Practical considerations in the European market for building and future-proofing robust, flexible FTTN infrastructures

Practical considerations in the European market for building and future-proofing robust, flexible FTTN infrastructures The European market presents service providers with some unique challenges in pushing fiber closer to the end user. With virtually no overhead distribution and very little buried fiber cable, a new physical plant is unlikely. Rather, service providers are seeking the best way to use existing ducted infrastructure—and network planners must be willing to consider what architectures will best serve their needs today and in the foreseeable future. ADC has taken the lead in successfully developing equipment and systems that meet the needs of service providers worldwide—each with their own unique set of challenges. Although, from a practical standpoint, FTTN architectures in Europe differ substantially from other parts of the world, there are some issues that planners need to consider in the early stages of planning how best to get fiber closer to the subscriber. Ducts are here to stay Most areas of Europe have copper cabling that runs through an intricate system of buried ducts between nodes. Historically, the network planners have only run fiber—a straight cable and a straight splice—from one building they own to another building they also happen to own. A distributed architecture that feeds multiple nodes and offers redundant routes has not really been a viable option for them. Building fiber rings where there has never been fiber is an expensive and disruptive operation. To deploy the ducts necessary to build any ring architecture would require tearing up both public and private property to link the trees and branches of the network. Even running fiber down existing copper-filled duct lines presents challenges and offers little in terms of flexibility or easy fiber access for reconfigurations or troubleshooting. Still, like elsewhere in the world, service providers in Europe are facing the task of building next-generation networks to increase available bandwidth by getting active equipment closer to the customer. New services are demanding a conversion from copper to fiber which, in turn, is placing the burden on network planners to figure out the best methods of shoring up networks to accommodate consumer needs for the coming years. With that in mind, the greatest obstacle facing European service providers is how to incorporate redundancy into an FTTN network architecture that will be deployed through an existing tree and branch duct system. Without redundancy, you risk outages and revenue loss during the operational life of the network. Practical considerations in the European market for building and future-proofing robust, flexible FTTN infrastructures Leveraging the existing ducts In deploying fiber from the central office (CO) to the node, European network planners have already come to one conclusion—fiber will follow the traditional tree and branch copper routes. Why? Because fiber must eventually reach the same locations, ducts already exist to get it there, and it’s more cost effective than deploying any new fiber ring. Running a “thumb-sized” fiber cable in the same ducts that currently accommodate a “forearm sized” copper cable is not an issue. Therefore, from the CO to the physical cross connect points in the existing duct network, the fiber will follow the exact same route. Figure 1 shows a generic view of a traditional main cable deployment. A large cable runs from the CO to feed different copper connection points. The fiber deployment for a next generation network must also hit each copper connection point. Therefore, it must logically follow the same physical path—there are no other options. Central Office These radial feeds from the CO provide coverage to a nominal circular area of between four and eight cabinets per main cable. The reach from the CO is approximately 4-5 km, dictated by the cable gauge. Two or more main cables might feed in the same direction, varying only in overall length or reach. One main cable would feed the closer cabinets while the other feeds the more distant cabinets. For example, there might be 35,000 copper pairs leaving a CO on 0 main cables of various sizes. With those 0 cables, providers are able to feed 80 to 100 cabinets. Converting to fiber When converting the service area to FTTN, the same rule applies in Europe as with other geographical areas— loops have to be cut back to below 5000 feet. For ADSL or VDSL services, distances must be within 1.5 km from the equipment to the customer. Since existing CO areas are typically about 5 km, fiber feeds would have to be built to service the outer two-thirds of the customers. Basically, the CO would feed the closer third of the customers, but the other two-thirds would require conversion to active cabinets. PCP 800 Pair PCP 400 Pair 2,400 Pair 1,200 Pair PCP 800 Pair 400 Pair 400-2,400 Pair x “n” PCP This raises several very practical issues for the network planner. Two-thirds of the cabinets will need to be fiber fed, meaning 60 cabinets must now be active. This will have to be achieved using existing ducts that normally travel in four different directions before branching out. Therefore, each route would typically cover about 1-18 cabinets. However, using the ducts is still more cost effective than building rings. For example, a 5 km serving area with four main routes would require about 0 km of fiber cable. A ring serving the same area would require more than 31 km of cable. A full ring would be cost prohibitive in other ways as well, including the requirement for extensive civil works. So the question remains—how can you attain some sort of redundancy in a tree and branch architecture? PCP 400 Pair PCP Figure 1: A generic view of a traditional deployment of main cables. These physical routes will be duplicated by fiber to service these Nodes in an FTTN deployment. A typical copper distribution duct system begins at the CO with multiple ducts running out a specified distance before some of the ducts branch out into other directions. Therefore, it’s not one cable running in one duct to one group of cabinets. Rather, it is multiple ducts containing multiple cables that share the infrastructure for part of the length and then branch in different directions. Additionally, planners must decide how many fiber drops per cabinet will provide enough bandwidth for today’s needs as well as tomorrow’s passive optical network (PON) upgrades. They should ensure there is plenty of fiber, particularly since the fiber counts from cable to cable don’t vary enormously in terms of price points today. Choosing 4 fiber drops per cabinet, for example, a provider could service six cabinets from a 144-count cable, 1 cabinets from a 88-count cable, or 4 cabinets from a 576-count cable. Using smaller feeder cables may provide some advantages. For instance, winching a 576-count cable through a congested duct is more difficult than pulling a 144-count cable through. Running smaller cables would also provide an easier means to achieve redundancy, as we’ll discover later in this paper. Page Practical considerations in the European market for building and future-proofing robust, flexible FTTN infrastructures Patch or splice? Finally, there is the age-old consideration of whether to splice or patch (connect) cables. Again, many service providers have their own rules and standards. In a patch, the cable is brought above ground into a patch cabinet. The alternative is to splice it in an underground splice closure. Since the mindset in Europe has always been a simple building to building connection, every fiber would be typically spliced to the exact same fiber in the next section. But when the requirement is to provide services to small groups of houses in a tree and branch configuration, this is no longer practical for achieving maximum flexibility. In a distribution network that branches in several directions, there are advantages in having patch cabinets, at least in certain locations. Again, it’s incumbent upon the planner to decide where advantage is gained from connectorization in the network. These would be areas that may require access by technicians for reconfiguration or troubleshooting sections of the network over the next 5 years. An all-spliced network could make operational costs soar when technicians must gain access to a particular part of the network. For example, getting access in a water-filled manhole would require the additional cost of rolling out a tanker truck to pump the water out to gain access to the splice closure. A patch solution, or at least a combination splice-patch solution, makes the technician’s life much easier and can save operational expense. A patch solution where it makes the most sense is the first step in building a more flexible and robust FTTN architecture. Even though existing ducts are being used, planners should create, at a minimum, one main fiber cross-connect (MFCC) at a suitable junction in the physical network. Figure shows two high-pair-count cables feeding back toward the CO. The cables are routed through the same physical duct routes or duct nests. The MFCC is the most convenient point to bring the fiber above ground to create easier access and improve network flexibility. Again, not every splice or cable should be above the ground—just where it makes sense within the physical infrastructure. A secondary fiber cross-connect point (SFCC) is also shown in Figure where the second cable branches in several different directions. PCP PCP Central Office > 2 km PCP Possible second fiber cross-connect point Create fiber PCP cross-connect point PCP Typical multiple PCP PCP way duct route PCP PCP PCP PCP Figure : Establishing fiber cross-connect points increases network flexibility and utilization, and reduces operational costs. Page 3 Achieving redundancy Achieving redundancy in a tree and branch network systems can be done by first giving consideration to cable size—for example, using two 144-count cables instead of a single 88-count cable. By bringing the two 144-count cables above ground into a fiber cabinet, the tubes in each cable can be split out. By putting 7 fibers of the first cable onto the second cable and vice versa, a second functional route is formed downstream. Should a break occur in either feeder cable, a redundant path is now available. Further redundancy can also occur farther downstream. In Figure , the one main feeder cable passing through the MFFC continues to the SFCC. At this junction, the fiber tubes can be split once again to create redundancy from that point downstream to each PCP. Using a 50/50 splitter at each cabinet allows automatic route transfer in the event of a tube or complete cable failure. Since only short distances are involved, loss budget issues associated with patching and splicing will be minimal. The benefit is in achieving a degree of security through redundant cable routes from the CO to the nodes. There are still a few other issues to consider in planning an FTTN architecture through existing underground ducts. For instance, planners should not focus on trying to squeeze more things into smaller spaces. Despite space considerations, they should consider leaving room at each FTTN node for adding splitter modules for future PON upgrades. They may even want to consider using a 90/10 splitter to feed one fiber back to the CO to provide a test field. This would provide technicians the ability to test and monitor every cabinet from a single point. Patch cabinets should also be allowed extra space for future additions. These could possibly become hubs for future PON configurations. ADC has always been a proponent of designing networks with the future in mind—making them as flexible, accessible, and uncomplicated as possible, while giving ample consideration to potential issues and challenges throughout the life of the network. Although there are capital expense implications in addressing most of these issues, they must be weighed against the potential operational savings in the future. Since each network is physically unique, planners must carefully consider the correct steps to achieving maximum flexibility, easy access, and the most robust architecture possible to meet the demands of tomorrow’s FTTN network. Web Site: www.adc.com From North America, Call Toll Free: 1-800-366-3891 • Outside of North America: +1-95-938-8080 Fax: +1-95-917-337 • For a listing of ADC’s global sales office locations, please refer to our Web site. ADC Telecommunications, Inc., P.O. Box 1101, Minneapolis, Minnesota USA 55440-1101 Specifications 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. An Equal Opportunity Employer 102473AE 5/06 Original © 2006 ADC Telecommunications, Inc. All Rights Reserved ... - tailieumienphi.vn