Adc 2008 Manual Ftth104918ae

The Book on

The essential information you need to know when deploying FTTX, from the central office to

the outside plant to the customer premises

Foreward by Jason Meyers Managing Director, Penton Custom MediaPenton Media is the publisher of Telephony Magazine

The eagerly awaited follow-up to ADCs

The Book on FTTX

ADC Telecommunications, Inc., P.O. Box 1101, Minneapolis, Minnesota USA 55440-1101Specifications published here are current as of the date of publication of this document. Because we are continuously improving our products, ADC reserves the right to change specifications without prior notice. At any time, you may verify product specifications by contacting our headquarters office in Minneapolis. ADC Telecommunications, Inc. views its patent portfolio as an important corporate asset and vigorously enforces its patents. Products or features contained herein may be covered by one or more U.S. or foreign patents.

104918 1/08 Original 2008 ADC Telecommunications, Inc. All Rights Reserved

The essential information you need to know when deploying FTTX, from the

Central Office to the Outside Plant to the Customer Premises

The Book on Next Gen Networks

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The Book on Next Generation Networksii

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iiiThe Book on Next Generation Networks

Foreward

The Problem with Innovation

By Jason Meyers, Managing Director, Penton Custom Media Penton Media is the publisher of Telephony Magazine

The above is a title most people probably would not expect to see on a foreword to a book about next generation networks. But there is a reason behind it and a point to it, both of which I will get to in a moment.

First, though, what is that problem? What could be problematic about innovationin particular, about the network technology innovation that drives communication networks into the next generation, driven by the need and demand for advanced services and increasingly ubiquitous and continuous and instantaneous communications capabilities?

The problem can be summed up in two words: expectation and execution.

Innovation creates expectation in droves. Industries like telecom live and die by the expectation that is created by innovation. Companies get put on the map because of it. Whole market sectors are created around that innovation and the accompanying marketing buzz it generates. Its electric. Industry associations and alliances are formed around those expectations. The media thrives on the expectation and multiplies it. (Some might say its the medias fault.) Promises are made.

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Foreward

Then comes the executionor lack of it. This is where the rubber hits the road (or skids off into the ditch). Its one thing to make promises, to build up expectations. Its another to deliver on the expectations created, regardless of how technologically promising the innovation may be. Those markets and buzz created by the expectation? Without proper execution, they are more than likely to fizzle.

So the problem with innovation, quite simply, is one of follow-through. The problem is an inadequate attention to the detail required to turn innovation into a market.

So why did I choose this phrase as a title to the foreword of The Book on Next Gen Networks? Because I contend that this book goes a long way toward solving the problem. This is a book about executionnamely, the execution required to leverage next generation network innovation and use it to build markets.

How does one volume accomplish that which whole market sectors have at times tried and failed to accomplish? By concentrating on the details. This book doesnt speak in broad strokes about what various technologies can potentially accomplish, the services they can potentially enable or how competitively important it is to deploy those technologies in your networks. Instead, this book is a practical exploration and application of specifics.

The Book on Next Gen Networks goes deep, into the central office, to the distribution hub, the access network and into the customer premises. It explores, for example, why a proper fiber cable management system is so critical to network performancenot only right now, but also in the not-so-distant future, when todays will be carrying applications no one has yet thought of, and expanding because of it. Or where (and why) splitters should be deployed in a PON environment, and how a decision like that can help a network accommodate new services.


vThe Book on Next Generation Networks

This book analyzes the performance and cost issues that can occur if the wrong moves are made, and the benefits that can be realized by making the right ones. To that end, this is a book about preparing for the future. In fact, it attemptsas much as is possible in this ever-adapting network environmentto actually predict the future: What could the long-term consequences of a deployment decision or process be? How will the role of the network technicians who deploy the networks evolve, and what training will be required of them? How will new construction and the changing architecture of buildings impact how FTTP will be deployed?

The Book on Next Gen Networks is conceived and written to help those who consume it bridge the gap between expectation and execution. Read it, apply it, repeat it. Industry associations and alliances and alliances are formed around that expectation. It will help you deliver on the promise of innovation.

Enjoy!

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The Book on Next Generation Networksvi

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viiThe Book on Next Generation Networks

Table of Contents

Introduction: The Motivation for GPON Migration ........................................... 3

Central Office

Chapter 1 The Elements of Fiber Cable Management ................................. 11

Chapter 2 Effective Integration of Reduced Bend Radius Fiber into the Network ........................................................................ 19

Chapter 3 Incorporating Passive CWDM Technology vs. Deploying Additional Optical Fiber .............................................................. 25

Chapter 4 Adding New Video Services Warrants New Central Office Considerations ................................................................. 31

Distribution

Chapter 5 Its Happening in the Hub ........................................................... 39

Chapter 6 Extreme-Environment Performance Considerations for FTTX Splitter Modules ........................................................... 51

Chapter 7 Plug and Play Splitter Architectures Drive Operational Savings .... 61

Chapter 8 The Economics of FTTN vs. FTTP ................................................. 65

Chapter 9 Resectionalizing the Distribution Area .......................................... 71

Access

Chapter 10 Creating a Cost-Effective Plug and Play FTTX Architecture .......... 79

Chapter 11 Innovative Installation Techniques for Fiber Drop Terminals ......... 83

Chapter 12 Above vs. Below Ground Drop Splicing: Considerations for Drop Cable Connections in the FTTX Network ...................... 89

Chapter 13 Outside Plant Connections You Can Rely On .............................. 93

Chapter 14 Cost Optimizing Outside Plant Cable Assemblies ...................... 105

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viii Table of Contents

Customer Premises

Chapter 15 Multiple Solutions for Connecting Multiple Dwelling Units (MDUs) .............................................................. 113

Chapter 16 Deploying Reduced Bend Radius Fiber in MDU Environments... 125

The Technician

Chapter 17 Properly Training Next-Generation Technicians on Next-Generation Products .................................................... 133

Chapter 18 The Technicians Perspective on Reduced Bend Radius Fiber ................................................. 137

Glossary ................................................................................................. 143

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The Book on Next Generation Networks

Introduction

High-Rise MDU Medium-Rise MDU

Horizontal MDU

Low Rise/Garden MDU

Residential

Residential

FeederDistributionDrop

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The Book on Next Generation Networks2

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3The Book on Next Generation Networks

Introduction

The Motivation for GPON Migration

By December 2007, approximately eight million homes had been passed with fiber for Fiber-to-the-Home (FTTH) or Fiber-to-the-Premises (FTTP) applications. Included in these numbers are an astonishing five hundred communities that have chosen fiber as a means of delivering broadband applications to homes and businesses. Of these numbers, it is estimated that almost half, or around 3.5-million of these homes and businesses are connected using Broadband Passive Optical Networking (BPON), Ethernet Passive Optical Networking (EPON) or Ethernet-in-the-First-Mile (EFM)1.

Predicting the telecom future is never easyand it follows that building an access network that is future-proofed against rising bandwidth demand and next-generation technologies is a major challenge for todays service providers. But that doesnt mean decisions have to be based on a coin flip either. There are many practical considerations that can be examined when selecting an FTTP infrastructure that will not only meet current demand, but also provide the flexibility for a smooth migration to next-generation demands.

This is particularly true of the passive optical network (PON) portion of the network. A close look at several practical considerations, based on informed decision making, will provide a firm foundation for designing a network that can cost-effectively transition between legacy and future access technologies. Our own telecommunication history provides many troubling examples of networks that were built without giving thought to future innovation. Building telephone networks with copper, our predecessors could not have predicted todays broadband revolutioneven though we seem to have made the most of this legacy infrastructure with xDSL technologies.

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Introduction

However, through the unpredictable performance of xDSL and the overall condition of the legacy copper networknot to mention some very costly lessons learnedservice providers have realized the importance of network flexibility. FTTP offers service providers a clean slate for deploying todays new services to their bandwidth-hungry subscribersand it all begins with designing the proper PON architecture.

For the access protocols and the movement to Gigabit PON (GPON) migration, some additional concepts may need to be considered:

GPON is the next generation of PON electronics currently being

introduced to the marketplace.

GPON will NOT be the final technology deployed.

The network design should accommodate flexibility for the

current migration and beyond.

In theory, the passive connectivity infrastructure must be

agnostic to the service delivery technology.

GPON is making it easier for PON networks to move to an all-IP format where the external interfaces to the core are moving to an all Gigabit Ethernet network creating a movement away from the traditional ATM transport to a pure IP transport. GPON is IP-centric while allowing the traditional services of voice and video, yet acknowledges the strengths of the service provider to differentiate themselves on quality of service (QoS) issues.



GPON continues to have the long reach that effectively eliminates active components in the access network with little or no significant changes to the physical architecture that has already been built for BPON and EPON. Architecture designs should account for a smooth transition between technologies by accommodating practical considerations for future architectures. We do not have a true crystal ball as to what these technologies will become. If we did, we would simply build for the future. However, isnt this exactly what we should be doing--building for the future?

Wheres the motivation?

As predicted, GPON, a culmination of the best in BPON and EPON, is poised to dominate the access market by offering a much-needed bandwidth boost. We can all agree that eventually everythingvoice, video, and datawill be moving to IP and the quadruple-play applications, including network appliances, security, videosurveillance, etc. The advantages of GPON are a key driver for gaining the commitment of the large-volume carriers toward the GPON standard.

GPON is emerging on queue with higher split ratios that can deal with the challenges of delivering high-speed, high-bandwidth packaged services to business and residential customers. This is putting pressure on service providers to make decisions for ramping up their networks for GPON from the central office (CO) to the outside plant (OSP).

Ensuring FTTP networks can easily migrate to GPON promises to pay huge dividends to service providers in the coming years. As GPON develops as the standard of choice for FTTP networks, both cost reductions and interoperability will be accelerated. Those providers who make informed choices in deploying flexible, interoperable, reconfigurable networks will reap substantial benefits in the move to GPON and beyond. They will be able to quickly offer new and improved services as they evolve, without the need for major network overhauls.

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Introduction

Standards bodies

If service providers arent already convinced by GPONs ability to provide future enhanced services, maximize interoperability, utilize enhancement bands, and provide increased capacity with the promise of higher split ratios, the International Telecommunication Union (ITU) provides further motivation. The ITU points out that we can expect a significant increase in demand for dedicated Gigabit Ethernet (GigE) and 10GigE services to both businesses and residential customers.

This means every service provider must decide how to best integrate all types of services onto a single backhaul fiber network. A smooth and easy migration capability to GPON is the most viable solution. GPON enables PON networks to easily move to an all-IP format while external interfaces to the core move to an all-gigabit ethernet formata movement away from the traditional ATM transport to pure IP transport.

The ITUs ratification of the GPON standard in 2003 has also helped put electronics vendors on the same page in terms of getting behind one standard. This standard will enable the major cost challenges associated with optical network terminals (ONTs) at the customer premise to be addressed and, in time, will bring those costs down significantly.

GPON combines the best of BPONs quality-of-service attributes with the best of EPONs ability to transport and interface on an all-IP network. It also addresses the higher application bandwidth needs by providing 2.4 Gbits/sec downstream and 1.2 Gbits/sec upstream.

The transition to GPON

Making the move from BPON or EPON to GPON involves three key architectural components. Addressing the fibers loss characteristics in terms of spectral attenuation, using the appropriate class of optics, and considering the advantages offered by greater split ratio capability will all



affect the networks migration to GPON. Each of these considerations will be addressed in greater detail within this book.

Connectorization also plays a role in creating a migration-ready FTTP network, particularly when considering the single fiber requirements of next-generation video applications in GPON architectures. The use of APC connectors that offer the lowest return loss characteristics of all current connectors will optimize high bandwidth and allow for longer reach.

Splitter configuration in the optical distribution portion of the networkbetween customers and the COhas been a hot topic over the last few years. We believe a centralized splitter approach offers the best flexibility advantages. It maximizes the efficiency of OLT PON ports, and unlike the cascaded approach, does not risk stranding unused ports in areas of low take rates. There will also be further advantages when it comes to testing and troubleshooting the network.

With the GPON standard already revolving around centralized 1x32 splitter architectures in the OSP, GPONs promise of a 1x64 splitter ratio offers even more incentive to service providers by doubling the number of homes serviced from a single splitter.

Moving to the CO, flexibility becomes the pathway to easy migration capability. A network must always be built as a flexible long-term entity that adapts to inevitable changes in both equipment and technology. A cross-connect network offers excellent flexibility for configuration points and should include high-quality APC connectors for handling the higher power necessary for any analog video application.

Cable management in the CO is also an issue worth consideration. In fact, the considerations for GPON within the CO can be summed up in just three wordsflexibility, quality, and protection.

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A final word

Weve covered a lot of ground in a short time, but these and other topics are covered in greater detail as you read through this book. Suffice it to say that network architects owe it to themselves to carefully plan ahead to avoid having to re-build the network to accommodate each new application or technology.

Summing it all up, the inevitable need to migrate to GPON is already upon us, and the future generations of PON are already on the drawing board. Making informed network decisions today will not only make a migration process less painful, but it is also good business sense. GPON not only supports TDM voice today, it has a true migration platform to an all-IP network. But most importantly, it guarantees that existing architectures will migrate to future technologies without requiring forklift upgrades.

I hope youll see this latest edition of The Book on Next Generation Networks as a tool for helping you make good decisions for upgrading your access network. It represents the experience and know-how of many fine architects, planners, and design technicians. I wish you the best of luck in meeting the unique challenges of your network and hope youll consider our ADC team as you work towards making your network plans a reality.

Enjoy!

Patrick J. Simms, RCDD Principal Systems Engineer, ADC [email protected]

1. Source: RVA LLC, Market Research & Consulting, Fiber to the Home: Advanced Broadband 2007

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Central Office



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Chapter 1

The Elements of Cable Management

As service providers continue upgrading their networks to transport high-bandwidth broadband services, an increase in fiber usage is essential to meet both bandwidth and cost requirements. But just deploying this ad-ditional fiber is not enougha successful, well-built network must also be based on a strong fiber cable management system.

Proper fiber management has a direct impact on the networks reliabil-ity, performance, and cost. Additionally, it affects network maintenance, operations, expansion, restoration, and the rapid implementation of new services. A strong fiber cable management system provides bend radius protection, cable routing paths, cable accessibility, and physical protection of the fiber network. Executing these concepts correctly will enable the network to realize its full competitive potential.

Introduction

With demand steadily increasing for broadband services that will include several bandwidth-hungry technologies like high-definition television (HDTV) and higher Internet speeds for handling larger file sharing re-quirements, fiber is being pushed closer and closer to the customer premises. This, in turn, creates a need for both additional fiber in the central office /data center and the active equipment that must be managed to accommodate future network growth.

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Central Office

Any new broadband network infrastructure must have the inherent capability to easily migrate to the next generation of technologies and services. This is a key consideration for service providers beginning to deploy triple-play broadband serviceswhether its from a multiple service operator (MSO) headend, a central office (CO), or wireless mobile switching center (MSC). As the amount of fiber dramatically increases, the importance of properly managing the fiber cables becomes a more cru-cial issue.

The manner in which fiber cables are connected, terminated, routed, spliced, stored, and handled will directly and substantially impact the networks per-formance and, more importantly, its profitability. New technologies and products have been developed in the last few years to improve bend radius protection, cable routing paths, accessibility, and physical protection.

Bend radius protection

There are two types of bends in fibermicrobends and macrobendsthat can affect the fiber networks long-term reliability and performance.

The microbend is a small, microscopic bend that may be caused by the cabling process itself, packaging, installation, or mechanical stress due to water in the cable during repeated freeze and thaw cycles. External forc-es are also a source of microbends. An external force deforms the cabled jacket surrounding the fiber, but causes only a small bend in the fiber. A microbend typically changes the path that propagating modes take, result-ing in loss from increased attenuation as low-order modes become coupled with high-order modes that are naturally lossy.

A macrobend is a larger cable bend that can be seen with the unaided eye and is often reversible. As the macrobend occurs, the radius can become too small and allow light to escape the core and enter the cladding. The result is insertion loss at best and, in worse cases, the signal is decreased



or completely lost. Both microbends and macrobends can, however, be re-duced and even prevented through proper fiber handling and routing.

The minimum bend radius will vary depending on the specific fiber cable. However, in general, the minimum bend radius of a fiber should not be less than ten times its outer diameter. Thus, a 3 mm cable should not have any bends less than 30 mm in radius. Telcordia recommends a minimum 38 mm bend radius for 3 mm patch cords. Also, if a tensile load is applied to a fiber cable, such as the weight of a cable in a long vertical run or a cable pulled tightly between two points, the minimum bend radius is increased due to the added stress.

The advent of bend insensitive or reduced bend radius fiber is an example of how technology has addressed the bend radius issue. Whereas the mini-mum bend radius should not be less than ten times the outer diameter of the fiber cable in typical fiber, reduced bend radius fiber provides more leeway. However, service providers must understand that these new fibers do not diminish the need for solid fiber cable management. On the con-trary, the increase in the sheer number of fibers being added to the system to accommodate broadband upgrades makes bend radius protection as important as ever.

As fibers are added on top of installed fibers, macrobends can be induced on the installed fibers if they are routed over an unprotected bend. A fiber that had been working fine for many years can suddenly have an increased level of attenuation, as well as a potentially shorter service life. The impor-tance of bend radius protection is critical to avoid operational problems in the network.

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Central Office

Cable routing paths

The second element of fiber cable management is cable routing paths and is related to bend radius protection. Improper routing of fibers by techni-cians is one of the major causes of bend radius violations. Wherever fiber is used, routing paths must be clearly defined and easy to followto the point where the technician has no other option than to route the cables properly. Leaving cable routing to the technicians imagination leads to an inconsistently routed, difficult-to-manage fiber network.

The quality of the cable routing paths, particularly within a fiber distribution frame system, can be the difference between congested chaos and neatly placed, easily accessible patch cords. Its often said that the best teacher in fiber routing techniques is the first technician to route it properly. Con-versely, the worst teacher is the first to use improper techniques, since sub-sequent technicians are likely to follow his lead.

Well-defined routing paths, therefore, reduce technician training time, in-crease the uniformity of the work done, and ensure and maintain bend radius requirements at all points, thus improving overall network reliability. It is important to note that, again, the use of bend insensitive fiber does not diminish the need for clear cable routing pathsthere are benefits that go beyond bend radius protection.

Having defined routing paths makes accessing individual fibers easier, quicker, and saferreducing the time required for reconfigurations. Fi-ber twists are reduced to make tracing a particular fiber for rerouting much easier. Even with new technologies, such as the use of LEDs at both ends of patch cords for easy identification, well-defined cable routing paths still greatly reduce the time required to route and reroute patch cords. All of this directly affects network operating costs and the time re-quired to turn up or restore service.



Cable access

Cable access is the third element to good fiber cable management and refers to the accessibility of the installed fibers. As the number of fibers increases dramatically in both the distribution frame and the active equip-ment, cable access becomes an increasingly important issue for broadband service providers. In the past, an active equipment rack might have had about 50 fibers exiting, and managing those fibers was much less of an is-sue. But as that same rack is fitted for next generation broadband services, there may be up to 500 fibers involved, making proper management and accessibility a vitally important matter.

With huge amounts of dataas well as revenuemoving across those fi-bers, the ability for technicians to have quick and easy access is critical. When there are service level agreements in place, particularly for customers with high priority traffic, the last thing any service provider wants is service interruptions caused by mishandling one fiber to gain access to another.

As previously mentioned, there are patch cords designed today with LEDs at both ends to help technicians identify particular cable runs with no chance of error. These innovations can be implemented into a good cable man-agement system to help minimize problems caused by disconnecting the wrong patch cord. There are many other tools and techniques for ensuring that every fiber can be installed or removed without bending or disturbing an adjacent fiber.

The accessibility of the fibers in the fiber cable management system can mean the difference between a network reconfiguration time of 20 minutes per fiber and one of over 90 minutes per fiber. Since accessibility is most critical during network reconfiguration operations, proper cable ac-cess directly impacts operational costs and network reliability.

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Central Office

Physical fiber protection

The last element of a fiber cable management system addresses the physi-cal protection of the installed fibers. Every fiber throughout the network must be protected against accidental damage by technicians or equipment. Fibers traversing from one piece of equipment to another must be routed with physical protection in mind, such as using raceway systems that pro-tect from outside disturbances.

Without proper physical protection, fibers are susceptible to damage that can critically affect network reliability. The fiber cable management system should always include attention to ensuring every fiber is protected from physical damage.

A final wordplanning

Finally, since many service providers are in the processor soon will beof upgrading networks for delivering high-bandwidth broadband services, it is important to stress the need for planning in terms of cable management. Todays network is a living and growing entityand what is enough today will almost certainly be too little tomorrow. With that in mind, future-proof-ing the network wherever possible should be a major considerationand fiber cable management is no different.

For example, the current upgrades to broadband service delivery taking place in COs, MSOs, or MSCs require more fiber deployment. Four- and six-inch fiber raceway systems are already becoming inadequate to properly manage these larger amounts of fiber. Service providers must plan ahead for a centralized, high-density fiber distribution frame lineup using 24-inch raceways that can accommodate not only todays fiber requirements, but also those expected in the future.

Although installing a 24-inch raceway system is more expensive today, hav-ing to go back in and retrofit the system in a few years represents a much higher cost and significant risk to the fiber. Ignoring future growth, particu-



larly in terms of fiber, will result in higher long-term operational costs result-ing from poor network performance or a requirement to retrofit products that can no longer accommodate network demand.

Another consideration in planning for good fiber cable management con-cerns the active equipment rack. Most manufacturers have traditionally overlooked the need for providing cable management within their equip-ment. Before purchasing, service providers should insist that cable manage-ment is included within every piece of active equipment to ensure their investment will operate at peak efficiency over time.

All four elements of a fiber cable management systembend radius protec-tion, cable routing paths, cable access, and physical protectionstrengthen the networks reliability and functionality while lowering operational costs and ensuring smooth upgrades when necessary.

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Chapter 2

Effective Integration of Reduced Bend Radius Fiber into the Network

Introduction

Bending of singlemode fiber has everyone talking these days. The idea that you can bend a fiber around a pencil without a dramatic increase in attenuation is a concept that has everyone considering new fiber applications and design possibilities.

Today, industry standards for traditional singlemode fiber typically specify a minimum bend radius of ten times the outside diameter of the jacketed cable or 1.5-inches (38 mm), whichever is greater. This new breed of flex-ible singlemode optical fiber has the potential to significantly reduce these minimum bend radius requirements to values as low as 0.6-inches (15 mm), depending on the cable configuration, without increasing attenuation.

There are many names for optical fiber that can endure a tighter bend radius bend insensitive, bend resistant and bend optimized are sever-al that come to mind. However, some of these terms can be somewhat misleading. Designers and installers may believe reduced bend radius optical fiber is impervious to all the forces that can increase attenuation and cause failure on an optical fiber link. Staff and contract technicians can make false assumptions on its durability and performance capabilities as well. Such beliefs can have a serious impact on network performance.

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Central Office

For purposes of accuracy, ADC uses the term reduced bend radius, be-cause this title best describes what the product actually delivers. As with any optical fiber, attention must be paid to how the cable is deployed and handled throughout the lifetime of the network, in order to ensure optimal performance.

What is reduced bend radius optical fiber?

As mentioned above, reduced bend radius fiber is able to withstand tight-er bends within frames, panels, and pathways. To understand how this is achieved, it is important to understand that all fiber types rely on principles of Total Internal Reflection, which allows light signal to travel from one end of the fiber to another (see Figure 1). By improving the bend radius of optical fiber, light entering the core is effectively reflected by the clad-ding back into the core. Instead of using a matched clad profile, some con-structions of reduced bend radius optical fiber use a depressed clad profile with a lower index of refraction than the core, causing light to stay within this core.

n1

n2

Refracted

Reflected

Cladding

Core

Figure 1Principle of Total Internal Reflection for Optical Fibers

Fiber cladding has a lower Index of Refraction (IOR) than the core, causing light to stay within the core. Depression of the cladding

profile promotes Total Internal Reflection

To achieve tighter bend radii, some constructions change the mode field diameter (MFD)the area across the core of the fiber that fills with light. Typical MFD for standard singlemode optical fiber is about 10.4m; reduced bend radius optical fiber may exhibit MFD of between 8.9m and 10.3m.



Regardless of the type of construction, all reduced bend radius fiber prod-ucts do one thing very wellthey can perform under a tighter bend radius where macrobends occur. Examples include a central office application, where fiber passes from a panel into a vertical cable route or in an FTTX deployment within the confines of an optical network terminal (ONT).

The fibers performance is definitely impressive. For example, in ADC tests a standard singlemode optical fiber with one turn around a 1.26-inch (32 mm) diameter mandrel shows induced attenuation of less than 0.50 dB at 1550 nm. This same test on a reduced bend radius singlemode 1550 nm optical fiber shows less than 0.02 dB of attenuation.

In general, reduced bend radius optical fiber is designed to perform with low loss across the spectrum of wavelengths, from 1285 nm to 1650 nm, using all the channels available on those wavelengths to maximize bandwidth. Current designs include low water peak or zero water peak so that high attenuation is avoided at 1383 nm. Many re-duced bend radius optical fiber products meet ITU-T Recommendation G.657, meaning they work well at 1550 nm for long distance and voice applications and at 1625 nm for video applications.

Does it improve performance?

Despite the improved bend radius, the reality of this fiber is that bend ra-dius protection is still a concernjust not to the extent that it is in standard fiber. There is still a mechanical limit on how tightly any optical fiber can be routed before the structural integrity of the glass is violated.

The assumptions about improved performance are not accurate either, at least beyond the exceptional bend radius performance. In reality, the perfor-mance of reduced bend radius optical fiberor any optical fiberdepends upon many factors, not just bend radius properties.

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Central Office

By itself, reduced bend radius optical fiber does not offer improvements in attenuation. True, it bends more tightly without causing additional attenu-ation. Yet laid out on a long, straight run next to a standard optical fiber, there is no difference in performance that can be attributed to the cables construction. It is inaccurate to believe that reduced bend radius optical fiber is the end-all solution when, in fact, there are many other factors that determine optical fiber link performance.

Durability Reduced bend radius optical fiber offers the same crush resis-tance and tensile strength as the same cable with standard singlemode fi-ber. As with standard optical fiber, excessive weight will crush reduced bend radius optical fiber and excessive pulling tension will damage the cable, both of which affect attenuation.

Connector pull-off resistance Cable assemblies and connectors must meet Telcordia (GR-326) requirements for strength of the fiber termination connector. Reduced bend radius optical fiber does not improve connector pull-off resistance. Connectors that are easily loosened or disconnected in-crease attenuation and cause failures.

Connector performance When it comes to connector performance, endface characteristics determines loss from the connector. Reduced bend radius optical fiber does not impact insertion loss from connectors, making termination and quality of connectors an important consideration in link performance.

Proper applications for reduced bend radius optical fiber

Singlemode reduced bend radius optical fiber offers benefits for applications that including the central office, FTTX deployments, data cen-ter, and OEM solutions. Singlemode reduced bend radius optical fiber is best suited for environments where little or no bend radius protection is available. It is also ideal for applications where space is an issue. Specific ap-plications that make sense for this type of fiber include places in which:



Space is tight For drop cable or termination of pigtails in multiple dwell-ing unit (MDU) and optical network terminal (ONT) boxes for FTTX deploy-mentswhere there is no space and often no cable managementreduced bend radius optical fiber offers less chance of increased attenuation during field installation and maintenance.

No fiber management is available The front of frames and routerswhere moves/adds/changes occuris ideal for use of reduced bend ra-dius patch cords and multifiber breakout assemblies. Many OEM active components do not have bend radius limiters or protection on the front of the equipment.

Space is at a premium Patch cords and multifiber breakout assemblies that can bend more tightly enable increasing density of active equipment in racks and cabinets without sacrificing access. For manufacturers of ac-tive equipment, reduced bend radius optical fiber can help reduce size of electronics, improving density and airflow. However, in these applications, even more consideration must be paid to the elements of proper cable management. Tighter bend radius also offers OEMs the chance to increase the functionality of active equipment by utilizing less chassis space.

Of course, a key advantage of reduced bend radius optical fiber is use in high bandwidth applications. For standard optical fiber, the 1625 nm to 1550 nm wavelengths are the first to go when the cable is wrapped around a mandrel. Preserving these wavelengths around tighter bends offers ben-efits for OEMs seeking to improve functionality of network equipment or network managers looking for the efficiency of having all wavelengths available on a given optical link.

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Conclusion

Singlemode reduced bend radius optical fiber has generated quite a buzz, and it is a great step forward in optical fiber construction. It makes much-handled patch cords and multifiber assemblies less susceptible to macrobends that affect attenuation and limit bandwidth of optical fiber links.

It is crucial for the health and performance of the network to be aware that reduced bend radius fiber does not, in any case, mean that the fundamen-tals of proper fiber management are to be ignored. In fact, as this fiber is used in higher density applications, factors such as connector access and cable routing paths become even more crucial. Reduced bend radius optical fiber is just one aspect of a complete strategy for efficient, future-proofed network management.



Chapter 3

Incorporating Passive CWDM Technology vs. Deploying Additional Optical Fiber

The recent advancement in telecommunication applications for voice, video and data places additional demands on fiber optic networks. Adding additional fiber to existing networks can be very costly to service providers. In most cases, a far betterand less costlyoption is found in coarse wavelength division multiplexing (CWDM) technology.

CWDM technology adds greater fiber bandwidth while increasing the flex-ibility, accessibility, adaptability, manageability and protection of the net-work for applications up to 60 km.

What is CWDM?

CWDM can be viewed as a third generation of WDM technology. WDM was developed as a fiber exhaust solution and traditionally employed the 1310 nm and 1550 nm wavelength signals. In most WDM scenarios, providers with a fixed number of fibers had run short of bandwidth due to rapid growth and/or unforeseen demand. By multiplexing a signal on top of the existing 1310 nm wavelength, they could create additional channels through a single fiber to increase the networks capacity.

However, demand continued to increase dramatically with new inno-vations and applications such as the internet, text messaging and other high bandwidth requirements. This created the need for very fine channel spacing to add even more wavelengths or channels to each fiber. Dense WDM (DWDM) was a major breakthrough as equipment provid-

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ers pushed to offer new equipment, promising nearly unlimited bandwidth potential. However, while DWDM was quickly adopted for long-haul and transoceanic optical networking, its use in regional, metropolitan, and cam-pus environments was, in most cases, cost prohibitive.

A more targeted and cost-effective solution followed with CWDM, a more recent standard of channel spacing developed by the International Telecommunication Union (ITU) organization in 2002. This standard calls for a 20 nm channel spacing grid using wavelengths between 1270 nm and 1610 nm (see Figure 1). The cost of deploying CWDM architectures today is significantly lower than its DWDM predecessors.

Prior to ITU standardization, CWDM was fairly generic and meant a number of things. For instance, the fact that the choice of channel spac-ing and frequency stability was such that erbium-doped fiber amplifiers (EDFAs) could not be used was a common thread. One typical definition for CWDM was two or more signals multiplexed onto a single fiber, one in the 1550 nm band and the other in the 1310 nm bandbasically, the original definition for early WDM.

1200 1300

O-band1260-1360

E-band1360-1460

Wavelength (nm)

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tenu

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)

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0ITU-T G.652 fiber

Waterpeak

1270 1290 1310 1330 1350 13701390

14101430 1450 1470 1490 1510 1530 1550 1570 1590

1610

Figure 1: CWDM wavelength grid as specified by ITU-T G.694.2 Todays standardized CWDM is better defined as a cost-effective solution

for building a metropolitan access network that promises all the key characteristics of a network architecture service providers dream

aboutoffering transparency, scalability, and low cost.



New developments

Even though the ITUs 20 nm channel spacing offers 20 wavelengths for CWDM, the reality is that wavelengths below 1470 nm are con-sidered unusable on older G.625 specification fibers due to the in-creased attenuation in the 1310-1470 nm bands. However, new fibers that conform to the G.652.C and G.652.D standards, such as Corning SMF-28e and Samsung Widepass, nearly eliminate the wa-ter peak attenuation peak to allow for full operation of all ITU CWDM channels in metropolitan and regional networks.

This enables a CWDM system to operate effectively at the low end of the ITU grid where attenuation was problematic for earlier fibers. For example, an Ethernet LX-4 physical layer uses a CWDM consisting of four wavelengths near the 1310 nm wavelength, each carrying a 3.125 Gbits/second data stream. Together, the four wavelengths can carry 10 Gbits/second of aggregated data across a single fiber.

As mentioned earlier, a major characteristic of the recent ITU CWDM standard is that the signals are not spaced appropriately for amplification by EDFAs. This limits the total CWDM optical span to somewhere near 60 km of reach for a 2.5 Gbits/second signal. However, this distance is suitable for use in metropolitan applications. The relaxed optical frequen-cy stabilization requirements also allow the associated costs of CWDM to approach those of non-WDM optical components.

Basic implementation

As stated earlier, CWDMs appeal is firmly rooted in meeting the additional demands being placed on fiber networks by a steady stream of new, bandwidth-hungry applications. Adding more fiber is one solution, but there are many possible obstacles that will likely make this solution cost prohibitive. Although every situation is different and brings unique considerations to the table, nearly any fiber deployment includes rights-of-way, trenching costs, additional equip-ment, manpower, and considerable time.

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Market studies have indicated accrued costs between $10,000 and $70,000 per mile to deploy new fiber cable. The large disparity is due to different situationsfor example, it costs far more to tear up a city street than to simply trench fiber in a rural setting. But the key issue is that network archi-tects can incorporate a CWDM system for much less cost and still achieve the bandwidth increases necessary to meet demand today and well into the foreseeable future.

Basically, a CWDM implementation involves placing passive devices, trans-mitters, and receivers at each end of the network segment. CWDM per-forms two functions. First, they filter the light to ensure only the desired combination of wavelengths is used. The second function involves multi-plexing and demultiplexing the signal across a single fiber link. In the multi-plex operation, the multiple wavelength bands are combined onto a single fiber for transport. In the demultiplex operation, the multiple wavelength bands are separated from the single fiber to multiple outputs. (See Figures 2 and 3)

ADCs passive network solution adds value by using the value-added module (VAM) platform to multiplex and demultiplex. These VAMs can easily be incorporated into central office (CO), multiple service operator (MSO), and mobile switching center (MSC) environments for leveraging the benefits of CWDM. The MSC uses CWDM to multiplex the different hosts on a wireless coverage system to multiple remotes using minimal fiber strands. Even a single fiber can service four, six, or eight different re-mote units. From there, an antenna is attached to each device to enable indoor wireless coverage.



Metro Transport RingUsing CWDM

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Figure 2: CWDMs in useFor example, MSOs can install a band system at the head-end that will drop one wavelength to each node along a particular ring configura-tion. This ring can be utilized as a single fiber. Each CWDM device is packaged into the VAM platformconnectorized and labeledfor integration into the fiber panel or cross-connect to save floor space and eliminate extra patch cords.

Designated, dedicated wavelengths

CWDM also offers the benefit of individual wavelengths for allocat-ing specific functions and applications. Out-of-band testing capability is achieved by simply dedicating a separate wavelength or channel for nonin-trusive testing and monitoring. In fact, any number of different applications can be applied to specific wavelengths. For example, a particular wave-length might be allocated specifically for running overhead or management software systems.

This is a common practice in using CWDM for cable television net-works, where different wavelengths are dedicated for downstream and upstream signals. It should be noted that the downstream and up-stream wavelengths are usually widely separated. For instance, the

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downstream signal might be at 1310 nm while the upstream signal is at 1550 nm. Another recent development in CWDM is the creation of small-form-factor pluggable (SFP) transceivers that use standardized CWDM wavelengths. These devices enable a nearly seamless upgrade in even legacy systems that support SFP interfaces, making the migration to CWDM more cost effective than ever before. A legacy system is easily con-verted to allow wavelength multiplexed transport over one fiber by simply choosing specific transceiver wavelengths, combined with an inexpensive passive optical multiplexing device.

Conclusion

ADC views the emergence of CWDM as the most cost-effective means of moving ever-increasing amounts of information across metropolitan access networks. For most providers, deploying new fiber as a means of combat-ing fiber exhaust is not a viable option. There are too many high costs involved with trenching the fiber cable, and obtaining rights-of-way can be an intensely complex issue.

CWDM simply makes sense, particularly with the technological advancements in todays fiber and transceiver options, including VAM sys-tems. CWDM achieves the critical goals of transparency, scalability, and low cost that providers seek in todays highly competitive industryan industry where new applications and increasing demand dictate the pace for mod-ern telecommunication networks.



Chapter 4

Adding New Video Services Warrants New Central Office Considerations

Although its fair to say the distribution and access elements within the outside plant (OSP) portion of the Fiber-to-the-Premises (FTTP) network de-mand the majority of attention during deployment, its still important not to overlook implications to the central office (CO). Any FTTP network requires the same flexibility as the transport networkand it all begins in the CO.

The addition of video services to FTTP network presents challenges to the CO requiring special consideration.

First, a review

Before discussing the unique challenges of video, its important to briefly review the overall implications that FTTP has on the CO architectureand the importance of making informed decisions in the early stages. The goal of network planners is always to minimize capital expenses and long-term operational expenses, while achieving the highest possible level of flexibility in the network.

Architectural decisions involve connection strategies between optical line terminal (OLT) equipment and OSP fibers, flexibility in terms of test access points, and WDM positioning. A key requirement for providing flexibility evolves from ensuring full cross-connect capability. With all OLTs, as well as OSP fibers, connected at the optical distribution frame (ODF), easy ac-cess and significant long-term network flexibility is achieved, enabling easy adds, moves, and changes to the ODF. Since the one constant in telecom-munications has always been change, any assumption that the network will remain static can result in significant long-term capital expense and flexibility issues.

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The second critical architectural decision involves placement of the video WDM within the CO environment. The video WDM combines the voice and data signals with video signals onto a single fibera key element of FTTP deployment. Again, with expense and flexibility in mind, ADC concludes that placing the video WDM in the cross-connect ODF lineup is the best option.

This is done by using patch cords to connect the OLT equipment to the inputs of the video WDM. A cross-connect patch cord connects the video WDM common port to the designated OSP port, providing an immedi-ate advantage of requiring just three connector pairs while still maintaining maximum flexibility. With the video WDM located at the ODF and all OLT patch cords routed directly to the ODF, even greater flexibility is provided regarding how the OLTs are combined and configured. Any OLT is easily combined with any other OLT, regardless of CO location.

Factoring in the video

The addition of video signals now presents new challenges to the con-figuration of the CO in order to maintain the same flexibility and price points desired in deploying FTTP. The video overlay onto the FTTP net-work adds additional fiber cable management requirements. Also, in or-der to split the video feed to multiple PONs, additional optical splitting is necessary. Optical path protection switches are also incorporated where the video signal enters the service office from the video serving office.

From the video OLT, video signals will pass through several erbium-doped fiber amplifiers (EDFAs) used to amplify and split the signal. Each EDFA output will be further split by additional optical splitters to maximize the video output, allowing the most PONs to be served using the fewest number of EDFAs. Each EDFA can have up to four outputs, each with its own optical splitter, depending on signal strength.



The use of optical splitters is critical, but there are several placement options. For instance, the splitters could reside in either the OLT equip-ment frame or the fiber frame. Placing the optical splitter in the fiber frame enables even more flexibility. For instance, if a particular PON is located a considerable distance away, a stronger video signal would be required and the signal should not be split. By having the optical splitter in the fiber frame, a patch cord can be run from the EDFA to the fiber frame, thus bypassing the optical splitter and allowing a stronger video signal to go to that PON. This flexibility allows video signals of various power levels to reach PONs at various distances. These optical splitters would reside in the fiber frame in a chassis very close to the WDM chassis on the 1550 nm input side.

Assuming the office providing the video service is not the same office in which the video signal originates, optical protection switching is also a consideration. Through diverse path routing, both a primary and protect video feed enters the optical protection switch in the video OLT equip-ment frame. The primary video feed throughputs to the video OLT, but should that signal drop below a preset power threshold, the system automatically switches to the redundant path (or protect) video feed. The diverse path routing takes place at the transmission side where a 1x2 splitter creates two diverse signals. This basically provides SONET-like protection without all the electronics by using a splitter and an optical switchmuch more cost effective.

Several important cable management considerations that apply in general to the FTTP network architecture will apply to a very great extent when it comes to video signals. Since video signals are usually high-power analog, they require considerations for the use of angled polish connectors, con-nector-cleaning techniques, and other cable management practices that contribute to signal quality.

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Every network designer wants to get the most out of existing electronics. In FTTP, that equates to getting the most PONs served and achieving the highest network flexibility for the least amount of expense. But the con-stantly-changing network still requires everyone to not only peer into the future, but to also design todays FTTP networks with the ability to adapt to the future.

Test access for the future

Testing the FTTP network is a serious challenge for service providers. Ad-vanced ODF solutions are being adopted that enable remote test and monitoring functionality. With traditional ODF functionality, performing tests or troubleshooting problems requires breaking into a patch and basically taking the network out of service. But monitoring and testing ca-pabilities can be incorporated into advanced ODF solutions that will enable remote monitoring and traffic identification, as well as reduce troubleshoot-ing and fault isolation time. The net result is more efficiency, reliability, and cost savings.

By placing an optical NxN switch between the test equipment and the access port on the fibers, any fiber can be tested with any test equip-ment from the network operations center (NOC). For example, if contact is lost with several optical network terminals (ONTs), an optical time do-main reflectometer (OTDR) trace can be performed over the particular fiber to isolate the fault. Performance monitoring tests can also be accomplished without having to dispatch a technician to the frame to man-ually perform testing.

Built-in diagnostics can identify problems within the electronic equipment, but to see whats happening within the fiber requires specific test equip-ment and non-intrusive access points. In any FTTP network, its a point-to-point connection from the OLT to the customer. If there is a failure in that network, the customer is out of servicethere is no redundant path available. Therefore, the ability to restore the network quickly and easily is



absolutely critical. The addition of this single switch provides technicians with quick, easy, and reliable access to the networkall of which greatly reduces network outage time and saves money.

Designing the CO to accommodate FTTP requires similar, if not more strin-gent, cable management and architectural attributes as any transport net-work. The video overlay makes even more demands on the CO in terms of efficiency, flexibility, and accessibility. Decisions made by service providers today will significantly impact the future reliabilityand profitabilityof their FTTP network. But with careful planning, future-proofing the CO is a good way to begin.

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Horizontal MDU

Low Rise/Garden MDU

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Chapter 5

Its Happening in the Hub

The Fiber Distribution Hub (FDH) continues to play a vital role in supporting rapid deployment and connection in Fiber-to-the-Premises (FTTP) networks. Innovation in FDH design occurs at a rapid rate and next generation fea-tures appear in newer FDH enclosures. Key innovations include:

Miniaturized splitter modules with plug-in installation that allow easy additions and upgrades

High-density termination fields with connectorized harnesses allowing modular growth and flexible rearrangement

A wide range of sizes and mounting configurations that retain craft-friendly fiber management and maintenance features

Performance enhancements to optical connectors and splitters due to the rigorous requirements of independent testing of all optical components and enclosures

Time- and space-saving parking lots providing cross-connect function-ality at interconnect loss and space levels

As a result, FDH products have been widely accepted in FTTP networks. FTTP is now seeing large-scale deployment and FTTP deployment is defi-nitely still happening at the hub.

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Network architectures

Fiber-to-the-Business

ONT

FDHCO/HE

OLT

Optical Distribution Network Fiber-to-the-Home

Fiber-to-the Multi-Dwelling Unit

After years of research and experimentation with access networks, many network providers have settled on passive optical network (PON) architectures as the direction for future subscriber access. The PON ar-chitecture has been adopted as a standard in ITU-T G.983.x that defines the protocols, data rates, and operating wavelengths necessary to sup-port network services. At the same time, the standards have established power budgets and parameters for the fiber optic plant to ensure reliable transport all the way to the home. The technology of high-speed PON equipment, combined with broadband fiber offers the potential for con-necting high bandwidth services directly to the home. The standards ensure interoperability of equipment and therefore have driven down the cost of deploying all optical networks. When adding in the cost savings associated with operating an all-passive optical plant, PON networks are attractive for overbuild as well as new network construction.

The initiative to build PON networks is often referred to as Fiber-to-the-Premises (FTTP), to emphasize the vision of connecting fiber from the central office/headend (CO/HE) all the way to the premises. PON architecture includes optical line terminal (OLT) equipment at the CO/HE that bundles voice and data services. OLT equipment utilizes wavelength



division multiplexing (WDM) technology to provide bidirectional voice and data services (1310 nm/1490 nm) over a single fiber. Additional WDM components at the CO/HE allow integration of video services onto the same fiber at the 1550 nm wavelength.

OLT equipment ports are connected through optical splitters, allowing a single port to serve multiple subscribers. The split ratio in PON networks can vary, but typically networks are planned with 32- or 16-way splits. The architecture may be configured by concatenating the splitters at a single point. Most networks are planned with 1x32 splitters centrally located for easy access for additions, service, and maintenance.

PON architecture includes optical network terminal (ONT) equipment at the premises for resolution of voice, data, and video services. Standardiza-tion of ONT equipment allows the same equipment to provide services for Fiber-to-the-Home (FTTH), Fiber-to-the-Business (FTTB), and Fiber-to- Multiple-Dwelling Units (MDU) applications. Combining these applications into the FTTP network architecture provides economies of scale for con-struction and service deployment.

The optical distribution network provides physical connection between the CO/HE and the premises and includes various cabling segments including feeder, distribution, and drop. These various segments are typi-cally joined together by connectors and splices. The fiber distribution hub (FDH) is one of the key elements located between the feeder and distribution segments and contains optical connectors and splitters to pro-vide easy access and flexibility. The advantage of configuring the network with connectors is to allow flexibility for service provisioning and for net-work testing.

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FDH network function

FDH Pad and Pole

Central Office/HeadendUnderground Distribution

Aerial Distribution

The FDH is a key interface between feeder cables extending from the cen-tral office to distribution fibers routed to subscribers. The FDH serves an analogous function to serving area cabinets (SAC) used in copper-based networks to interconnect the feeder and distribution segments of the net-work. The hub becomes a primary point of flexibility in the network to con-nect subscriber circuits. As service is required, technicians access the FDH enclosure to route connections to complete subscriber circuits. The FDH also serves as a central location for fiber optic splitters. This is where the PON network differs significantly from a copper network.

The optical splitters allow the PON OLT port to be shared among multiple subscribers via the 1xn split, thus defraying the cost of the OLT. By locating the splitters in the outside plant close to the serving area, the cost of feeder fiber is also significantly reduced. For instance, when a 1x32 splitter is placed in the FDH, one feeder fiber may be routed into a neighborhood and provide service connection to 32 subscribers. Another reason to locate splitters in the FDH is that splitters can be deferred until they are needed to satisfy service requirements. The FDH can be accessed to add splitters as service demands grow. Newer hub designs accept modular splitters that quickly plug into the FDH to allow capacity to be expanded within a few minutes.

Typically, the FDH is equipped with one stub cable that is spliced into a feeder cable and another stub cable that is spliced to a distribution cable. Construction is usually completed using standard splicing techniques (usu-ally mass splicing) with splices stored in standard splice closures. Some FDHs are even equipped to handle the splicing inside the cabinet.



Key FDH capabilities and innovations

The FDH enclosure provides a crucial craft interface in the outside plant environment. Therefore each major function of the hub supports easy craft access for service and maintenance.

Fiber Management

Termination Splice Shelf and Trays

Splitter Shelf and Modules

Termination field

The termination field provides a location for terminating fiber distribution cable on optical connectors and adapters. The termination field is sized to support the number of subscribers located in the distribution serving area downstream from the FDH. FDH enclosures support a range of termination field sizes.

The termination field provides easy access to both sides of the adapt-er to facilitate cleaning and maintenance. ADC FDH enclosures feature a unique swing frame design, a hinged chassis containing all the key optical components including splitters, connectors, and splices. The de-sign allows easy access to optical components from the front and rear for cleaning and troubleshooting and is especially valuable in installations where access is limited to the front of the cabinet only, for example, in pole mounted applications. Large cabinets deployed in ground mount applica-tions feature doors on the front and rear to allow full access to connectors and splitters from the front and back.

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Terminations in the field are clearly marked to provide accurate identifica-tion of each subscriber termination. The termination field provides organi-zation and protection for fiber jumper connections as they transition into the fiber management section of the enclosure.

Recent FDH innovations include high-density component packaging resulting in significant reduction of enclosure sizes. High-density termi-nation fields with connectorized harnesses allow modular growth and flexible arrangements.

High-density termination Early FDH termination requirements were often matched exactly to the requirements for subtending living units in the immediate fiber serving area. For instance, a 216 fiber hub was speci-fied to support a fiber serving area of approximately 200 subscribers, pro-viding a small (approximately five to ten percent) portion of spare fibers routed into the serving neighborhoods. With more experience, planners realized that additional fiber capacity downstream could be required for unforeseen changes in the network or in services supplied. However, while specifying increased numbers of spare fibers, resulting in increased fiber termination requirements, users were reluctant to increase the overall size of the enclosures. Therefore, fiber termination fields had to handle the increased capacity within already defined enclosure sizes. This involved in-creasing termination density and also increasing the fiber handling capac-ity for a particular enclosure. For example, enclosures previously handling 216 fibers were upgraded to terminate 288 fibers. This increase in density provides the desired fiber counts along with the spare growth capacity re-quired for typical fiber serving areas, while maintaining the overall size of the enclosure.

Modular, scalable distribution In overbuild scenarios, the termination field on the distribution side is fully populated with connectors at the initial installation, and the enclosure is provided with fully-terminated stub cables sized for the enclosures direct termination needs. Network planners, how-ever, considering newer greenfield developments, look for ways to defer cost and match the FTTP build to the pace of the developments build.



A new development, constructed in phases over a period of years, may not initially require an FDH with a fully-populated termination field. This situation may be better served by gradually deploying terminations as needed. To satisfy this requirement, the FDH enclosure includes modular blocks that allow terminations to be added as required. The modular termi-nation block allows upgrades to the FDH to match the requirements of the FTTP network deployment, thus deferring hardware costs.

Improved overall performance Advances in planar splitter technology have dramatically decreased the amount of signal loss when a single fiber is split into several outputs. Innovation in component performance has re-sulted in lower loss connections, in both the termination fields and the split-ters. Improved connector performance for the widely used SC components, allows connectorization to replace splicing on both feeder and distribution fibers while still meeting the overall loss limits within the FDH. Using con-nectorization for input fibers and distribution panels greatly reduces the amount of time required to install and upgrade an FDH.

Splitter field

Splitter modules are designed to snap-in to the splitter field and can be added as required by service demands. The splitter field protects, organizes, and routes both the input and output fibers. The optical splitter modules provide up to 32 connectorized pigtail outputs and one pigtail input.

Early generations of FDH were deployed fully loaded with splitter modules that featured storage ports, sometimes referred to as parking lots, located on the front of the module to stage splitter output pigtails temporarily until they were connected into service. The splitter module assembly included modular parking adapters, each holding 16 or 32 connectors. As a split-ter module was installed, the fibers were fed into the fiber management trough and the parking adapters were snapped into place in the parking area. Individual connectors were then easily separated from the parking adapter and routed to the termination field during service turn-up.

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Recently, the parking lots have been relocated to a spot in the FDH away from the splitter modules. The parking adapters are removed from the split-ter module, allowing the splitter module to be reduced in size.

Today, most carriers take an incremental approach to adding splitter mod-ulesdeploying FDH enclosures initially with just the splitter modules re-quired to begin service connections. This reduces the number of parking lots required for pigtail outputs. In essence, splitter outputs time share parking lots; as the outputs of the initial splitter modules are placed into service, the parking lots associated with those outputs become available for parking subsequent splitter module outputs This allows a significant reduc-tion in the size of the parking lot, and consequently, a reduction in the size of the FDH.

Blind-mate connections New miniaturized splitter modules feature planar optical splitters and are 75 percent smaller, another contributing factor in the reduction of the FDHs size. Additionally, innovation has im-proved the way splitter modules are installed into the enclosure. First gen-eration modules were designed with the splitter module input extended as a pigtail, which was spliced to feeder fibers. As each subsequent splitter was installed, it was spliced to feeder fibers staged in splice trays. Splic-ing consumes valuable time, and adds costs to service turn-up. Earlier improvements included connectors on the feeder fibers that allow quick connection during splitter module installation, or a connector on the pig-tailed input and a connector on the feeder fibers mated at a connector panel in the enclosure. This approach provides a simple, much improved method for quickly installing splitters. Connectorization of the feeder fi-bers at the FDH also allows testing on the feeder from the FDH if required. However, connectorization of the feeder fiber also raised a safety concern regarding high power when analog video is transmitted over the path. To address this concern, connectors can be angled or adapters with shutters provided to prevent a technician from accidentally looking into the high-powered termination.



Further innovations have resulted in a backplane connector system for in-stalling splitter modules. In this configuration, feeder fibers are terminated with a standard connector pre-positioned on the backplane to receive a plug-in splitter module with a mating connector. The backplane connector is shuttered for safety so that a technician cannot accidentally look into an unmated splitter module. As a splitter module is inserted into the backplane receptacle, the module presses open the shutter to allow the splitter mod-ule connector to mate with the backplane connector. This blind-mate ap-proach using a common backplane technology improves efficiency in future expansion activities.

Splice area

The FDH features a splice area to connect feeder fibers or other cables routed into the enclosure. One use for this area is the splicing of addition-al splitter modules to feeder fibers as the modules are added to the FDH enclosure. An alternative to splicing the input is to include a connector at this location.

Factory pretermination FDH enclosures typically include two pretermi-nated stub cables. One stub cable is pre-connected to the optical splitter module input so that it can be field-spliced to the feeder cable. The other stub cable is pre-connected to the termination field, so that it can be field-spliced to the distribution cable. These cables attach to the enclosure using standard grip clamps and liquid-tight compression fittings seal the cables at the enclosure entrance. Orientation of the enclosure stub cables varies, depending on the FDHs mounting method.

Craft-friendly fiber management

The FDH provides total fiber management using a unique front facing cross-connect design. The front fiber management allows splitter module outputs to be routed and staged within the enclosure for efficient connec-tion into service at a later date.

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Vertical channels using storage loops manage excess fiber slack. The entire cabinet can be interconnected without congestion. Connectorized pigtail ends are stored on bulkhead adapters on the front of the module so that connector ends can be identified quickly and connected into service. Fiber strain relief and radius control is provided through the enclosure.

Indoor configurations

As FTTH moves into densely populated areas, the use of indoor fiber distribution hubs becomes popular due to the number of units within a particular building, as well as space restrictions outside the buildings. Indoor FDHs provide all the same features as an outdoor FDH, but are typically smaller and lighter. They do not need to meet the same harsh environmental requirements as the outdoor FDHs. Fiber count capac-ity ranges from 72 fibers to 432 fibers, accommodating small to large high-density buildings.

Below-grade configurations

Another option for high-density areas, as well as areas that do not allow above ground enclosures for zoning reasons, are below-grade fiber distri-bution hubs. These compact enclosures are stored in below-grade vaults when not being accessed for service configurations.

Qualification

A complete FDH qualification program draws from a wide array of exist-ing standardized tests with existing procedures. In some cases, new test procedures have been developed and refined to support the new con-figurations and new technologies. The overall program is composed pri-marily of testing regiments drawn from Telcordia Generic Requirements.



First and foremost, the qualification program involves testing optical con-nectors to GR-326-CORE, Issue 3. All connectors utilized in the FDH en-closure are subject to the complete outdoor service life requirements and to the full spectrum of long-term reliability tests. In addition to testing at 1310 nm and 1550 nm as required in GR-326, the test programs include additional test wavelengths of 1490 nm and 1625 nm to assure users that all operating wavelengths and all potential maintenance channels would function under the harshest conditions.

Optical splitters are fully tested to ensure trouble free performance over the life of the network. The splitters use planar technology and follow a qualification program aligned with service life testing in GR-1209-CORE and long-term reliability testing in GR-1221-CORE. Because of the nature of testing very large devices (1x32 ports), special sampling techniques were developed for optical measurement characteristics such as directiv-ity. Splitter qualification is conducted at the full operation spectrum of four wavelengths including 1310, 1490, 1550 and 1625 nm. All testing is done in the format of the optical module that plugs into the FDH enclo-sure, representing the exact configuration deployed in the field. Tests for the new enclosures include a full range of environmental and mechanical tests. Optical characterization is conducted at the same four wavelengths as the connectors and splitters. Additionally, several of the tests such as thermal cycling and seismic qualification are optically monitored during the test at 1625 nm, which represents the worst-case scenario from a fiber integrity perspective.

Independent testing of the qualification program demonstrated the FDHs reliability, assuring a performance level and longevity expected in an FTTP network. Successful testing of all aspects of the enclosures, including per-formance of optical connectors and splitters, have given users the evidence and confidence to support wide scale deployment of FDH enclosures in the distribution portion of FTTP networks.

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Chapter 6

Extreme-Environment Performance Considerations for FTTX Splitter Modules

Optical splitter modules used in FTTX networks contain the splitters that make passive optical networks possible. The module physically pro-tects the splitter and provides a means to connectorize the splitter inputs and outputs.

Figure 1: Typical FTTX Splitter Module

Module housing (1xN splitter inside)

Bending Strain Relief

Input

Connectors

2 mm Furcation tube

A housing, constructed of plastic or metal, holds the splitter and provides a means to up-jacket the splitter fibers with 2mm furcation tube for connec-torization. A certain number of outputs are connectorized. The input fiber may be connectorized, can be a pigtail, or can be attached to the module by means of a backplane.

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Industry standards

Telcordia GR-1209 and GR-1221 standards define the operating requirements for splitter modules in North America. GR-1209 defines ba-sic optical performance requirements such as insertion and return loss, polarization-dependent loss (PDL), and uniformity. GR-1209 also de-fines short-term environmental and mechanical requirements such as input and output proof strength and side loading, and a temperature and humidity profile. GR-1221 defines the splitter modules long-term reliability requirements. GR-1221 requires splitters to go through 2,000 hours of high temperature aging, low-temperature aging, thermal cycling, and humidity aging. GR-1221 also subjects samples to impact and vibration testing.

The operating extremes defined in GR-1209 and GR-1221 are -40C to +85C and up to 95% relative humidity. GR-1209 and GR-1221 will typically be called out by North American service providers deploying passive optical networks. Some service providers may require their network to function at lower temperatures. In these cases, military specifications (MIL SPECs) requiring -55C minimum operating temperatures may be called out.

These operating extremes present challenges when designing split-ter modules. Before large-scale North American deployment of FTTX in 2004, most modules containing splitters and connectors were used in central offices. Splitter modules saw stable environments and were there-fore not extensively tested. Testing to extreme conditions and deploy-ment in outside plant environments forced service providers and equip-ment manufacturers to re-evaluate the requirements of splitter modules. GR-1209 and GR-1221 do not consider many characteristics that are important for devices deployed in the OSP. For example, GR-1209 and GR-1221 do not define material properties such as chemical resistance or installation considerations such as the handling of furcation tubes at extreme temperatures.



Furcation tubing

Furcation tubing is the material slipped over the splitter inputs and outputs. The furcation tube protects the fiber from physical damage and makes con-nectorization possible. The furcation tube is usually identical in construction to a 2mm simplex jumper, but the .900mm tight buffered fiber is replaced by a hollow tube. The hollow tube has a .900mm outside diameter and the inside diameter is larger so that a fiber can be inserted. Once the fiber is inserted into the inner tube, a connector can be terminated to the ends.

2 mm Outer Jacket

Inner .900 mm Tube

Aramid StrengthMembers

Splitter Input and Output Fibers

Inserted Into This Space

Figure 2: Furcation Tube Construction

2mm simplex jumpers are typically used in controlled environments. They are not required to meet the more stringent requirements for outside de-ployment. It would be risky to choose a furcation tube made out of materi-als used for controlled environment jumpers that are only rated to -20C. Some specific requirements of furcation tubing that arent explicitly called out in GR-1209 or GR-1221 include cold-temperature handling and cable routing, and thermal expansion and contraction.

Cold-temperature handling and cable routing The outer 2mm jacketing of furcation tube is made of thermoplastic materials. The tub-ing can become very stiff at cold temperatures. This is no issue in a static situation. However, if new service is turned on at cold temperatures, a technician will have to re-route the up-jacketed splitter outputs in the fiber distribution hub (FDH). If the furcation tube is too stiff because of the cold temperature, routing becomes difficult and bending can occur, causing high insertion loss.

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Standard jumper jacketing materials such as PVC become very stiff at tem-peratures lower than -20C. Proper design requires that furcation tubes be made of different materials. Polyurethane is one possible choice for the outer jacket. This material remains relatively flexible to temperatures as low as -60C and is resistant to chemicals commonly used in tele-communications and to fungus. Some types of PVC outer jacketing can also become permanently stiff if exposed to high tempera-tures for extended periods of time. As the PVC ages, plasticizers in the cable degrade causing the jacket to stiffen. Polyurethane is also resistant to this phenomenon, making it suitable for both very hot and extremely cold environments.

Cold-temperature handling of furcation tube can be evaluated several ways. First, the furcation tube should be tested to FOTP-104 (Fiber Optical Cable Cyclic Flexing Test), but performed at -40C. It could also be tested to FOTP-37 (Low or High Temperature Bend Test for Fiber Optic Cable). There should be no evidence of cracking of the outer jacket after the tests

are completed. Second, the ability to re-route furcation tube within a cable management system must be evaluated. There are no exist-ing industry standards to evaluate this property. However, this prop-erty can still be subjectively tested by simulating cable routing at cold temperatures.

A test was performed where furcation tube made of PVC and polyurethane were wrapped around a small mandrel and aged at -40C for 2 hours (see Figure 3). The mandrel was removed and the cables were allowed to uncoil themselves using only the weight of the connector (see Figure 4). The poly-urethane furcation tube was much more flexible at -40C than PVC. This property makes polyurethane an ideal choice for furcation tube jacketing because bending losses are less likely to occur when an installation take place at cold temperatures.

Figure 3: Test sample on Mandrel at -40C



Thermal expansion and con-traction All furcation tubes are made of thermoplastics. Plastics tend to expand at high tempera-tures and contract at low tempera-tures. However, the optical fiber will remain the same length over these temperature extremes. If the expansion and contraction of the plastic materials over the fiber are not accounted for, fiber bend-ing and high insertion loss could occur.

Thermal affects usually cause inser-tion loss p

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