FTTH-PON Q and A

Our recent webinar with Light Reading, Lessons Learned: Efficient Deployment & Maintenance of FTTH/PON Networks, garnered several questions from the attendees. We thought that even those who may not have caught the live webinar might benefit from this Q&A. If you’d like to see the webinar recording, please visit the Light Reading Testapedia page

Q. Is there a certification/training program to ensure that installation is done according to your standards?

A. We have various partners who can provide training. Please contact VIAVI at tac@viavisolutions.com for recommendations in your region. We also have a library of Quick Tip videos on our website that you can browse for more information.

Q. How are the splitter secured (physically)?

A. Splitters are usually mounted on backplanes or frames in cabinets that are securely locked with a key.

Q. What is a “5G-PON”? Is it an ITU (e.g., G.984 or G.989) or IEEE PON that is supporting 5G use cases?

A. To cover the needs of the 5G Wireless standard, data could be transmitted over a PON infrastructure to remote radio heads achieving speeds of up to 10 Gbps with today’s standards, or higher with next generation PON standards like NG-PON2.

Q. How is cleanliness of connectors insured after the installation? How do you cope with the high humidity areas, or high dry areas?

fiber inspectionA. Once two connectors are matted, the high pressure keeps them connected. If the connector is not plugged to a piece of equipment or another connector yet, it must be re-inspected before the final connection. This “Inspect Before You Connect” web page has a series of videos that will walk you through best practices and considerations for fiber connection inspection and cleaning.

Q. Any major advantages of cascaded split?

A. It depends on the network topology and density. If the network is dense, like in cities (apartment buildings, etc.), then a single split is better. In less dense area covering longer distances a cascaded split is commonly used.

Q. Would you comment on the operator workforce challenges presented as next generation PONs (e.g., G.989) begin supporting the convergence of traditional residential services, business services, and wireless front/backhaul for emerging 5G use cases? (Operators have traditionally used separate workforces for these commercial domains, which could mean lots of hands touching the OSP in the future, perhaps impacting reliability.)

A. I agree this is becoming a real challenge. Fiber cannot be handled like copper. Proper care of the cable routing, connectors and other passive components is necessary and critical. Some operators have told us they have three times more issues with FTTH compared to DSL.

Q. Have you considered using MPO connectors pigtails and splice boxes to reduce the number of connectors tested?

MPO, Parallel OPticsA. We have heard of some networks where MPO connectors are being adopted for that very reason and it is a great idea to automate the measurement of multiple fibers via MPO. VIAVI offers an MPO switch than can be used with our OTDRs plus a simple software app to automate the test and certification of MPO fibers. We also have the MPO inspection piece covered with a fully automated fiber scope that can check and cert (pass/fail) a 12 fiber MPO in about 12 seconds. You can learn more on our website about Testing Parallel Optics like MPO.

Q. Do you recommend the operator create a “birth certificate” at the time of acceptance testing that can be used in the future as a benchmark to determine ODN degradations?

A. Definitely, yes. And with the new cloud database solutions (such as VIAVI StrataSync), it is easier to handle larger volumes of fiber test results and perform analytics to anticipate eventual network physical degradation.

Q. What is the recommend launch cable length for characterize first and last connector?

A. It mainly depends on the dead zones (ADZ) of the OTDR and if a multi-pulse function is available. With a multi-pulse function, it can be possible to look at events very close to an OTDR, even if the link under test is very long. VIAVI OTDRs have a feature called SmartAcq to do just this, you can read about it in this fiber testing blog post. As for launch cable length, we’d recommend a minimum 20m launch cable when using the multi-pulse function.

Q. What will be the Cable Management system to use in this case? Are you able to recommend one?

A. There are a number of cable management systems available today, we don’t have preference but do recommend use of these systems.

Q. Why is it recommended to use 1550nm wavelength rather than 1490 nm on GPON for acceptance testing? Is this also preferred for service activation?

A. We prepared a PON white paper about this, but in short, for PON fiber-link construction qualification using OTDRs and/or loss test sets, the traditional 1310/1550nm wavelength solutions provide equal value as 1490nm. However, testing at 1490nm with a PON-selective power meter is essential for network turn-up and installation troubleshooting.

Q. For fiber characterization, is it necessary to have an OTDR with 1310 and 1550 nm or could an OTDR with just 1650nm do?

A. Fiber characterization is usually performed at two wavelengths: 1310 & 1550nm. Because of the difference of the fiber characteristics at those wavelengths, it gives you the ability to detect bends.

SmartOTDRQ. To measure the GPON, you recommend the Smart OTDR or a specific module?

A. For standard GPON up to 1×64 split, the SmartOTDR 100B is perfect.

Q. Who certifies the measurements and the network?

A. This is usually the contractor or the construction crew’s responsibility, typically they will have to provide certification of the network build to the owner/operator in order to get paid.

Q. Why the Amplifiers are not used in GPON?

A. Optical amplifiers only work in the C-band near 1550nm, also PON = Passive Optical Network, by design they do not contain any active elements.

Q. I am missing fault localization. This would help in fast recovery of service.

Optical Network Monitoring System
ONMSi Remote Monitoring

A. OTDRs will provide you with distance to fault information and can be used on a live network, you just need to troubleshoot at a different wavelength to the live service. Typically, 1625 or 1650nm is used. If you’re thinking of a more proactive notification and dispatching a tech directly to the fault location then a fiber monitoring system is what you’ll need (such as our ONMSi or SmartOTU solution). Continuous monitoring combined with an accurate plant map will allow you to get pro-active notifications whenever a degradation or outage occurs including the GPS location.

Q. Does the reflector contain a filter to isolate 1650, so it is the only lambda reflected? how much does a reflector cost per ONT?

A. ITU standard specifies that ONT must have built-in isolation against U band (>1625nm). FYI Reflector isolation is typically 20dB. So you are correct, a reflector isolates and returns a specific wavelength while allowing up and downstream service wavelengths to pass. This allows a fiber monitoring system (such as our ONMSi or SmartOTU solution) to operate on a live network without disrupting services. Reflector cost is usually $10 USD for a large deployment (hundreds of thousands of units).

Q. What is the function of reflectors?

A. The reflector is necessary when a PON is measured from the central office (feeder). It is used for the measurement of insertion loss between the central office (OLT location) and the ONT (Home) or any other points after the splitter. A reflector is used in a subscriber’s home or office near to the ONT and allows a fiber monitoring system (such as our ONMSi or SmartOTU solution) to better locate that ONT on the fiber plant. You can monitor for the presence of the reflector to check the fiber link is still there and there are no breaks, and analyze the reflected peak value for loss measurement.

Q. By fiber it is possible to transmit speeds in Tb/s? What are the limitations?

A. Theoretically fiber has the capability/capacity to do this however, the transmit and receive equipment is the limitation. At some point (data rate) they cannot differentiate the 0 from the 1, but there are improvements being made to transmission equipment all the time.

Q. What manufacturer and model OTDR do you recommend?

A. Well, of course we recommend VIAVI Solutions! We have an award-winning, comprehensive portfolio for OTDR and Fiber Characterization.

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