Network Operator Requirements for the Next ...

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Network Operator Requirements for the Next Generation of Optical Access Networks Philippe Chanclou, Anna Cui, Frank Geilhardt, Hirotaka Nakamura and Derek Nesset Abstract This article describes FSAN operator perspectives on the drivers and system requirements for fiber access beyond 10-Gigabit-class PON systems (i.e., NGPON2 in FSAN terminology). Additionally, a review of potential solutions in scope for NG-PON2 is given in the context of these operator drivers and requirements.

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igabit passive optical networks (PONs) are being deployed by operators in several countries and are among the fastest access technologies currently available. Such systems play a key role in delivering high-bandwidth services to a diverse range of users. Furthermore, deployments of 10 Gb/s PONs are expected in the next couple of years. This article intends to define operator drivers and system requirements for fiber access beyond “legacy” GPON and XG-PON systems standardized to date [1–3]. In the Full Services Access Network (FSAN) group, such systems are called NG-PON2. FSAN has begun investigating NG-PON2 technologies that enable a further bandwidth increase compared to existing standards and further enhance the capabilities to address anticipated market. Studies into NG-PON2 will also consider new fiber architectures to take the benefit of the maturing WDM technologies and their necessary adaptations for the access network. The main objective of this article is to present a preliminary but consolidated view from FSAN operators concerning their requirements for NG-PON2 systems. This article also describes some investigations on what technologies the NGPON2 optical access solutions could employ. Key factors considered are the potential for network consolidation, and enabling smooth technology migration and incremental bit rate increases. The first section of the article reviews the NG-PON2 system drivers from both service and network perspectives. The second section focuses on specific technical requirements and architectural options. Finally, a brief review of potential technical solutions in scope for NG-PON2 is given in the context of the operator drivers and requirements. It is desirable that a single solution be standardized for NG-PON2 to exploit the economies of scale. However, it is not clear yet which solution is most suitable, and meets the operator requirements for flexibility and the various application domains. Further study is required to facilitate the reduction of the solution space to select the best option for potential standardization in the International Telecommunication Union — Telecommunication Standardization Sector (ITU-T.)

Drivers for NG-PON2 With the rise of new content-rich services and the increasing

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demand for services such as HD video, it is expected that the required bandwidth will steadily increase [4], with some reports suggesting residential bandwidth requirements could surpass 250 Mb/s by 2015 [5]. This service bandwidth increase, along with the rise of business and mobile backhaul applications, could create a bottleneck in today’s gigabit-class PON deployments. NG-PON2 targets fulfilling this demand trend as well as offering a cost-efficient PON upgrade path and facilitating the phase-out of legacy technologies. An NG-PON2 solution that fully exploits the capacity and low transmission loss of optical fibers and inherent advantages of the PON architecture has the potential to lower the total cost of ownership for operators and offer better value to end users [6]. For example, NG-PON2 could offer an increase in the number of users per PON feeder fiber and also increase the system reach to facilitate node consolidation, among other enhancements.

Service Drivers The growing bandwidth demand is mainly driven by the evolution of video services which, including all variants (i.e., linear TV, video on demand, Internet, and peer-to-peer [P2P]) will represent 90 percent of the global consumer traffic by 2014 [4]. More video content will be provided over unicast platforms which increase the traffic volume dramatically and, moreover, video bandwidths will increase due to the evolution from today’s SDTV and upcoming HDTV formats towards Super HD (4k) and Ultra HD (8k) and 3D formats. In addition to the traditional ways of consuming video services, there are some further trends driving up bandwidth demand, for instance: • The growth of video over instant messaging and video calling [4] • The increasing number of connected devices in a fully integrated digital home • The increased popularity of social networking evolving from today’s mainly text-based content to high-bandwidth video upload and streaming • The accessibility of a wide range of on-demand cloud services for both residential and business users • The rise of online gaming and the online distribution of gaming content The predominance of traditional video distribution services (linear or on demand) means that residential traffic will

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remain asymmetric. However, this may change if direct distribution is adopted, for instance, to offer live video streaming through P2P as in PPLive. The convergence of residential and business applications on a common access platform also drives the need for more bandwidth-symmetric systems. End User Requirements — Beyond higher bandwidth, residential and business users also expect a number of basic features from future broadband access. For instance: • Security and integrity of all user data • Simple configuration (plug and play) and minimal or no administration of customer premises equipment (CPE) by end users • Access to a rich service portfolio that is not limited by the capabilities of the access technology (high service quality is expected independent of user behavior and service demand) In addition, business users often have higher requirements regarding data security and integrity guarantees, network availability, network performance (e.g., delay and jitter), and bandwidth provisioning, which also need to be considered for NG-PON2. Backhauling — Network convergence offers the prospect of optimizing the total cost of ownership (TCO) for network operators by eliminating heterogeneous and manifold network technology solutions in the access and aggregation domains. In this context, fixed access backhauling and mobile backhauling must be considered. Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are the relevant mobile network technologies within the FSAN timescales for which NG-PON2 systems must provide backhauling solutions.

Network Drivers PON Upgrade Path — As the total cost of a fiber to the home (FTTH) deployment is dominated by the infrastructure investments, it is necessary to future-proof them by enabling a system migration path that allows as much reuse of the fiber infrastructure as possible. Simplification of Operational Processes — It is preferred by network operators to have multivendor-capable NG-PON2 solutions with seamless interworking between OLT and ONT. The migration toward all-packet platforms, and the trend toward a common access and aggregation for residential, business, and mobile backhaul lead to high end-to-end availability and reliability requirements in the access network. Resiliency, including automatic reconnections through redundant network elements, should minimize the impact in the event of failures. Suitable fault management and optical diagnosis and measurement solutions for fault detection and localization up to the customer premises are also necessary. Node Consolidation — Node consolidation enables the network operator to simplify the network structure and reduce the number of access sites. This is expected to enhance the overall cost efficiency of the network. NG-PON2 systems must support operator objectives concerning node consolidation by offering enhanced reach and capacity. Power Reduction — Access network equipment consumes a major share of the total network power, and power saving in telecommunication systems has become an increasingly important concern in operators’ operating expenditures (OPEX) and its contribution to greenhouse gas emission [7]. A primary service driver for power saving functions at the ONU is to maintain the lifeline service(s) such as voice through the use

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of a backup battery during power outages. NG-PON2 systems must be designed in the most energy-efficient way to also reduce power consumption during normal operation without sacrificing service quality and user experience. System Flexibility — The NG-PON2 system should enable flexible deployment options to fit operator needs and engineering choices. For example, the system should allow capacity to be added in a modular way as service demand grows or as spectrum is vacated by the decommissioning of legacy systems. Furthermore, the system should allow different customer types to be supported depending on the markets being addressed (e.g., business customers and residential customers on the same optical distribution network [ODN]), where the proportion of each type may need to be flexible to meet demand. The system flexibility should enable a range of legacy coexistence scenarios to be supported whist maximizing the use of free spectrum. System flexibility can also enable multiple NG-PON2 systems to use the same infrastructure whereby the optical line terminations (OLTs) may belong to different business units within the same network operator or even to different operators. In some regions, such ODN sharing may be required for regulatory reasons. The costs of such flexibility should be minimized for those operators that do not need it or in situations where it is not required.

NG-PON2 System Requirements As NG-PON2 systems are not expected to be deployed before 2015, solutions should take into account optical access technologies that could be suitable for deployment at that time.

Required Capacity NG-PON2 shall be capable of offering significantly more capacity per customer than current GPON[1] and NGPON1[2] systems. NG-PON2 must support at least 40 Gb/s aggregate capacity per feeder fiber downstream and at least 10 Gb/s in the upstream. Typically any NG-PON2 ONU shall be able to support at least 1 Gb/s service, whereas the actual capability per ONU on the PON will depend on operator requirements concerning split ratio and the application mix considered. For example, some scenarios may require a 100 Mb/s service on the same PON as a 10 Gb/s service. The various envisaged access applications drive the need for different sustained and peak data rates, as well as different symmetry ratios between upstream and downstream data rates. For example, business services or mobile backhaul will require sustained and symmetric 1 Gb/s data rates, while residential customers may be less bandwidth demanding and require the available peak bandwidths for short durations with less symmetry of data rates. Hence, NG-PON2 solutions that increase the overall level of data rate symmetry, for example, between 2:1 and 1:1 (downstream:upstream), are desirable. Example applications demanding higher data rates include serving MDUs, enterprise connectivity, distributed eNodeB, and mobile backhaul applications, especially with LTE data rates in the region of up to 300 Mb/s and increasing to 1 Gb/s for LTE-Advanced. In addition, mobile operators looking to reduce capital expenditures (CAPEX) and OPEX costs and improve performance of wireless infrastructure are considering the introduction of distributed eNodeB architectures. In supporting distributed eNodeB applications, NG-PON2 can be leveraged to support high-speed transport (e.g., CPRI/ OBSAI with up to 3 Gb/s or higher) between a baseband unit and remote radio units.

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Legacy ONT

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Figure 1. Co-‐existence scenarios: a) full ODN and b) feeder only.

Passive and Active Reach The maximum passive fiber reach capability for NG-PON2 should be at least 40 km. A maximum differential fiber distance of up to 40 km (configurable as either 20 or 40 km) should also be supported. Meeting these requirements will make NG-PON2 backward compatible with deployed infrastructure. NG-PON2 must also be capable of reaching at least 60 km. Preferably, this would be achieved while maintaining passive outside plant, but solutions exploiting mid-span reach extenders (REs) could also be useful. Mid-span REs must be remotely manageable through an OLT to enable configuration and monitoring functions for maintenance and fault location. RE-based deployments should also be compatible with resiliency and redundancy options. Furthermore, being remotely located in the outside network, the REs should have minimal power requirements and operate over outdoor temperature ranges typically specified by operators (e.g., –45°C to +45°C ambient plus solar loading).

End-User Terminations per PON Optical distribution networks exploiting power splitters are typically deployed today with a split size in the range 16–128. The maximum number of ONUs that NG-PON2 should support is ≥ 64, but this could be 1000 or greater by exploiting wavelength multiplexing, depending on individual operators’ requirements. Support for a higher number of ONUs per ODN enables a high degree of infrastructure sharing and node consolidation if available in conjunction with longer reach.

Coexistence and Migration The use of the terms related to coexistence and migration may generate uncertainty in increasingly complex network environments. Below we capture the meaning assumed here: ODN reuse: The ability to reuse existing ODN/ODS plant as is (with “legacy” optical budget). Stacking: The ability for a generation of independent systems based on the same protocol layer to share part or all of the ODN/ODS through WDM. The physical layer characteristics for each stacked system only differ through wavelength allocations. Coexistence: Ability for two or more system generations to operate simultaneously on at least one section of the fiber plant. Coexistence facilitates a smooth migration from legacy PON to NG-PON2 and provides an enhanced end-user experience by minimizing the disruption of the existing optical

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Legacy ONT Legacy ONT Legacy ONT Legacy ONT Legacy ONT NG-PON2 ONT NG-PON2 ONT NG-PON2 ONT NG-PON2 ONT NG-PON2 ONT

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Co-existence in feeder NG-PON2 OLT (b)

plant. This capability is of great interest to operators provided it does not introduce unacceptable compromises elsewhere in the NG-PON2 system. To facilitate coexistence, NG-PON2 should be capable of reusing deployed optical power splitters and also operate in available spectrum not used by legacy PONs. Coexistence over the end-to-end ODN or just in the feeder fiber can be considered (Fig. 1). However, feeder-only coexistence (Fig. 1b) may be complicated or impractical in the case of ODNs with multiple splitter stages. NG-PON2 should support at least a migration path from GPON over XG-PON to NG-PON2. Some operators may be interested in migration directly from GPON to NG-PON2 and not deploy XG-PON technology. The highest level of flexibility could be realized by an NG-PON2 solution that enables coexistence of GPON, XG-PON, and NG-PON2. While this option is the most challenging, it is important to explore the technical feasibility. The coexistence capability makes the legacy ODN future-proof and offers operators a high level of flexibility. In any migration scenario with coexistence, the legacy ONU and OLT must remain unchanged and not require an additional filter to protect against interference from NG-PON2 signals. The coexistence of NG-PON2 with legacy RF overlay is desirable. However, it is expected that the use of RF overlay will diminish over time as in-band IP-based service delivery becomes more prevalent.

Optical Spectrum Issues and Availability When migration and coexistence is considered, we need to bear in mind the wavelength plans (Fig. 2) of the legacy PON systems with which NG-PON2 may need to coexist. A further factor that limits the available spectrum are the legacy filter characteristics built in to deployed systems. Most significant may be the radio frequency (RF)-video filter, which could require guardbands that occupy most of the C-band where the fiber loss is low, and systems could exploit erbium doped fiber amplifiers (EDFAs). There is little available spectrum if NG-PON2 needs to coexist with all the legacy PON systems. Only those technologies requiring very narrow spectrum per wavelength and able to be tightly controlled would be able to coexist. Otherwise, compromises will be necessary such as restricting the coexistence scenarios. Any technical assessment of candidates will have to consider various coexistence possibilities and the extent of its applicability.

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Spectral Flexibility

10GE/XG-PON U/S 10GE/XG-PON D/S GPON U/S B/GPON B/GPON (narrow/reduced) GE-PON U/S GE-PON D/S RF-video

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A cost-effective approach to support various deployment scenarios and network applications is to utilize a degree of spectral flexibility in the Wavelength (nm) NG-PON2 system. Such flexibility can enable the support of different customer types on the same O-band E-band S-band C-band L-band U-band PON in a flexible way. Furthermore, operators may use this flexibility to enable capacity Figure 2. Wavelength plans of legacy PON systems. upgrades in a progressive or modular way as demand grows. Additionally, spectral flexibility may facilitate a range of co-existence scenarios and allow operators to avoid interference with legacy systems and subsePrimary Passive OLT quently enable new wavelength bands when these legacy syssplitters 1...n NG-PON2 tems are decommissioned. Moreover, regulation in some ONT OLT 1...n regions will require NG-PON2 technologies to allow open Secondary 1...n access at layers 1 and 2. OLT (optional) To meet the above requirements, any candidate NG-PON2 technology must offer the possibility to access multiple waveOLT lengths, groups of wavelengths, or wavelength bands that can be physically and logically separated and driven independentFigure 3. Illustrating NG-PON2 resilience scenario (Example). ly, either by a single OLT or by multiple independent OLTs, with fully independent operation. In order to facilitate spectral flexibility requirements and reduce operational costs due requirements at the OLT and in the backhaul transmission to inventory management, deployed ONUs should be “colorequipment (towards the metro/core), operators require feeder less,” i.e. they are not specific to a certain wavelength. redundancy to avoid large scale customer outages. Figure 3 Support for Legacy ODN shows an example of fiber path diversity ensuring resilience against cuts in the most vulnerable part of the access network. The total cost of a FTTH deployment is dominated by longThe redundant feeder fiber could terminate at a diverse CO lived infrastructure investments. Given that many operators location, or at the same CO location as the primary OLT. have already deployed, or will soon deploy, power splitter Redundant splitters, especially in the highest level of hierbased ODNs, it is naturally desirable that NG-PON2 is comarchy, may also be deployed. Typically redundancy requirepatible with these legacy ODNs, enabling an upgrade path for ments become less stringent the nearer to the customer this deployed infrastructure throughout its life. NG-PON2 premise, unless the end customer is, for example, a large scale should be able to accommodate flexibility in terms of stages enterprise or premium user. In the redundant architecture, and number of splits in each stage no matter what splitting rapid restoration may be required e.g. service interruption technology is used (power splitting, wavelength splitting, or a time < 50 ms. combination of both). A non-wavelength-selective, legacy ODN is preferred by Operational Requirements some operators in order to obtain a transparent distribution network with no barriers to flexible wavelength upgrades and Given the significant effort in defining a converged managefurther usage of the fiber spectrum. Filters inside the ODN ment framework across optical access systems, ONU managedefine a wavelength allocation that limits flexibility and can ment must be largely based on OMCI (G.988). High levels of increase network planning complexity. Nevertheless, the security are expected from NG-PON2 systems and these advantages of low loss splitting are also recognized and the should be at least as secure as XG-PON1 and preferably aforementioned transparency needs to be weighed against the include enhanced security features. potential for reduced loss budget requirements and physical NG-PON2 should support PON supervision features that security in wavelength-selective ODNs. enable enhanced user experience through early identification and location of faults at the physical and service layers. This Service-Specific Requirements could include ODN monitoring/checking and end-to-end performance monitoring up to the Ethernet layer. Optical layer NG-PON2 is required to fully support various services for resmonitoring should not impact PON operation nor limit coidential subscribers, business customers, mobile and fixed backhauling applications through its high quality of service existence with legacy PON systems and their associated moniand high bit-rate capability, and is expected to at least meet toring systems e.g. OTDR. NG-PON2 systems should also be the system requirements as defined in G.987.1 section 7 able to monitor transmissions at the PON and ONU to guard (including Synchronization, QoS, etc.) and furthermore against ONUs that exhibit Rogue behavior (e.g., transmitting achieve better delay and jitter performance. NG-PON2 should in another ONU’s timeslot or wavelength band). support legacy services (via emulation or simulation as speciIn many of the envisaged applications for NG-PON2, outfied in G.987.1) and emerging packet based services. Addidoor operation may be needed; thus ONUs shall operate over tionally, NGPON2 systems are required to meet the latency outdoor temperature ranges typically specified by operators limits imposed by mobile backhaul systems such as LTE. (e.g., –45°C to +45°C ambient plus solar loading). Optionally, the OLT should also be able to operate over the extended Resilience, Redundancy Requirements outside temperature range. PON resilience will become more important in supporting business applications and high value consumer applications. In node consolidation scenarios especially an efficient redundancy mechanism is required to avoid service disruption to thousands of users. Besides the usual hardware redundancy

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NG-PON2 • ≥40Gbit/s aggregated capacity per feeder • ONU sustainable down 1G, up to 0.5G

“Coexistence” enables gradual migration from preexisting PON systems over the same ODN.

“OLT&ONT replacement” enables migration over a legacy ODN by a “complete” replacement of pre-existing PON terminals.

“Modified ODN” something other than only power splitter ODN

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G-PON

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Figure 4. Potential NG-PON2 solutions and migration paths.

Overview of Multiplexing and Multiple Access Technologies Associated with Architectural Options for NG-PON2 This section reviews the key optical technologies to realize the network access and medium multiplexing functions as well as possible architectural options that currently appear to be candidates to meet NG-PON2 requirements. In defining our terminology, we assume: • Multiplexing corresponds to the downstream and allows the combination of multiple data streams, each dedicated to one or several terminals, over the transmission medium. • The multiple access method corresponds to the upstream and allows several terminals to share the same transmission medium.

Time-Division Multiplexing Time-division multiplexing (TDM) and time-division multiple access (TDMA) are the methods employed in the downstream and upstream link in power-splitter-based ODNs of previous PON generations (BPON, GPON, XG-PON1). Very simple (on-off keying with non-return-to-zero format optical modulation) is employed. A drawback of this approach is that each ONU needs medium access control (MAC) and physical (PHY) layers working at the line-rate to deliver a fraction of this rate at the user–network interface (UNI). To address this issue, bit interleaving is possible in the downstream.

Frequency-Division Multiplexing The digital-to-analog converter (DAC) and analog-to-digital converter (ADC) speed evolution combined with the capacity of digital signal processors (DSPs) make new multiplexing and access techniques worthy of consideration. A first option is frequency-division multiplexing (FDM) and frequency-division multiple access (FDMA) where multiple electrical RF carriers are transported jointly over one optical carrier [8]. For the

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downstream, one or more carriers are dedicated to an ONU. For the upstream, each subscriber emits its traffic over one predefined RF carrier. This solution solves the identified drawback of pure TDM(A) PON as here the ONT processes only the allocated RF channel at a fraction of the total bit rate. Another solution exploiting the recent evolution of DAC/ADC and DSP is orthogonal FDM (OFDM) [9] combined with OFDMA, whereby all the RF carriers form the OFDM(A) signal on one optical carrier. OFDM(A) offers maximum flexibility in terms of frequency and time allocation, and achieves high spectral efficiency. OFDM adopts a “divide and allocate” approach based on the utilization of large number of low-bit-rate subcarriers to carry different M-ary quadrature amplitude modulation (M-QAM) symbols simultaneously while maintaining carrier orthogonality. For the downstream, the ONT processes the whole carrier set and extracts, as in the case of TDM, a part of this data for the UNI. For the upstream, each subscriber emits traffic using a dynamic allocation in both frequency and time.

Wavelength-Division Multiplexing Wavelength-division multiplexing/multiple access, WDM(A), PON allocates one or more wavelengths per customer to achieve downstream and upstream virtual point-to-point connections[10–13]. Here we consider three WDM(A) PON realizations differentiated by the way the WDM(A) ONT is implemented: “colorless” WDM(A) PON, “colored” WDM(A) PON, and “coherent” WDM(A) PON. Several approaches are possible to achieve a colorless ONT. One approach is based on locking (or seeding) the wavelength of low-cost Fabry-Perot lasers using a spectrally sliced emission source. Variations of this approach include the use of reflective semiconductor optical amplifiers or reflective electro-absorption modulators. There are also various seeding choices including sliced source and laser arrays with narrow linewidth. A last approach uses tunable (or selectable) emit-

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ters and receivers. In contrast to a colorless WDM(A) PON, a colored WDM(A) PON would employ cost-reduced versions of standard long-haul transceivers. A hybrid of TDM and WDM can exploit a combination of wavelength and time to implement multiplexing and multiple access [14–16]. The coherent WDM(A) PON exploits optical coherent reception, which allows the selection of the required receive wavelength [17]. Additionally, this solution offers a very high optical loss budget through enhanced receiver sensitivity and enables the use of a high number of optical wavelengths with very narrow frequency spacing.

PON Evolution Roadmap Figure 4 illustrates the roadmap for NG-PON2 showing three possible PON evolution paths in terms of ODN migration. The timeline axis is the expected period for commercial availability after system specification has been agreed and standard recommendations have been published. The evolution path named “coexistence” represents NGPON2 solutions that enable gradual migration from pre-existing legacy PON systems on an ODN, which may require the addition of a coexistence element at the OLT site. The second evolution path, named “OLT and ONT replacement,” represents NG-PON2 solutions that enable migration over a legacy ODN through a complete replacement of pre-existing PON terminals at both ends. The last alternative evolution path, named “modified ODN,” concerns the addition to, or modification of, the ODN outside the OLT site. A first point to be made in this analysis is that pure TDM(A)-based PON most likely will not meet NG-PON2 requirements as a burst-mode transceiver at 40 Gb/s needs a significant technological breakthrough, so a pure TDM(A) PON over 40 Gb/s is considered very challenging for NGPON2, which has a target timeline of 2015. Some WDM(A)-PON (colorless or colored) solutions require a new ODN based on wavelength splitting, which is not compatible with legacy ODNs as desired by operators. Nevertheless, deployments of proprietary WDM(A)-PON systems already exist; thus, rapid standardization could be possible. However, a power-splitter-based ODN could be used by incorporating a tunable transceiver at the ONU, which would need to be uncooled in order to achieve low cost. Wavelength stacked TDM(A) PON is a straightforward solution that allows reuse of the legacy power-splitter-based ODN. However, fitting the stacked PON channels within the wavelength enhancement band defined in G.984.5 will need further study to realize a cost-effective approach under the coexistence or modified ODN scenarios. In the OLT and ONT replacement scenario, the absence of a pre-existing system makes the wavelength allocation simpler. Another family of candidate solutions where wavelength allocation will be critical is WDM(A) and TDM(A). The large wavelength tunability range these solutions require pushes potential availability further into the future with respect to pure WDM(A)-PON. Such solutions could be compatible with a new or legacy ODN depending on the ONU transceiver solution. Optical budget and wavelength allocation would be typical parameters allowing the choice of the migration scenario. In this synthesis, this solution is positioned with the possibility of following the three evolution path scenarios, although with a slight favoring of OLT and ONT replacement. Under the coexistence scenario, we consider solutions where the number of wavelengths is low. FDM(A)-PON is considered as an interesting way to preserve legacy ODN and to preserve pre-existing wavelength allocations. However, a larger technological development barrier to market availability is expected compared to WS or WDM(A) PON. Other solu-

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tions such as OFDM(A)-PON and coherent WDM(A) PON need further technology innovation to achieve appropriate suitability for the optical access market.

Conclusions NG-PON2 was initially defined by FSAN as a technology with no requirement for coexistence with GPON or XG-PON on the same fiber infrastructure and with the option to utilize a new type of optical plant not based on power splitting alone. However, as discussions among FSAN operators progressed, it became clear that NG-PON2 should preferably support operation over legacy power-splitter-based PONs and possibly aggregate several such legacy PONs. Furthermore, coexistence on the same PON with legacy PON systems should also be in scope to enable NG-PON2 to be used where previous PON solutions are already deployed. Therefore, FSAN operators are requesting NG-PON2 solutions that offer a clear migration route from legacy systems and with legacy coexistence capabilities. Thus, NG-PON2 can be exploited for some greenfield applications over a new optical plant, and should also meet growth in bandwidth demand and provide new revenue streams on legacy plant. An important driver for NGPON2 is central office consolidation, which has already started by exploiting the reach of current fiber access technology, and could enable a reduction of the total cost of building and operating optical access networks. Furthermore, NGPON2 can be exploited to meet the growing demand for mobile backhaul, due to the rise in smart phone use and applications for business users. The goal for the industry is to cost-effectively address these diverse markets, and their demanding requirements, with a single standardized solution. This represents a significant challenge for the standards community and will require innovative thinking from system vendors, component vendors, and network operators alike. This is currently the subject of further study within the FSAN group with the aim to progress mature contributions into ITU-T in the future.

References [1] ITU-T G.984 Series of Recs., “Gigabit-Capable Passive Optical Networks (GPON).” [2] ITU-T G.987 Series of Recs., “10-Gigabit-Capable Passive Optical Networks (XG-PON).” [3] J.-I. Kani et al., “Next Generation PON — Part 1: Technology Roadmap And General Requirements,” IEEE Commun. Mag., Nov. 2009. [4] Cisco Visual Networking Index: “Hyperconnectivity and the Approaching Zettabyte Era,” Cisco Systems, San Jose, CA, 2010. [5] Mckinsey & Company, “Creating A Fiber Future,” Next Generation Telecom Infrastructure (NGTI) Initiative, Feb. 2010. [6] D. Breuer et al., “Opportunities for Next-Generation Optical Access,” IEEE Commun. Mag., Feb. 2011. [7] C. Lange et al., “Energy Consumption of Telecommunication Networks and Related Improvement Options,” IEEE J. Selected topics in Quantum Electronics, vol. 17, no. 2, Mar./Apr. 2011. [8] B. Charbonnier, N. Brochier, and P. Chanclou, “(O)FDMA Pon Over A Legacy 30db ODN,” OFC 2011, 6–10 Mar. 2011. [9] N. Cvijetic, “OFDM for Next-Generation Optical Access Networks,” IEEE/OSA J. Lightwave Tech., invited tutorial, to appear Feb. 2012. [10] N. J. Frigo et al., “A Wavelength-Division Multiplexed Passive Optical Network with Cost-Shared Components,” IEEE Photon. Tech. Lett., vol. 6, no. 11, Nov. 1994, pp. 1365–67. [11] S. J. Park et al., “Fiber-to-the-Home Services based on Wavelength-Division-Multiplexing Passive Optical Network,” J. Lightwave Tech., vol. 22, no. 11, Nov. 2004, pp. 2582–91. [12] S. S. Wagner and H. Kobrinski, “WDM Applications in Broadband Telecommunication Networks,” IEEE Commun. Mag., vol. 27, no. 3, Mar. 1989, pp. 22–30. [13] A. Banerjee et al., “Wavelength-Division-Multiplexed Passive Optical Network (WDM-PON) Technologies for Broadband Access: A Review,” J. Opt. Net., vol. 4, issue 11, 2005, pp. 737–58. [14] Fu-Tai An et al., “Success: A Next-Generation Hybrid WDM/TDM Optical Access Network Architecture,” J. Lightwave Tech., vol. 22, no. 11, 2004, pp 2557–69.

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[15] G. Talli and P. D. Townsend, “Hybrid DWDM-TDM Long-Reach PON for Next-Generation Optical Access,” J. Lightwave Tech., vol. 24, no. 7, July 2006, pp. 2827–34. [16] S. Kimura, “10-Gbit/s TDM-PON and over-40-Gb/s WDM/TDM-PON Systems with Opex-Effective Burst-Mode Technologies,” OFC 2009, OWH6, 2009. [17] S. Smolorz et al., “Demonstration of A Coherent UDWDM-PON with RealTime Processing,” OFC 2011, PDPD4, 6–10 Mar. 2011.

Biographies Philippe Chanclou joined Orange Labs in 2004 where he was engaged in research on next-generation optical access networks. He is the manager of the Advanced Studies on Home and Access Networks R&D unit and is an active contributor to FSAN studies concerning NG-PON. He received Ph.D. and Habilitation degrees from Rennes University, France, in 1999 and 2007, respectively. A NNA C UI received her M.S. degree from Northeastern University, China, in 1988 and her Ph.D. from North Carolina State University, Raleigh, in 1995. She has been working in broadband technologies for several companies, including Hughes Network Systems, Broadband Technologies, and Tellabs. In 2005 she joined BellSouth, now AT&T, in architecture and planning organization, working on broadband access target architecture and roadmap, and RAN strategy. She has been participating in FSAN, ITU-T, and BBF initiatives since 2005. FRANK GEILHARDT received a Dipl.-Ing. (FH) degree in telecommunication engineering from the University of Applied Sciences of Berlin in 2001. Since joining Deutsche Telekom AG in 2001, he has mainly been developing optimization strategies for optical and hybrid optical broadband access networks. In 2009 he joined Deutsche Telekom Laboratories, Berlin. His current research interests include developing upgrade strategies and concepts toward next-generation broadband optical access networks. He actively contributes to FSAN studies in relation to NG-PON. HIROTAKA NAKAMURA received his B.E. degree in applied physics from the University of Tokyo, Japan, in 1999, and his Ph.D. degree from Hokkaido University, Japan, in 2011. In 1999 he joined NTT Access Network Service Systems Laboratories, NTT Corporation, where he has been engaged in research on WDM-based high speed optical access systems. He has been participating in FSAN activities relating to NG-PON2 since 2009. He is a member of the IEICE Communications Society. DEREK NESSET leads BT’s research into future optical access networks. He started at BT in 1989 researching advanced fiber optic components and systems. In 2000 he joined Marconi to develop ultra-long-haul DWDM systems. Since returning to BT in 2004 his research interests concern next-generation optical access systems. He has a B.Sc. in physics and an M.Sc. in telecommunications engineering, serves on OFC and ACP conference subcommittees, and is co-chair of the NG-PON task group in FSAN.

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IEEE Network • March/April 2012