDM networks

In recent years, owing to the consistent increase in volume and heterogeneity of the traffic, telecommunication networks have undergone significant innovations. Existing studies have shown that, by adopting a mixed-line-rate (MLR) strategy, wavelength division multiplexed (WDM) optical networks can cost-effectively respond to the diverse variety of traffic requirements which have heterogeneous service demands. However, due to the existence of physical layer impairments [specifically cross-phase modulation (XPM)], adjacent channels on different line rates may exhibit serious degradation of signal quality and optical reach. In such cases, launch power governs the bit-error rate as it affects both the signal and the noise power due to XPM. Therefore, an intelligent choice of launch power on different line rates can significantly reduce the network cost. Further, in MLR optical networks, trade-off between regenerator placement and the launch power attains importance and needs to be addressed. In this work, we investigate the launch power and regenerator placement effect on the design of a MLR WDM optical network. The obtained simulation results show that the network cost is (i) mainly controlled by power values of the 10/100/400 Gbps channels, and (ii) decreases for a cost model in which, compared to 10 G transponders, high-bit-rate transponders have higher cost decay. Further, with a lower cost model, it is found that more numbers of regenerators can be deployed, simultaneously minimizing the network cost.

Spectral, cost and energy efficiencies analysis in WDM MLR networks with OTN switching

The application of OTN switching can bring significant improvements in the resource utilization to conventional WDM networks. In this paper, spectral, cost and energy efficiencies have been comprehensively analyzed in optical core networks by introducing OTN switching on top of the WDM layer with mixed line rate transmissions for both dedicated protection 1+1 (DP 1+1) and unprotected network scenarios. The simulation results show remarkable performance improvements by solely installing OTN switching matrices in the optical core nodes and applying grooming. More specifically, in the Spanish core network model of Telefonica I+D, the spectral efficiency can be improved by up to 567 and 288%, the cost efficiency 564 and 265%, the energy efficiency 1335 and 423%, compared to the conventional WDM networks for protected and unprotected scenarios, respectively.

Effect of Traffic Uncertainities on the Design of Mixed Line Rate (MLR) Optical Networks

In the existing studies on Mixed Line Rate (MLR) optical networks, the network design methodology is based on the assumption of deterministic traffic, and hence, the effect of traffic uncertainty on the design of an MLR network remains an open problem of research. In this study, we upgrade our previously proposed cost-efficient mixed integer linear program (MILP) formulation for an MLR network, which considered a specific mean traffic for every network source-destination pair. Our upgraded model employs an optimization technique to account for the traffic uncertainties that an actual MLR optical network may encounter. Our simulation results show that (i) if the MLR network is cost-optimized under the assumption that approximately 10-20% of the demands are at their maximum (or peak) value then, the network demonstrates robustness to traffic peaks in approximately all the other demands, and (ii) the saturation of network cost for a number of source-destination pairs is network topology dependent.

Investigation of Influence of Mixed Configurations on Performance of WDM-PON

This paper aims at assessing of implementation of the concept of mixed systems in wavelength-division-multiplexing passive optical networks (WDM-PONs). At the first stage, the authors evaluate performance of two equal-channel transmission systems with non-return-to-zero (NRZ) and duobinary (DB) coding in terms of Q-factor, minimal channel spacing and supported data rate. At the second stage, two configurations of mixed transmission systems are proposed. The system with unequal channel spacing and multiple modulation formats (MMFs) as well as the system with mixed line rates (MLRs) and MMFs are investigated. The obtained results reveal that the impact of implementation of both systems is positive and concept of mixed transmission system can be considered as a potential solution for the increase of spectral efficiency (SE) of WDM-PON transmission system.DOI: http://dx.doi.org/10.5755/j01.eie.23.2.18003

Energy‐efficient multiperiod planning of optical core network to support 5G networks

AbstractWith the rapid growth of traffic and power consumption in information and communication technology industry for decades, improving energy efficiency has become a challenging issue in recent years. Especially, the pervasive access to Internet via mobile devices will cause wireless traffic volume increment by 1000+ times in near future, which is expected to be carried by the fifth generation ultradense cellular network. Following this trend, the core network where optical fibers are deployed to deliver aggregated traffic needs upgrading to accommodate the increasing traffic volume. To match with the traffic growth rate, we should conduct efficient network planning over multiple time periods. Moreover, considering the heterogeneity in the bandwidth requirements among various network services, flexible mixed line rate scheme is adopted in network provisioning. In this paper, we study the long‐term multiperiod planning of optical core network by considering the traffic growth with the objective of high energy‐efficiency. Three planning strategies, say All‐period, Incremental, and End‐of‐Life, respectively, are studied and formulated as mixed integer linear programming models with the objective to minimize power consumption of optical core network. Given the estimation on the reduction of power consumed by various network devices, we can deploy network devices flexibly in each period through the optimization models. Performance of the proposed models is also evaluated and compared via case studies.

Energy Minimized design of Mixed Line Rate IP-over-WDM Network

Energy Minimized design of Mixed Line Rate IP-over-WDM Network

Power-Efficiency Comparison of Spectrum-Efficient Optical Networks

With steady traffic volume growth in the core networks, it is predicted that the future optical network communication will be constrained mainly by the power consumption. Hence, for future internet sustainability, it will be a mandate to ensure power-efficiency in the optical networks. Two paradigms known to support both, the traffic heterogeneity and high bandwidth requests are the: (i) next generation flexible (or elastic) orthogonal frequency division multiplexing (OFDM) based networks which provide flexible bandwidth allocation per wavelength, and (ii) currently deployed mixed-line-rate (MLR) based networks which provision the co-existence of 10/40/100 Gbps on varied wavelengths within the same fiber. In this work, the power-efficiency of an OFDM, and a MLR based network has been compared for which, a mixed integer linear program (MILP) model has been formulated considering deterministic traffic between every network source-destination pair. The simulation results show that in regard to power-efficiency, the OFDM based network outperforms the MLR based network.

Comprehensive design methodology for control and data planes in wavelength-routed optical networks

We propose a comprehensive design methodology for control and data planes of wavelength-routed optical networks (WRONs) employing mixed-line-rate (MLR) transmission for cost-effective resource provisioning. The proposed approach attempts to minimize the maximum lightpath capacity demand in Gbps (representing the measure of lightpath congestion) in network for a given traffic matrix by using a mix of a heuristic scheme and linear programming (LP). In the first step of the proposed three-step design, some lightpaths are set up on a set of judiciously selected fiber links (with point-to-point lightpaths between neighboring nodes), on a specific wavelength throughout the network, and an appropriate fraction of the same set of lightpaths is utilized for carrying control information, forming therefore the control plane (CP) of the WRON. The remaining bandwidth of these lightpaths is utilized to carry the data traffic along with all other designed lightpaths of the WRON using appropriate algorithm, forming the overall data plane (DP) of the WRON. In the second step, traffic routing is carried out through LP to minimize lightpath congestion in the network. In the third step, we utilize the results of LP to assign rates to lightpaths, such that the cost (considering only the transceiver cost) of the network is minimized. This design leads to congestion-aware MLR network with due consideration to cost-effectiveness without compromising the network restoration response against link failures. We carry out simulation studies employing possible CPs using both symmetric (CP topology being same as the physical topology) as well as asymmetric (using fewer fiber links than the symmetric case) topology. The results of our simulations indicate that the proposed design of CP with symmetric/asymmetric topology and in-band transmission with sub-lightpath capacity can bring down network congestion and cost with respect to symmetric out-of-band transmission (using fully reserved lightpaths for CP), without any perceptible sacrifice in respect of the network restoration time. Failure can occur either in CP or DP, or in both the planes. We investigate the effect of design of CP with symmetric/asymmetric topology on network restoration time for single- and double-link failures. We further present DP design methodology with hybrid restoration scheme, i.e., combination of dedicated (1:1) path protection and path restoration. We analyze the effect of symmetric CP topology and degree of protection on the congestion of the network. Some lightpaths, that support more traffic, are protected against failures, while the others are left for path restoration in the event of failures. As more lightpaths are protected, the congestion and power consumption of network increase. We provide an analysis of the factors that come into play while altering the degree of protection and observe how the choice for the degree of protection in DP can be arrived at using an appropriate design methodology.

Distance-adaptive, Low CAPEX Cost <inline-formula> <tex-math notation="LaTeX">$p$</tex-math> </inline-formula>-Cycle Design Without Candidate Cycle Enumeration in Mixed-Line-Rate Optical Networks

Even though elastic optical networks (EONs) are promising to provision increasingly dynamic and heterogeneous traffic, the requirements on bandwidth-variable optical devices bring upgrading challenges in current wavelength-division multiplexing (WDM) optical networks. Mixed-line-rate (MLR) optical networks offer a transitional solution that allows several coexisting line rates (e.g., $10/40/100$ Gb/s). In this paper, we investigate distance-adaptive preconfigured-cycle ( $p$ -Cycle) protection scheme in MLR optical networks. Path-length-limited $p$ -cycles are designed to be assigned line rate depending on the length of each protection path. Instead of conventional candidate cycle enumeration, a mixed integer linear programming (MILP) model is formulated to directly generate the optimal $p$ -cycles with the minimum capital expenditures (CAPEX) cost. We also develop two algorithms to make the proposed MILP model scalable. Simulation results indicate that the algorithms are time efficient for solving the MILP-based $p$ -cycle design. We further compare our $p$ -cycle design method with other schemes, and demonstrate that our method largely reduces the CAPEX cost for more than $40\%$ , mainly in transponder cost. To the best of our knowledge, this is the first time that distance-adaptive $p$ -cycle design without candidate cycle enumeration is proposed for MLR optical networks.

Spectral and power efficiency investigation in single- and multi-line-rate optical wavelength division multiplexed (WDM) networks

In order to tackle the increasing heterogeneous global Internet traffic, mixed-line-rate (MLR) optical wavelength division multiplexed (WDM) networks have emerged as the cost- and power-efficient solution. In MLR WDM networks, channels are structured as sub-bands, each of which consists of wavelengths operating at a similar data rate. By reducing the (1) spacing within a sub-band, or (2) spacing between sub-bands operating at different data rates, spectral efficiency can be improved. However, owing to high physical layer impairment levels, decrease in sub-band spacing adversely affects transmission reach of the channels, which results in higher power consumption due to requirement of increased signal regeneration. In this work, we compare power efficiency of various MLR and single-line-rate (SLR) solutions, and also investigate the trade-off that exists between spectral and power efficiency in a WDM network. Simulation results indicate that (1) for high transmission capacities, a combination of 100 Gbps transponders and 40 Gbps regenerators will obtain the highest power efficiency; (2) for long connection distances, a point ofmerging occurs for various SLR and MLR designs, where power consumption is independent of the frequency band distribution; and (3) for MLR systems, both spectral and power efficiency can be improved by using either shorter links with higher bandwidth assignment to 100 Gbps wavelengths, or longer links with higher bandwidth assignment to 40 Gbps wavelengths. Finally, the results indicate that focusing on spectral efficiency alone results in extra power consumption, since high quality of transmission and spectral efficiency leads to increased regeneration.

Power-aware virtual optical network provisioning in flexible bandwidth optical networks [Invited

Considering the virtual network infrastructure as a service, optical network virtualization can facilitate the physical infrastructure sharing among different clients and applications that require optical network resources. Obviously, mapping multiple virtual network infrastructures onto the same physical network infrastructure is one of the greatest challenges related to optical network virtualization in flexible bandwidth optical networks. In order to efficiently address the virtual optical network (VON) provisioning problem, we can first obtain the virtual links' order and the virtual nodes' order based on their characteristics, such as the bandwidth requirement on virtual links and computing resources on virtual nodes. We then preconfigure the primary and backup paths for all node-pairs in the physical optical network, and the auxiliary graph is constructed by preconfiguring primary and backup paths. Two VON mapping approaches that include the power-aware virtual-links mapping (PVLM) approach and the power-aware virtual-nodes mapping (PVNM) approach are developed to reduce power consumption for a given set of VONs in flexible bandwidth optical networks with the distributed data centers. Simulation results show that our proposed PVLM approach can greatly reduce power consumption and save spectrum resources compared to the PVNM approach for the single-line rate and the mixed-line rate in flexible bandwidth optical networks with the distributed data centers.

A novel partition-plane impairment aware routing and spectrum assignment algorithm in mixed line rates elastic optical networks

In mixed line rates elastic optical networks, different line rate signals can coexist on the same fiber. As different line rates coexist in the same fiber, the impairments, especially the cross-phase modulation (XPM), become more and more serious affecting the quality of transmission of signals. Moreover, the spectrum constraints limit the efficient allocation of spectrum resources. In this paper, we propose a novel spectrum Partition-topology Plane impairments aware routing and spectrum assignment algorithm to set up lightpaths for connection requests, therefore decreasing the XPM impairments and increasing spectrum utilization. The proposed algorithm can satisfy the spectrum constraints restriction and avoid the XPM impairment together. The simulation results show that the proposed algorithm can significantly improve the performance of networks in blocking probability and the spectrum efficiency.

A Novel Dynamic Physical Layer Impairment-Aware Routing and Wavelength Assignment (PLI-RWA) Algorithm for Mixed Line Rate (MLR) Wavelength Division Multiplexed (WDM) Optical Networks

AbstractThe ever-increasing global Internet traffic will inevitably lead to a serious upgrade of the current optical networks’ capacity. The legacy infrastructure can be enhanced not only by increasing the capacity but also by adopting advance modulation formats, having increased spectral efficiency at higher data rate. In a transparent mixed-line-rate (MLR) optical network, different line rates, on different wavelengths, can coexist on the same fiber. Migration to data rates higher than 10 Gbps requires the implementation of phase modulation schemes. However, the co-existing on-off keying (OOK) channels cause critical physical layer impairments (PLIs) to the phase modulated channels, mainly due to cross-phase modulation (XPM), which in turn limits the network’s performance. In order to mitigate this effect, a more sophisticated PLI-Routing and Wavelength Assignment (PLI-RWA) scheme needs to be adopted. In this paper, we investigate the critical impairment for each data rate and the way it affects the quality of transmission (QoT). In view of the aforementioned, we present a novel dynamic PLI-RWA algorithm for MLR optical networks. The proposed algorithm is compared through simulations with the shortest path and minimum hop routing schemes. The simulation results show that performance of the proposed algorithm is better than the existing schemes.

All-optical and digital non-linear compensation algorithms in flex-coherent grouped and un-grouped contiguous spectrum based networks

We have evaluated that in-line non-linear compensation schemes decrease the complexity of digital backward propagation and enhance the transmission performance of 40/112/224 Gbit/s mixed line rate network. Multiple bit rates, i.e. 40/112/224 Gbit/s and modulation formats (i.e. DP-QPSK and DP-16QAM) are transmitted over 1280 km of Large \(\hbox {A}_{eff}\) Pure-Silica core fiber. Both grouped and un-grouped spectral allocation schemes are investigated. Optical add-drop multiplexers are used to drop the required wavelength for signal processing in the transmission link. Moreover, hybrid mid-link spectral inversion and in-line non-linear compensation methods are also analyzed. This gives us enhanced system performance and DBP step-size of 400 km in WDM 224 Gbit/s DP-16QAM system, significantly reducing the complexity of digital backward propagation.

Energy efficiency in WDM fiber-optical links considering OADM/OXC nodes

In this paper, authors discuss the energy consumption for 1bit transmission as a function of spectral efficiency (SE, bps/Hz), aggregated traffic amount (C, bps), and overall transmission distance (LP2P, km) in wavelength division multiplexing (WDM) systems with optical add-drop multiplexer/ optical cross-connect (OADM/OXC) nodes. The choice of bitrate and modulation formats was limited to three options: 10G non-return-to-zero on-off keying (NRZ-OOK), 40G NRZ differential phase-shift keying (NRZ-DPSK) and 100 dual polarization quadrature phase-shift keying (DP-QPSK). The reasons for that is the legacy in transmission networks and high energy efficiency of 3R (re-amplification, re-timing, re-shaping) regenerators and transponders, respectively. In addition, these formats are commonly used for 10-40-100G mixed-line rate solutions in core networks. It is found out that 100G DP-QPSK is the best solutions among two other considered in terms of both energy consumption per bit and spectral efficiency. Finally and foremost, it is estimated that for the WDM channels added at the OADM/OXC node, energy consumption per 1 transmitted bit could growth more than two times as compared to wavelengths transmitted over point-to-point fiber-optical links and then dropped at the receiving node.

Optimization of p-Cycle Protection in Mixed Line Rate WDM Networks with Limited Transmission Reaches

We consider the problem of routing and rate assignment with p-cycle protection for mixed line rate (MLR) networks that are limited by transmission reaches. The problem is formulated mathematically as integer linear programming (ILP) problems under two different assumptions. First, we consider using each p-cycle to protect working lightpaths at common fixed line rate, and refers to this case as the fixed cycle rate (FCR) approach. We then perform comparative study between the FCR approach and the mixed cycle rate (MCR) approach, which is the second case and allows each p-cycle to protect working lightpaths with various rates. The objective of each ILP problem is to minimize the overall cost function, which consists of transponder operating cost, as primary costs and p-cycle operating costs, as secondary costs. Number results show that the MCR approach yields lower cost and is more efficient as the traffic increase when compared the FCR approach. In addition, we compare the use of MLR networks to the use of single line rate (SLR) networks to verify that MLR networks yield lower costs.

Virtual topology reconfiguration for mixed-line-rate optical WDM networks under dynamic traffic

For the mixed-line-rate (MLR) wavelength-division multiplexing (WDM) networks, each wavelength in a fiber can provide different transmitting rates (in 10/40/100 Gbps) by using different modulation formats. Since the MLR-WDM becomes a cost-efficient technique for the network upgrading, the problem of supporting virtual topology reconfiguration (VTR) becomes an important issue. In this paper, the VTR problem is studied for MLR-WDM networks under dynamic traffic demand. By monitoring traffic of the lightpaths, a reconfiguration method is proposed to follow the changes in traffic without a priori knowledge of the future traffic pattern. The proposed algorithm can optimize resource utilization and network traffic performance by either adjusting (increasing or decreasing), adding or deleting one or more lightpaths at a time. Simulations reveal the effects of the various system parameters. Specifically, we find that the proposed method adapts very well to the changes in the offered traffic on MLR-WDM networks.

Genetic algorithm for virtual topology design on MLR WDM networks

For the mixed-line-rate (MLR) wavelength-division multiplexing (WDM) networks, each wavelength of fiber can provide different transmitting rates (in 10/40/100Gbps) by using different modulation types. Since the MLR-WDM is becoming the key and a cost-efficient technique for the network upgrading, the problem for constructing an efficient virtual topology becomes an important issue. In this paper, the Virtual Topology Design (VTD) problem on MLR-WDM network is considered. Given the physical backbone network and traffic demand matrix between nodes of the network, the goal of the VTD problem is to determine which node-pairs to be connected by establishing lightpaths, the actual routes of the lightpaths, the transmitting rates of lightpaths, and the assigned wavelengths of lightpaths such that the total cost of deployed transceivers can be minimized. Since the VTD problem on MLR-WDM network is a hard problem, in the paper, a heuristic algorithm (HA) and a genetic algorithm (GA) are proposed to solve it. Experimental results indicate that the proposed GA is robust for this problem.

A Survey on Next-Generation Mixed Line Rate (MLR) and Energy-Driven Wavelength-Division Multiplexed (WDM) Optical Networks

AbstractWith the ever-increasing traffic demands, infrastructure of the current 10 Gbps optical network needs to be enhanced. Further, since the energy crisis is gaining increasing concerns, new research topics need to be devised and technological solutions for energy conservation need to be investigated. In all-optical mixed line rate (MLR) network, feasibility of a lightpath is determined by the physical layer impairment (PLI) accumulation. Contrary to PLI-aware routing and wavelength assignment (PLIA-RWA) algorithm applicable for a 10 Gbps wavelength-division multiplexed (WDM) network, a new Routing, Wavelength, Modulation format assignment (RWMFA) algorithm is required for the MLR optical network. With the rapid growth of energy consumption in Information and Communication Technologies (ICT), recently, lot of attention is being devoted toward “green” ICT solutions. This article presents a review of different RWMFA (PLIA-RWA) algorithms for MLR networks, and surveys the most relevant research activities aimed at minimizing energy consumption in optical networks. In essence, this article presents a comprehensive and timely survey on a growing field of research, as it covers most aspects of MLR and energy-driven optical networks. Hence, the author aims at providing a comprehensive reference for the growing base of researchers who will work on MLR and energy-driven optical networks in the upcoming years. Finally, the article also identifies several open problems for future research.

A joint multi-layer planning algorithm for IP over flexible optical networks

We consider the multi-layer network planning problem for IP over flexible optical networks, which consists of three subproblems at two layers: the Routing problem at the IP-layer (IPR), the routing, modulation level (RML), and the spectrum allocation (SA) problems at the optical layer. The input includes the IP end-to-end traffic matrix, the modular model of the IP/MPLS routers, and the feasible transmission configurations of the flexible optical transponders. Demands are served for their requested rates by selecting the IP/MPLS routers modules to be used, the routes in the IP (virtual) topology, and the corresponding paths and spectrum slots in the underlying optical topology, together with the optical transponders' configurations. The proposed algorithm follows a multi-cost approach that solves jointly the IPR, the RML, and the SA problems. It serves demands one-by-one, reusing existing equipment and favoring the deployment of new equipment that could also be reused by subsequent connections, aiming to minimize the total network cost. The problem definition is generic and the proposed algorithm is applicable to both fixed- and flex-grid optical networks. We evaluate the performance gains that can be obtained by the proposed joint multi-layer network planning solution, as opposed to a sequential planning solution that separately plans the IP and optical layers. We also compare a flexible network, using flex-grid optical switches and flexible optical transponders, to a mixed line rate (MLR) network, using fixed-grid or flex-grid optical switches but fixed optical transponders.