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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68 | BROADBAND COMMUNITIES | www.broadbandcommunities.com | MAY/JUNE 2014 FIBER TESTING The Unique Test Challenges Of PON Deployment Part 2 of a two-part article details troubleshooting procedures for a passive optical network in operation. Part 1 described testing procedures at the time a passive optical network is installed. By Michael Scholten / AFL M ost fber optic networks are deployed as point-to-point connections. When a fault occurs in the point-to-point fber, all trafc through that fber is disrupted. Trafc is typically rerouted to a spare fber, and the failed fber may be tested using the same tools and techniques as for out-of-service fbers. Fiber-to-the-home (FTTH) passive optical networks (PONs) are deployed with point-to- multipoint connections. An optical line terminal (OLT) in a central ofce transmits downstream trafc at 1490 nm or 1550 nm. Tis trafc is passively split, and identical copies are delivered to 32, 64 or even 128 subscribers connected to the PON. Upstream communications at 1310 nm from each subscriber are recombined in the optical splitter and transmitted back to the OLT over the same fber. Unlike a point-to-point network, a PON may have one or only a few subscribers experiencing loss of service while others remain in service. Troubleshooting at the failed subscriber locations must not interfere with communications to existing in-service subscribers. Additionally, troubleshooting equipment must be able to perform its function in the presence of live trafc signals. Tis creates unique requirements for optical time-domain refectometers (OTDRs) used to troubleshoot live (in-service) PONs. When one or only a few subscribers lose service while other subscribers on the same PON continue to receive service, there are several possible causes: • Equipment or connection problem inside the customer premises • Failed optical network terminal (ONT) at the customer premises • Fault in the distribution or drop fber from the splitter to the subscriber • Fault introduced at the splitter connection to the subscriber's distribution or drop fber (for example, a macrobend introduced while adding another subscriber or inadvertently disconnecting the distribution or drop fber to an active subscriber). If some but not all subscribers are afected in an FTTx PON built using distributed splitter architecture, it is possible that all afected customers are served from a single secondary splitter. In this case, likely causes include • Fault in the distribution fber serving the secondary splitter • Fault in the secondary splitter itself. In either case, a fault in the feeder fber or a failure within the OLT at the central ofce is not likely, as subscribers who are still receiving service also share the feeder fber and OLT. Troubleshooting normally requires a visit to the subscriber premises. A recommended BBC_May14.indd 68 5/29/14 9:19 AM