ROC 3 PART 1
What are the most common single-mode wavelengths used by OTDRs?
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.
Optical power meters used for testing fiber-to-the-user (FTTx) installations operating downstream from the headend should be calibrated for which wavelengths?
1,490 nm, 1,550 nm, and 1,577 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.
After accounting for the synchronization bytes, what is the practical data rate of the asynchronous serial interface (ASI)?
214 megabits per second (Mbps).
What 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 done to ensure that those digital receivers not controlled by the cable operator receive Emergency Alert System (EAS) messages?
A program and system information protocol (PSIP) message is inserted into the transport stream that automatically tunes the receiver to the emergency details channel.
What is a carrier?
A simple fixed-frequency voltage whose amplitude and frequency are initially fixed.
What are the primary differences between the transmission protocols used on the return data channel, ALOHA, and time division multiple access (TDMA)?
ALOHA is a collision recovery protocol; if a collision occurs, the data is resent. Time division multiple access (TDMA) is a channel-based protocol; time slots are allocated for the reliable and orderly transmission of upstream data with no collisions.
Which of the following includes the protocols for measuring audience viewership?
AMOL-48 and AMOL-96
Which of the following is true in regard to 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.
When converting an HDTV transmission to an SDTV or analog transmission, which system imbeds instructions from the broadcaster for picture reconstruction?
Active format description (AFD).
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 settings on the OTDR until the measured distance matches the sequential distance markings.
A final test point in the headend should be located:
After all the downstream carriers have been combined.
What is the intermediate frequency (IF) used for?
Amplification, filtering, and other controls.
The patch panel is a demarcation point between the output from a source and the input to another device or destination. In the headend, the serial data interface (SDI) patch panel is used to route the SDI signal from a local origination studio to what?
An MPEG-2 encoder.
If isolation of carriers is a major concern in a headend, the best solution is provided by:
An isolation amplifier.
Which of the following is true when using troubleshooting equipment to test 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.
A protocol used to transport signals in the headend is called:
Asynchronous serial interface (ASI).
How would an input converter compensate for fluctuations in received signal strength?
Automatic gain control.
How can an optical time domain reflectometer (OTDR) operator compare an old fiber trace with a new one?
By overlaying a new trace on top of a previously saved trace.
The frequency of an analog channel is identified by the video carrier frequency, but the frequency of a digital channel is identified by the:
Center frequency.
Differential gain and phase errors can affect the ________ in the picture.
Color.
There are three types of ancillary data prevalent in digital television (DTV) transmissions that must make the conversion to analog television. Two of these are closed captioning data and Nielsen Automated Measurement of Lineups (AMOL) data. What is the third?
Content advisory data.
For content advisory data to work after conversion from digital to analog, what must the analog television receiver do after decoding the signal
Decode the content advisory from the vertical blanking interval (VBI) and compare it to the V-chip setting, blocking the display of the program if the program rating exceeds the selected rating level.
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.
What documentation changes should occur as changes are introduced to a fiber-optic network?
Documentation must be updated to reflect the new configuration and performance data.
Each DTV-to-analog decoder must convert the ATSC digital audio signal into an analog television signal, which includes compensating for program loudness adjustments and dynamic range compression (DRC). What is the third feature the decoder must adjust?
Down mixing to a single audio signal If closed captioning data that is present on a DTV signal is converted to analog, how does the decoder include the closed captioning data? The closed captioning data stream is extracted from the digital stream and reconstructed onto line 21 of the vertical blanking interval (VBI).
When are splice points in the MPEG-2 Transport Stream created?
During encoding, by the digital television content provider before distribution.
Digital upconverter input levels are critical to prevent:
Excessive bit errors.
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.
What is done to prevent the output of the QAM modulator from experiencing intersymbol interference (ISI) and exceeding the 6 MHz bandwidth?
Install a Nyquist filter on the output of the QAM modulator to remove unwanted sidebands and harmonics. A Nyquist filter on the input of the receiver reduces input noise and interference from the other carriers.
Some carrier frequencies are "offset" slightly to avoid:
Interference with aeronautical communication and navigation. The depth of modulation of the video carrier.
The sum or difference frequencies generated when a local oscillator and input signal are mixed is called the:
Intermediate Frequency.
What is the most important concern in passive combining?
Isolating each individual carrier.
Which of the following is true regarding additional optical attenuation?
It 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.
Which of the following is true regarding digital channel signal testing?
It can be performed in either the upstream or downstream directions.
Which of the following is true when choosing the appropriate optical measurement for post-installation fiber-optic span tests?
It 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 best way to plan proficiency training for fiber restoration?
It is often best accomplished by simulating a fiber-optic cable failure.
Which of the following is true regarding the optical fiber acceptance test?
It is the best opportunity to adjust the fiber's index of refraction to match the sequential markings of the cable jacket prior to installation.
What is unique to a fiber break locator?
It is the least expensive type of optical time domain reflectometer (OTDR).
Which piece of fiber optic cable has a connector on both ends?
Jumper.
If the levels on the return path are excessive, a problem known as ____ will occur and cause extreme distortion.
Laser clipping.
The ability of the CMTS to control the output level of customer premises equipment is called
Long loop AGC.
While locating problems on a fiber with an optical time domain reflectometer (OTDR), which of the following is true?
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.
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 what problem?
Microbends.
During installation of fiber-optic cable, what does damage to the cable jacket cause?
Moisture migration into the cable.
Active format descriptor (AFD) and program and system information protocol (PSIP) in digital video signals contain information that
Must be preserved and distributed along with the program.
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.
For a device to operate as a mixer it must be:
Nonlinear.
Which of the following is true regarding optical time domain reflectometers (OTDR)?
OTDR measurements of loss in a dark fiber can help identify the possible cause and location of a fault on an active fiber.
Regarding the various pieces of fiber-optic troubleshooting test equipment, which of the following is true?
Optical power meters determine the overall loss of an optical fiber, but the OTDR can display the fiber's loss characteristics throughout.
At the headend, the device that converts the optical signal to RF is called the:
Optical receiver.
What should be done when performing an optical fiber acceptance test?
Organize the fibers by color, per the TIA-598-A standard.
The video signal is ____________ modulated and the audio signal is __________ modulated.
Phase, amplitude.
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).
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.
The device that adjusts the data rate in a digital signal for best performance in a system is called a:
Rate shaper.
Which of the following is true regarding reflections in an optical fiber?
Rayleigh scattering is caused by compositional fluctuations or core imperfections in the fiber.
Test points help a technician diagnose a problem without:
Service interruption.
For fiber restoration, what can facilitate necessary documentation?
Software packages, which electronically automate system records.
What is a desirable feature of a routing switcher?
Switching from one content source to another so that the receiver does not lose stability.
Isolation of a splitter or directional coupler is measured with the common port
Terminated.
What is the safety standard for confined spaces?
The ANSI Z117.7 standard covers confined spaces.
How can an Emergency Alert System be inserted into a processor?
The EAS composite IF must be inserted in the alternate IF when needed.
Video-on-demand (VOD), switched digital video (SDV), and Internet protocol television (IPTV) are examples of switched services deployed in many cable systems. Which common networking protocol is being used as cable services transition from broadcast to these switched services?
The Gigabit Ethernet (GigE) Protocol.
In a system offering interactive services such as video-on-demand (VOD), what determines the amount of data going into the QAM modulator that is connected to the VOD server?
The amount of data is dependent upon the number of orders being fulfilled by the VOD server.
What happens to the bandwidth of a downstream signal when the limits of the Nyquist filter are set to the standards of the American National Standards Institute (ANSI) and Society of Cable Telecommunications Engineers (SCTE) standards for 64-QAM and 256-QAM?
The bandwidth of a 64-QAM downstream signal is less than 6 MHz but the bandwidth of a 256-QAM signal slightly exceeds 6 MHz and is therefore "close enough" to be called 6 MHz.
Negative polarity modulation means
The carrier level decreases as the picture gets brighter.
Within the packet identifier (PID) assignments there are three tables. Which table lists all of the programming/services that have assigned PIDs of scrambled programs on that transport stream?
The conditional access table (CAT).
In concatenated coding, Reed-Solomon coding/decoding and convolutional coding are used to mix and arrange packets. Which part of the concatenated coding scheme produces a matrix that is used to map the paths of data bits, so deviation caused by noise or interference can be detected and corrected?
The convolutional coding arranges the transport stream packet data into a matrix that maps the paths of data bits
When a high definition TV (HDTV) signal is transcoded to a standard definition (SDTV) MPEG-2 signal, what is the change in data rate?
The data rate changes from 19.39 Mbps down to 2-4 Mbps.
Which of the following describes the demodulation process?
The demodulation process extracts the baseband information from a modulated carrier.
Which description of fiber documentation is correct?
The fiber route diagram is a quick reference diagram of the fiber distribution network.
Which of the following is true regarding an optical power measurement?
The input on most optical receivers used in the broadband cable industry is accomplished by including a DC voltage test point.
What must the technician be aware of when measuring end-to-end attenuation?
The light source and optical power meter must be referenced together prior to making any field measurement.
Which of the following best describes the modulation process?
The modulation process increases the distance that a baseband signal can be transported.
The headend combining network design needs to be examined if
The modulator output level in the combining network is too low when the unit output is at the highest value.
Which device in a conditional access controller (CAC) system populates the encryption control field on programs that are to be encrypted?
The multiplexer populates the encryption control field on programs that are to be encrypted by the QAM modulator.
What happens when a patch cable is removed from a full-normal patch panel jack?
The normal connection between the equipment connected to the top and bottom jacks is restored.
The edge QAM (EQAM) communicates with a session manager and a resource manager, which are two content management devices that can be integrated within the EQAM. What is the purpose of the resource manager?
The resource manager determines which EQAM is being used for the delivery of content.
Which of the following is true 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 multicasting in the context of over-the-air (OTA) broadcasting of digital TV (DTV) content?
The transmission of a high definition TV (HDTV) service with one or two standard definition TV (SDTV) services within a single 8-VSB channel.
Which of the following is true regarding the troubleshooting process?
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.
The entitlement control message (ECM) and entitlement management message (EMM) are generated from three different types of data - a control word, a service key, and a user key. What two pieces of data typically comprise the user key?
The user key is typically either a receiver serial number or a unique unit address.
What must the entitlement management message (EMM) receive from the conditional access (CA) controller before it can decrypt the entitlement control message?
The user key.
Which of the following is true regarding forward and return sweeps?
They are most valuable for comparing sweep traces over periods of time.
What was the original application of the proprietary digital headend expansion interface (DHEI) protocol?
To chain multiple General Instrument integrated receiver/transcoders (IRT) together to function as a single unit.
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.
Why did the Society of Motion Picture and Television Engineers (SMPTE) develop active format description (AFD)?
To prevent the postage stamp condition from appearing in SDTV displays.
Where are Emergency Alert System (EAS) messages received from authorized sources delivered in the headend?
To the SCTE 18 compliant encoder/decoder (ENDEC) via the antenna.
When converting a high definition TV (HDTV) signal to a standard definition (SDTV) display using the center cut option, what portion of the picture is cropped?
Typically, 16.5% from each side of the picture.
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.
Modulator output levels should be set
Within the manufacturer's design range.
To meet manufacturer's noise and distortion specifications, the modulator output level should be set
Within the manufacturer's specified range.
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 data rate does the original serial data interface (SDI) standard for standard definition TV (SDTV) support?
270 megabits per second (Mbps).
What occurs 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.
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.
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?"
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.
Which of the following is true 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.
Which of the following is true 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 OTDR?
Both reflective and nonreflective events are located at the start of the knee where the average slope of the trace first changes.
Full-feature optical time domain reflectometers (OTDR), 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.
Which of the following is true when programming an optical time domain reflectometer (OTDR)?
Configuration settings include index of refraction, pulse width, range, wavelength, dead zone, event dead zone, masking, noise floor, and loss variables.
Which of the following is true regarding dense wavelength division multiplexing (DWDM) systems?
DWDM systems in a fiber network create the need for an additional piece of test equipment, the optical spectrum analyzer.
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?
Detect live traffic signals or modulated test signals on an individual optical fiber
Which of the following is true regarding 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, which of the following is true?
Disconnect the jumper from the input to the receiver, clean the optical connectors, and connect the receive jumper to the power meter.
How has the optical power meter changed?
Enhanced power meters evolved where more complex records are required, and 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 OTDR on both sides of the major event for any inconsistency in the trace.
Which of the following is true regarding FCC proof-of-performance?
FCC proof-of-performance tests for 24-hour carrier-level variation must be conducted in July or August and December or January.
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 are possible causes of a nonreflective optical time domain reflectometer (OTDR) trace signature?
Fusion splices, connectors, microbends, and planar splitters.
Which of the following describe optical time domain reflectometer (OTDR) nonreflective signatures?
Fusion splices, macrobends, and microbends.
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 regards 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.
Which of the following is true regarding fiber-optic restoration?
It 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.
What do most models of laser light sources use as operational status indicators?
Light-emitting diodes (LED).
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.
A wavelength-isolating power meter is most commonly used in
Point-to-multipoint FTTx installations.
Which of the following is true about 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.
When mobilizing resources for emergency repair, who is responsible for confirming the best equipment setup locations?
Restoration crew foreman (RCF)
Which of the following is true regarding the return path?
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.
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.
What criteria should be met at the forward RF output levels at the node?
Should have close to the same frequency response across the bandwidth that was measured at the headend transmitter, ideally within 1 dB.
What do optical time domain reflectometer (OTDR) displays and controls encompass?
Task options, which include range, pulse width, wavelength, measuring mode, backscatter coefficient, and index of refraction. The pulse width is set too long.
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.
To test the optical path between the receiver and the transmitter in order to analyze a fiber problem, which of the following is true?
The 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 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.
What must the technician be aware of 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.
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 purpose of the fiber-optic acceptance test?
The purpose of the acceptance test is to make sure that the optical cable that has been ordered and received matches both the optical and physical requirements of the order.
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.
Which of the following statements is true regarding optimum performance in the 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 what source?
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.
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.
Which of the following is true regarding fiber node acceptance tests?
They include performance measurements such as carrier-to-noise ratio (C/N), composite second order (CSO), composite triple beat (CTB), and hum modulation.
What is required when working with micron, or sub-micron dimensions and tolerances, as well as very fragile components?
This requires that some procedures are made more by feel than by sight.
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.