Network technologies for broadband access

<p>The high capacity demand, to support broadband services and everything-to-internet connectivity is pushing the limits of both access and metro networks, requiring the adoption of novel strategies for the optical transceiver modules. This represents an opportunity for the adoption in these network scenarios of novel photonic technologies based on single-mode vertical cavity surface emitting lasers (VCSELs) at long wavelengths. On one hand, the access network evolution requires a line rate increase beyond 10 Gb/s, targeting 50 Gb/s propagation in passive optical networks (PONs) over a few tens of kms in standard single mode fiber (SSMF) with simple, cost effective and energy efficient transceivers. On the other hand, the future metropolitan area network (MAN) will need to handle multi-Tb/s traffic in a very dynamic scenario, over variable distances up to hundreds of kms while promoting sustainability, reducing the CapEx and OpEx costs and power consumption. Both needs can be fulfilled by adopting VCSEL direct modulation with multicarrier modulation formats such as discrete multitone (DMT), in combination with distinct transmitter architectures and receiver solutions to support different aggregate capacity requirements and transmission reaches. In any case DMT with bit/power loading enables flexible rate and adaptive distance for metro network applications and link adaptation and PON resource usage optimization for future access networks. In this work, we report our recent results on the adoption of VCSEL technology in both scenarios, with special focus on the receiver and transmitter adopted architectures.</p>

Network infrastructure plays a key role in the success of added services and in user satisfaction. It is widely accepted that Passive Optical Networks (PON) are the most promising, cost-effective, and high-performance access network solutions. Access networks are also commonly referred to as either ‘the last mile’ by the operators, or ‘the first mile of the network’ in IEEE terminology. The term ’mile’ is often related to the path portion that is used to reach the user from a network node, however access networks go as far as 20 km depending on the technology used. An access network comprises connections between different subscribers and a Central Office (CO), which is attached to the metro or core network. The wired technology deployed varies significantly from one country to another, i.e. Digital Subscriber line (xDSL), based on copper wires; Hybrid Fiber-coax (HFC), and optical fiber. The trends for Next Generation Access Networks (NGA) based on PON are: Wavelength Division Multiplexing (WDM), 10 Gb/s or more, and longer reach/higher splits. NGA must be able to cope with challenges, such as delivering diverse broadband services and facilitating the integration of different technologies. Moreover, NGA should provide higher bandwidths or further reduce the cost of existing delivering services, and serve as backhaul of wireless access networks (WiFi, WiMAX). The last one constitutes a relevant issue for the convergence between wireless and wired technologies.

Problem statement: Wired broadband Internet access can be realized using various technologies, configurations and protocols. It is widely deployed and able to provide both high data rates and high reliability. These features are of strong importance for many advanced applications. Since the number of broadband subscribers worldwide grows exponentially, the power efficiency of access networks becomes increasingly important. Approach: The aim of this study is to study power consumption of different wired broadband access technologies including both those already widely used and those which are state-of-the-art, but not yet widely deployed. For this purpose, we developed a model for evaluating energy efficiency of wired access networks. The model is presented and applied to study energy efficiency of various access networks such as Hybrid Fiber Coax (HFC), Digital Subscriber Line (DSL), 1 and 10 Gbit/s point-to-point ethernet and Passive Optical Networks (1G-PON and 10G-PON). The metric for energy efficiency we used in this study is energy consumed per bit transmitted. Results: Results of the comparative study on energy efficiency of different access networks are shown and discussed. Additionally, we estimated environmental implications of different access options by means of reductions in Green House Gas (GHG) emissions caused by the electricity consumption of access network infrastructure. Conclusion: We found out that high-speed optical access technologies providing up to 10 Gbit/s per user have the potential to achieve the highest energy efficiency when assuming future broadband Internet access and broad use of advanced services and applications. However, for lower access data rates, 1G-PONs are the most energy efficient access options. Coper-based access technologies provide generally lower energy efficiency than the fiber based solutions. For transferring a large amount of data and when network equipment is switched off during its inactivity times, optical access technologies have the highest potential to reduce GHG emissions caused by the electricity consumption of access network infrastructure.

Next generation access networks are leveraging on the efficiency of fiber access networks to deliver higher data rates in a sustainable manner balancing network deployment costs and the network energy footprint. Towards this direction Passive Optical Networks have been attracting a lot of interest since they can deliver an optimal balance of these two critical factors. However, the transition to next generation optical networks is still an issue under research since no mature technology has yet prevailed. Beyond the cost of the equipment that is used to develop the access systems the overall network architecture must be carefully studied and engineered in order to optimize overall system costs, taking power consumption into account. In this paper we demonstrate how a hybrid fiber access network architecture can combine mature TDM PON technologies and WDM multiplexing to exploit the benefits of an ultra long reach access network leading to a collapsed access and metro network architecture. We show that this combination can lead to lower overall power consumption mainly due to efficient traffic aggregation, node consolidation and simplification of metro and core network design.

This article describes Ethernet passive optical networks, an emerging local subscriber access architecture that combines low-cost point-to-multipoint fiber infrastructure with Ethernet. EPONs are designed to carry Ethernet frames at standard Ethernet rates. An EPON uses a single trunk fiber that extends from a central office to a passive optical splitter, which then fans out to multiple optical drop fibers connected to subscriber nodes. Other than the end terminating equipment, no component in the network requires electrical power, hence the term passive. Local carriers have long been interested in passive optical networks for the benefits they offer: minimal fiber infrastructure and no powering requirement in the outside plant. With Ethernet now emerging as the protocol of choice for carrying IP traffic in metro and access networks, EPON has emerged as a potential optimized architecture for fiber to the building and fiber to the home.

The tremendous demand on carriers for bandwidth in the access network, as well as demands on carriers to manage that bandwidth, continues to drive the technical evolution of access networks. As one approach to satisfy these demands, DOCSIS® Provisioning of EPON (DPoE), combines two access technologies: Ethernet passive optical network (EPON) and Data Over Cable Service Interface Specification ( DOCSIS). DOCSIS makes possible mature service provisioning mechanisms based on centralized back-office automation. EPON provides a transport layer between the DPoE System and a number of connected DPoE optical network units (D-ONUs) for distances of 20 km and more. The completely passive interconnection structure of EPON also reduces capital expenditures (CAPEX) and operational expenditures (OPEX) by requiring no electrical power outside of the hub.

Passive Optical Network (PON) deployments have recently been aiming to combine the capacity of metro and access networks in the last mile of the Internet service provisioning. Deployment of PONs by running fiber to the premises introduces the advantage of huge capacity but at the same time, it calls for a robust design in order to avoid long service outage durations in case of network failures where survivable network design is mostly limited to the deployment budget. In this paper, we propose three mixed integer linear programming (MILP) models for various survivability policies to deploy reliable long-reach PONs under the budget limitations. Each MILP model aims to place the ONUs in optimal locations so that the covered area is maximized while availability requirements of the users are satisfied within the deployment budget. We solve the MILP models under the uniform and heterogeneous availability requirement scenarios and show that service availability and coverage introduce a trade-off so as the coverage and deployment cost do. Two out of the three survivability policies can guarantee 99.99% service availability while the third one is able to guarantee 99.999% by running the proposed MILP models. However, the first two schemes are able to cover larger area when compared to the third scheme which is the most reliable protection policy.

FTTH development is slow but steady in China. The phenomenon is rooted from some major challenges, such as cost, limited bandwidth in metro networks, bandwidth consumption behaviours. To address above challenges, FTTH architectures and bandwidth consumption behaviours are studied in the paper. To remove the bandwidth bottleneck between access and Metro networks and reduce cost, LR-PON (Long-Reach Passive Optical Network) is suggested to be applied in two ways in China. For resolving the challenge of bandwidth exhaustion in Metro networks caused by high-capacity consumption in access networks, a new bandwidth scheduling, Bandwidth on Schedule (BoS) is proposed to improve efficiency of bandwidth utilization. In the paper, the proposed solutions to challenges will be helpful to increase the penetration rate of FTTH deployment in China.

Ethernet passive optical networks (EPONs) have emerged as the one of the most promising candidates for next-generation access networks. These new architectures couple low-cost optics with advanced edge electronics to offer vastly improved scalability over competing digital subscriber line and cable modem offerings. This paper proposes several novel architectural enhancements for EPON, which will help increase the viability of optical access over a broader range of subscriber access scenarios. Specifically, this paper proposes a two-stage EPON architecture that allows more end-users to share an optical line terminal link, and enables longer access reach/distances (beyond the usual 25 km distance). In addition, a new dynamic bandwidth allocation (DBA) algorithm is proposed to effectively allocate bandwidths between end users. This DBA algorithm can support differentiated services in a network with heterogeneous traffic. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed architecture and algorithms.

Optical fibre step by step substitutes existing copper cable infrastructure in the carriers' access networks, enabling new broadband services. One common approach, a passive optical network (PON) infrastructure, basically consists of optical fibres and splitters, which are lit up by G-PON (Gigabit/s-PON) or XG-PON (10 Gigabit/s-PON). These systems are attenuation limited, therefore the loss budget of a PON is of high importance. For the deployment process the total attenuation of the PON, between Central Office (CO, OLT) and customer site (ONT), must be accurately monitored and kept below the values specified in G.984.x and G.987.x standards. In FTTH scenarios the PON attenuation measurements must include the in-house networks up to the subscriber fibre cable termination unit. During operation, the Optical Line Supervision (OLS) parameters (e.g. G.984.2, Amd2) are continuously monitored, processed and correlated for appropriate alarm generation. In the case of a fibre failure, additionally non-intrusive in-service measurements from the CO site must be supported for fault localisation. This is enabled by an appropriate WDM-filter per PON in the CO, providing access to the PON for OTDR measurements at wavelengths of 1625/1650 nm. In this paper possible solutions for PON measurement and monitoring for the deployment and operation of FTTH networks will be described in detail from a carrier's perspective. All these activities must be carried out in a minimum of time and with low operational efforts in order to guarantee a cost efficient network operation.

Exponential growth in the volume of wireless data, boosted by the growing popularity of mobile devices, such as smartphone and tablets, has forced the telecommunication industries to rethink the way networks are currently designed, and to focus on the development of high-capacity mobile broadband networks. In response to this challenge, researchers have been working toward the development of an integrated wireless optical broadband access network. Two major candidate technologies, which are currently known for their high capacity as well as quality of service (QoS) for multimedia traffic, are passive optical networks (PON), and fourth generation (4G) wireless networks. PON is a wired access technology, well known for its cost efficiency and high capacity; whereas 4G is a wireless broadband access technology, which has achieved broad market acceptance because of its ease of deployment, ability to offer mobility, and its cost efficiency. Integration of PON and 4G technologies in the form of wireless-optical broadband access networks, offers advantages, such as extension of networks in rural areas, support for mobile broadband services, and quick deployment of broadband networks. These two technologies however, have different design architectures for handling broadband services that require quality of service. For example, 4G networks use traffic classification for supporting different QoS demands, whereas the PON architecture has no such mechanism to differentiate between types of traffic. These two technologies also differ in their power saving mechanisms. In this paper, we propose a service class mapping for the integrated PON-4G network, which is based on the M/G/1 queuing model. We also propose a class-based power saving mechanism which significantly improves the sleep period for the integrated optical wireless unit, without compromising support for QoS. Results indicate that our proposed class-based power saving scheme reduces power consumption by up to 80%, and maintains the QoS within the requirements of the service level agreement.

The ever-increasing demand for improved speeds, expanded bandwidth, and reduced latency in emerging applications has not only driven the recent advanced algorithm breakthroughs but also fostered closer integration of metro and access networks. This work proposes a novel all-optical metro-access integration network (MAIN) enabled by coherent digital subcarrier multiplexing technology. This specially designed architecture can effectively eliminate the latency and jitters caused by the optical–electrical–optical conversion in the conventional scheme and save wavelength resources at the same time. For experimental validation, we successfully demonstrate 400G bidirectional coherent transmission within our proposed architecture, involving three nodes in the metro network and the access network as an example. Also, the related problems during the transmission are extensively discussed with the experimental results. Finally, we reach an aggregation rate of 4×100Gbps using a DP-16QAM signal. By integrating a SOA into the transmitter of the ONU, a power budget of 32.6 dB with a 29 dB dynamic range is achieved. In addition, the experimental results also show that the proposed all-optical MAIN architecture can be smoothly combined with the TFDM scheme to further enhance the flexibility, which also paves the way for further research on the next-generation coherent metro and access network.

In modern, competitive, and dynamic access networks the underlying bandwidth distribution mechanism has to be capable of understanding user requirements, meeting stringent quality of service (QoS) demands, and satisfying a broad spectrum of user traffic dynamics. Undoubtedly, optical fiber is the dominant transmission medium enabling practical and cost-effective optical infrastructures in the last mile. Passive optical networks (PONs) represent one of the most promising player towards the fiber to the home (FTTH) vision allowing users to experience high quality, demanding multimedia services and applications. The 10-gigabit-capable passive optical network (XG-PON), one of the latest PON standard, incorporates a set of profound conditions a contemporary PON should ensure. Fairness provisioning constitutes one of the most critical features a PON should provide. However, ensuring fairness in an access network with numerous different users, requesting multiple traffic flows in any time, is not a straightforward task. In this work, we focus on the fairness issue by devising an adaptive, efficient, and fair dynamic bandwidth allocation (DBA) scheme called Insistent FAIr STrategy prOcesS (IFAISTOS). IFAISTOS investigates and maintains user traffic profiles. Overloaded users are carefully treated by gaining greater granting windows than other users; however bandwidth monopolization is prevented. Fairness is ensured for all users in terms of traffic load and average delay. A steering, adaptive mechanism records user traffic profiles by changing and defining bandwidth weights proportional to individual traffic needs. Extensive simulation results reveal the efficacy of the proposed DBA in terms of fairness and average packet delay.

Cloud-Integrated WOBAN: An offloading-enabled architecture for service-oriented access networks

With the growing interest on wireline network architectures for residential triple-play and business Ethernet services there is a renewed demand for efficient and reliable packet-based transport capabilities between the content providers and the end users. Voice and data traffic carried over a variety of access technologies is collected via technology-specific access networks (e.g., digital subscriber line [xDSL], passive optical network [xPON], and wireless fidelity [WiFi]). Metro and core networks need to aggregate the various user flows from different access network nodes and provide scalable and cost-effective distribution of various flow types (e.g., Internet access, voice, video on demand, and broadcast TV services) to the relevant service access points. Varying quality of service and resiliency requirements for these services are being reflected in a new breed of converged Ethernet and optical network elements with capabilities to interwork the bearer-planes of these two networking technologies seamlessly. Network elements based on Ethernet/Optical converged technology are able to select the most fitting mechanisms from each networking technology to meet the transport requirements for each individual service demand better while providing significantly enhanced implementation and operational efficiencies. This paper discusses network architecture models and network elements addressing these goals. © 2007 Alcatel-Lucent.