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FTTX Installation Verification Testing & Maintenance Troubleshooting

FTTX Installation Verification Testing & Maintenance Troubleshooting

FTTH-installation-testing-troubleshootingWith the increasing demands for bandwidth, FTTH (Fiber to the Home) is considered as a next-generation technology for delivering more bandwidth, reliability, flexibility and security to end-users. PON (Passive Optical Network) is the main structure of FTTH network which can provide optical fiber bandwidth advantages at a lower cost than P2P (Point to Point) architecture affords. However, PON presents unique test challenges when installing and maintaining the FTTH network. Furthermore, optical testing is typically performed at various points in a network’s lifetime. Thus, it is very necessary to know which tests should be done and when and where to do it.

In general, optical testing in FTTH can be divided into two part—installation verification testing and maintenance troubleshooting. This is a very general classification according to the state of the network. Installation verification testing occurs as the network is being constructed or after network installation is complete, but before the network is activated. While maintenance troubleshooting is performed when service outages occur, and typically requires rapid response to restore service as quickly as possible.

In installation verification testing, the most complete testing is performed, including insertion and return loss testing as well as OTDR (Optical Time Domain Reflectometer) testing. Pass/fail criteria may be applied to end-to-end length, loss and optical return loss results, as well as to individual event loss and reflectance measurements for splices, connectors, and splitters. Formal reports may be generated, including all of the measurements, OTDR traces, pass/fail criteria and pass/fail results.

Maintenance troubleshooting is done through reroute restoration and/or fault location, repair, and verification before restoring active service. Troubleshooting may also require non-disruptive fiber identification to ensure in-service fibers are not disconnected. Maintenance personnel may require a visual fault locator (VFL) to precisely pinpoint the location of breaks or macro-bends in splice or access enclosures.

Actually, the installation verification testing and maintenance troubleshooting is not as simple as description above. They usually include various test according to different test location and purpose. And for different tests, the performed time and test equipment, as well as the test wavelengths are not fully consistent. To understand this better, here I use a table to summarize.

Click the table to view large version.

FTTx-test

FQA of FTTH (Fiber to the Home)

FQA of FTTH (Fiber to the Home)

FTTHWith the growing popularity of FTTH (Fiber to the Home) in recent years, the term “FTTH” has caused people’s attentions. In many small places, there still use copper network. Even if there is FTTH, it is very expensive for use. To those people who are unfamiliar with FTTH, they may have many questions to ask. Today, we are going to talk some basic questions and answers of FTTH.

Q. What is FTTH?
A. FTTH the delivery of a communications signal over optical fiber from the operator’s switching equipment all the way to a home or business, thereby replacing existing copper infrastructure such as telephone wires and coaxial cable. Fiber-to-the-home is a relatively new and fast-growing growing method of providing vastly higher bandwidth to consumers, and thereby enabling more robust video, internet and voice services.

Q. What is the Fiber-to-the-Home Council?
A. The Fiber-to-the-Home Council is a non-profit organization consisting of companies, organizations and municipalities engaged in advancing FTTH solutions. Our members are manufacturers who build equipment used in FTTH deployments, residential developers that install fiber in their housing developments, public utilities and local governments that have built their own FTTH systems, and independent and rural telephone carriers who have gotten into the business of providing fiber-tothe-home. Among the Council’s activities are providing ways for our members to share their knowledge and build industry consensus on fiber-to-the-home.

Q. What is optical fiber?
A. Optical fiber uses light instead of electricity to carry a signal. It is unique because it can carry high bandwidth signals over long distances without degradation. Copper can also carry high bandwidth, but only for a few hundred yards – after which the signal begins to degrade and bandwidth narrows. Optical fiber has been used in communication networks for more than 30 years, mostly to carry traffic from city to city or country to country.

Q. Why is fiber optic cable now being connected directly to homes?
A. Connecting homes directly to fiber optic cable enables enormous improvements in the bandwidth that can be provided to consumers. While DSL and cable modems generally provide transmission speeds of up to five megabits per second on the download (and are generally slower when uploading), current fiber optic technology can provide two-way transmission speeds of up to 100 megabits per second. Further, while cable and DSL providers are struggling to squeeze small increments of higher bandwidth out of their technologies, ongoing improvements in fiber optic equipment are constantly increasing available bandwidth without having the change the fiber. That’s why fiber networks are said to be “future proof.”

Q. Why do we need all that bandwidth? Aren’t cable and DSL systems good enough for what most people want to do?
A. If all you want to do is surf web pages, download a few songs, send and receive some photographs, or watch streaming video at current picture quality levels, then the bandwidth provided by today’s cable modems and DSL lines is probably good enough. But the world is moving toward vastly higher bandwidth applications. Companies like Netflix, Amazon and Wal Mart are preparing to offer featurelength movies for download. More people are looking to upload their own home movies into emails or web pages. Consumer electronics companies are coming out with devices that connect televisions to the Internet. High-definition video is fast becoming the state-of-the-art – and one high definition movie takes up as much bandwidth as 35,000 web pages. All of these applications – and many others we haven’t even dreamed of yet – are going to require much greater bandwidth than what is generally available today, even from so-called “broadband” providers.

Q. But it was only a few years ago that I upgraded from dial-up to DSL. Are you telling me I’m going to have to upgrade again?
A. Think about it. A little more than two years ago, the Internet video service You Tube didn’t even exist. Today, You Tube viewers watch 100 million video clips a day. It was the advance from dialup to DSL and cable modem that made You Tube possible. And now a growing number of Americans are watching their favorite television programs and news and sporting events over the Internet. We have no reason to believe these innovations will stop. This trend will continue into high-definition video, telemedicine, distance learning, telecommuting and many other broadband applications that have thus far been limited only by the amount of high-bandwidth connections into people’s homes. Only fiber-to-the-home can deliver the bandwidth we are going to need in the future. Fiber-to-thehome providers are now providing this higher capacity at competitive prices.

Q. Why can’t I get these high-bandwidth applications with DSL or cable modem?
A. DSL and cable modem rely on copper wire to deliver signals to your home – and copper can deliver high bandwidth only over very short distances. That’s fine if you happen to live a few hundred yards form your provider’s switching station, but most people don’t. Optical fiber does not have this limitation and thus is able to carry high bandwidth signals over great distances to homes and businesses. Only fiber-to-the-home can deliver the immense bandwidth that the applications of the future will require.

Q. I’ve heard that wireless technologies like WiFi and WiMAX can deliver the same kind of service as fiber-to-the-home without having to go through the trouble of installing new wires into homes. Is this true?
A. No. Wireless broadband is subject to spectrum availability – the cost of which limits the bandwidth, and hence the applications it can provide. The wireless technologies cannot deliver high definition television – and, in fact, they have trouble delivering standard television. And HDTV is only one of the many high-broadband applications now being developed for our broadband future.

Q. What about satellite? Most people have that choice, don’t they?
A. Satellite offers video, of course, but it cannot offer robust broadband Internet service because the subscriber can only download the signal. Upload is normally provided through the subscriber’s telephone lines, which limits transmission speeds for user-generated content.

Q. Is FTTH service affordable?
A. Fiber-to-the-home services are being rolled out nationwide at prices that are competitive with video, voice and data services being delivered by incumbent carriers. In places where consumers have previously had little or no choice in their video and Internet services, the addition of a fiber-to-thehome competitor has helped keep prices down and lift service quality.

Q. Is there a calculated value of having a FTTH?
A. Yes. A recent study by RVA & Associates, a Tulsa-based consulting firm, surveyed home buyers and developers. It found that fiber-to-the-home adds about $5,000 to the purchase price of an individual dwelling.

Q. Is FTTH primarily a technology for getting high-definition movies on demand?
A. Not at all. While the vastly higher bandwidth and transmission speeds offered by fiber-to-the-home is certainly enabling video providers to offer a wider range of products and services, users of other applications that will benefit as well. Gamers will get access to more powerful multi-player applications. Avenues will open for distance learning and telemedicine. Opportunities for telecommuting and working at home will increase. And, just as Internet applications and solutions have grown more sophisticated with the expansion of available bandwidth thus far, you can be sure that this leap into next-generation broadband will inspire further innovations that we cannot even imagine at this point.

Reference Source: Fiber-to-the-Home Council

PON (Passive Optical Network) Troubleshooting Overview

PON (Passive Optical Network) Troubleshooting Overview

PON (Passive Optical Network) architecture is commonly used for FTTx (Fiber to the x, x=home, curb, building…) networks because it employs optical splitters to deliver signals to multiple users without conversion or intervention. This reduces the cost of the system substantially by sharing one set of electronics and an expensive laser with up to 32 terminations. PON troubleshooting is an important part in FTTx installation and maintenance. If all customers connected to a PON system are out of service, testing can proceed at the CO (Central Office) without danger of interfering with existing service. System diagnostics will usually detect a problem with the OLT (Optical Line Terminal) and the solution is normally a line-card replacement. The OLT manager will usually identify a broken fiber on the main leg as all branches associated with the OLT will become nonresponsive. Troubleshooting can then proceed with an OTDR (Optical Time Domain Reflectometer) or a simpler break indicator.

The following picture outlines a methodology for troubleshooting PON networks in the more difficult situation where one or some customers connected to the PON are out of service. When a fault occurs in the subscriber’s FTTH service, if other subscribers sharing the OLT are not experiencing the same fault, then the problem is either in the drop cable between the FDH (Fiber Distribution Hub) and the ONU/ONT (Optical Network Unit / Optical Network Termination), in the ONU/ONT or in the subscriber’s home network. The technician should begin by disconnecting the optical fiber from the ONU/ONT and checking the optical signal level with a power meter.

PON-troubleshooting-overview

If no power is measured on the drop cable, the chances are that the problem is either a break in the fiber or a high loss event such as a bad splice. Since no power is being received at this ONT location, there is no danger of interfering with traffic on the PON when testing the fiber using an OTDR. But to be safe it’s a good idea to troubleshoot with an OTDR using the 1650nm wavelength to avoid interfering with the ONT in the event of a mistake. If the optical power level is lower than the specification, there is a good chance that there is a break or damage in the drop cable. Maintenance of a PON drop cable requires care when the rest of the network is still in service. One approach is to isolate the drop cable under test from the rest of the network but this is not easy because the connections are often high on utility poles and wires, and disconnecting fiber splices is difficult. The solution is to use a short wavelength OTDR with test pulses at a wavelength of 780 nm. Testing from the subscriber’s side at 780 nm has no effect at all on the in-service customers. The dynamic range at 780 nm is 8 dB so faults in a 2 km or shorter drop cable can be accurately pinpointed.

If the power is OK, then test down the stream from the coupler with an OTDR and bare fiber adapter to pinpoint the attenuation.

For more information about PON troubleshooting with OTDR, please visit this paper link.

Brief Introduction to Fiber Optic Splice Closure

Brief Introduction to Fiber Optic Splice Closure

FTTH Splice ClosureLook at the picture on the left. Do you know the “black box” on the ground? Yes, many people who work with FOC (fiber optic cable) may be very familiar with it. It is called fiber optic splice closure, or fiber splicing closure. In fact, except underground application, fiber optic splice closure is also used for aerial, strand-mount FTTH “tap” locations where drop cables are spliced to distribution cables. It is usally used with outdoor fiber optic cables which provides space for the outdoor fiber optic cables to be spliced together. The fiber optic splice closures and the fiber trays inside will protect the spliced fiber and the joint parts of the outdoor fiber cables.

Generally the fiber optic splice closures are horizontal types and dome type (also called vertical type). Horizontal types are used more often than vertical type (dome type) closures.

fiber splice closure

Horizontal Types

Horizontal types splice closure look like a flat or cylindrical box which provide space and protection for fiber optic cable splicing and joint. They can be mounted aerial, buried, or for underground applications. Most horizontal fiber optic splice closure can fit hundreds of fiber connection. They are designed to be waterproof and dust proof. They can be used in temperature ranging from -40°C to 85°C, can accommodate 70 to 106 kpa pressure and the case are usually made of high tensile construction plastic.

horizontal-closure

Vertical Types

Vertical type of fiber optic splice closure looks like a dome. This is why they are also called dome type. They meed the same specification as the horizontal types. They are usually designed for buried applications.

dome type closure

WDM-PON and XWDM-PON Interface Technology

WDM-PON and XWDM-PON Interface Technology

Differently from GPON, WDM-PON needs one optical interface per user not only in the ONU but additionally in the OLT. Because of this, optical interface technologies are a key in implementing a cost-effective WDM-PON.

Fiberstore WDM-PONA trivial method of realizing a CWDM-PON is to use standard CWDM Transceiver. In this way, however, the price of optical interfaces scales linearly with the number of users, being too high if a large number of users is considered. Moreover, colored ONU have to be used, thereby increasing operational costs because of the more complex control over spare parts. Both problems might be solved by a new class of components, called Photonic Integrated Circuits (PICs). The functional scheme of the transceiver containing a transmitting along with a receiving PIC is represented within the figure. In the transmitting PIC, a bar integrating a certain number of lasers is coupled with a PLC MUX/DeMUX (generally an AWG) that launches the multiplexed channels into the output fiber. The scheme of the receiving PIC is identical, with a DeMUX, a bar of photodiodes, along with the WDM signal incoming in the input fiber. Similarly to CWDM SFP, it seems easy to implement CWDM PIC without thermal stabilization.

Besides reducing the cost of OLT colored sources, PIC technology may be used also to design colorless ONUs. In this case, a PIC may be used like a tunable source, switching on only the lasers tuned on the desired wavelength. Since PIC technology is still under development, especially CWDM PIC that the market expects to be uncooled, it is difficult to foresee just what the cost of one PIC for any certain production volume will be. In any case, considering a 16 wavelength CWDM-PON, in order to have an industrial cost equal to that of a GPON, a 16 elements PIC should cost around the unique burst mode interface of the GPON, and this is really very hard cost wise. The PIC is also the method of try to reduce interface costs in XWDM-PON. It’s to underline the first PIC prototypes were realized at 10 Gbps because of application within the digital optical network or just to reduce the price of metro equipment.

Also, when it comes to WDM-PON, the adoption of PICs have to be taken into account when handling the network. The problem, as in the case of the DON, is OLT PIC failure. In this case, a set of ONUs, otherwise a complete WDM-PON, loses the signal. Individual protection of PICs in to the OLT is thus practically mandatory, and this also impacts around the final OLT cost.

As far as the XG-PON is concerned, the discussion is much more complex. In the point of view of optical interfaces, on the floor of standard requirements, there aren’t so many choices from one of the state of the art. The options of the transmitter and receiver are summarized in the table for class 1 XG-PON1 (28 dB power budget) and sophistication 2 XG-PON1 (31 dB power span). These optoelectronics components can be nounted onto a package using micro-optics methods and they can also be assembled inside a hybrid or monolithic chip. In almost any of these cases, all the considerations already done for the GPON still hold using the further issue the circuit to share the electrical signal to the modulator at 10 Gbps is much more complex with respect to that working at 2.5 Gbps, thereby further increasing the cost of the OLT optical module package.

Fiberstore XG-PON

Besides these components that are just about all in common with the GPON case, when it comes to the XG-PON1, another difficulty arises, that is not present in the GPON. Due to the broadcast nature of the ODN and the continuous change of frame slot allocation among the ONUs due to the DBA, the signal arriving at the ONU is really a burst signal and it needs a burst mode receiver. Every ONU receiver should be able to detect the appearance of a burst and also to rapidly lock the sampler in the burst, so as to sample the signal at the right point of the bit interval.

While at 2.5 Gbps, a burst mode receiver is tough to implement, at 10 Gbps it’s a real technology challenge. The first experimental components were presented in the year 2009, but more development will be needed to attain the desired performance and cost targets imposed through the applications.


About the writer:

As a largest provider of fiber network solutions, Fiberstore has been supplying Passive CWDM/DWDM devices for WDM-PON applications for years. There are CWDM MUX/DeMUX/OADM/Transceivers, DWDM MUX/DeMUX/OADM/Transceivers, DWDM EDFAs, Transponders, etc..