NOKIA SIEMENS Ngoa Whitepaper 210311 2

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Optical connectivity for the ‘Gigabit’ society

White Paper

2 Next Generation Optical Access (NGOA)

Executive summaryNext Generation Optical Access (NGOA) will force operators to re-think their entire business model, with a sharp focus on their Total Cost of Ownership (TCO). It heralds a fundamental change from just providing a connection or ‘bit-pipe’.

With NGOA, furnishing operators with the ability to provision faster and longer connections will enable them to do much, much more, from software to content as well as the provision of a connection. These new revenue streams will mean increased profit and

Introduction

increased profit means growth: something that is scarce in the face of stiff competition and a harsh economic climate.

The volume of communication traffic is exploding, due to ever increasing subscriber numbers and the rise of multimedia based ‘data-hungry’ applications.

The popularity of applications such as social networking and video sharing are turning consumers into content creators, while interactive services change people’s behavior from merely just consuming content into full participation.

This growth continually accelerates, with subscribers demanding multi-channel, interactive high definition television (HDTV) and more bandwidth intensive applications, looking for the ‘personalized’ experience.

Peer-to-peer (P2P) traffic is expected to be the dominating network traffic type going forward, but traffic is also becoming more of a two-way street in other areas of online activity. For example, the rise of online communities and video-sharing sites such as Facebook and YouTube mean that subscribers are generating and uploading their own content.

Typically, operators couch these challenges within the Fiber-to-the-Home (FTTH) connectivity arena. But it’s not just about the FTTH arena: an operator’s view should be broadened, with focus also on the needs of business and enterprise connectivity.

Figure 1 Turning consumers into content creators

Next Generation Optical Access (NGOA) 3

For the end-user, it’s always about accessing and utilizing the latest application or service. They require more and more applications and higher service flexibility, underpinned with connectivity that is always ‘on’ and accessible ‘anywhere’.

Multi-channel, interactive HDTV is getting closer. The ‘semantic’ web starts to become a reality, whereby content can be read and understood by machines. By understanding the meaning of content, intelligent software agents pull together relevant information from across the Web to achieve a wide range of tasks, from booking your next holiday to research for an academic paper.

As technology becomes more sophisticated, life will get easier for users as applications become more natural and intuitive to use. For example, there will be “open identity” services that will enable users to be recognized wherever they go on the Web, without having to remember multiple user names and passwords.

Cloud computing is also becoming a reality, allowing users to store information and run applications on the Web rather than on their own equipment. The ‘cloud’ will enable users to access technology-enabled services from the Internet (located in the cloud) without knowledge of, expertise in, or control over the technology infrastructure that supports them.

Taken together, all these developments add up to increased demand for bandwidth. Demand will continually grow, with 1Gbit/s or more per household soon being the reality.

Always-on connectivity


Today’s connectivity networks will not ultimately be able to cope with the level of bandwidth previously outlined. All-optical technology provides the only practical way of delivering the required network capacity, while providing a unified platform for connectivity, aggregation and backhaul.

As the call for increased bandwidth grows, operators must be able to respond in a flexible and cost effective manner. In order to meet the challenges imposed, a radical rethink of current network architecture needs to be undertaken, with tight controls on CAPEX and OPEX in the forefront.

Operators will likely invest in incremental changes as and when they are needed, signaling a smooth migration from today’s technologies to future optical connectivity networks. As depicted in Figure 2, some network operators have already started to deploy FTTH technologies, in the form of Gigabit passive optical networks (GPON) and Ethernet PON (EPON). The fiber tree structure of GPON not only reduces the total length of fiber required in the network, it also minimizes the number of aggregation ports required to organize the traffic from different subscribers once it reaches the

network’s central office.This is just a first step. The mid- to long-term target is not only to downsize the equipment in each office, but also to reduce the number of local and central offices, with a future high capacity optical connectivity architecture being used to reduce the number of offices across a region or even country. To turn this vision into a reality, future technology needs to have a reach of 80 kilometers or more between subscribers and central offices.

At the same time as reducing CAPEX, reducing the number of offices will have a major impact on both OPEX and the environmental performance of networks, through cutting energy consumption. As

Network consolidation to drive down costs

environmental legislation begins to intensify, reducing energy use will help operators meet their targets for emissions reductions.

Operators will welcome a smooth migration to a future optical connectivity architecture, having already invested in a range of different infrastructures and technologies, such as xDigital Subscriber Line (xDSL), Passive Optical Network (PON), Ethernet and Cable TV. The pressure is on to maximize returns and optimize future investments. So it must be possible for each operator to migrate smoothly, regardless of which architecture and infrastructure they currently have in place.

Metro Core

Mobile

Internet

VoIP

Video

CopperDSLAM

GPON

Figure 2 The complexity of modern network infrastructures


Currently deployed optical connectivity networks are typical based on PONs, underpinned by Time Division Multiplexing (TDM)-based technologies which require high speed electronics and optics, yet are capable of delivering comparably low data rates over short distances.

Gigabit Passive Optical Networking (GPON) is one of these technologies, relying on TDM to split signals between different services and subscribers, offering a limited splitting factor (up to 64 subscribers) and a limited distance between the subscriber and their nearest network office (around 20 kilometers). GPON is also unable to offer true scalability, in terms of reach & number of users that can be connected, coupled with the fact of its characteristic of shared bandwidth. GPON also requires active components in intermediate office locations, which continue to cost money to install and maintain.

The increased distance necessary for future optical connectivity networks will never be practical for conventional GPON architectures, primarily due to its TDM characteristics and its inability to carry more than one signal on a fiber. Furthermore, GPON technology also suffers from the following limitations:

Constraints of current optical connectivity

• TDM struggles with issues of timing if the users vary too widely in their distance from the point of aggregation

• GPON offers a limited signal splitting capacity that is unable to cope with the high number of users in the catchment area of a networkofficewithawiderreach

• It would take more powerful lasers to send a reliable signal furtheralongafiber,thusincreasing equipment costs bothattheofficeandatthesubscriber’s premises

The truth is that current connectivity technologies, even though perhaps adequate for the short to mid-term, will not cater for the massive bandwidth that is forecast for the future.

It is also true that for these reasons, some technologies will render part of an operator’s investment useless after a relatively short period of time, certainly unable to achieve the flat architecture that is imperative to really reduce TCO.


As the world heads towards a Gigabit society, subscribers will expect the kind of services that generate traffic volumes beyond the reach of today’s connectivity networks. The architecture of next-generation networks will require a radical rethink, with a clear need to increase the reach of network offices and the capacity of each access node.

For Nokia Siemens Networks, a disruptive approach, combining advanced technology ingredients to achieve the highest flexibility, the best use of operator resources (fibers, bandwidth, etc) and the most competitive TCO is needed.

As depicted from Figure 3, for the end-user, an Optical Network Terminal (ONT) will comprise advanced laser technology and associated electronics. being compact, attractive and affordable, with a correspondingly small demand for power. The ONT should be able to cope with bandwidth expectations of 1Gbit/s (and higher for the future), including features such as WiFi and router capabilities.

Challenges for future optical networks

With the potential to support far more subscribers per fiber than current technologies, a future optical connectivity system should support an extremely high splitting factor. This in turn will require the development of Ultradense Wavelength Division Multiplexing (UDWDM) to split the optical signal reliably into much finer chunks of spectrum. UDWDM will demand significant advances in laser technology and this will also impact on the price of equipment, where the laser technology will need to be stable, tunable and cost effective.

Future optical connectivity networks will experience significantly more subscribers (~1000) on a single fiber, with each subscriber demanding up to 1Gbit/s at any one time. This will create a truly enormous amount of traffic between the subscribers and the network core, where equipment will need to handle Terabits of information.

Subscribers’ connections will be shifted from the network in the central office to the very edge of the core, rather than lower network layers (e.g. access and aggregation). Together with the fact that a large number of users are enjoying a wide range of services, this shift requires intelligent traffic and service handling throughout all the network layers (e.g. transport, Ethernet and IP).

Figure 3 Future optical connectivity

DSLAM

GPON

ONU

OLT

Core

Splitter

UDWDM


A smooth migration path that allows for incremental change and the protection of previous investments is key. The ability to re-use the fiber that is already being rolled out by operators is also important, if we consider typical investment cycles. Therefore any approach to a future optical connectivity system needs to cope with the full range of existing architectures (e.g. Fiber-to-the-Curb (FTTC), Fiber-to-the-Building (FTTB) or FTTH), including enterprise and business connectivity (e.g. mobile backhaul). This includes the ability to incorporate all existing fiber types, splitters and passive infrastructure.

Primarily due to operators wishing to protect their previous connectivity investments (e.g. xDSL, GPON), we believe one of the first applications of a future optical connectivity infrastructure will be that of backhaul, depicted from Figure 3. Operators will slowly begin to migrate the uplinks of these legacy systems, carrying their consolidated traffic over the higher capacity system. Even if they use separate fibers for the uplink and downlink between the Digital Subscriber Line Access Multiplexer (DSLAM)/GPON Optical Line Terminal (OLT) and the central office, this approach reduces the backhaul fiber count and creates a PON-like topology.The move to a future optical connectivity architecture is then relatively straightforward. The operator swaps the xDSL cable for fiber dropped to each home and swaps the filter for a splitter. The short-distance office is eliminated and a high-capacity access node in the long-distance office completes the migration.

Making the business case for each wave of investment is essentially about choosing the right time to invest in order to provide the “best fit” network capacity to suit current services and applications.

Our vision of a future optical connectivity architecture is one realized through an UDWDM-based PON approach, characterized by the complete absence of any active equipment between subscribers and the long-distance office location. It represents a significant breakthrough in the architecture and philosophy of an all-passive fiber optic network. This resulting architecture and technology is known as Next Generation Optical Access (NGOA), which will take the form of a fully optical network from the subscriber to the core.

The NGOA architecture will be flat, without the need for a separate aggregation layer and eliminating active components. Instead, a virtual point-to-point connection will be achieved between the subscriber and the central office, up to 100 kilometers away. Passive splitters and filters will effectively direct the correct wavelengths to the different users and the ONTs will access the wavelength dedicated to them.

Aggregation will take place in central offices, which will act as “Terabit access nodes” and handle the traffic for thousands of users. In this architecture, the central office represents the edge of the IP core network.

This simple architecture means that NGOA networks can be planned flexibly to optimize the network layers for transport, Ethernet and routing.

The path towards change


As depicted in Figure 4, NGOA will be able to deliver symmetric speeds in the range of 1Gbit/s and beyond for each subscriber, being more than adequate for the coming years, even with the heaviest usage levels. Importantly, it will provide this extra capacity in a way that keeps infrastructure and running costs to a minimum, including re-using the optical fibers operators are deploying right now.

It will also be a vehicle to provide a single, cost-effective delivery platform for all communication applications, including traditional end-user as well as business and enterprise connectivity.

NGOA will permit the assignment of one wavelength per subscriber, allowing for flexible use of the network.

The ultimate optical connectivity that is NGOA

DSLAM

GPON OLT

Splitter

NGOA OLT

MetroPoint-of-Presence

Arrayed WaveguideGrating (AWG)

MobileBackhaul (MBH)

PhotonicIP core

Home

Appartments

Passive Optical Distribution Network

Through the use of UDWDM to provide each subscriber with their own wavelength, NGOA enables a level of security and privacy to suit even the most fastidious users.

The move to a passive, all-optical network will bring with it step-changes in network capacity and environmental performance. With NGOA, it will be possible

to make enormous savings in energy by reducing the number of local offices. Eliminating a high proportion of network offices will lead to a massive reduction in operating costs. In addition, passive optical components require less regular maintenance than active electronic network elements, leading to further savings for operators.

More widely, further environmental benefits will result from a reduction in travel by users, since the technology will enable users around the world to enjoy a natural, almost face-to-face communication experience, without leaving home.

Nokia Siemens Networks, in conjunction with the Open Lambda Initiative (OLI), pushes for open standards. This will encourage the development of a healthy community of suppliers in both applications and equipment Promoting easier development and competition will help to drive innovation and keep costs down in the long term.

Figure 4 Architectural overview of NGOA


Standardization with competing technologies

With the ever increasing bandwidth demand from consumer and business applications, the most general requirement for a next generation PON (NGPON) is to provide higher bandwidth than existing Gigabit PONs. The standardization of NGPONs is currently under discussion within the Full Service Access Node (FSAN) group, with various alternatives being pushed by the various member organizations (including suppliers and operators).

As both Gigabit PONs and NG-PONs will continue to co-exist for a relatively long period of time, relevant standards that are adopted for NGPONs will have to ensure the following criteria:

• Coexistence between Gigabit PON and NGPON on the same ODN must be supported tosatisfycaseswherefiberresources are not abundant

• Service interruption for subscribers who are not migrated to NGPON should be minimized

• NGPON must support/emulate all GPON legacy services in case of full migration

NGPON technologies are divided into two categories: NGPON1 and NGPON2:

• NGPON1 - this supports the coexistence with GPON on the same ODN. The coexistence feature enables seamless upgrade of individual customers to NGPON on a live ODN without disrupting services of other customers

• NGPON2 - known as ‘disruptive’ NGPON, with no requirement in terms of coexistence with GPON on the same ODN

NGPON1 includes several technology options. One of these technologies, XGPON, represents a PON system with a 10Gbit/s line rate, with upstream line rate candidates including 2.5 and 10Gbit/s (depending on the target applications as well as cost and feasibility of such devices). XGPON supporting 2.5Gbit/s upstream and 10Gbit/s downstream line rates is referred to as XGPON1. XGPON supporting a 10Gbit/s symmetric line rate is referred to as XGPON2.

NGPON2 is looking out further to future optical connectivity systems, with many technical candidates, including NGOA, higher data rate TDM and DWDM systems. NGPON2 is not constrained by coexistence requirements, although coexistence is not precluded. With NGOA, coexistence is possible, which combines GPON & NGOA signals over the same fiber medium.


The ecosystem around NGOA

Before any technology can be deployed mainstream, there needs to be the relevant standards and the creation of the ‘ecosystem’ around the development of the technology. Even though technology that is vying for the adoption of the NGPON2 standard is optical-based and an optical ecosystem already exists, this ecosystem needs to be enlarged.

Innovative components need to be designed to meet the requirements being laid down for NGPON’s, along with the relevant cost and performance points being reached.

To this end, Nokia Siemens Networks has already established partnerships with component manufacturers and suppliers, enabling it to deliver the most advanced, affordable and efficient optical networking solutions to its customers.


Nokia Siemens Networks strives further ahead with NGOA, heralding it as ‘the’ ultimate optical connectivity system, spanning all networks layers outside of the core and providing symmetrical, unshared 1Gbit/s bandwidth per end-user. Furthermore, NGOA is not only applicable to the use cases of FTTH; mobile backhaul and enterprise connectivity scenarios are also ideally suited.

NGOA can effectively cover all existing and future application scenarios. With its potential evolution to 10Gbit/s, which will offer even mixed operation with 1Gbit/s, it is the ideal system to consolidate different network technologies. This will simplify network planning and operation.

With its long reach of up to 100km and truly passive Optical Distribution Network (ODN) infrastructure, it can also serve to consolidate local office sites.When comparing NGOA with an ‘Active Ethernet’ architecture (which is actually the only real alternative that can deliver the requirement of symmetrical 1Gbit/s services), significant TCO advantages of NGOA are clearly visible. The passive nature of the system and the much lower demand of fibers offer a huge OPEX savings potential.

A significant portion of the OPEX savings comes from better utilization of existing fibers or lower fiber leasing fees respectively. Reduced fibers in local offices also mean less effort in fiber patching and smaller Optical Distribution Frames (ODFs).

Although there are significant technical challenges to overcome going forward (e.g. standards, technology, integration, etc), Nokia Siemens Networks is convinced that NGOA is the shape of the future of optical connectivity.

Conclusion

NOKIA SIEMENS Ngoa Whitepaper 210311 2

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