BROADBAND COMMUNITIES is the leading source of information on digital and broadband technologies for buildings and communities. Our editorial aims to accelerate the deployment of Fiber-To-The-Home and Fiber-To-The-Premises.
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104 | BROADBAND COMMUNITIES | www.broadbandcommunities.com | NOVEMBER/DECEMBER 2014 TECHNOLOGY Nontraditional PON Architectures Fiber-to-the-home network designers need creative solutions for areas with limited fber and those that have long distances between neighborhoods. By Tom Anderson / CommScope A s the deployment of FTTH solutions increases, real-world network topologies are challenging the abilities of traditional passive optical network (PON) architectures. PON technology was conceived, and standards were developed, by the Institute of Electrical and Electronics Engineers and International Telecommunication Union around a centrally located optical line terminal (OLT) that delivered services over a single- fber architecture to 32, 64 or 128 optical network units (ONUs, also called optical network terminals, or ONTs) at a 20-kilometer range. Standards-based optics have been developed to extend that range to 30 and 40 kilometers, providing good solutions for simple range extensions while keeping the optical distribution network (ODN) truly passive. Tose traditional PON architectures are quite suitable for delivering the benefts of PON to the majority of network operators' subscriber bases; however, there are situations for which those solutions are not a perfect ft. For example, areas with limited fber availability and deployments that need to provide service beyond the range of traditional PON are driving the need for alternative answers. Tis challenge demands a solution; here are three ways CommScope is actively engaged in solving these problems. PUT THE OLT IN A NODE For brevity, let's call this approach a node-based OLT or an N-OLT. Te OLT can be placed practically anywhere in the outside plant (OSP), with traditional PON distribution from that point on. By using available Ethernet-over-fber technologies, an N-OLT uses its fber feeds efciently, requiring as few as one fber to serve the OLT. Tose same technologies also allow the N-OLT to be located at long distances from the headend and close to subscribers, where short drops and high split counts can optimize the network. Trade-ofs include the challenges posed by active elements in the OSP, such as powering, back-up power and increased maintenance logistics. TEMPERATURE-HARDEN A SMALLER, REMOTE OLT Let's call this approach a remote OLT (R-OLT). Tis can be deployed outside an environmentally controlled headend environment in a rack-mounting form factor. Hardening enables R-OLTs to be installed in equipment rooms, OSP cabinets and similar locations in which temperatures are not controlled as they are in a headend but that are protected from rain and snow. Tis accomplishes several things. Like an N-OLT, an R-OLT is closer to end users, allowing for shorter drops and less fber from the splitter to ONUs. And, as with an N-OLT, feeds from the network are fber-efcient and have a great deal of range fexibility. Deployment locations are more limited than with N-OLTs and require external enclosures, but power is typically available where R-OLTs can be deployed, accessibility can be limited (for example, when R-OLTs are in customer premises) and the expense and complexity of a weather-sealed housing is avoided.