Mixed Line Rate Networks Research Articles

Crosstalk reduction in multiwavelength VOA-loop-based photonic cross-connect for mixed line rate networks

Abstract The effect of crosstalk is investigated in this paper using a multiwavelength photonic cross-connect (OXC) based on the variable optical attenuator (VOA) loop for mixed line rates. It displays efficient behaviour with a BER of 10−15, 96 % eye-opening, and an eye height of 0.000138 a.u. at 10 Gbps of data rate. The proposed structure is tested for 20 and 40 Gbps data rates also in terms of crosstalk, output power, and BER. The structure is also efficient with a minimum latency of 0.56 ns with a pseudo-random binary sequence of order 14. It has been observed that VOA-SMZI-SOA-based significantly reduced cross-channel interference that is produced within the cross ports with crosstalk of −24.6 dB proving its superiority in comparison to previously reported techniques.

Quality aware path finding algorithm for mixed line rates WDM/DWDM networks

Abstract The optical network plays a vital role in the current technology for providing high-speed data communication, which the networks operate at Tb/s. In this case, different modulation techniques can be used for different line rates to achieve high-speed data transmission. The light paths and various data rates such as 10, 40, and 100 Gb/s are the important parameters for mixed line rate networks. The wavelengths and line rates are powerful tools for mixed line rates networks. It can exist on different optical fibers. In this paper, advanced modulation techniques achieve a relative performance with the required Q-factor. This paper analysis for different matrix computations to achieve a superior Q-factor. It can affect the data rates and quality of transmission. This paper also proposed an algorithm that can improve the Q-factor. Q-factor is analyzed and proposes routing and wavelength assignment (RWA) techniques based on the Q-factor obtained at different line rates. This paper is a brief overview of a quality-aware path-finding algorithm for mixed line rates WDM/DWDM networks are present and discussed.

Energy-Efficient and Spectral-Efficient Mixed Line Rate Optical WDM Networks: A Comparison

The tremendous increase in volume and heterogeneity of traffic has resulted in significant innovations in telecommunication networks. In view of optical networks, by adopting a mixed line rate (MLR) strategy, wavelength division multiplexed networks can cost-effectively respond to diverse variety of traffic requirements which have heterogeneous service demands. From existing studies on MLR networks, it can be inferred that depending upon channel configuration, modulation format and link length, a spectral-efficient network can outperform a power-efficient network. In the current work, we compare the performance of a MLR network which is spectral-efficient and power-efficient. We conduct extensive simulations considering realistic parameters and physical layer impairments. To the network designers, our study advocates a MLR network which is spectrally efficient since; our results demonstrate that, in addition to achieving close packing of the channels, a spectrally-efficient MLR network is also able to achieve close performances to that shown by power-efficient MLR network.

Effect of Channel Spacing on the Design of Mixed Line Rate Optical Wavelength Division Multiplexed Networks

Abstract The ever increasing heterogeneity and growing traffic volume has resulted in significant innovations and paradigm shifts within the telecom backbone networks. In order to cost-effectively respond to the diverse variety of traffic requirements having heterogeneous service demands, wavelength division multiplexed (WDM) optical networks have adopted the mixed line rate (MLR) strategy. In MLR networks, many wavelength channels with various line rates can co-exist within the same fiber which, however, raises many important design issues; one of them being the choice of the channel spacing. The quality of signal is affected by the channel spacing in terms of the bit-error rate (BER), which in turn affects the maximum optical reach of the lightpaths that depends on the line rates. In regard to the aforementioned, different methods can be adopted in order to set the width of the channel spacing, viz., (a) choice of a 50 GHz uniform fixed channel spacing specified by the ITU-T grid, (b) exploring various channel spacing values for different line rates so as to optimize the usage of the fiber spectrum, or (c) seek for an optimal value of the channel spacing which results in the minimum network cost. In the current work, we evaluate the MLR network cost for various channel spacings; hence, we find an optimal value of the channel spacing that leads to the minimum MLR network cost. The simulation results reveal that, for a MLR network, even with the assumption of uniform channel spacing, optimal values of the channel spacing for a minimum cost network can be identified.

Performance Evaluation of OOK, DPSK and Duo-binary Modulation Format based Mixed-Line-Rate (MLR) Optical Network

With the steady increase in the heterogeneous Internet traffic, the optical wavelength division multiplexed (WDM) networks based on a mixed line rate (MLR) strategy have emerged as an efficient-solution. Also, with the migration from the legacy to the higher line rate(s), the advanced modulation format(s) (MF) is/are required. However, use of appropriate MF(s) for the higher line rate(s) still remains an open problem. In this article, we compare the performance of an On-Off Keying (OOK), Differential Phase Shift Keying (DPSK) and Duo-binary (DB) MF based MLR network in the presence of various physical layer impairment(s) (PLIs) for which, we propose a mathematical model based on various MFs. As a novelty, we validate the proposed theoretical model’s results by comparing them with the results obtained through simulations from OptSim, which has not been conducted in any existing study(s) thus far. Our simulation results show that the DB MF is perfectly suitable for high spectral-efficient MLR systems owing to its high resistance to various PLIs.

Performance investigation of MLR optical WDM network based on ITU-T conforming fibers in the presence of SRS, XPM and FWM

This article investigates the performance degradation of a mixed line rate (MLR) optical wavelength division multiplexing network in the presence of the combined FWM, XPM and SRS effects. For performance evaluation a novel mathematical model is developed which evaluates the results in terms of quality-factor. Further, the simulations are performed (i) based on the optical frequency grid defined by the ITU-T Recommendation G.692, and (ii) considering the ITU-T compliant optical fibers viz., G.652, G. 652D, G. 653, G. 654, G.655, and LEAF. The obtained results show that among the various considered fibers and modulation format configuration cases, irrespective of spacing between the channels (i) SMF (G.652) and DSF (G.653) fibers provide the best and the worst performances, respectively, and (ii) a combination of the central channel transmitting at 40 Gbps using the duo-binary modulation format with adjacent channels transmitting at 10 Gbps using OOK modulation format, provides the best performance. However, with increase in spacing between the channels, the performance is enhanced owing to mitigation of the deleterious non-linear effects. Overall, the results clearly show that choice of the data rate of both, the central channel and its adjacent channel has a major effect on the MLR network performance.

On the Performance of MLR Optical WDM Network Based on ITU-T Conforming Fibers in the Presence of Dominant Physical Layer Impairments

The tremendous and consistent increase in the volume and heterogeneity of traffic has resulted in major innovations in the telecommunication networks. In regard to the optical networks, existing studies have shown that by adopting a mixed line rate (MLR) strategy, the wavelength division multiplexed optical networks can cost-effectively respond to the diverse variety of traffic requirements which have heterogeneous service demands. Unlike existing studies which focus on various MLR network issues by considering deployment of the standard single mode fiber only within the network, in the current work, we investigate the signal quality deterioration due to the combined effects of dominant physical layer impairments for an MLR optical network conforming to the various ITU-T compliant fibers and also considering the optical frequency grid based on ITU-T Recommendation G.692. The main aim of our current study is to identify, for a given fiber, the modulation format configuration which provides the highest performance. We conduct extensive simulations on the considered MLR system using the obtained optimum channel spacing values between the single and mixed line rates. Our results show that the existence of 10 Gbit/s line rate has a detrimental effect on the 40 Gbit/s and/or 100 Gbit/s line rate; however, the 40 Gbit/s and/or 100 Gbit/s line rate’s effect on a 10 Gbit/s line rate is not so detrimental, as well as between the similar line rates. Overall, our results clearly show that choice of the line rate of both, the central channel and its adjacent channels, has a major effect on the MLR network performance.

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.

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.

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.

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.

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.

Degraded Service Provisioning in Mixed-Line-Rate WDM Backbone Networks Using Multipath Routing

Traffic in optical backbone networks is increasing and becoming more heterogeneous with respect to bandwidth and QoS requirements due to the popularity of high-bandwidth services (such as cloud computing, e-science, telemedicine, etc.), which need to coexist with traditional services (HTTP, etc.). Mixed-line-rate (MLR) networks that support lightpaths of different rates such as 10, 40, 100 Gb/s, etc., are being studied to better support the heterogeneous traffic demands. Here, we study the important topic of degraded services in MLR networks, where a service can accept some degradation (i.e., reduction) in bandwidth in case of a failure in exchange for a lower cost, a concept called partial protection. Network operators may wish to support degraded services to optimize network resources and reduce cost. We propose using multipath routing to support degraded services in MLR networks, a problem that has not been studied before and is significantly more challenging than in single-line-rate (SLR) networks. We consider minimum-cost MLR network design (i.e., choosing which transponder rates to use at each node), considering the opportunity to exploit multipath routes to support degraded services. We propose a mixed-integer-linear-program (MILP) solution and a computationally efficient heuristic, and consider two partial-protection models. Our illustrative numerical results show that significant cost savings can be achieved due to partial protection versus full protection and is highly beneficial for network operators. We also note that multipath routing in MLR networks exploits volume discount of higher-line-rate transponders by cost-effectively grooming requests over appropriate line rates to maximize transponder reuse versus SLR.

Impairment-aware dynamic lightpath provisioning in mixed-line-rate networks

In Mixed-Line-Rate (MLR) networks, different line rates on different wavelengths can coexist on the same fiber. MLR brings flexibility to handle diverse demands by allowing each lightpath to be established end-to-end with different line rates, if necessary. However, advanced modulation techniques, which are required for high line rates, are highly susceptible to physical-layer impairments (PLIs), especially to the cross-phase modulation (XPM) induced by intensity-modulated channels.In this study, we investigate the impairment-aware lightpath provisioning problem for MLR networks. We consider a transparent optical network where we aim to maximize the number of established connections, while avoiding disrupting the existing lightpaths. We propose two different approaches: the first approach, Fixed Wavelength-Interval Allocation, takes PLIs into account implicitly, as signals for different line rates with different modulation formats are placed on channels over separate wavelength intervals. The second approach, Weighted Routing and Wavelength Assignment, handles the problem with a novel weight assignment scheme. We employ an auxiliary graph to capture the effects of PLIs on each channel with a weight-assignment scheme. Simulation results show that our approaches have better performance, in terms of bandwidth blocking ratio, utilization, and resource consumption with respect to the existing approaches.

Provisioning of dynamic traffic in mixed-line-rate optical networks with launch power determination

In mixed-line-rate (MLR) networks, different line rates on different wavelengths can coexist on the same fiber. MLR architectures can be built over transparent optical networks, where the transmitted signals remain in the optical domain along the entire path. Along the transparent optical path, a signal experiences various physical layer impairments (PLIs), and its quality degrades as it travels through each optical component. One of the major factors that affect the transmission quality is the launch power of the optical signal. The power must be large enough to ensure noise resiliency at the receiver, but it must be below the limit where fiber nonlinearities distort the signal. Moreover, high launch power is disruptive not only for the actual lightpath itself but also for neighboring lightpaths, and this effect is particularly critical in MLR networks since advanced modulation techniques used for high line rates are highly susceptible to PLIs. In this study, we investigate the problem of determining the appropriate launch power for provisioning of dynamic connection requests in MLR networks. By setting the appropriate launch power for each connection, we aim to maximize the number of established connections. We propose two different heuristics to determine the appropriate launch power of a lightpath. Worst-case best-case average (WBA) is based on optical reach of signal in a transparent optical network. In impairment-aware launch power determination (I-ALPD), current state of the network and impairments are evaluated to determine the launch power. The proposed approaches are practical and can adapt to the needs of network operators. Simulation results show that the performances of the proposed approaches show better results than the existing schemes in terms of blocking probability and bandwidth blocking ratio.

Efficient Shared Subconnection Protection in Mixed-Line-Rate Optical WDM Networks

Mixed-line-rate (MLR) networks have been proposed recently to support emerging traffic demands with diverse capacity requirements. In such networks, wavelength channels of the optical paths can have a variety of capacities (10/40/100 Gbps). It has been shown that this feature enables new paradigms for protection in optical wavelength-division-multiplexing (WDM) networks. In this paper, we propose to design transparent MLR networks with shared subconnection protection (SSP). SSP in an MLR network, compared with other more classical approaches (dedicated or shared protection), can also address the cost-versus-capacity trade-off in providing shared protection in a transparent network. The design problem is solved by a two-step approach that formulates part of the problem as an integer linear program (ILP). Our results show that SSP enables higher sharing of backup capacityin an MLR network in that the design cost is up to 37% less than a single-line-rate network with SSP and around 40% less than MLR with dedicated protection.

Impairment-aware lightpath provisioning using inverse multiplexing in mixed-line-rate networks

In Mixed-Line-Rate (MLR) networks, different line rates on different wavelengths can coexist on the same fiber. MLR brings flexibility to handle diverse demands by allowing each lightpath to be established end-to-end with different line rates, if necessary. High line rates require advanced modulation techniques, such as DQPSK and DP-QPSK. On the other hand, signals being propagated over transparent paths are exposed to detrimental effects of physical-layer impairments (PLIs). Advanced modulation techniques are highly susceptible to PLI, especially to the cross-phase modulation (XPM) induced by intensity-modulated channels.Inverse multiplexing (IM), in MLR networks, is a technique which exploits the advantage of transmitting the signals with low line rates where the high line rate is not possible due to PLIs.In this study, we propose new algorithms employing IM to account for the impairment-aware dynamic lightpath establishment problem in MLR networks. Experimental results show that our approaches improve the performance in terms of blocking ratio with a cost of additional network resource usage.

Performance of Elastic and Mixed-Line-Rate Scenarios for a Real IP Over DWDM Network With More Than 1000 Nodes [Invited

A real network with 1113 physical nodes and 1+1 protection is evaluated by varying the fraction of core/metro nodes to find the optimum network size regarding cost and power efficiency of elastic in comparison to mixed-line-rate (MLR) IP over dense wavelength-division multiplex networks. No significant benefit for any of the network concepts can be deduced, neither for a hierarchical/flat nor for a MLR/elastic network concept. On the other hand, the results confirmed that the use of the flex grid is beneficial for both MLR and elastic network scenarios.

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.

Impairment-Aware Optical Network Virtualization in Single-Line-Rate and Mixed-Line-Rate WDM Networks

Optical network virtualization enables network operators to compose and operate multiple independent and application-specific virtual optical networks (VONs) sharing a common physical infrastructure. To achieve this capability, the virtualization mechanism must guarantee isolation between coexisting VONs. In order to satisfy this fundamental requirement, the VON composition mechanism must take into account the impact of physical layer impairments (PLIs). In this paper we propose a new infrastructure as a service architecture utilizing optical network virtualization. We introduce novel PLI-aware VON composition algorithms suitable for single-line-rate (SLR) and mixed-line-rate (MLR) network scenarios. In order to assess the impact of PLIs and guarantee the isolation of multiple coexisting VONs, PLI assessment models for intra- and inter-VON impairments are proposed and adopted in the VON composition process for both SLR and MLR networks. In the SLR networks, the PLI-aware VON composition mechanisms with both heuristic and optimal (MILP) mapping methods are proposed. A replanning strategy is proposed for the MILP mapping method in order to increase its efficiency. In the MLR networks, a new virtual link mapping method suitable for the MLR network scenario and two line rate distribution methods are proposed. With the proposed PLI-aware VON composition methods, multiple coexisting and cost-effective VONs with guaranteed transmission quality can be dynamically composed. We evaluate and compare the performance of the proposed VON composition methods through extensive simulation studies with various network scenarios.