Showing papers in "IEEE\/OSA Journal of Optical Communications and Networking in 2014"
TL;DR: Advantages such as increased data rate, DC-bias elimination, no bandwidth, and PAPR penalty make this scheme very attractive for OW systems using IM/DD.
Abstract: In this paper, we present a hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (OFDM) system. This system uses a combination of asymmetrically clipped optical OFDM (ACO-OFDM) and pulse amplitude modulated discrete multitone (PAM-DMT) techniques, which can be used in intensity modulated direct detection (IM/DD) optical wireless (OW) systems. In this hybrid scheme, ACO-OFDM and PAM-DMT signals are transmitted together. Clipping noise is estimated at the receiver and canceled to recover the PAM-DMT symbols. This scheme does not require any DC bias for transmission, which makes the transmitter less complex and very power efficient. With this system, we can increase the data rate of the ACO-OFDM system by almost twice. In addition, no bandwidth penalty is incurred. Extensive computer simulations show that the bit-error rate (BER) performance of ACO-OFDM in the additive white Gaussian noise environment is not affected by any kind of interference, but only due to half of the available transmit power, we see a 3 dB degradation. However, the BER performance of PAM-DMT shows some degradation at low signal-to-noise ratio (SNR) but is identical to the conventional scheme at higher SNR. We also see a slight improvement in peak-to-average power ratio (PAPR) of the output combined signal. Therefore, advantages such as increased data rate, DC-bias elimination, no bandwidth, and PAPR penalty make this scheme very attractive for OW systems using IM/DD.
149 citations
TL;DR: In this paper, the authors proposed an on-demand spectrum and core allocation method that reduces both the crosstalk and fragmentation in elastic optical networks with multicore fiber (MCF).
Abstract: In the past few years, many researchers have studied elastic optical networks, which exhibit a dramatically improved transmission capacity compared with conventional optical networks. However, the transmission capacity per fiber will soon reach the physical limit for traditional single-mode fibers. Multicore fiber (MCF) is among the innovative fibers based on space-division multiplexing technology. MCF has multiple cores and achieves a far larger transmission capacity than traditional single-mode fibers. However, signals transmitted in these crowded multiple cores interfere with each other and are degraded. This degradation has a serious impact on the network resource management in elastic optical networks. Previous research indicates that the crosstalk effect of MCF is dependent on an arrangement of signals regarding the spectrum and core. Therefore, we approach the problem of the crosstalk in MCF with regard to the spectrum and core allocation, from the network perspective. First, this paper summarizes the related work regarding elastic optical networks and MCFs. Next, we propose an “on-demand” spectrum and core allocation method that reduces both the crosstalk and fragmentation in elastic optical networks with MCFs. This proposed method is based on two predefined policies related to the crosstalk and fragmentation. The first, the core prioritization policy, is based on the MCF's structure, and the other is a core classification policy based on the required bandwidth of the connections. The core prioritization policy realizes the core allocation that reduces crosstalk by avoiding filling adjacent cores. The core classification policy reduces the spectrum fragmentation by allocating a uniform bandwidth connection for each core. Finally, we evaluate the proposed method using computer simulations. The results indicate that the proposed method can, under various network conditions, improve both the crosstalk and blocking probability of the total network through our two policies.
140 citations
TL;DR: A novel technique for simultaneous multi-impairment monitoring and autonomous bit-rate and modulation format identification (BR-MFI) in next-generation heterogeneous fiber-optic communication networks is proposed by using principal component analysis-based pattern recognition on asynchronous delay-tap plots.
Abstract: We propose a novel technique for simultaneous multi-impairment monitoring and autonomous bit-rate and modulation format identification (BR-MFI) in next-generation heterogeneous fiber-optic communication networks by using principal component analysis-based pattern recognition on asynchronous delay-tap plots. The results of numerical simulations performed for three commonly used modulation formats at two different bit-rates each demonstrate simultaneous and independent monitoring of optical signal-to-noise ratio, chromatic dispersion, and differential group delay with mean errors of 1 dB, 4 ps/nm, and 1.6 ps, respectively, without knowing the signal's bit-rate and modulation format. Similarly, the results for joint BR-MFI validate accurate identification of all the bit-rates and modulation formats despite the presence of various network impairments. The effects of fiber nonli-nearity and transmitter variations on the performance of the proposed technique are also investigated.
88 citations
TL;DR: In this article, a real-time base-band orthogonal frequency division multiplexing (OFDM) transceiver with a simple symbol synchronization and channel estimation scheme is implemented on only one off-the-shelf commercial field programmable gate array (FPGA).
Abstract: A real-time base-band orthogonal frequency division multiplexing (OFDM) transceiver with a simple symbol synchronization and channel estimation scheme is implemented on only one off-the-shelf commercial field programmable gate array (FPGA). The real-time optical OFDM long-reach passive optical network (PON) system with direct detection over 100 km standard single-mode fiber (SSMF) employing a cost-effective directly modulated distributed feedback (DFB) laser has been successfully demonstrated experimentally. The experimental results show that the simplified symbol synchronization with low complexity and high accuracy is effective for long-reach optical OFDM transmission systems. After 100 km SSMF transmission, the power penalty at a bit-error rate of 1e-3 is only about 1.1 dB.
74 citations
TL;DR: Novel mechanisms to optimally attack the spectrum fragmentation effect in elastic optical networks are presented and the benefits of the proposed mechanisms are highlighted through illustrative results and various implementation solutions are compared in terms of average network cost.
Abstract: The spectrum fragmentation effect in elastic optical networks is one of their main limitations. Multiple techniques have been proposed to address this problem, with the split spectrum approach (SSA) being a very interesting candidate among them. This technique is based on splitting a demand into smaller sub-demands when a blocking situation arises. In split-spectrum-enabled networks, the route, spectrum, and modulation level assignment (RSMLA) problem that appears in elastic optical networks is further complicated due to the signal splitting operation. In this paper we present novel mechanisms to optimally attack this problem; various possible implementations of the SSA are also discussed. We highlight the benefits of the proposed mechanisms through illustrative results and compare the various implementation solutions in terms of average network cost.
55 citations
TL;DR: A theoretical model to precisely analyze the service availability of networks with preconfigured cycles (p-cycles) and proposes a service availability oriented p-cycle configuration algorithm for dynamic elastic optical networks (EONs), namely, the number of relevant links (NRL)-based p- cycle design algorithm (N RL-p-cycle).
Abstract: In this paper, we develop a theoretical model to precisely analyze the service availability of networks with preconfigured cycles (p-cycles). By considering the dependence among protection domains and all the scenarios when a lightpath is available, our model can estimate the service availability more precisely than those in previous work. Then, based on the availability analysis, we propose a service availability oriented p-cycle configuration algorithm for dynamic elastic optical networks (EONs), namely, the number of relevant links (NRL)-based p-cycle design algorithm (NRL-p-cycle). The simulations compare the proposed algorithm with two benchmark p-cycle design algorithms that are based on the protection efficiency of p-cycles. Simulation results show that the proposed algorithm can effectively improve the service availability in EONs while keeping the blocking probability almost unchanged.
49 citations
TL;DR: In this paper, a sliceable bandwidth variable transponder (SBVT) has been proposed, which can provide even higher levels of elasticity and efficiency to the network than traditional transponders.
Abstract: Elastic optical networking (EON) is a solution that promises to improve infrastructure utilization by implementing flexible spectrum allocation with small spectrum slots instead of the rigid 50 GHz fixed grid of current dense wavelength division multiplexing deployments. This new EON flexible grid supports bandwidth variable transponders (BVTs) that can tune their bit rate and bandwidth dynamically with a trade-off between reach and capacity. However, when BVTs need to transmit at low bit rates, part of their capacity is wasted. Therefore, the sliceable bandwidth variable transponder (SBVT) has been proposed, which can provide even higher levels of elasticity and efficiency to the network. SBVTs enable transmitting from one point to multiple destinations, changing the traffic rate to each destination and the number of destinations on demand. The aim of this work is to identify the target cost of 400 Gb/s and 1 Tb/s SBVTs to reduce, by at least 50%, transponder costs in a core network scenario. This target cost is calculated in relation to estimations for BVTs of 400 Gb/s and 1 Tb/s (non-sliceable). In light of our results, cost savings of 50% are feasible for 1 Tb/s transponders until 2020 with a higher cost than non-sliceable transponders. Savings of 50% for the 400 Gb/s case are possible in the short-term before 1 Tb/s SBVTs can appear in the market. Feasibility of such savings with a target cost higher than current non-sliceable transponders shows that SBVTs can be a reality. Moreover, this work assesses the IP port savings thanks to the utilization of the SBVTs.
49 citations
TL;DR: Numerical results reveal that the key rate is not sensitive to the strength of the atmospheric turbulence; the per-symbol signal-to-noise ratio and the training sequence length are the dominating factors.
Abstract: Security issues of free-space optical (FSO) communications are discussed. Based on a subcarrier intensity-modulated air-to-ground FSO system model, we first analyze the coherence time of the air-to-ground FSO link and show that under practical assumptions, scintillation reciprocity holds in the FSO communication system. A private secret-key-based cryptosystem with key management is introduced to enhance FSO security, and a key agreement approach is proposed based on statistics of the random atmospheric-turbulence-induced fading channel measurements. The secret key rate of the key agreement scheme is investigated for the gamma-gamma turbulence model. Practical key agreement protocols based on bidirectional channel identification are designed for different FSO communication scenarios. Our numerical results reveal that the key rate is not sensitive to the strength of the atmospheric turbulence; the per-symbol signal-to-noise ratio and the training sequence length are the dominating factors.
49 citations
TL;DR: A heuristic SA algorithm, which intentionally increases the spectral fragmentation in the network, is proposed and validated and results show a significant improvement in terms of network blocking probability when utilizing the proposed algorithm.
Abstract: Elastic optical network (EON) technology arises as a promising solution for future high-speed optical transport, since it can provide superior flexibility and scalability inthe spectrum allocation for seamlessly supporting diverse services, while following the rapid growth of Internet traffic This work focuses on lightpath adaptation under time-variable traffic demands in EONs Specifically, we explore the possibility of utilizing the spectral fragmentation to increase the spectrum allocation (SA) capabilities of EONs In this context, a heuristic SA algorithm, which intentionally increases the spectral fragmentation in the network, is proposed and validated In our proposal, the spectrum assigned to each new connection is in the middle of the largest free spectral void over the route, aiming to provide considerable spectral space between adjacent connections These free spectral spaces are then used to allocate time-varying connections without requiring any lightpath reallocation The obtained simulation results show a significant improvement in terms of network blocking probability when utilizing the proposed algorithm
43 citations
TL;DR: The results show that the use of multiple modulation formats instead of one selected format can bring significant savings in terms of all performance metrics (up to 40% for spectrum usage).
Abstract: In this paper, we analyze distance-adaptive transmission in cloud-ready elastic optical networks (EONs). To this end, we focus on the routing, modulation, and spectrum allocation problem, which we formulate as an integer linear programming problem, taking into account such optimization criteria (network performance metrics) as network capital expenditure and operating expenditure network cost, power consumption, and spectrum usage. The experiments are carried out with two representative network topologies and realistic data traffic models built on Cisco traffic predictions. The aim of this study is threefold. First, we examine the impact of distance-adaptive modulation formats on network performance. Second, we analyze how the optimization of a particular criterion influences other performance metrics. Finally, wefocuson the benefitsof using anycasting instead of typical unicast transmission in EONs. The results show that the use of multiple modulation formats instead of one selected format can bring significant savings in terms of all performance metrics (up to 40% for spectrum usage).
39 citations
TL;DR: Simulation results prove that the proposedynamic RSA algorithms are time efficient and perform better than existing dynamic RSA algorithms in terms of bandwidth blocking probability and spectrum fragmentation ratio in EONs with mixed line rates.
Abstract: Elastic optical networks (EONs) are considered a very promising solution for next-generation optical networks. Elastic spectral bandwidth allocation promotes spectrum utilization efficiency and thus increases the network capacity. One of the fundamental problemsinEONs is the routing and spectrum allocation (RSA) problem. Since real EONs may provide only a few regular line rates, we comprehensively study in this paper the dynamic RSA problem in EONs with several mixed line rates. To solve the dynamic RSA problem efficiently, we decompose the problem into RSA subproblems. For the routing subproblem, we propose an efficient multiconstrained routing algorithm named sorted feasible paths searching (SFPS) to find the shortest feasible paths for dynamic traffic demands. The completeness, optimality, and complexity of SFPS are proved. For the spectrum allocation subproblem, we propose two spectrum allocation strategies named fixed segmentation and adaptive segmentation to assign spectrum for the noncommensurate traffic demands of EONs with mixed line rates. Simulation results prove that the proposed dynamic RSA algorithms are time efficient and perform better than existing dynamic RSA algorithms in terms of bandwidth blocking probability and spectrum fragmentation ratio in EONs with mixed line rates.
TL;DR: This paper addresses network energy efficiency at the architectural and service levels and proposes a unified network architecture that provides both intra- data-center and inter-data-center connectivity together with interconnection toward legacy IP networks.
Abstract: The expected growth of traffic demand may lead to a dramatic increase in the network energy consumption, which needs to be handled in order to guarantee scalability and sustainability of the infrastructure. There are many efforts to improve energy efficiency in communication networks, ranging from the component technology to the architectural and service-level approaches. Because data centers and content delivery networks are responsible for the majority of the energy consumption in the information and communication technology sector, in this paper we address network energy efficiency at the architectural and service levels and propose a unified network architecture that provides both intra-data-center and inter-data-center connectivity together with interconnection toward legacy IP networks. The architecture is well suited for the carrier cloud model, where both data-center and telecom infrastructure are owned and operated by the same entity. It is based on the hybrid optical switching (HOS) concept for achieving high network performance and energy efficiency. Therefore, we refer to it as an integrated HOS network. The main advantage of the integration of core and intra-data-center networks comes from the possibility to avoid the energy-inefficient electronic interfaces between data centers and telecom networks. Our results have verified that the integrated HOS network introduces a higher number of benefits in terms of energy efficiency and network delays compared to the conventional nonintegrated solution. At the service level, recent studies demonstrated that the use of distributed video cache servers can be beneficial in reducing energy consumption of intra-data-center and core networks. However, these studies only take into consideration conventional network solutions based on IP electronic switching, which are characterized by relatively high energy consumption. When a more energy-efficient switching technology, such as HOS, is employed, the advantage of using distributed video cache servers becomes less obvious. In this paper we evaluate the impact of video servers employed at the edge nodes of the integrated HOS network to understand whether edge caching could have any benefit for carrier cloud operators utilizing a HOS network architecture. We have demonstrated that if the distributed video cache servers are not properly dimensioned they may have a negative impact on the benefit obtained by the integrated HOS network.
TL;DR: In this paper, the role of phase conjugate (OPC) modules in CO-OFDM systems is investigated by formulating the four-wave mixing (FWM) process generated along a co-channel with two and three OPCs, and the results indicate that increasing the number of OPC modules improves the bit error rate (BER) performance and enlarges the transmission reach.
Abstract: In this paper, we propose utilizing multiple optical phase conjugate (OPC) modules along fiber spans, in order to improve the performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) communication systems in long-haul fiber-optic channels. The role of OPC in CO-OFDM systems is investigated by formulating the four-wave mixing (FWM) process generated along a CO-OFDM with two and three OPCs. Analytical results reveal that increasing the number of OPC modules reduces the average FWM power along the transmission link and as a result mitigates the degrading effect of interaction between amplified spontaneous emission noise and FWM. The proposed schemes have also been investigated using numerical simulations. The results indicate that increasing the number of OPC modules improves the bit error rate (BER) performance and enlarges the transmission reach of CO-OFDM systems. In the case of using three OPC modules, compared to utilizing only one, the BER performance is enhanced nearly two orders of magnitude, and the transmission reach of the system increases in dispersion-unmanaged and dispersion-managed scenarios by 52% and 37%, respectively.
TL;DR: In this paper, the authors investigated how a wavelength relocation mechanism can reduce power consumption and deployment cost of transceivers in time and wavelength division multiplexed PONs (TWDM-PONs).
Abstract: Power consumption in current communication networks including the access networks is increasing rapidly; energy efficiency is therefore one of the key design considerations in the next generation passive optical networks (PONs). In this paper, we investigate how a wavelength relocation mechanism can reduce power consumption and deployment cost of transceivers in time and wavelength division multiplexed PONs (TWDM-PONs), in which wavelengths and transceivers can be shared among multiple PONs. We analyze how the percentage of deployed wavelengths and transceivers will impact the average available bandwidth and cause extra delay for the working optical network units (ONUs). We show through simulation that under typical ONU online profiles, the percentage of wavelength and transceivers that need to be deployed can be reduced to as low as 30% as compared to conventional PONs, with no resource sharing and wavelength relocation.
TL;DR: In this article, the economic risk of dark fiber deployment can be estimated and/or reduced in different settings by applying the model on specific scenarios, which differ in area type, demand uptake, and revenue scheme, it is concluded that the business case is only viable in adense urban area withan aggressive take-up.
Abstract: Upgrading telecommunications access networks requires large investments in deploying new optical infrastructure, especially in terms of construction works and costs to reach the end-user, which seem only affordable in densely populated areas. By evaluating a cost-benefit analysis for the deployment of a point-to-point dark fiber infrastructure, this paper investigates how the economic risk of dark fiber deployment can be estimated and/or reduced in different settings. By applying the model on specific scenarios, which differ in area type, demand uptake, and revenue scheme, it is concluded that the business case is only viablein adense urban area withan aggressive take-up. In the other scenarios, the paper investigates possibilities and opportunities to improve the business case and hence decrease the investment risk. Examples of this improvement include prolonging the planning horizon, ensuring revenue from the start of the project by performing demand aggregation, or examining where public funds might help.
TL;DR: Applying the network and traffic model, this paper derives such a model from the practice of a large national carrier and demonstrates its use by presenting various optimization cases related to energy-efficient telecommunication.
Abstract: As a basis for meaningful simulation and optimization efforts with regard to traffic engineering or energy consumption in telecommunication networks, suitable models are indispensable. This concerns not only realistic network topologies but also models for the geographical distribution and the temporal dynamics of traffic, as well as the assumptions on network components and technology. This paper derives such a model from the practice of a large national carrier. Applying the network and traffic model, we demonstrate its use by presenting various optimization cases related to energy-efficient telecommunication. Here, we focus on load adaptivity by employing sleep modes to the network hardware, where several constraints on the reconfigurability of the network over time are considered.
TL;DR: An evolutionary based multi-objective framework for optimizing network deployments with flexible-grid channel formats ranging from 40 to 400 Gbits/s with varying degrees of resilience to both link and transponder failures, and evaluates how the channel format selection for each demand evolves when considering single-rate or bit-rate variable transponders.
Abstract: Emerging trends in optical transport networks aiming to support increasing data rates are reshaping the possibilities for network planning. The deployment of a flexible grid with multiple available channel bit rates and spectral widths gives way to a more clearly defined trade-off between spectrum and cost in the planning process. Furthermore, providing redundancy in these types of services is both crucial and costly. For this reason, it is important to consider all these aspects simultaneously in order to have an accurate view of the cost/spectrum trade-off in the optical backbone. This paper presents an evolutionary based multi-objective framework for optimizing network deployments with flexible-grid channel formats ranging from 40 to 400 Gbits/s with varying degrees of resilience to both link and transponder failures. The multi-objective algorithm can consider all these different aspects simultaneously and highlight the degree to which cost can be traded for spectrum, and how the protection/restoration schemes influence both parameters. After benchmarking the proposed algorithm on both objectives, we use it on two reference networks to trace the non-dominated front for multiple resilience schemes, offering different levels of protection against link and/or transponder failures. We also evaluate how the channel format selection for each demand evolves when considering single-rate or bit-rate variable transponders.
TL;DR: In this article, the authors demonstrate the seamless integration of full duplex system frequency division duplex (FDD) long-term evolution (LTE) technology with radio over fiber (RoF) for eNodeB (eNB) coverage extension.
Abstract: In this paper, we experimentally demonstrate the seamless integration of full duplex system frequency division duplex (FDD) long-term evolution (LTE) technology with radio over fiber (RoF) for eNodeB (eNB) coverage extension. LTE is composed of quadrature phase-shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM) and 64-QAM, modulated onto orthogonal frequency division multiplexing (OFDM) and single-carrier-frequency division multiplexing for downlink (DL) and uplink (UL) transmissions, respectively. The RoF system is composed of dedicated directly modulated lasers for DL and UL with dense wavelength division multiplexing (DWDM) for instantaneous connections and for Rayleigh backscattering and nonlinear interference mitigation. DL and UL signals have varying carrier frequencies and are categorized as broad frequency spacing (BFS), intermediate frequency spacing (IFS), and narrow frequency spacing (NFS). The adjacent channel leakage ratio (ACLR) for DL and UL with 64-QAM are similar for all frequency spacings while cross talk is observed for NFS. For the best case scenario for DL and UL transmissions we achieve error vector magnitude (EVM) values of ~2.30%, ~2.33%, and ~2.39% for QPSK, 16-QAM, and 64-QAM, respectively, while for the worst case scenario with a NFS EVM is increased by 0.40% for all schemes.
TL;DR: In this article, the feasibility of a wireless link at 220 GHz based on electronic upconversion and downconversion is demonstrated, connecting two optical links at data rates of up to 20 Gbit/s.
Abstract: The feasibility of a wireless link at 220 GHz based on electronic upconversion and downconversion is demonstrated, connecting two optical links at data rates of up to 20 Gbit/s. We use either non-return-to-zero on-off keying with data rates up to 20 Gbit/s or electrical orthogonal frequency division multiplexing with data rates up to 9 Gbit/s. The wireless bridge connects the gateways of two spatially separated fiber sections, each with a length of up to 20 km.
TL;DR: It is shown that the proposed adaptive registration scheme in a TWDM-PON with ONU migrations reduces average migration delay and increases the bandwidth utilization, especially when a large number of ONUs are involved in a registration process.
Abstract: In time and wavelength division multiplexed passive optical networks (TWDM-PONs), optical network unit (ONU) migration (equivalently retuning working wavelength pairs) is an effective approach to reducing power consumption at the optical line terminal (OLT) side. Migration delay, the time from when a migration is initiated until the migrating ONU(s) have successfully joined the target wavelength pair, may affect the user service level agreement (SLA) and should be minimized. After an ONU migration process has been triggered, both the ONUs to be migrated (the migrating ONUs) and the newly incoming ones will have to register (referred to as activation in the ITU-T G.984.3 standard) in the upcoming quiet windows. This makes the number of ONUs competing in a single quiet window much more dynamic and leads to unpredictable registration performance and longer registration delay, which in turn will have a negative impact on the migration delay. In this paper, we propose an adaptive registration scheme in a TWDM-PON with ONU migrations. In the proposed scheme, the size of the quiet window is adaptively adjusted according to the up-to-date number of involved ONUs (including both ONUs to be migrated and the newly incoming ones). We show through simulations that the proposed scheme reduces average migration delay and increases the bandwidth utilization, especially when a large number of ONUs are involved in a registration process. In addition, we further investigate the length of the discovery cycle and find a shorter discovery cycle is needed to reduce migration delay and satisfy the requirement of the ONU SLA for a large number of involved ONUs. To realize a 99.999% ONU SLA, the length of the discovery cycle has to be shorter than 0.1 s for 128 involved ONUs and 0.15 s for 32 involved ONUs.
TL;DR: A scalable DCN architecture based on optical switching and transmission, with the distributed placement of optical switches and server racks at different nodes in a given optical network is proposed, which solves the scalability issue by relaxing power and cooling constraints and by reducing the number of (electronic) switches using high-capacity optical switches.
Abstract: Cloud services are fundamentally supported by data center networks (DCNs). With the fast growth of cloud services, the scale of DCNs is increasing rapidly, leading to great concern about system scalability due to multiple constraints. This paper proposes a scalable DCN architecture based on optical switching and transmission, with the distributed placement of optical switches and server racks at different nodes in a given optical network. This solves the scalability issue by relaxing power and cooling constraints and by reducing the number of (electronic) switches using high-capacity optical switches, as well as by simplifying DCN internal connections using wavelengths in the optical network. Moreover, the distributed optical switches provide service access interfaces to meet demand within areas, and thus reduce the transmission cost of the external traffic. The major concern is the additional delay and cost for remote transmissions of the DCN internal traffic. To this end, we study the component placement problem in DCNs under a given set of external demands and internal traffic patterns. By leveraging among multiple conflicting factors such as scalability and internal overhead of the DCN as well as the transmission cost of external traffic, we propose both an integer linear program and a heuristic to minimize the system cost of a DCN while satisfying all service demands in the network. This addresses both scalability and cost minimization issues from a network point of view.
TL;DR: This paper presents network control algorithms based on both nonfading and fading communication channels using the physical interference model for the RF portion of the network and shows that the throughput of the original RF network can be increased dramatically by properly adding FSO links.
Abstract: A hybrid free space optics/radio frequency (FSO/RF) technology has recently been proposed as a means of significantly increasing the throughput and reliability of wireless mesh networks (WMNs) for broadband communication. Current network control approaches assume quasi-static communication channels and use the simple protocol model to handle RF network interference. Depending on the application, these assumptions may not be sufficient for optimizing hybrid FSO/RF networks. In this paper, we present network control algorithms based on both nonfading and fading communication channels using the physical interference model for the RF portion of the network. We study the throughput improvement achievable by augmenting the RF WMN with FSO links. We address two questions: given a fixed number of FSO links, where should they be installed to maximize the throughput for given traffic demands, and how should the traffic be routed and scheduled in the hybrid FSO/RF network to achieve this throughput? We formulate these problems as one mixed integer linear program and provide a computationally efficient heuristic for scheduling and routing traffic demands through the hybrid FSO/RF network. The results show that the throughput of the original RF network can be increased dramatically by properly adding FSO links.
TL;DR: In this article, the authors proposed a new integrated OTN/WDM switching architecture in which the number of OTN switches is minimized, and proposed an analytical model for the evaluation of the switch blocking probability when two different OTN switch assignment policies are used.
Abstract: In packet-optical integrated transport nodes for metropolitan networks, the wavelength data rate of the transponders has increased quickly to 10, 40, and 100 Gbps to reduce the cost of the transported bit. Meanwhile, the majority of the client data rate in routers and packet switches are still operating at 1, 2.5, and 10 Gbps. In this scenario, the introduction of optical transport network (OTN) switching technology enables an efficient wavelength bandwidth utilization and reduces the number of wavelengths, leading to reduced network costs. It has been shown that the use of integrated OTN/WDM switch architecture is cost effective because it reduces the number of short-reach client interfaces. The OTN/WDM also reduces the rack space and the power consumption compared to an architecture that uses a reconfigurable optical add-drop multiplexer and a separate standalone OTN switch or one that uses back-to-back muxponder connections to perform manual grooming. We introduce and investigate the performance of a new integrated OTN/WDN switching architecture in which the number of OTN switches is minimized. We propose an analytical model for the evaluation of the switch-blocking probability when two different OTN switch assignment policies are used. We show how the number of OTN switches can be reduced if a suitable dimensioning procedure is performed and depending on the traffic percentage needing OTN switching. As an example, if traffic is less than 45%, then the new proposed OTN/WDM switching architecture allows for 25% savings in OTN switching resources in the case of a switch with 4 input/output lines, 48 wavelengths, and 12 × 12 OTN switches.
TL;DR: In this paper, the authors proposed a next-generation long-reach access optical network (35 dB loss budget + 2 dB margin) delivering up to 40G/40G per passive 1:256 optical distribution network.
Abstract: We introduce a next-generation long-reach access optical network (35 dB loss budget +2 dB margin) delivering up to 40G/40G per passive 1:256 optical distribution network, supporting symmetrical 1 Gb/s rates per home user or up to 40 Gb/s for business users (e.g., enterprises, antenna sites). The proposed system is based on a novel spectrally efficient orthogonal frequency division multiplexing/wavelength division multiplexing OFDM/WDM architecture symmetrically using 16-QAM OFDM polarization diversity in both the downstream and upstream in order to serve low-cost energy-efficient symmetric 1 Gb/s optical network units (ONUs), which are self-coherent, laserless, colorless, and tunable-filter-free. Each ONU comprises a standard semiconductor optical amplifier (SOA), a silicon-based photonic integrated circuit (PIC), and mixed-signal electronic integrated circuits (ICs) performing the signal processing at a relatively slow rate as compared with the overall passive optical network (PON) throughput: digital to analog converters (DACs) and analog to digital converters (ADCs) at 417 MS/s for the home user ONUs.
TL;DR: This paper provides the problem definition of SIC-VONM, and develops a novel heuristic algorithm, together with a baseline algorithm and a lower bound for comparison, which achieves results that are very close to those of the ILP for small-scale problems.
Abstract: In this paper, we study the problem of survivable impairment-constrained virtual optical network mapping in flexible-grid optical networks (SIC-VONM). The objective is to minimize the total cost of working and backup resources, including transponders, regenerators, and shared infrastructure, for a given set of virtual optical networks, which can survive single link failures. We first provide the problem definition of SIC-VONM, and then formulate the problem as an integer linear program (ILP). We also develop a novel heuristic algorithm, together with a baseline algorithm and a lower bound for comparison. Numerical results show that our proposed heuristic achieves results that are very close to those of the ILP for small-scale problems and that our proposed heuristic can solve large-scale problems very well.
TL;DR: It is demonstrated that a heuristic traffic grooming algorithm enhanced by comparison with direct bypass routing improves both energy and delay performances in a high energy-traffic proportionality regime and a hottest-first sorting policy in flow provisioning can further improve delay performance even in a low energy-Traffic proportionalities regime.
Abstract: As energy consumption has become a major concern of networks, traffic grooming studies on Internet protocol over wavelength division multiplexing (IP-over-WDM) networks have been revisited for energy-efficient optical network applications. Traffic grooming techniques can save on the number of installed lightpaths and corresponding IP router line cards at the cost of traffic processing overhead. Energy awareness in networking device development has initiated improvement of the energy-traffic proportionality of networking devices. Accordingly, networks will consist of networking devices with a wide range of energy-traffic proportionalities. Therefore, previously known traffic grooming techniques may not achieve energy-efficient networking in high energy-traffic proportional networks. Moreover, the traffic grooming technique tends to prefer longer paths, which are responsible for longer transmission delays. These two concerns trigger investigation of new aspects of heuristic traffic grooming algorithms for green and low delay optical networks consisting of network devices with diverse energy-traffic proportionalities. This paper demonstrates that a heuristic traffic grooming algorithm enhanced by comparison with direct bypass routing improves both energy and delay performances in a high energy-traffic proportionality regime. A hottest-first sorting policy in flow provisioning can further improve delay performance even in a low energy-traffic proportionality regime.
TL;DR: In this article, the authors proposed an upstream and a downstream sleep-aware traffic scheduling scheme to avoid missing packets during the sleep states, which does not need the handshake process and is based on the mutual inference at the OLT and the ONU.
Abstract: Environmental concerns have motivated network designers to further reduce energy consumption of access networks. This paper focuses on reducing the energy consumption of the Ethernet passive optical network (EPON) as one of the most efficient transmission technologies for broadband access. In the EPON, downstream traffic is sent from the optical line terminal (OLT) located at the central office to all optical network units (ONUs). Each ONU checks all arrival downstream packets and selects the downstream packets destined to itself. Therefore, receivers at ONUs have to always stay awake, thus consuming a large amount of energy. On the other hand, an ONU transmitter can be triggered by the arrival of upstream traffic, so it can go to the low power mode when no traffic is observed. Putting ONUs into the low power mode during light traffic is a known strategy for energy saving. In this article, we address the downstream challenge and also improve the ONU transmitter sleep time by proposing a simple sleep control scheme. We also propose an upstream and a downstream sleep-aware traffic scheduling scheme to avoid missing packets during the sleep states. The proposed sleep control scheme does not need the handshake process and is based on the mutual inference at the OLT and the ONU. Simulation results show that the proposed scheme can save energy by as much as 60% when network traffic is light.
TL;DR: A novel cooperative SEC policy is examined, which takes into consideration the spectrum allocation of neighboring connections and a class of cooperative SD policies is proposed, based on the capabilities of current technology.
Abstract: Flexible optical networks appear as the most prevalent candidates for next-generation core transport networks. The transition from a fixed to a flexible frequency grid calls for novel spectrum allocation techniques. This work focuses on the notion of dynamic cooperative spectrum sharing and addresses the issue of dynamic cooperative spectrum allocation for flexible optical networks. In orderto cope with the dynamicity of the traffic demands, spectrum expansion/contraction (SEC) policies attempt to accommodate incoming requests by means of expanding/contracting the allocations of connections. When spectrum expansion is limited by neighboring connections, appropriate spectrum defragmentation (SD) policies undertake the task of reallocating connections in order to free up the spectrum. In this work, a novel cooperative SEC policy is examined, which takes into consideration the spectrum allocation of neighboring connections. Additionally, a class of cooperative SD policies is proposed, based on the capabilities of current technology. Simulation results from two reference core networks quantify the benefits that can be reaped in terms of blocking rate. Trade-offs with respect to the achieved reduction in blocking rate and the number of reallocated connections during the SD procedure are examined.
TL;DR: In this paper, the authors identify a realistic expectation of modulation formats for the next 10 years and quantifies the possible capacity gains, and study when the capacity will be exhausted using current fixed-grid optical channel assignment, and compare this with a pack of novel evolution strategies toward flexi-grid.
Abstract: It is widely acknowledged by operators and market analysts from all parts of the telecommunications industry that bandwidth demand is increasing dramatically, year by year. This traffic growth highly impacts on all network segments and pushes network operators to consider new networking solutions. Flexi-grid technologies enable more flexible use of the spectral resources, increasing the overall network spectral efficiency. However, the currently deployed fixed-grid dense wavelength division multiplexing (DWDM) optical infrastructure might be replaced with new components to enable this technology. This paper first identifies a realistic expectation of modulation formats for the next 10 years and quantifies the possible capacity gains. Second, we study when the capacity will be exhausted using current fixed-grid optical channel assignment, and compare this with a pack of novel evolution strategies toward flexi-grid. Results show that the capacity will be exhausted by 2019 in the Spanish core network, and that by applying the flexi-grid evolutionary model, the network life can be extended up to five years. A shorter-term rationale to migrate to flexi-grid is the availability of cost-effective 400 Gbps and 1 Tbps transmission.
TL;DR: A gigabit capacity fiber-wireless system that enables smooth integration between high-speed wireless networks and dense wavelength-division-multiplexing (DWDM) access networks by employing a centralized optical frequency comb is reported on.
Abstract: In this paper, we report on a gigabit capacity fiber-wireless system that enables smooth integration between high-speed wireless networks and dense wavelength-division-multiplexing (DWDM) access networks. By employing a centralized optical frequency comb, both the wireline and the wireless services for each DWDM user can be simultaneously supported. Besides, each baseband channel can be transparently upconverted tomultiple radio-frequency (RF) bands for different wireless standards, which can be flexibly filtered at the end user to select the on-demand RF band, depending on the wireless applications. For demonstration, we transmit a 2.5 Gbit/s signal through the proposed system and successfully achieve a bit-error-rate (BER) performance well below the 7% overhead forward error correction limit of the BER of 2 × 10-3 for both the wireline and the wireless signals in the 60 GHz band after 25 km single-mode fiber plus up to 6 m wireless distance.