HFC Designer I - II
What is the expected DC voltage on most Hybrid fiber/coax network equipment?
+24 VDC, ±0.5 V.
What is the minimum amount of slack that must be provided for splicing fiber-optic cable in underground installations?
15 meters on both the inbound and outbound span.
In terms of bandwidth, how wide is a video signal in a U.S. cable system?
6 MHz
What can be attached to the pulling line to prevent the fiber-optic cable from twisting during installations?
A break-away swivel.
What is installed in the input stage of a distribution amplifier for a flat frequency response into the input amplifier when the input signal has negative tilt?
A cable equalizer with positive slope.
What are some prerequisites before performing a fusion splice of optical fibers?
A controlled environment such as a splicing van, trailer, or tent and stable work surface that is large enough to accomodate the fusion splicer, tools, and the splice closure.
Shorts in the coaxial cable and excessive amounts of current can damage the distribution amplifier. Several devices can be used to protect the distribution amplifier from these problems. Which device shorts to ground when an overvoltage situation occurs?
A fast transfer electronic crowbar (FTEC)
What is required of mechanical splices used for acceptance testing?
A mechanical splice used for acceptance testing should be simple to use and reusable.
What is spliced into the hardline coaxial cable to combine the AC power with the transported RF signal in a hybrid fiber/coax (HFC) network?
A power inserter
What is MPEG (Moving Picture Experts Group)?
A universally accepted standard for digital television, first released in 1992.
What is a positive-intrinsic-negative diode?
An optical detector with current flow that is linear to the intensity of light photons, with one electron/hole pair created for every absorbed photon until saturation.
Where would you expect Fresnel reflections to occur in a fiber-optic network?
At connections and mechanical splices where the signal source is entering or exiting the cable.
Why are Velcro straps preferred over standard plastic tie wraps when bundling pigtails for storage in a splice panel?
Because Velcro straps are removable and can hold the pigtails together without placing undue strain on the optical fibers.
What is required for checking the physical network integrity when maintaining the coaxial cable network?
Being observant and performing some minor tasks while engaged in regularly scheduled activities.
How often does the Federal Communications Commission (FCC) require cable operators to perform proof-of-performance(POP) measurements on the signals in the headend and at specified test locations throughout the network?
Bi-annually
What is the purpose for distribution amplifiers in a HFC network?
Boost the downstream singals before being divided and circulated throughout neighborhoods in the coaxial cable portion of the network.
How is the AC voltage separated from the RF signal in a distribution amplifier?
By a capacitor that passes RF but blocks the low frequency 60 Hz AC voltage which finds a low resistance path through the RF choke that blocks RF.
How should surface particulates usually be removed from optical connectors?
By using a compressed-air cleaner designed for optical connectors.
What are two critical factors for a successful installation of fiber-optic cable?
Cable pulling tension and cable bend radius.
What group established the data-over-cable-service-interface-specification(DOCSIS)?
CableLabs
What functions does the detector in an optical receiver perform?
Conversion of an optical carrier to an electrical signal, and demodulation of the modulated optical carrier.
Broadband cable operators provide customers with HSD high-speed data connections to the internet via their HFC networks using what standard?
DOCSIS
List the six methods by which signals arrive at the cable system headend.
Direct feed, satellite, over-the-air, terrestrial microwave, local origination, and PTSN.
Which optical splitter package is similar in appearance and size to a standard fusion splice protector?
FBT
What technologies are defined in DOCSIS 4.0 to help sustain the HFC network infrastructure for several more years?
FDX and ESD
Where does a distribution amplifier module receive the direct current (DC) required for operation?
From a DC power supply module that converts the alternating current (AC) voltage to DC voltage.
Besides protection, what else must the coating on an optical fiber do?
Function over a wide temperature range; be compatible with cable gels; adhere to the glass cladding over the lifetime of the cable; and be mechanically strippable for splicing operations.
What do diameter differences between spliced fibers look like on an OTDR?
Gain in one direction and high loss in the opposite direction.
When would a mid-entry splice in a fiber-optic network be used?
In a self-healing ring network that requires only two fibers to feed an optical fiber drop.
How are optical splitters used in the forward path?
In the forward path, optical splitters are used as passive branching devices that divide an optical signal across multiple output fibers.
What information is documented at fiber-optic slack and splice locations?
Incoming and outgoing sequential markings showing the cable's physical length.
What should be done to prevent the buildup of lethal amounts of static electricity on long lengths of aerial fiber-optic cable?
Install grounding clamps, which connect the cable exterior and metallic messengers to a good solid ground at every odd-numbered pole site.
Monitoring the status of optical nodes:
Involves the use of a node transponder that continuously monitors a number of critical functions.
What is the function of an optical node?
It converts light energy to RF.
What is the current standardized OD Outside diameter of the cladding of single-mode fiber?
It is 125 μm, with an accuracy of ±1 μm.
What does a thermal control circuit in a distribution amplifier do?
It maintains the amplifier output levels as the input levels vary with temperature changes.
Why are laser diodes most effective when coupled to singlemode fiber?
Its high coupled power, directionality, and speed.
When preparing fiber-optic cable for connection to a patch panel, how much buffer tube and fiber slack should be provided?
Leave enough slack in the buffer tubes to allow the splice trays to reach the splicing equipment and enough fiber slack to store on individual trays for later additions, moves, and changes.
Which of the following statements about local ad insertion is true?
Local ad insertion is performed usually by a video server.
Which of the following best describes basic service provided by the cable company?
Local origination channels.
Which type of fiber-optic cable provides the most stable transport characteristics and additional protection from stresses caused by macrobends and microbends?
Loose-tube Cable.
What step should be performed at the beginning of every fusion splicing operation?
Make a number of test splices to set up the fusion splicer and to verify the instrument's settings and calibration for both the environment and the type of fiber to be spliced.
What are the primary causes of intrinsic loss in single-mode fiber?
Material absorption and Rayleigh scattering.
Chromatic dispersion is a combination of which two dispersions?
Material and waveguide dispersion.
The NESC (National Electrical Safety Code) provides guidelines concerning which portion of the fiber-optic cable network?
Minimum safety clearances between different conductors of overhead and underground electric supply and communications lines.
The process of combining digital services in the headend is called:
Multiplexing
What term describes the frequency spectrum into an amplifier having higher amplitude at low frequencies than the high frequencies?
Negative tilt.
What is a common solution when congestion from modem activity and traffic becomes unacceptable in a HFC network?
Node splitting, the subdividing of serving areas into two or more smaller serving areas.
What does the amplification process in an Avalanche photodiode introduce into the electrical output of an optical detector?
Noise
What are the factors that contribute to an optical receiver's sensitivity?
Noise, responsivity, response time, linear response, back reflection, and optical detector material.
What happens if the optical signal exceeds the maximum specified input power into a photodetector?
Nonlinear operation resulting in distortion, data errors, and signal loss.
What product based on the DOCSIS defines the protocols for IP telephony over HFG?
PacketCable
What is used to select which distribution amplifier secondary downstream output ports are active and whether they have equal or unequal output levels?
Plug-in modules or jumpers.
Which statement about pigtails used for optical fiber terminations is true?
Prior to splicing, pigtails should be labeled to correspond with the correct color code and patch panel designation.
In an optical network, what is reflectance?
Reflectance is the reflected light from a single Fresnel reflection event.
What is a consideration for the use of ribbon fiber?
Ribbon fiber requires different tools and equipment to perform splicing.
Which of the following is true about the SONET standard?
SONET is the North American standard used for telephony applications.
What is used in outside plant fiber-optic cable to protect and isolate the optical fibers from stress?
Strength members and buffer tubes.
What test instrument sends out a test signal and displays any reflections caused by impedance mismatches in the cable that are characteristic of cable faults?
TDR
In regard to providing HSD service,
The CMTS Cable modem termination system can provide a data transfer rate up to 38 Mbps, using 256-QAM in a single 6 MHz channel.
Since they provide the same functions, what is the primary difference between the fiber distribution hub (FDH) and fiber access terminal (FAT)?.
The FAT is typically easier to install and has lower fiber counts that the FDH.
Which standards organization is considered to be the creator of the world's most recognized communications standards, known as recommendations?
The ITU
What type of single-mode fiber is intended for FTTH installations?
The ITU-T G.657 BIF Bend-insensitive fiber.
What is safety concern when aerial fiber-optic cable is installed between poles, even though there are no high-voltage power lines?
The buildup of lethal amounts of static electricity on the fiber-optic cable that can discharge through a person on a ladder or some other conductor connected to ground.
When delivering high-speed Internet service, the cable modem tunes to the downstream carrier and communicates with which of the following?
The cable modem termination system (CMTS)
What Provides the cable network's interface to the internet?
The cable modem termination system(CMTS)
What value of interstage equalizer should be installed if the associated amplifier tombstone field is blank and the amplifier output slope is 7 dB?
The default factory value.
What should you be looking for when analyzing the network design maps to troubleshoot a problem?
The device common to those customers affected before traveling to make signal status checks.
The phenomenon, total internal reflection, is what enables an optical fiber to guide light. What characteristic of optical fiber causes total internal reflection?
The difference in refractive indexes, between cladding and core, causes light to be reflected off the cladding and back into the core along the optical fiber.
How can a distribution amplifier be identified in the network or on a network design map?
The distribution amplifier has multiple downstream outputs.
When configuring the upstream return in a distribution amplifier with multiple upstream ports, the amplitude levels for which port should be adjusted first?
The distribution amplifier upstream port with the most attenuation in its upstream path.
If tight-buffered distribution fiber-optic cable is installed between the master splice panel in an optical entrance enclosure (OEE) and a rack-mounted fiber-optic distribution panel, where in the facility must the distribution panel be located?
The distribution panel can be located anywhere in the facility since the distribution cable complies with indoor code requirements for riser or plenum installations.
What is a drawback of using Fabry-Perot (F-P) lasers in high-speed data networks?
The emission of a number of discrete wavelengths or side modes.
What are the two critical elements that align the optical fibers in a connection?
The ferrules and the mating adapter.
Which type of fusion splicer is ideal for fiber-to-the-x (FTTx) splicing?
The fixed V-groove splicer.
When opening a distribution amplifier station housing, why is it usually unnecessary to loosen the bolts at the bottom of the housing?
The housing lid is usually attached to the base of the housing with hinges.
When configuring the input stage of a distribution amplifier, what element values can vary from those in the amplifier tombstone, depending on the input amplitude measurements?
The input equalizer and attenuator pad values.
What is one advantage and one disadvantage of single-mode fiber with a large MFD (Mode field diameter)?
The larger the MFD, the easier it is to splice and connectorize the fiber, although it becomes more sensitive to bending losses.
What is a characteristic of light in a laser beam?
The laser beam consists of a limited range of wavelengths (monochromatic), with all light waves in phase (coherent light).
How can a less-experienced technician identify what non-standard symbols on the network design maps represent?
The legend at the bottom of the network design map that defines the map symbols, cable types, and amplifier data.
In a centralized server VOD architecture,
The number of servers needed for video content storage is smaller than in the distributed server architecture.
Why is the term "gain control" applied to amplifier gain and controls inaccurate?
The only way to vary the output of any amplifier is to adjust the amplitude level of the signal going into the amplifier.
In which component in a fiber-optics communication system do changes to the intensity of the optical signal occur?
The optical transmitter.
Which fusion splicer alignment method uses a camera to align the optical fibers before splicing?
The profile alignment system (PAS) method.
The quality and attenuation value of a mechanical splice of optical fibers is dependent on which tool during the preparation process?
The quality and attenuation value of the mechanical splice of optical fibers is dependent on the quality of the cleaving tool.
What is the RF distribution tap value indicated on the tap face plate by a sticker or number stamped into the housing?
The signal loss between the tap downstream input ports and tap ports
When working on a ladder, which rungs are forbidden for standing?
The top two rungs of any ladder.
What characteristics about upstream signals from cable modems and set-top boxes make them impractical for verifying and aligning a distribution amplifier return section?
They are of short duration and originate from various locations.
Which of the following is true about optical nodes?
They contain four main sections: the optical receiver, the RF amplifier module, the reverse optical transmitter, and the DC power supply.
How do technicians know the specific type of single-mode fiber used in a particular project?
They have read the project's specification records.
How does a distribution amplifier in a fiber node receive the downstream RF signals?
Through a coaxial cable that is connected to the downstream optical receiver.
Describe an application for a distribution amplifier in a Hybrid fiber/coax network?
To maintain downstream amplitude levels to the addresses farthest from the fiber-node.
What is the purpose of grounding to earth?
To protect against the adverse effects of lightning and assist in the reduction of static.
In a distribution amplifier, why is the frequency response at the input of the second output stage sloped?
To reduce intermodulation distortion levels caused by amplifying high amplitude input levels.
Why is there a diplex filter at each downstream output port in a distribution amplifier?
To separate the downstream RF from the upstream RF signals.
Why was the zero-dispersion point in single-mode fiber moved to 1,550 nm?
To take advantage of the low intrinsic absorption and lower attenuation at 1550nm in single-mode fiber.
What is the basic amplifier application that increases the amplitude of the radio frequency (RF) signal to compensate for the signal loss of cable and passive devices preceding the amplifier called?
Unity gain
Digital return path transmissions:
Use dense wavelength division multiplexing (DWDM) digital return transmitters in hub-to-headend architectures.
Many of the potential drawbacks from early coaxial tree-and-branch distribution can be overcome by
Utilizing an HFC or PON architecture
In the tree-and-branch architecture, how is the downstream signal from the trunk fed to the distribution branches?
Within each trunk amplifier, a portion of the downstream is fed to a bridger amplifier to boost the signal before being split and routed to the distribution branches.