Full Service Access Network Research Articles

Asymmetric 160/80 Gb/s TWDM PON with supported transmission method utilizing FBG and DML

Abstract The primary objective of time wavelength-division multiplexing passive optical networks (TWDM-PONs) development at the moment is the cost-effective capacity acquisition. This work addresses this issue by demonstrating a full-system TWDM-PON was selected as a primary choice to NG-PON2 by Full-service access network (FASN) unanimously agreed and International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.989. An asymmetric TWDM NG-PON2 was demonstrated that provides 160 Gbps downstream and 80 Gbps upstream which is the target capacity by ITU-T G.989.1 based on OptiSystem-7 software. We propose to use fiber Bragg grating (FBG) and Er-doped fiber amplifier (EDFA) to reduced both of the chromatic dispersion effect and system attenuation until given permission to enhance the distance communication system. The proposed system’s performance is evaluated and compared with other works and ITU-T G.989.2 recommendations to demonstrate how the system can be enhanced in terms of capacity, link distance, bit error rate (BER), Q-factor and receiver sensitivity. According to the results, the optimum possible distance under communication requirements (6 for the Q-factor and 10−9 for the BER) is around 65 km for the system with dispersion compensation. With the help of the low-cost directly modulated laser (DML) for uplink, we successfully improve the power budget to 41.2 dB along 65 km of bidirectional fiber at a 1:512 splitting ratio.

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.

Progress of ITU-T higher speed passive optical network (50G-PON) standardization

This paper reviews the key factors in the discussion and selection process before the launch of the higher speed passive optical network (PON) standards project in the Full Service Access Network and ITU-T SG15/Q2. It reviews the requirements for such a system and the progress of the related ITU-T standards documents. The key technologies necessary for the physical and protocol layers of the 50G-PON are also discussed.

How Does Passive Optical Network Tackle Radio Access Network Evolution?

This paper describes full service access network operator group perspectives on the feasibility of optical access networks to carry radio access network traffic for the existing and future mobile generations. The paper discusses topics related to the evolution of radio access interfaces, such as backhaul, midhaul, and fronthaul, their transmission through optical distribution networks, and passive optical network technology feasibility based on both time and wavelength division multiplexing and multiple accesses. Technology extensions are also discussed to provide guidance for future research.

Novel ring-based architecture for TWDM-PON with high reliability and flexible extensibility

Time and wavelength division multiplexed passive optical network (TWDM-PON) was determined as a primary solution to NG-PON2 by the full service access network (FSAN) in 2012. Since then, TWDM-PON has been applied to a wider set of applications, including those that are outage sensitive and expansion flexible. So the protection techniques with reliability and flexibility should be studied to address the above needs. In this paper, we propose a novel ring-based architecture for TWDM-PON. The architecture can provide reliable ring protection scheme against a fiber fault occurring on main ring (MR), sub-ring (SR) or last mile ring (LMR). In addition, we exploit the extended node (EN) to realize the network expansion conveniently and smoothly for the flexible extensibility. Thus, more remote nodes(RNs) and optical network units (ONUs) could access this architecture through EN. Moreover, in order to further improve reliability of the network, we design the 1:1 protection scheme against the connected fiber fault between RN and EN. The results show that the proposed architecture has a recovery time of 17ms under protection mode and the reliability of the network is also illustrated to be greatly improved compared to the network without protection. As the number of ONUs increases, the average cost of each ONU could be gradually reduced. Finally, the simulations verify the feasibility of the architecture.

Flexible tunable optical transceiver based on field-programmable gate array for time and wavelength-division multiplexed passive optical network systems

Time- and wavelength-division multiplexed passive optical networks (TWDM-PONs) have been selected by the full services access network community as the most suitable technology for next-generation optical access networks. A key technology in TWDM-PON is the colorless optical network unit transceiver. This paper proposes a flexible, tunable optical transceiver that uses directly modulated tunable lasers. Using a field-programmable gate array (FPGA), programmable reconfigurations and testing capabilities can be embedded into the transceiver in order to implement wavelength control, signal generation, pre-emphasis for upstream, and a bit error rate (BER) test for the downstream. To ensure high-quality signal generation at different bitrates, impedance matching between the laser driver circuit and the laser diodes is optimized. Using the proposed transceiver, three-section-distributed Bragg reflector tunable lasers at or below 2.5 Gb/s direct modulation through a 40-km standard mode fiber transmission were successfully implemented.

ZTE’s perspective on applying OFDM-PON in next converged optical and wireless networks

Driven by ZTE and other telecom vendors and operators in order to meet the ever increasing bandwidth demand from fixed optical network users and mobile backhaul/fronthaul services, the latest next generation passive optical network (NGPON2) is being standardized by Full Service Access Network (FSAN) and International Telecommunication Union (ITU-T) which consists of two separated sub-systems, hybrid time- and wavelength-division multiplexing PON (TWDM-PON) and point-to-point wavelength- division multiplex (PtP WDM). The TWDM-PON will be used for traditional residential, business and wireless backhaul services which are not sensitive to time delay and delay variation, whereas the PtP WDM is mainly used for emerging wireless fronthaul service which is very sensitive to the time delay and time delay variation. However, as a main international standards’ contributor, ZTE thinks for those operators who offer multiple-level of services to both residential, business and mobile backhaul/fronthaul users, this obviously raises significant economic and power concerns by demanding to deploy two separated systems. Therefore, in this paper, for the first time, ZTE proposes a new converged optical and wireless integrated network architecture and topology by applying orthogonal frequency division multiplexing (OFDM) PON technology, which is able to simultaneously support residential, business and mobile backhaul/fronthaul services in terms of meeting the requirements of both time delay sensitive and non-sensitive services, and also address the economic and power concerns compared with conventional technologies. This architecture is further investigated and analyzed in depth on functional block, Quality-of-service (QoS), synchronization and deployment considerations. Also ZTE reports in this paper the first 40Gbps OFDMPON prototype in which eight wavelengths each with 5Gbps Ethernet data via 10G-PON encapsulation method (X-GEM) and 10G-PON transmission convergence (X-GTC) framing are demonstrated.

PON versus AON: Which is the best solution to offload core network by peer-to-peer traffic localization

Video streaming and video-on-demand are gaining popularity nowadays which dictates a need of bandwidth upgrade for Internet users. Many next generation optical access network architectures have been proposed to meet high capacity requirement on a per-user basis. However, the capacity upgrade in access networks, may lead to a huge traffic growth in the aggregation/core network. One way to avoid this problem is to keep the traffic locally (i.e., inside the access network area) as much as possible. It can be obtained by using locality-aware peer-to-peer (P2P) applications for content distribution and has the potential to offload the core segment. However, various optical access network architectures accommodate the P2P traffic in different ways. Thus, it is important to study these differences in order to identify the best architecture option for capacity offloading in the core network, energy efficiency and network resource utilization. By deploying a proper architecture in the access segment along with an efficient traffic locality aware strategy, the extra investment and capacity upgrade of the expensive core network resources needed to support the future traffic expansion can be minimized. However, to the best of our knowledge this kind of assessment is so far not available.Therefore, in this paper, we analyze the efficiency of supporting locality-aware P2P video distribution algorithm in three main types of optical access network architectures, i.e., active optical network (AON), wavelength division multiplexing passive optical network (WDM PON) and time/wavelength division multiplexing PON (TWDM PON). Our goal is to provide important design guidelines for the next generation broadband access architectures, while minimizing the need for the core network upgrade. We obtain this objective by utilizing the unique characteristics of each access network architecture in accommodating P2P video delivery applications. We have done an extensive literature study and for the first time we have compared performance of these architectures with respect to the amount of the traffic on the links in different aggregation levels, power consumption taking into account sleep mode functionality at the user premises, and required switching capacity in the nodes. Our results reveal that both active and passive architectures have good ability to localize P2P traffic, whereas they show distinct performance with respect to the other aforementioned aspects. This is caused by the different number of aggregation levels, link capacity, and resource allocation protocols. Considering the overall performance evaluation, it is shown that TWDM PON is the most promising option for the future broadband access, where locality-aware P2P video distribution is applied, thanks to its low energy consumption and required switching capacity of the network equipment needed to deliver this service. This conclusion is against the general intuition because of the PON׳s centralized control plane and passive infrastructure without switching capability in the field. Our unexpected conclusion can be of particular interest to operators as it is perfectly aligned with next generation optical access architecture identified by Full Service Access Networks (FSAN).

Low cost TWDM by wavelength-set division multiplexing

After extensive comparison of candidate technologies, the Full Service Access Network (FSAN) Group in early 2012 made the decision to define Time/ Wavelength Division Multiplexing (TWDM) as the primary solution for the next-generation passive optical network (NG-PON2). A minimum of four wavelengths are foreseen as providing a total capacity per feeder line of 40 Gbit/s downstream and 10 Gbit/s or more upstream. Conventional wavelength division multiplexing (WDM) lasers from core or metro networks are too expensive for fiber to the home (FTTH) systems, because every optical network unit (ONU) will need a tunable laser for upstream transmission. In this paper we will compare different technical solutions and present wavelength-set division multiplexing (WSDM), a scheme developed by Bell Labs as the preferred solution for cost reasons. WSDM uses a laser that can be tuned by an on-chip heater stripe. To exploit this partial wavelength tunability, we do not use contiguous wavelength bands, but wavelength-sets consisting of cyclic interleaved wavelength slots on a fine grid. This wavelength plan can be implemented, e.g., by a cyclic arrayed waveguide grating (AWG) with a small free spectral range. We will describe the concept in detail and report on its experimental validation.

Characterization of energy-efficient and colorless ONUs for future TWDM-PONs

The Full Services Access Network group has recently selected the time and wavelength division multiplexed passive optical network (TWDM-PON) as the base technology solution for next-generation PON stage-2 (NG-PON2). Meeting the core requirements of NG-PON2 necessitates the following additional features in the transceivers of the optical network unit (ONU) that is located at subscriber premises: (a) legacy system compliant; (b) wavelength tunable; (c) cost-efficient; and (d) energy-efficient. To address these features, we investigate the properties of short-cavity vertical-cavity surface-emitting lasers (SC-VCSELs) for implementation as colorless ONU transmitters in future TWDM-PONs. Specifically, we investigate the tunability and transmission performance of the SC-VCSEL across the C-minus wavelength band for legacy system compliance. We report on error-free transmission across a 800 GHz tuning range with a potential aggregate upstream capacity of 80 Gbps over a system reach of 40 km and with a split ratio of 1:128 per wavelength channel. Results were achieved without dispersion compensation and electronic equalization. We also evaluate the energy efficiency of the SC-VCSEL in active, doze, and sleep mode. When in active mode, the SC-VCSEL transmitter block consumes 91.7% less power than a distributed feedback (DFB) laser transmitter block. When transitioning between doze and active modes, the transmitter block has a short settling time of only 205 ns, thus increasing the power-saving duration and consequently reducing the overall power consumption of the ONU. Through numerical analysis, evaluation of the energy-savings of the SC-VCSEL ONU over the DFB ONU under various modes of operation, demonstrates up to 84% of energy-savings. The capacity, tuning range, split ratio, system reach, and energy-savings arising from SC-VCSEL ONU implementation as reported in this work, exceed the minimum requirements of NG-PON2 for future TWDM-PON deployments.

Symmetric 40-Gb/s TWDM-PON With 39-dB Power Budget

Time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been selected by full service access networks as a primary solution for next generation PON stage 2 in April 2012. In this letter, we propose and demonstrate a symmetric 40-Gb/s TWDM-PON with 39-dB power budget. A reflective semiconductor optical amplifier is used in optical network unit as a pre-amplifier to enhance the sensitivity of downstream signals. For the upstream direction, a thermally-tuned directly modulated laser with 10-Gb/s modulation rate is used as upstream colorless source, and a chirp management filter is employed in optical line terminal to mitigate chromatic dispersion therefore enabling fiber transmission. Symmetric 40-Gb/s TWDM-PON is experimentally demonstrated with a power budget of 39 dB, which could support 25-km fiber transmission and 1:1000 splitting ratio.

Time- and Wavelength-Division Multiplexed Passive Optical Network (TWDM-PON) for Next-Generation PON Stage 2 (NG-PON2)

The next-generation passive optical network stage 2 (NG-PON2) effort was initiated by the full service access network (FSAN) in 2011 to investigate on upcoming technologies enabling a bandwidth increase beyond 10 Gb/s in the optical access network. The FSAN meeting in April 2012 selected the time- and wavelength-division multiplexed passive optical network (TWDM-PON) as a primary solution to NG-PON2. In this paper, we summarize the TWDM-PON research in FSAN by reviewing the basics of TWDM-PON and presenting the world's first full-system 40 Gb/s TWDM-PON prototype. After introducing the TWDM-PON architecture, we explore TWDM-PON wavelength plan options to meet the NG-PON2 requirements. TWDM-PON key technologies and their respective level of development are further discussed to investigate its feasibility and availability. The first full-system 40 Gb/s TWDM-PON prototype is demonstrated to provide 40 Gb/s downstream and 10 Gb/s upstream bandwidth. This full prototype system offers 38 dB power budget and supports 20 km distance with a 1:512 split ratio. It coexists with commercially deployed Gigabit PON (G-PON) and 10 Gigabit PON (XG-PON) systems. The operator-vendor joint test results testify that TWDM-PON is achievable by the reuse and integration of commercial devices and components.

The Available Options for Wavelength Group Selection and Transceiver Design for Next Generation PON Stage 2 (NG-PON2)

The full service access network (FSAN) task group meeting was held in April 2012, where they agreed to adopt time and wavelength division multiplexed passive optical network (TWDM-PON) as a primary solution to NG-PON2. Major requirements includes at least 40 Gbit/s aggregate rate in downstream, 1:64 split ratio, 40 km differential reach, and at least 1 Gb/s access rate per optical network unit (ONU). In this paper, a performance analysis will be carried out for downstream 4-wavelengths group selection from S-band, L-band, and C-band. A comparison for optimal transmitter design is also investigated among probable options of chirp managed laser diode, Lithium Niobate (LiNbo3) Mach Zehnder modulator, besides examining tunable transceivers in contrary to remotely fed colorless ONUs.

Key technologies and system proposals of TWDM-PON

In this paper, key technologies, system propo- sals and future directions of next generation passive optical networks stage 2 (NG-PON2) are reviewed. We first discuss the potential solutions for NG-PON2 standardiza- tion. Then we focus on time and wavelength division multiplexed PON (TWDM-PON), which is the primary solution selected by Full Service Access Network (FSAN). The key technologies in TWDM-PON configuration are analyzed, including how to improve the bandwidth capacity and power budget of the system, and choose upstream tunable transceiver, etc. Several system proposals are illustrated as candidates for NG-PON2 configuration. Keywords next generation passive optical networks stage 2 (NG-PON2), time and wavelength division multiplexed PON (TWDM-PON), tunable transmitter, tunable receiver, power budget

The XG-PON System: Cost Effective 10 Gb/s Access

The ten gigabit passive optical network (XG-PON) system is the newest member of the ITU-T family of passive optical network standards. XG-PON is the result of a 3 year project involving the full service access network (FSAN) group and ITU-T study group 15 (SG15) question 2. This paper reviews the deliberations that led to the selection of the XG-PON system, and then explains the three primary layers of the system: physical, protocol, and management. The paper concludes with information on standards and implementations of the system, and on future work in this area.

Comparison of collision avoidance mechanisms for the discovery process in xPON

Operation of all time division multiple access passive optical networks (PONs), regardless of the layer 2 protocol in use, requires the utilization of the so-called discovery process allowing for identification and registration of newly activated optical network units (ONUs). For the duration of the discovery process, all transmissions from already registered ONUs are halted, decreasing the available upstream bandwidth. The number of discovery windows required to successfully register all contending ONUs depends on the collision probability for their registration requests. To decrease such a collision probability for registration requests, several types of collision avoidance mechanisms (CAMs) can be used in various flavors of passive optical network (xPON), as we examine in more detail. A random delay mechanism (RDM) is typically exploited in 1 Gbit/s Ethernet PON (1G-EPON) and gigabit PON (GPON), though other CAMs are also available. It is our goal therefore to examine the efficiency of all known CAMs, compare them in quantitative and qualitative manner, and recommend the best mechanism for the next generation of xPON systems, minimizing the average number of discovery cycles required to register contending ONUs (maximizing thus the registration success probability). The results indicate that RDM is indeed the best of simple, single-stage CAMs available, thus confirming the choice of both the P802.3ah Task Force (TF) and Full Service Access Network (FSAN)/ITU-T at the time when their respective 1G-EPON and GPON specifications were written.

Common technical specification of the G-PON system among major worldwide access carriers

Gigabit-capable passive optical networks (G-PONs) have been successfully standardized at ITU-T following the work done by the Full-Service Access Network (FSAN) group. G-PON is a powerful and flexible optical access system with various options to accommodate many services and interface types. In order to provide guidance to vendors on the key options required by operators at this time and hence speed up early volumes for large field trials and deployments, many of the major worldwide access carriers (AT&T, BT, DT, FT, KT, NTT, and TI) have developed a common technical specification (CTS) for G-PON systems. This article describes the G-PON standard and underlines the scope and results of the CTS

FSAN interoperability efforts: building toward G-PON interoperability

The full service access network's (FSAN) interoperability task group (TG) addresses interoperability between PON systems. Recently, the TG has focused on gigabit passive optical network (G-PON) system interoperability between optical line terminations (OLT) and optical network terminations (ONT) of different vendors, which has leveraged the lessons learned from broadband passive optical network (B-PON) interoperability. The TG members have made progress with interoperability by analyzing the International Telecommunications Union-Telecommunications (ITU-T) Recommendations to develop test plans and demonstrate implementations that work across multiple vendors' OLTs and ONTs. This article defines interoperability and conformance and describes the FSAN's interoperability program to develop common test plans. It describes recent and planned G-PON interoperability demonstrations, as well as current challenges facing the industry

Efficient transport of packets with QoS in an FSAN-aligned GPON

The standardization of passive optical networks capable of transporting Ethernet frames at gigabit-per-second speeds, currently in progress in both ITU-T and IEEE, constitutes a major milestone toward cost-effective photonization of the last (aka first) mile. The article presents an Ethernet gigabit PON (GPON) system aligned with the philosophy of the evolving FSAN (full service access network) ITU-T specification, which focuses on the efficient support of any level of quality of service. The intelligence of this system, in terms of traffic quality guarantees, lies in the MAC protocol, which controls the distributed multiplexing/concentration function by allocating variable length slots to every user of the shared upstream (toward the network) medium. The way transport of information is organized in an ITU-T GPON system and the operation of a MAC protocol that preserves all QoS guarantees are presented and evaluated.

Methods of summing crosstalk from mixed sources. I. Theoretical analysis

Digital subscriber lines (DSLs) are fundamentally limited by crosstalk. The case where all crosstalk is from the same type of DSL has been studied over the years and accurate models have been standardized. However, crosstalk from multiple different types of DSLs is a relatively new area of study and models of summing mixed crosstalk have only recently been postulated. As more and more types of DSLs are deployed by multiple service providers, it is imperative to gain confidence in the method of modeling worst-case mixed crosstalk and to understand its limitations in order to enable efficient spectrum management of the loop plant. All known crosstalk summation methods are described here in detail and their properties are compared. This paper also presents a new methodology for deriving sound crosstalk summation methods. This new methodology consists of deriving lower bounds to the worst-case method, which is intrinsically too pessimistic. In particular, it has been ascertained that the Minkowski inequality and, to a lesser extent, the Holder inequality, yield new crosstalk summation methods that exhibit appealing properties. It is also shown here that the standardized full service access network (FSAN) method is a particular case of the more general Minkowski-bound method.