WHITE PAPER GPON Migration Ensuring my Network is Ready to Migrate to GPON The demand for higher bandwidth by residential customers has led carriers to one simple conclusion – optical fiber with its almost limitless bandwidth capability will be a network necessity. The driver for such high consumer bandwidth usage is the need for carriers to deliver video, along with voice and data services, to complete the “triple play” package. As traditional carriers experience declining revenue from voice services, they must find ways to increase the revenue from data and video services. Since video is the highest revenue generator, the ability to compete with cable companies is critical. Delivering the same high-quality video customers have received from their cable provider can only be accomplished using video-over-IP technologies. Passive optical network (PON) architecture is the key element for allowing carriers to support the demand for advanced broadband services today, while also providing the flexibility to scale outside plane infrastructures to meet next generation broadband requirements. But deploying PON technology requires one particularly careful consideration – how easily will the network migrate from one PON flavor to the next as bandwidth demand continues to rise. GPON Migration Ensuring my Network is Ready to Migrate to GPON Ensuring my Network is Ready to Migrate to GPON Page 3 Standardizing PON As with many telecom technologies, standards have played an important role in the development of PON protocols. These standards drive the underlying protocols and the basic specifications for specific telecom and data systems. Ultimately, standards define the specifications to make interoperability a reality and ensure product performance. PON standards and recommendations were established by the Full Service Access Network (FSAN) and the International Telecommunications Union (ITU). ATM PON (APON) was the first iteration of the technology for fiber- to-the-premise (FTTP) solutions. However, APON lacked the bandwidth required for more robust applications and its popularity was short-lived. Broadband PON (BPON) was standardized in 2001 as the first viable PON flavor for general use in early FTTP applications. It provided 622 Mbits/sec downstream and 155 Mbits/sec upstream. More importantly, it provided carriers with the capability to overlay RF video. Still, as bandwidth demand increases in the FTTP market with newer services, BPON will struggle to meet the grade in many deployments. Ethernet PON (EPON), also referred to as Ethernet in the First Mile (EFM), is an ongoing standard that uses Ethernet protocol for packet data transport. Even with its higher level protocols, offering 1.2 Gbits/sec symmetrical bandwidth, it may not be enough to handle the requirements of higher bandwidth applications. It is the view of ADC that Gigabit PON (GPON), standardized in 2003, will be the target for the majority of PON migration paths while transitioning from one PON to another for meeting higher bandwidth demand. GPON combines the quality of service capabilities of BPON with EPON’s ability to transport and interface on an all IP network. It can address higher application bandwidth requirements by offering 2.4 Gbits/sec downstream and 1.2 Gbits/sec upstream. The promise of 1x64 split capabilities adds to the attractiveness of GPON solutions in FTTP networks. This enables carriers to double the number of customers served from a single splitter in a fiber distribution hub (FDH). PON architectures Architectural decisions regarding any FTTP network buildout are driven by initial and targeted take rates and a focused design. This applies equally to overbuilds, Greenfield applications, or even a migration network. To be profitable, it’s imperative to understand the impact of the decisions made early in the planning stages of the process. The best example of how an early decision can affect future operational costs can be found in the particular point-to-multipoint PON architecture selected for the initial FTTP outside plant. There are three possible scenarios and each has advantages in certain situations. But network architects should also be concerned with the aspects of future-proofing the PON portion of the system to make migrations to next-generation architectures as bandwidth demands reach new levels. The first PON architecture is the central switched, or home run, whereby splitters are placed within the central office (CO), headend, or remote terminal. A key advantage of this design is that all changes, either in the electronics or split ratios, can be done at one centralized location. Next, there is the distributed or cascaded splitter configuration which uses some combination of multiple splitters (usually 1x4 and 1x8) at multiple locations. This design is particularly effective in rural or widely spaced networks where the number of customers per mile is relatively sparse. Transitioning to a GPON in a distributed architecture presents significant challenges since carriers are forced to migrate every subscriber or make costly modifications to the OSP portion of the network. Finally, there is the centralized splitter design where a single coupler is placed within the central hub or cabinet. From there, the distribution fiber interfaces with the entire splitting scheme with drop cables extending directly to each customer. This scheme offers great flexibility for future migration to GPON and typically involves an upgrade of electronics at each end of the PON. Additional considerations There are several additional considerations when designing a PON for ease of migration to GPON. These include the fiber optic cable characteristics, optics classes, and split ratio implications. We’ll briefly address each of these topics. Fiber optic cable Different fiber cable from various manufacturers may have similar loss characteristics – but they may also be quite different. The spectral attenuation refers to the loss of a signal as a direct correlation between the wavelength and the distance traveled. The lower the wavelength, the higher its spectral attenuation will be. When applied to distances and calculating the link loss budget for a given architecture, fiber optic cable manufacturers must specify the spectral attenuation for their products. When designing the FTTP network, the network engineer typically designs for the wavelength with the highest loss characteristics. For BPON and GPON, this will always be 1310 nm, but the loss will differ between manufacturers. When increasing split ratios from 1x32 to 1x64 or even higher, for example, spectral attenuation will become an important factor to consider. Additionally, due to the phenomena of hydrogen aging, attenuation increases in fiber optic cables as they get older. The molecules of hydrogen atoms in the silica or glass tend to break down over time, making the fiber less clear for transporting light pulses. This may be an additional consideration when re- using fiber in an overlay scenario. PON optics classes Optical link budgets are determined by individual vendors’ active components – PON chips within the electronics, lasers, and receivers. The loss range for each class is as follows: Class A – Min. 5 dB to max. 20 dB Class B – Min. 10 dB to max. 25 dB Class B+ -- Min. 10 dB to max. 28 dB Class C – Min. 15 dB to max. 30 dB Traditional BPON equipment has typically used Class B optics, but it was determined that some of the PON network of 20 km were actually stretching the budget to the limits, forcing active equipment manufacturers to increase budgets to 26.5 dB. These increased budgets, coupled with a possible requirement to increase the split ratios of GPON, resulted in an increase in the Class B receiver photo detectors to allow for a 28 dB loss budget – thus, establishing the Class B+ optics category. However, despite the increase, these Class B+ optics have not escalated to the higher Class C pricing while maintaining better PON loss characteristics. In the future, however, the need to transport greater distances (30 km or 40 km) and even higher split ratios (1:128) could eventually force equipment manufacturers to use the Class C optics. With Class A optics typically associated with fiber-to-the-curb (FTTC) applications, Class B and Class B+ optics provide today’s FTTP PONs with the best reach and split ratios. However, the need to reach longer distances could make Class C optics tomorrow’s choice – with significant cost implications. Split ratio implications Splitter loss depends mainly on the number of output ports on the splitter and, contrary to some expectations, adds about the same loss whether traveling in the downstream or upstream direction. Each splitter configuration is assigned a particular maximum split ratio loss, including connectors, defined by the ITU G.671 standard and Telcordia GR-1209. Since the GPON standards have not yet defined the current split ratio maximum for 1x64 splitters, network designers must use a single 1x2 splitter interfacing two 1x32 splitters to make up the 1x64 configuration. Although this is allowable with today’s packaging, using Class B optics only leaves 5.35 dB of “head room.” Therefore, even with the best fiber manufactured, where the spectral attenuation is 0.31 dB per kilometer, only a 17.25 km PON network is achievable without including any of the connectors within the CO or the splices in the OSP. However, the design engineer does have some options. In designing the network, premium splitters and low loss connectors can be deployed, and fusion splices must be kept well below 0.05 dB of loss per splice. There are other techniques ADC will be using until the standards line up with the technology for 1x64 and higher split ratios. ADC is working closely with customers to ensure their networks can easily and cost-effectively migrate as higher bandwidth demand dictates. At the end of the day, making the correct initial decisions regarding PON implementation techniques, carriers will maximize the flexibility of their networks to enable smooth and rapid migration to the next PON level – and provide customers with many years of reliable cutting edge services and applications. Web Site: 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 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 orfeatures contained herein may be covered by one or more U.S. or foreign patents. An Equal Opportunity Employer 103132AE 7/06 Original © 2006 ADC Telecommunications, Inc. All Rights Reserved WHITE PAPER . the network migrate from one PON flavor to the next as bandwidth demand continues to rise. GPON Migration Ensuring my Network is Ready to Migrate to GPON. PAPER GPON Migration Ensuring my Network is Ready to Migrate to GPON The demand for higher bandwidth by residential customers has led carriers to one