Maintaining Optical Networks

The most common single-mode wavelengths used by OTDRs are:

1,310 nm and 1,550 nm.

Fiber-optic power meters used in fiber-to-the-home (FTTH) networks should be able to measure which of the following two additional wavelengths?

1,490 nm and 1,625 nm.

The National Electrical Safety Code (NESC) requires drop cables to be placed at what minimum depth?

18 inches.

What is the optical channel spacing of coarse wavelength division multiplexing (CWDM) systems?

20 nm.

What length of fiber should be encased in a dead zone box according to industry standards?

20 times the length of the OTDR's shortest pulse width.

Optical power meters used for testing fiber-to-the-user (FTTx) installations operating downstream from the headend should be calibrated for which wavelengths?

490 nm, 1,550 nm, and 1,577 nm.

When a laser light source is used to test fibers,

A 2 kHz modulation provides a test signal that allows the fiber under test to be detected by an optical fiber identifier.

Besides RS-232 ports, what type of interface is common on an optical power meter?

A USB interface can provide easy download of information to a PC.

Which type of optical time domain reflectometer (OTDR) trace results when two fiber strands with dissimilar cores are fusion spliced together?

A gain and loss signature.

What is true of a diagram of restoration responsibilities?

A lead technician would likely document troubleshooting results.

What is the difference between a reflectance measurement and an optical return loss (ORL) measurement with an optical time domain reflectometer (OTDR)?

A reflectance measurement measures an individual component and an ORL measurement measures the sum of all components.

Optical loss test sets perform multiple functions because they include the features of multiple pieces of test sets. The features of which other test sets are combined into an optical loss test set?

A stabilized light source, an optical return loss meter, an enhanced optical power meter, and an optical talk set.

Which of the following is an important piece of a restoration planning questionnaire?

A useful question might be, "What is the time allowance for service restoration from notification of the problem to restored service?"

In optical time domain reflectometer (OTDR) terminology,

Acceptance testing consists of checking two-point attenuation, the index of refraction vs. the actual cable length, and zooming in to correctly place markers.

What is the best course of action for the optical time domain reflectometer (OTDR) operator when the distance measurement for a strand of fiber doesn't match the sequential distance markings on the outside of the cable jacket?

Adjust the index of refraction (IOR) settings on the OTDR until the measured distance matches the sequential distance markings.

When testing a fiber-optic splitter with an optical time domain reflectometer (OTDR), what would cause all the splitter output ports to look the same on the OTDR's display?

An equal percentage fiber-optic splitter with all the same drop lengths.

When testing the fiber-optic plant,

An optical power meter is used to measure the strength of light signals anywhere in a fiber system where a connection can be made.

When working with specialized tools to troubleshoot and fix a fiber-optic system,

An optical time domain reflectometer (OTDR) transmits pulses of light into the fiber, then detects and measures the amount of reflected light.

Forward and return sweeps

Are most valuable for comparing sweep traces over periods of time.

When establishing a timing sequence or communication flow for a restoration flow chart,

As experience in emergency restoration deployment is gained via actual deployments or rehearsals, the sequence time chart becomes more detailed and realistic.

What will you find when locating trouble in the outside plant with the optical time domain reflectometer (OTDR)?

Both reflective and nonreflective events are located at the start of the knee where the average slope of the trace first changes.

Additional optical attenuation

Can be obtained by use of an in-line optical attenuator. Some manufacturers provide a front panel interface allowing the user to add or remove optical attenuation.

Full-feature OTDRs, also known as platform OTDRs, have these as options:

Chromatic dispersion and polarization mode dispersion (PMD) module interfaces.

Which class of optical transmitter is the safest to the human eye?

Class 1

When programming an optical time domain reflectometer (OTDR),

Configuration settings include index of refraction (IOR), pulse width, range, wavelength, dead zone, event dead zone, masking, noise floor, and loss variables.

What are possible causes of a reflective optical time domain reflectometer (OTDR) trace signature?

Connectors, mechanical splices, optical planar splitters, and fiber ends.

Optical fiber identifiers

Detect live traffic signals or modulated test signals on an individual optical fiber.

When testing the optical receiver portion of an optical link with an optical power meter,

Disconnect the jumper from the input to the receiver, clean the optical connectors, and connect the receive jumper to the power meter.

Index of refraction (IOR) is calculated by what formula?

Divide the speed of light in a vacuum by the speed of light through an optical fiber.

As changes are introduced to a fiber-optic network,

Documentation must be updated to reflect the new configuration and performance data.

Regarding various optical power meter types,

Enhanced power meters evolved for roles where measurements need to be easily stored, recalled, transmitted, and downloaded.

What should you do to begin diagnosing the cause of a problem that has been isolated?

Examine the fibers with the optical time domain reflectometer (OTDR) on both sides of the major event for any inconsistency in the trace.

What can happen inside fiber-optic equipment room facilities?

Failures can typically arise at patch panels, somewhere in opto-electronic systems, and because of installation practices.

What are potential sources of problems in aerial installations?

Falling branches, pole attachment problems, and improper sag and loading considerations.

What criteria should be met when setting up the optical return path?

First, the technician at the receiver location (headend) should measure and document the optical input power level (measured in dBm) using a power meter.

Which of the following describe optical time domain reflectometer (OTDR) nonreflective signatures?

Fusion splices, macrobends, and microbends.

What are possible causes of a nonreflective OTDR trace signature?

Fusion splices, macrobends, microbends, and fused biconical taper (FBT) splitters.

Regarding outside plant fiber-optic restorations,

If a suitable path exists, an aerial span replacement may be accomplished by converting to an underground installation.

Which of the following is true in regard to the operating parameters of a fiber node?

If optical power is within +/- .5 dBm of the original acceptance documentation, no further action is required.

Dense wavelength division multiplexing (DWDM) systems

In a fiber network create the need for an additional piece of test equipment, the optical spectrum analyzer.

When using mechanical splices and other connection techniques on bare optical fibers,

In some cases, the bare optical fiber can be indirectly connected to the optical time domain reflectometer (OTDR) using a system jumper, interconnection sleeve, and a bare fiber adapter.

Fiber node acceptance tests

Include performance measurements such as carrier-to-noise ratio (C/N), composite second order (CSO), composite triple beat (CTB), and hum modulation.

Optical time domain reflectometer (OTDR) signatures

Include reflective, nonreflective, gain, roll-off, and ghost types.

Choosing the appropriate optical measurement for post-installation fiber-optic span tests

Includes splice loss, attenuation measurements of fiber segments, component reflectance, optical splitters, accumulated loss, dual wavelength testing, bi-directional testing, and pass/fail analysis.

What is the key benefit to using a DOCSIS-based cable modem termination system (CMTS)?

Increased network reliability and improved technician access to critical network data.

A light source

Is crucial for accurately measuring optical fiber power and attenuation.

The optical fiber acceptance test

Is the best opportunity to adjust the fiber's index of refraction (IOR) to match the sequential markings of the cable jacket prior to installation.

What is the best way to plan proficiency training for fiber restoration?

It is often best accomplished by simulating a fiber-optic cable failure.

What is unique to a fiber break locator?

It is the least expensive type of OTDR.

When cleaning the optical port of an optical time domain reflectometer (OTDR), which connector port requires the use of a 1.25 mm swab?

Lucent connector (LC).

When troubleshooting radio frequency over glass (RFoG) and passive optical network (PON) FTTx systems that use longer wavelengths, what is the common cause of higher losses that should be addressed?

Macrobends and microbends caused by improper bending and pinching of cables and patch cords.

While locating problems on a fiber with an optical time domain reflectometer (OTDR),

Measurements made manually for distance measurements identifying reflective events tend to be easier to make and are more accurate than those manually taken for nonreflective events.

Optical time domain reflectometer (OTDR)

Measurements of loss in a dark fiber can help identify the possible cause and location of a fault on an active fiber.

What is an optical return loss test set used for?

Measuring the amount of reflected energy from the fiber's internal Rayleigh scattering and Fresnel reflections.

Improper use of nylon tie wraps can induce this problem

Microbends

During installation of fiber-optic cable, what does damage to the cable jacket cause?

Moisture migration into the cable.

As you begin to identify trouble within fiber-optic systems, it's important to consider which of the following?

No matter how complex, all systems are composed of point-to-point links consisting of a source (transmitter) and a detector (receiver) connected by an optical fiber.

An optical power measurement

Of the input on most optical receivers used in the broadband cable industry is accomplished by including a DC voltage test point.

Regarding the various pieces of fiber-optic troubleshooting test equipment,

Optical power meters determine the overall loss of an optical fiber, but the optical time domain reflectometer (OTDR) can display the fiber's loss characteristics throughout.

When performing an optical fiber acceptance test,

Organize the fibers by color, per the TIA-598-A standard.

How can an optical time domain reflectometer (OTDR) operator compare an old fiber trace with a new one?

Overlaying a new trace on top of a previously saved trace.

What topology do most fiber-to-the-user (FTTx) networks use, which requires greater fiber color code management in its documentation?

Point to multipoint (P2MP).

A wavelength-isolating power meter is most commonly used in

Point-to-multipoint FTTx installations.

Which of the following statements about fiber restoration safety is true?

Proper signage should be used to alert passers-by of work in progress, as required by local and national safety codes.

Which optical time domain reflectometer (OTDR) configuration setting must always exceed the length of the span under test?

Range

Regarding reflections in an optical fiber,

Rayleigh scattering is caused by compositional fluctuations or core imperfections in the fiber.

Fiber-optic restoration

Requires preparation for dealing with factors that affect outage repair, including foul weather, darkness, electric utility failures, and the need to repair the system quickly.

In fiber network restoration planning,

Responsibility for update and control of the restoration plan document must be defined or it will quickly become obsolete and useless.

What should inspections of fiber-optic aerial and underground plants include?

Safely making a repair on the spot if the problem represents a potential safety hazard or imminent risk to system operations.

Digital channel signal testing

Should be performed in both the downstream and upstream paths and should include bit error rate and modulation error rate performance measurements.

The troubleshooting process

Should include steps that identify, analyze, and locate the problem as well as diagnose its source, repair the problem, and test to ensure the problem is resolved.

For fiber restoration, what can facilitate necessary documentation?

Software packages, which electronically automate system records.

What do OTDR displays and controls encompass?

Task options, which include range, pulse width, wavelength, measuring mode, backscatter coefficient, and index of refraction.

Return path

Testing must ensure that the RF input signals to the return laser transmitters are of proper amplitude and are free of ingress, common path distortion (CPD), or other impairments.

Federal Communications Commission (FCC) proof-of-performance

Tests for 24-hour carrier-level variation must be conducted in July or August and December or January.

Which wavelength is the most sensitive to macrobends and microbends and has been specified by standards groups for testing and monitoring of fiber-optic spans?

The 1,625 nm wavelength is the most sensitive wavelength for micro- and macrobend detection.

What is the safety standard for confined spaces?

The ANSI Z117.7 standard covers confined spaces.

What is the result of increasing (making wider or longer) the pulse width on an optical time domain reflectometer (OTDR)?

The OTDR's range increases and its ability to distinguish closely spaced events decreases.

How is a restoration posture for a fiber network acquired?

The basic resources required to respond to a major system outage are documentation, technical skill, and basic troubleshooting/repair equipment and materials.

Which description of fiber documentation below is correct?

The fiber route diagram is a quick reference diagram of the fiber distribution network.

When measuring end-to-end attenuation,

The light source and optical power meter must be referenced together prior to making any field measurement.

When measuring transmit and receive power with an optical power meter,

The meter's calibration must be traceable to the National Institute of Standards Technology (NIST).

What does the laser array diagram show?

The number of optical transmitters, splitters, couplers, and receivers in the headend.

What do optical power meters measure?

The optical output power of the laser transmitter and the input optical power level at the receiver.

In regard to the different fiber-optic test sets, which of the following statements is true?

The optical return loss test set is used to measure the amount of reflected energy caused by Fresnel reflections.

To test the optical path between the receiver and the transmitter in order to analyze a fiber problem,

The optical time domain reflectometer (OTDR) must be set up prior to proceeding with any test, or at least the set-up information must be checked and confirmed.

What is the best way to prevent problems in outside fiber-optic splice enclosures?

The outer jacket and the internal cable structures must be secured individually to protect the closure and splice trays from the effects of expansion and contraction.

What is the probable cause if an OTDR trace shows one optical splice but it is a known fact that there are two?

The pulse width is set too long.

In a temporary fiber-optic restoration,

The restoration kit should be clearly marked and placed to protect it from damage and from becoming a safety hazard.

What is an important consideration in structuring a flow chart of basic restoration activities?

The restoration plan prescribes the sequence of events described in the flow chart.

In a fiber-optic network,

The role of maintenance is to proactively maintain network tolerances and recognize, locate, and remedy potential problems.

Optical return loss (ORL) is used to define the amount of reflection from

The sum of all Fresnel reflections and the fiber's Rayleigh backscatter.

A fiber-optic network maintenance plan should be developed with which of the following in mind?

The task of compiling the physical document must become the responsibility of an identifiable position or organization.

Regarding variables that can affect a potential fiber-optic restoration scenario,

The three variables that in general terms may be discussed as combinations are: availability of slack cable; temporary vs. permanent restoration; and aerial vs. underground restoration.

What is a key attribute of network operation centers (NOC) developed by many cable operators in large metropolitan areas?

They are typically staffed 24/7/365 with highly trained technical analysts to monitor critical network functions in real time.

What is true of mainframe optical time domain reflectometers (OTDR)?

They are used mainly in the fiber manufacturing industry.

What do effective fiber-optic restoration plans acknowledge?

Three separate types of activities: identification, location, and resolution.

What is the first order of business for the fiber-optic field restoration coordinator (FRC)?

To conduct a site visit to verify the extent of the damage.

What is the purpose of the call list with regards to fiber-optic restorations?

To provide quick access to the proper departments and staff required for restorations.

What is an advantage of having slack fiber-optic cable?

When available during a restoration, it decreases down time and repair costs and omits additional splice attenuation.