Time And Wavelength Division Multiplexing Research Articles

Coherent time- and wavelength-division multiplexed point-to-multipoint optical access network using low-cost DFB lasers enabled by a frequency comb

Coherent reception, along with time- and wavelength-division multiplexing (TWDM), is a promising concept to simultaneously support multiple services in future high-speed point-to-multipoint passive optical networks (PONs). The next-generation PON 2 (NG-PON2) standard describes a TWDM-PON based on IM/DD intensity modulation and direct detection (IM/DD) which employs tunable-lasers and optical filters such as tunable optical filters or cyclic arrayed-waveguide gratings. Here, we investigate what we believe to be a novel coherent TWDM-PON architecture based on a frequency comb source in the optical line terminal (OLT), and thermally-tuned distributed-feedback (DFB) lasers in the optical network units (ONUs). For downstream operation, we broadcast multiple copies of two 25 GBd dual-polarization quadrature phase shift keying (DP-QPSK) signals, resulting in a total PON downstream capacity of 200 Gbit/s. The copies of the downstream signals are spanning ±2 nm (±250 GHz). In the ONUs, we align the wavelengths of the DFB lasers, which act as local oscillators (LOs), to one of the downstream signals by a thermal heater or by changing the direct current. In upstream, the already aligned DFB lasers act as transmit lasers and the frequency comb as LO. We demonstrate TWDM upstream by emulating two ONUs with 25 GBd DP-QPSK, resulting in a total PON upstream capacity of 200 Gbit/s.

Energy evaluation for a dynamic and reconfigurable TWDM‐PON on a novel network traffic adaptable pattern

SummaryEven with existing methodologies, dynamic resource allocation, service inconsistency, operational costs, and excess energy/power consumption in optical access networks remain the key challenges for the next‐generation passive optical network (NG‐PON) design and development. This paper introduces a novel method for analyzing energy/power consumption in time and wavelength division multiplexed (TWDM) passive optical networks (PONs) with a ring‐based topology. We propose subscriber‐based channel allocation models (CAMs) for on‐demand services, allocate bandwidth dynamically, and evaluate their downstream power consumption. To determine the necessary optical devices for the various CAMs, we investigate subscriber take‐up rates by optimizing the utilization of optical components based on active subscribers. Implementing a novel Poisson distribution‐based network traffic model addresses energy‐related concerns and explores optimization techniques to minimize power and improve energy efficiency. With a take‐up rate of 64 active subscribers, simulation results show significant power consumption reductions ranging from 62.2 to 67.7%, achieved by the proposed subscriber‐based architecture models with varying subscriber counts, when compared with the conventional model. The model with the most subscribers (2048 subscribers) saves the most energy by reducing power consumption to 292 W from the conventional model's (2048 subscribers) 440 W. Furthermore, the model with the most subscribers saves 33.4% of energy, outperforming other subscriber‐based architecture models without affecting QoS even during peak hours of the day. These numerical results show that TWDM‐PONs with the most subscribers exhibit improved energy efficiency than the conventional and other proposed subscriber‐based architecture models.

TWDM-assisted passive quadrature phase demodulation for a Fabry-Perot-based ultrasound localization detection.

We propose a time and wavelength division multiplexing (TWDM)-assisted passive quadrature phase demodulation mechanism in this Letter. Combining wavelength division multiplexers (WDMs) with a programmable modulated grating Y-branch (MG-Y) laser, this method realizes both fast switching of discrete wavelengths and fast activation of multiple sensing paths simultaneously. Deploying it on a fiber-optic dual-cavity Fabry-Perot (F-P) ultrasound sensor array, we achieve high-precision localization of partial discharge (PD) signal sources in a two-dimensional (2D) plane with a maximum distance error of 1.53 cm and a maximum angle error of about 3.02°. This demodulation scheme can balance the relationship between sensitivity, sampling rate, and time-delay-induced errors, and provides an innovative solution for high-frequency phase demodulation applications of sensor arrays, which is especially significant for high-frequency detection in specific environments like partial discharges, industrial nondestructive testing, and so on.

Integrated long reach and energy-efficient NGPON-VLC system with OCDM/WDM for smart green buildings

Smart green buildings (SGBs) are composed of numerous services and offer hopeful solutions to the world's continuous and rapid urbanization. Conventional data transmission systems are insufficient to deliver acceptable services because to the sudden surge in high-quality information transmission requirements over long distance for numerous linked residents in SGBs. Consequently, a hybrid next generation passive optical network (NGPON) along with visible light communication (VLC) indoor/outdoor broadcast network is presented in this work to increase the reliability with intelligence, exalted overall efficiency, cost efficiency, and security of SGBs. Bidirectional PON-VLC system incorporates the time and wavelength division multiplexing (TWDM), wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) techniques. In order to improve system performance, various OCDM codes are used in this work at 10/2.5 Gbps per channel throughput via fiber-VLC channels. According to the simulation results, the modified new zero cross-correlation (MNZCC) code performs better than previous codes and supports 200 active residents at reliable 100 km fiber along with 5 m VLC range. Furthermore, by expanding the received aperture diameter to 25 cm, VLC coverage may be increased till 10 m. Moreover, it provides adequate receiver sensitivities of − 13 to − 12 dB in uplink with − 9.8 to − 6 dBm in downlink for 200 to 600 fields of view angles compared to 00 view angle having sensitivity of − 15 dBm. Additionally, the numerical analysis and comparison performance show that PON-VLC outperforms fiber-VLC link-based scenarios when it comes to noise and channel impairments.

Impairment strained analytical modeling evaluation and cross-talk analysis of symmetric and coexistent channels for extended class-1 NG-PON2 access network.

The analytical modeling for linear and non-linear impairments (LNI) for single mode fiber (SMF) and simulative analysis of extended power budget class-1 i.e. E1-class of next generation passive optic network-2 (NG-PON2) is presented in the paper. The proposed power-budget class time and wavelength division multiplexing (TWDM) based NG-PON2 network configuration is delivering symmetric 2.5 point-to-multi point (PtM) representing time and TWDM XGS-PON along with 10 Gbps point-to-point (PtP) wavelength division multiplexing (WDM) symmetric and coexistent channels (Ch) in worst-case scenario. Channel modelling of LNI is carried out under the incremental and aggregate strain of estimated chromatic dispersion CD, self-phase modulation (SPM), cross-phase modulation (XPM) of single mode fiber (SMF) channel deployed in optical distributing network (ODN) between 20 and 50 km link lengths. Downlink (D/L) and uplink (U/L) ODN is optimized to PTODN = 7.1 dBm and 4.09 dBm, respectively and corresponding channel imparities including Kerr parameter γ, corresponding SPM, XPM, CD, four-wave mixing (FWM) analysis and corresponding component power and efficiency, interchange crosstalk (Cc) attracting power penalties (Pc) are estimated and incorporated in the simulation for the real response of lossy SMF channel. Further, splitter power budget (SP) and slitter configuration for respective PtM and PtP D/L Ch are estimated under the aggregate impact of CD, SPM, XPM and FWM. Analytical modeling of LNI and simulative analysis has confirmed the configuration delivered rise in receiver sensitivity (Rxs) of − 39.75/− 33.45 dBm and − 29/− 35.34 dBm for D/L and U/L Ch respectively. The estimated power of FWM element is between 1.34 × 10−52 to 2.15 × 10−53 and 3.87 × 10−52 to 2.41 × 10−51 contributing crosstalk between Ch (Cc) of − 31.97/− 30.12 dB for down/up spectrum under the impact of SPM and XPM respectively accommodating splitter configuration of 768 at 40 km.

Flexible energy-efficient and direct intra-ODN/OPN communication capable TWDM PON architecture with centralized OLT sharing among multiple optical networks

Nowadays, service reliability, operation cost, transmission latency of optical access networks are the major challenging issues that need to be addressed while planning and developing the next-generation passive optical networks (NG-PONs). This paper proposes a flexible, energy-efficient, time and wavelength division multiplexed (TWDM) PON architecture that has the capability of centralized optical line terminal (OLT) resource sharing with multiple optical networks. The architecture has the point-to-point direct inter-optical networking unit (dedicated inter-ONU) transmission capability among the various ONUs located within the same optical distribution network (ODN). Such transmission may also be referred to as direct intra-ODN communication. The architecture also has the potential of transmitting an inter-ONU signal to the ONUs residing in the different ODNs (inter-ODN) belonging to the same optical network (OPN). Such transmission may be referred as the direct inter-ODN or intra-OPN transmission. The architecture reduces the normalized energy consumption of approximately 2.21875 Wh per hour, normalized transmission latency of approximately 148 µs for the direct inter-ONU transmission. This is achieved by diverting the inter-ONU signal from the remote nodes (RNs) itself towards the intended ONUs. The percentage energy saving of the proposed architecture is approximately 74 % as compared to the conventional architecture. The proposed architecture is suitable for strengthening the existing information and communication technology (ICT) infrastructures and can be implemented in next-generation flexible, energy-efficient, latency-aware, and reliable optical networks for developing smart rural and urban communities.

Analytical modeling and impact analysis on multichannel symmetric optical and wireless NG-PON2 networks of CD, SPM, XPM and FWM impairments

A conceptual model for optical wireless (OW) interfacing with NG-PON2 access network is analyzed using N1-class backbone optical distribution and OW free-space optics (FSO) channels in the frontend to connect ONUs to symmetric 1.25/2.5/10 Gbps channels incorporating Time and Wavelength Division Multiplexing (TWDM) technique to deliver applications and services based on Fiber-to-the-X (FTTX), IoT and 5 G technologies. We successfully demonstrated the design and analysis of ODN channel attributes supporting coexistence approach in contiguous with fiber channel linear and nonlinear impairments (LNI), and atmospheric attenuations β due to haze, dry particles inside the premises for high-speed OW channel for indoor applications along with optimization of hybrid N1-power budget class distributing configuration propagating multi-channel (MC) OW-FSO TWDM NG-PON2 configurations supporting symmetric configuration. Multichannel input power is calculated to optimize up/down link spectrum ODN power to 4 and 3 dBm respectively at worst-case scenario accommodating eight symmetric channels. Simulation results achieved at 50.011 km in either direction are − 41.85/− 36.67/− 39.04/ dBm and − 33.63/− 42.78/− 37.92 dBm receiver sensitivities supporting 448 splitter configuration at 50.011 km, FWM efficiency is 1.65e-52 and FWM component power at as low as − 53 to − 54 dB in conjunction with CD, SPM, XPM, and FWM LNI for spectrum in either directions.

A QoS-Aware Dynamic Bandwidth Allocation Algorithm for Passive Optical Networks with Non-Zero Laser Tuning Time

The deployment of new 5G services and future demands for 6G make it necessary to increase the performance of access networks. This challenge has prompted the development of new standardization proposals for Passive Optical access Networks (PONs) that offer greater bandwidth, greater reach and a higher rate of aggregation of users per fiber, being Time- and Wavelength-Division Multiplexing (TWDM) a promising technological solution for increasing the capacity by up to 40 Gbps by using several wavelengths. This solution introduces tunable transceivers into the Optical Network Units (ONUs) for switching from one wavelength to the other, thus addressing the ever-increasing bandwidth demands in residential broadband and mobile fronthaul networks based on Fiber to the Home (FTTH) technology. This adds complexity and sources of inefficiency, such as the laser tuning time (LTT) delay, which is often ignored when evaluating the performance of Dynamic Bandwidth Allocation (DBA) mechanisms. We present a novel DBA algorithm that dynamically handles the allocation of bandwidth and switches the ONUs’ lasers from one wavelength to the other while taking LTT into consideration. To optimize the packet delay, we introduce a scheduling mechanism that follows the Longest Processing Time first (LPT) scheduling discipline, which is implemented over the Interleaved Polling with Adaptive Cycle Time (IPACT) DBA. We also provide quality of service (QoS) differentiation by introducing the Max-Min Weighted Fair Share Queuing principle (WFQ) into the algorithm. The performance of our algorithm is evaluated through simulations against the original IPACT algorithm, which we have extended to support multi-wavelengths. With the introduction of LPT, we obtain an improved performance of up to 73% reduction in queue delay over IPACT while achieving QoS differentiation with WFQ.

Design and investigation of N1-class next-generation passive optical network-2 (NG-PON2) coexistence architecture in the presence of Kerr effect and four-wave mixing (FWM) for fiber to the home (FTTX) access networks

Abstract In this paper, we investigated N1-class Time and Wavelength Division Multiplexing (TWDM) Next-Generation Passive Optical Network-2 (NG-PON2) supporting symmetric and coexistence configuration in a worst-case scenario. The network is optimized in the presence of linear and nonlinear impairments such as chromatic dispersion (CD), self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM). On-off key (OOK) modulation technique incorporating hybrid optical distribution network (ODN) i.e., wavelength select (WS) and wavelength-routed (WR) ODN is used to connect downstream (D/S) and upstream (U/S) channels supporting symmetric 80 Gbps data rate operating at 2.5/2.5 and 10/10 Gbps, respectively. G.652 single-mode (SM) fiber channel is modeled for fiber launch power PTODN = 3 dBm and 4 dBm for D/S and U/S channels to implement N1-class network. The D/S and U/S receiver sensitivity (Rxs) demonstrated are −44.23/−37.46 dBm and −28.46/−35.32 dBm and inter-channel crosstalk (Cc) is −31.97/−31.39 dB accommodating 640 splitter configuration at 50 km in the presence of impairments at 10E-7 bit error rate (BER) and Quality (Q)-factor of 5 for 10 Gbps channel.

Design and analysis of hybrid optical distribution network for worst-case scenario of E2-class symmetric coexistence 80 Gbps TWDM NG-PON2 architecture for FTTX access networks

In this paper, we investigated the cost-effective design and validation of E2-class coexistence 80 Gbps symmetric 8 × 8 Time and Wavelength Division Multiplexing (TWDM) NG-PON2 optical access network considering worst-case scenario for the deployment of Fiber-to-the-X (FTTX) access network using hybrid optical distribution network (ODN). Full-service access network (FASN) unanimously agreed and ITU-T G.989.2 described recommendations for TWDM PON NG-PON2 technology to cater to the need of ever-increasing demand for higher bandwidth and data speed beyond 10 Gbps per user through access networks. Wavelength select (WS) and wavelength-routed (WR) ODN for downstream (D/S) and upstream (U/S) channels symmetric coexistence functionality supporting 80 Gbps accommodating GPON and XGS-PON legacy channels i.e.4-TWDM and 4 point-to-point (PtP) WDM channels operating at 1.25/2.5/10 Gbps respectively in D/S and U/S direction with error free higher splitter configuration of 2304 at 20 km, 640 at 40 km, 576 at 60 km. Precise calculations are done to ensure 11 dBm and 9 dBm ODN launch power (PTODN) to implement worst-case scenario for symmetric E2-class TWDM NG-PON2 network. Calculated inter-channel cross-talk (Cc) is -33.57 dB/-34.74 dB and corresponding cross-talk power penalty (Pc) is 0 dB for D/s and U/S channels respectively. Simulation results demonstrated and verified with the recommendations made in ITU-T G.989.2 confirmed that the proposed network configuration supports extended to reach upto 60 km in D/S and 80 km in U/S direction delivering incremental receiver sensitivity (Rxs) as -34.40/-34.40/42.21 dBm and -34.11/-37.25/-33.37 dBm, ODN path loss 29.40 dB.

TWDM-Assisted Active Quadrature Demodulation of Fiber-Optic Fabry–Perot Acoustic Sensor Network

In this article, we propose a hybrid time and wavelength division multiplexed (TWDM) active quadrature demodulation technique for fiber-optic Fabry–Perot acoustic sensor network. A modulated grating Y-branch (MG-Y) laser is utilized to achieve fast and programmable wavelength tuning. For each sensing channel, two operating wavelengths with quadrature phase difference are determined by the initial cavity length of the sensor. According to the DC voltages of the detected signal, the operating wavelength is feedback-controlled to locate on the spectral slope, maintaining the high sensitivity of the sensing system. Compared with traditional passive quadrature demodulation and quadrature point intensity demodulation methods, the feedback control logic is simple and flexible. Moreover, the proposed active quadrature demodulation scheme is easily applicable to sensors with different cavity lengths. Combined with a hybrid TWDM technology, simultaneous multi-point acoustic detection can be achieved, requiring only one tunable laser and one photodetector. A two-point sound velocity sensing system and a four-point sound source localization system are constructed. Experimental results show that different sensing channels can work effectively without crosstalk.

Bidirectional Transmission in TWDM Optical Access Network with Tunable Wavelength ONU

In this paper, a novel configuration for bidirectional hybrid time and wavelength division multiplexing (TWDM) optical access network is presented that fulfills the growing broadband requirements of next generation 5G customers. A purely passive system module is suggested for 512 subscribers that can communicate at a line rate of 240 Gbps in downlink and 160 Gbps in uplink over the common fiber cable. Shared network infrastructure helps in amortization of the installation and recurring operational expenses. Subscriber optical network unit (ONU) consists of tunable wavelength transmitter that can adjust uplink channel on the instructions of the medium access control layer (MAC). Improved Bandwidth Optimization Hybrid Scheduling Algorithm (BOHSA1) is implemented in the network to reduce the wastage of time slots per channel that helps in improving the channel utilization. The demonstrated architecture is extensively investigated to know the impact of diverse encoding scheme; photo-detector and electric filter have on the network performance.

Dual MAC Based Hierarchical Optical Access Network for Hyperscale Data Centers

A dual media access control (DMAC) based hierarchical optical access network (HOAN) is proposed for data center networks, consisting of passive optical distribution modules (PODMs) at passive optical access layer and top-of-cluster (ToC) switches at electronic access layer. A PODM organizes a group of servers into a computing cluster and forms the intra-cluster channel. Each ToC switch connected with several PODMs forms the inter-cluster channel based on time and wavelength division multiplexing (TWDM). A load-sensing dual-mode (LSDM) protocol is presented for the intra-cluster channel to realize distributed low-load competition and high-load polling operation; the inter-cluster channel applies any polling based TWDM protocol to offer flexible bandwidth allocation. Simulations show that the LSDM can reach 0.95 throughputs at high traffic load, less than 32 μs frame latency, 128 μs frame latency on the 99.9th percentile of the simulated results at 25 Gbps with high priority, verifying the LSDM protocol can realize high throughput, low latency, and the measured latency variation. Compared the performances of DMAC based HOAN with those of passive optical cross-connection network (POXN) and passive optical top-of-rack interconnect (POTORI) architecture, when the normalized intra-rack traffic load reaches 0.8, average frame latencies in one computing cluster are 70.4, 184, and 2480 μs at 10 Gbps, and normalized available bandwidths for inter-cluster channels are 1, 0.2, and 0.2, respectively. Furthermore, the DMAC based HOAN is characterized with the scalability capable of organizing up to 320000 servers with only 500 ToC switches.

Economics of TWDM PONs With Nonlinear Pricing

This letter develops an analytical model to describe the economics of time- and wavelength-division multiplexed (TWDM) passive optical networks (PONs). The network operator is modeled as a profit maximizer that offers multiple subscription plans. The end users either select one of these offers or refrain from availing the service. In this circumstance, the profit maximization problem of the operator appears to be a mixed-integer nonlinear program. The solution to this problem provides insights into the economics of PONs. For example, the analysis systematically identifies the range of parameters where the operator earns a positive profit and thus ensures that the network is economically sustainable.

Economic Analysis of TWDM PONs: A Sustainability and Policy-Making Perspective

The time- and wavelength-division-multiplexed (TWDM) passive optical network (PON) is a popular choice for future access technology. However, a comprehensive understanding of its economics is still beyond the reach of the current literature. For example, it is not clearly understood which techno-economic factors make this technology sustainable. Similarly, the role of the government in influencing the users' welfare has also remained opaque. In this paper, we uncover these important issues. Portraying the operator as a profit maximizer, we develop a mathematical model that encapsulates both economic and technical aspects of the network. Within this framework, the profit maximization problem of an operator turns out to be a mixed-integer nonlinear program that, in general, is exponentially complex. Fortunately, using a widely accepted assumption on user demand, we reduce this to a discrete optimization. Moreover, for a large class of demands, a polynomially complex algorithm is developed to solve this problem. For homogeneous linear demands, we analytically characterize the system parameters that ensure the sustainability of the network in the long run. In addition, the influence of different system parameters on the economic outcomes is studied. Our investigation reveals several policy-making insights. For example, it unveils a fundamental trade-off between the number of users and the aggregated welfare. Also, it suggests that the leasing of fibers isa better deployment policy for the government as compared to the other alternatives. Finally, we show that the architectural details of the network play a key role in deciding the economics. In particular, one variant of the PON is shown to be more viable than another.

An ILP-based CapEx and OpEx efficient multi-stage TDM/TWDM PON design methodology

Abstract With reference to huge investment needed for greenfield passive optical network (PON) deployment, it is immensely important to define procedures and algorithms aimed towards optimal layout and network planning to reduce the overall expenditure due to capital expenditure and operational expenditure as much as possible. We propose an integer linear programming (ILP) based optimization model that explores optimal network dimensioning and placement of network equipment at appropriate locations so as to minimize the overall expenditure. Based on the number of users [optical network units (ONUs)], user’s bandwidth demand, power budget, maximum distance from optical line terminal (OLT) to users, available number of wavelengths and OLT ports, and geographical locations of ONUs, OLT and candidate locations of remote nodes (RNs), the model selects the number, type, splitting ratio and locations of passive devices. The RN device type is selected to be either power splitter or array waveguide grating. Optimal PON architecture is appropriately identified to be time division multiplexing or time-and wavelength division multiplexing (TWDM) depending on the requirement. It provides complete interconnection details among all devices, the overall expenditure, the number of OLT ports and the number and associated data rates of wavelengths to be used. We show exhaustive results for two deployment regions (viz. urban and rural) with different number of ONUs and bandwidth demands from users.We also show result with actual locations of OLT, ONUs and RNs selected from Google map. The proposed ILP model has low computational complexity and offers optimal solution within a reasonable time limit, without requiring a heuristic approach that provides a sub-optimal solution. The TWDM-PON conforms to next-generation PON stage 2 (NG-PON2) specifications and can be used as a useful tool for setting up NG-PON2.

Frequency Drift Reduction in a Four-Laser Array for TWDM PON Applications

Burst-mode operation of laser arrays suitable for next-generation passive optical networks (PON2) employing time and wavelength division multiplexing (TWDM) is impaired by frequency drifts under variable burst duration. In this work, the issue of frequency drifts under burst and wavelength switching operation is addressed in a four-laser array integrated with a multimode interference coupler using a regrowth-free technology. Frequency drifts are shown to be significantly reduced in a TWDM-PON configuration thanks to the introduction of a thermal management technique based on the use of inactive lasers in the array. Thanks to this method, up to 22% drift reduction is obtained under burst and wavelength switching operation.

Hybrid optical wavelength demultiplexer and power combiner for TWDM PON

In this paper, we have proposed a hybrid optical wavelength demultiplexer and power combiner for a hybrid time- and wavelength-division multiplexing (TWDM) passive optical network (PON), i.e., a single passive optical device that functions as a 1×N wavelength demultiplexer for distributing the downstream signal in multiple wavelengths from the optical line terminal (OLT) to the N optical network units (ONUs), and simultaneously as an N×1 power combiner for collecting the upstream signal in the same wavelength from the N ONUs to the OLT. Through a design example of a 32 channel hybrid optical wavelength demultiplexer and power combiner on the silicon-on-insulator platform, our numerical simulation result shows that the insertion loss and adjacent channel crosstalk of the downstream wavelength demultiplexer are as low as 4.6 and −16.3 dB, respectively, while the insertion loss and channel non-uniformity of the upstream power combiner can reach 3.5 and 2.1 dB, respectively. The proposed structure can readily be extended to other material platforms such as the silica-based planar lightwave circuit. Its fabrication process is fully compatible with standard clean-room technologies such as photo-lithography and etching, without any complicated and/or costly approach involved.

Exploiting SDN for Integrating Green TWDM-PONs and Metro Networks Preserving End-to-End Delay

In time and wavelength division multiplexed (TWDM) passive optical networks (PONs), energy efficiency can be traded with increased average frame delay. However, because some IP services have strict end-to-end delay requirements, such increased delay must be compensated in other network segments. To achieve such compensation, an interaction between control and management planes of different network segments is required. So far, such interaction could be achieved only by custom interfaces at the border of each network segment. Recently, software defined networking (SDN) has emerged as a de facto standard to provide a versatile control and management plane for any network segment. This paper proposes and successfully demonstrates an aggregation node based on a lightweight SDN solution scaled to operate as an intranode controller. The node connects a TWDM-PON, which implements an optical line terminal energy efficient scheme based on dynamic bandwidth and wavelength allocation, and a metro/aggregation network based on OpenFlow switches. Results show that sleep mode in TWDM-PON could increase the traffic delay by hundreds of microseconds, but, by prioritizing such traffic in the metro network, the delay experienced by it in the metro segment is reduced by at least the same amount. Thus the end-to-end delay is maintained.

Delay fairness in reconfigurable and energy efficient TWDM PON

In Time and Wavelength Division Multiplexed (TWDM) Passive Optical Networks (PONs), dynamically (de)activating Optical Subscriber Units (OSUs) and assigning Optical Network Units (ONUs) to the active OSUs helps improving the OLT energy efficiency and balancing the network load.However, energy efficiency improvement is traded with a delay increase due to the finite ONU tuning speed and the potential increase of the normalized load with respect to the number of active OSUs. Moreover, even though load balance potentially assures delay balance, the scheduling and assignment of ONUs to OSUs might cause ONU delay unbalance (i.e., delay unfairness). Indeed, if an ONU is forced to tune at each reconfiguration it suffers a high delay penalty due to its limited tuning time.In this study, the impact of the ONU scheduling and assignment to OSUs upon network reconfiguration on the average frame delay unbalance is evaluated. Then, a method that balances the average frame delay by swapping the tuning ONU upon reconfiguration is proposed, for some critical scenarios. Simulation and experimental results show that the delay unbalance is large when the number of active ONUs is small (e.g., at network start up or when the majority of the ONUs is inactive/sleeping). In this case, the proposed method effectively balances the delay experienced by ONUs without impacting the OLT energy savings.