WHITE PAPER It's Happening in the Hub It’s Happening in the Hub Fiber Distribution Hubs (FDH) continue to play a vital role in supporting rapid deployment and connection in FTTP networks. Innovation in FDH design occurs at a rapid rate and next generation features 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 • Highest performance optical connectors and splitters available; all the optical components and enclosures have completed a rigorous regiment of independent testing far beyond any test program seen in the industry to date. As a result, FDH products have been widely accepted in FTTP networks. FTTP is now seeing large-scale deployment and FTTP deployment is definitely still happening at the hub. Page 3 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 architecture has been adopted as a standard in ITU- T G.983.x that defines the protocols, data rates and operating wavelengths necessary to support 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 connecting 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. A typical FTTP PON distribution network is depicted below. 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 (1310nm/1490nm) over a single fiber. Additional WDM components at the CO/HE allow integration of video services onto the same fiber at the 1550nm wavelength. OLT equipment ports are connected through optical splitters, thus 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. Standardization 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 construction 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 typically 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 provide easy access and flexibility. The advantage of configuring the network with connectors is to allow flexibility for service provisioning and for network testing. It's Happening in the Hub Fiber-to-the-Business ONT FDH CO/HE OLT Optical Distribution Network Fiber-to-the-Home Fiber-to-the Multi-Dwelling Unit Network Architectures It's Happening in the Hub Page 4 The Fiber Distribution Hub is a key interface between feeder cables extending from the central 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 network. The hub becomes a primary point of flexibility in the network to connect 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 (usually mass splicing) with splices stored in standard splice closures. 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. FDH Pad and Pole Central Office/Headend Underground Distribution Aerial Distribution Fiber Management Parking Adapter Termination Splice Shelf and Trays Splitter Shelf and Modules FDH Network Function Page 5 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 (144-, 216-, 432-, 576-, 816- or 1152-terminations). The termination field provides easy access to both sides of the adapter 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 design 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 applications feature doors on the front and rear to allow full access to connectors and splitters from the front and back. Terminations in the field are clearly marked to provide accurate identification of each subscriber termination. The termination field provides organization 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 termination 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 specified to support a fiber serving area of approximately 200 subscribers, providing 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 increasing termination density and also increasing the fiber handling capacity 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 required 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 enclosure’s direct termination needs. Network planners, however, considering newer greenfield developments, look for ways to defer cost and match the FTTP build to the pace of the development’s 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. Termination blocks can easily be spliced into the enclosure or the enclosure can be connectorized with multifiber connectors (MFC) to provide quick connection to termination blocks as they are installed. The modular termination 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 resulted in lower loss connections, in both the termination fields and the splitters. Improved connector performance for both the widely used SC, as well as MFC connectors proposed for modular components, allows connectorization to replace splicing on both feeder and distribution fibers while still meeting the overall loss limits within the FDH. Using connectorization for input fibers and distribution panels greatly reduces the amount of time required to install and upgrade an FDH. It's Happening in the Hub It's Happening in the Hub Page 6 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 splitter 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. 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 splitter module, allowing the splitter module to be reduced in size. One design includes hinged parking that allows 50 percent reduction in splitter module size, and hence FDH enclosures that are 50 percent smaller. Today, most carriers take an incremental approach to adding splitter modules – deploying FDH enclosures initially with just the splitter modules required 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 reduction 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 FDH’s size. Additionally, innovation has improved the way splitter modules are installed into the enclosure. First generation 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. Splicing 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; a connector on the pigtailed 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 fibers 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 installing 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 module connector to mate with the backplane connector. This “blind-mate” approach using a common backplane technology improves efficiency in future expansion activities. It's Happening in the Hub Page 7 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 additional 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 preterminated 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 FDH’s 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 connection into service at a later date. 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 capacity 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 Distribution 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 existing standardized tests with existing procedures. In some cases, new test procedures have been developed and refined to support the new configurations and new technologies. The overall program is composed primarily of testing regiments drawn from Telcordia Generic Requirements. First and foremost, the qualification program involves testing optical connectors to GR-326-CORE, Issue 3. All connectors utilized in the FDH enclosure are subject to the complete outdoor service life requirements and to the full spectrum of long-term reliability tests. In addition to testing at 1310nm and 1550nm as required in GR-326, the test programs included additional test wavelengths of 1490nm and 1625nm 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 directivity. Splitter qualification is conducted at the full operation spectrum of four wavelengths including 1310, 1490, 1550 and 1625nm. All testing is done in the format of the optical module that plugs into the FDH enclosure, 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 1625nm, which represents the worst- case scenario from a fiber integrity perspective. Independent testing of the qualification program demonstrated the FDH’s reliability, assuring a performance level and longevity expected in an FTTP network. Successful testing of all aspects of the enclosures, including performance of optical connectors and splitters, have given users the evidence and confidence to support wide scale deployment of FDH enclosures in the access portion of FTTP networks. Website: www.adc.com From North America, Call Toll Free: 1-800-366-3891 • Outside of North America: +1-952-938-8080 Fax: +1-952-917-3237 • For a listing of ADC’s global sales office locations, please refer to our website. 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 105057AE 8/07 Original © 2007 ADC Telecommunications, Inc. All Rights Reserved WHITE PAPERWHITE PAPER . WHITE PAPER It's Happening in the Hub It’s Happening in the Hub Fiber Distribution Hubs (FDH) continue to play a vital role in supporting rapid deployment. greatly reduces the amount of time required to install and upgrade an FDH. It's Happening in the Hub It's Happening in the Hub Page 6 Splitter