NTCI: Troubleshooting Advanced Services
Regarding digital video quality at the customer premises,
(QOS) metrics are important to help identify potential problems before they can affect a customer's more subjective (QOE).
When troubleshooting a continuous dial tone problem, what is necessary to do?
Identify where the polarity of the telephone wiring is reversed.
How is silver satin cable used to connect telephone equipment to wall outlets typically pinned?
Reversed at opposite ends, or cross-pinned.
Interframe coding, a form of temporal compression, uses...
An intra-coded frame to compare picture information between consecutive frames, using motion vectors, which results in predicted frames (P-frames).
What information about the digital carrier can be learned by accessing the adaptive equalizer function of the digital signal analyzer?
How much the adaptive equalizer has to compensate for linear distortions of the digital carrier.
How does IP multicast differ from IP broadcast?
IP multicast traffic is only sent to specific modem addresses on the network, IP broadcast traffic is sent to all modems on the network.
A loud click can be heard if the circuit is closed when troubleshooting which side of a fault?
The battery side of the fault.
If a digital video service customer reports that the set-top box does not respond to the remote control, what is the quickest and easiest thing to do first?
Check the line of sight between the remote control and the set-top box.
A customer reports a problem of no dial tone (NDT), Upon inspection, the technician notices that new carpeting has been installed. What should the technician do next?
Look for a cable that runs under the carpet; it is likely that the cable has a short from the carpeting tack strip.
What are two features that were added in DOCSIS 3.1 to extend the viability of hybrid fiber/coax (HFC) networks into the next decade?
Orthogonal frequency division multiplexing (OFDM) and low-density parity-check (LDPC).
Which type of signal impairment cause the constellation symbol points to spread out toward the grid lines?
Random noise.
Rate shaping, a possible point of failure for digital video in the headend, describes...
The process of managing the data rates of multiplexed individual channels on a quadrature amplitude modulation (QUM) carrier.
When using a digital signal analyzer to troubleshoot data throughput in the DOCSIS network, what is the minimum modulation error ratio (MER) into the cable modem for a 256-QAM carrier?
32 dB or greater.
Modulation error ratio (MER) is an indicator of digital modulation signal quality. For error-free reception and adequate margin, what should be the minimum MER reading fro a 256-quam signal?
32 dB.
When you use a digital analyzer to examine a digital signal, one of the values you should check is the symbol rate. What should the symbol rate setting for a 256-QAM signal specified by the (ITU) in ITU-T J.83 Annex B?
5.360537 megasymbols per second (MS/s)
What would be the downstream throughput if two 256-QAM channels with a throughput of 38 megabits per second (Mbps) were bonded?
76 Mbps.
To eliminate possible causes of audio issues, a technician can...
Check the set-top box and the television set to ensure audio connections have been made correctly.
In a DOCSIS network, why is the data throughput over the return or upstream path typically less than the throughput of data over the forward or downstream path?
Compared to the downstream path, the narrower bandwidths and lower orders of modulation used to transport data over the return path cause the downstream and upstream data throughput to be unequal or asymmetrical.
Chrominance subsampling, which usually takes place in the studio environment, is the process of...
Compressing a raw digital video file so that each pixel retians its own luminance information, but the chrominance is averaged from the original pixel pairs to a 4:2:2 profile
Coherent interference causes the constellation display to look like a series of small donuts. What is one cause of coherent interference?
In-channel ingress.
Tiling, missing audio, and picture are examples of artifacts that...
Are likely under control of the technician in the hybrid fiber/coax (HFC) network or at the customer premises.
In troubleshooting a digital-to-analog converter, try the suspect converter in a different, working outlet to...
Determine if the original outlet needs to be repaired.
What was done in DOCSIS 3.0 to allow enough bandwidth for upstream carriers from previous DOCSIS versions?
The option to increase the top frequency of the upstream to 85 MHz.
Which step in the troubleshooting process requires a discussion with the customer to gather more detail about the problem?
Step 1: Identify the problem.
The digital artifacts referred to as blockiness, blurring, mosquito noise, and contour represent...
Video capture and processing artifacts that cannot be addressed at the customer premises.
How are 8-position, 8-connect (8P8C) modular connectors pinned to (UTP) cable, which is used for connecting computers and broadband modems to a local area network (LAN)?
Identical at opposite ends, or straight-through.
What will any short in the premises wiring or connected CPE do to telephone or HSD service in the premises network.
It will disable both services.
Bit error ratio (BER) is one of the measurements a technician used to determine how well the network is operating. What is the acceptable post-BER at the end of the drop?
<1.0E-9.
In walking through the flowchart for the six-step process of troubleshooting a report of tiling by a single customer, one of the first questions asked should be...
Are there similar complaints from other customers?
What internet protocol (IP) address modes can a DOCSIS 3.0 and 3.1 modem be provisioned in?
IP version 4 (IPv4), IP version 6 (IPv6), alternate provisioning mode (APM), and dual-stack provisioning mode (DPM).
The poor quality of analog programming displayed on a digital TV set, a common complaint of customers, can be caused by...
Image rescaling that standard definition TV (SDTV) analog programs require to be displayed in a 1080p resolution display.
When a communications issue is suspected in an HDMI device, the technician should...
Try an alternate HDMI port on the device, if one is available.
How should the digital multimeter (DMM) be used to troubleshoot problems in the telephone wiring?
Use the voltmeter function; both the NID and the EMTA provide a steady on-hook voltage.
In addition to being accurate and detailed, a successful troubleshooter knows that...
A critical step in troubleshooting is verifying the signal levels and signal quality at the tap to establish the baseline performance for the installation.
Describe the difference between a "short" and a "cross" in unshielded twisted-pair (UTP) cable.
A short is an undesired electrical connection between the paired wires. A cross is the term for when the connection is complete to the proper terminals, but either wire of one pair shorts to either wire of another pair.
Although off-network programming is not the responsibility of a cable operator.
A technician needs to understand that customers viewing video through the internet may report problems with a video program that has not been scrutinized by the cable operator.
Which of the following scenarios describes the hybrid wiring topology?
A three-bedroom house: The master bedroom telephone jack is connected directly to an EMTA, and bedrooms two and three are fed from the master bedroom telephone jack.
What is the term for the error caused when one end of an unshielded twisted-pair (UTP) cable is terminated in the T568A configuration and the other end in the T568B configuration
A transposition.
Perceptual quality metrics (PQM) provide cable operators with...
An objective measurement of human visual perception based on a statistical analysis of quality of service (QOS) measurements and MPEG encoding data.
What is the likely problem when there is dial tone on one phone connected to an outlet, but not on two other phones connected to two different outlets?
An open circuit caused by a break in a conductor, poor contact in a modular connector, or an incorrect wire connection.
A logical progression of events for resolving a customer's report of digital video artifacts on various channels could include...
Analyzing the problem further to get a more narrow definition of the issue before trying to diagnose the symptoms of the problem.
The telephone wiring is in the bus topology and the twisted-pair cable tester is connected at the EMTA, with the remote unit connected to the last outlet in the loop. If the tester indicates a wiring error, what is the quickest way to locate the incorrectly wired outlet?
Break the loop into smaller sections and retest the two sections to identify which one has the wiring error. Continue to divide the section with the error into smaller sections until the wiring error is identified.
What must be done before using a twisted-pair cable tester to diagnose unshielded twist-pair (UTP) cable wired in the star topology inside the customer premises?
Disconnect all customer premises equipment (CPE) from all the jacks in the customer premises.
Why does it take a few minutes for a cable modem analyzer to become functional once connected to the network?
Every time the cable modem analyzer function is enabled, the instrument performs a self-provisioning of the instrument's internal modem which enables communication with the cable modem termination system (CMTS).
When can the T568A wiring configuration, recommended in ANSI/TIA/EIA 570-B, be used for installing (8P8C) modular plugs and jacks for residential telephone service?
For telephone only installations that do not include data connections.
When equipment is connected via the component video output...
Format settings for vertical resolution, scan method, and aspect ratio may need to be adjusted manually.
One of the first things a technician needs to address in troubleshooting issues with digital video quality is...
Identify the problem by asking the customer to describe the problem and whether or not it is intermittent or constant.
Some of the common causes of digital video impairments in a distribution network include...
Incorrect signal levels, common path distortion caused by corroded connections and impedance mismatches due to unterminated taps.
What information is provided from a Ping command?
Ping is used to measure the round-trip time for a ping packet to travel over the network form the cable modem to the (CMTS), or other server, and back.
Quality of service (QOS), as measured by availability, describes the...
Ratio of time that a system or service is available for use to total time.
Digital set-top box diagnostics can aid a technician with which of the following parameters while troubleshooting?
Service authorization, received signal quality, and return path operation.
What should be checked as a possible cause of hum on a customer's telephone line?
Shielding problems in the station wiring, poor terminations, or poor grounding and bonding.
In the telephone test set, placing the T/M switch in the TALK position establishes an off-hook condition for dialing and talking. What is an off-hook condition of a telephone?
The active, in use state of a telephone.
What are some Advantages of using a twister-pair cable tester to troubleshoot telephone station wiring and UTP cable in the customer premises>
The twisted-pair cable tester is designed specifically to test and diagnose twisted-pair cable and its connections, as well as measuring data throughput while being fairly inexpensive and easy to use.
The digital video artifacts of loss of lip sync and smearing are associated with...
The type of artifacts generally found at the customer premises due to timing delay and frame rate, respectively.
When a viewer receives a "channel not available, try again later" message, the probable cause is...
There is insufficient bandwidth from the headend to the hub to accommodate the data stream for the requested channel.
Many cable operators have a drop certification program and require measurements using a digital signal analyzer with minimum and maximum criteria programmed into the instrument. Why should the technician recognize and understand which channels are being measured when automated measurements are being performed by the digital signal analyzer?
To save measurement time, some cable operators perform automated measurements on a sample of channels which can result in problems going undetected in unmeasured channels.
In intraframe coding, data for redundant pixel arrays are...
Transmitted once with data that tells the decoder where, on the single frame, the array is displayed.
Which of the following are among the reasons why a customer may not be able to order video-on-demand?
VOD or pay-per-view credit limits might have been reached, indicating that purchases have not been collected due to a return path problem.
After resolving the problem with the premises wiring issue, which of the following is the next step in the six-step process that the technician should take?
Verify that the problem has been resolved and that phone service is running perfectly on all phones.
One of the last things a technician does when following a process for troubleshooting and resolving problems with digital video quality is...
Verify the problem is resolved by taking measurements to confirm the resolution and ensuring the resolution did not introduce new problems.
What could cause some dual tone multifrequency (DTMF) touch-tone telephones in the customer premises to have continuous dial tone caused by polarity reversal, but not other telephones?
The telephone wiring polarity is incorrect, and the customer has a mix of older and newer DTMF touch-tone telephones.
What is a limitation of using the shorted modular plug for testing the wiring of a modular connector?
A wiring error such as a transposition can go unidentified because each pair is terminating into the same value of resistance, which is a short.
Which Data Over Cable Service Interface Specification (DOCSIS) layer is used by the CMTS to differentiate between cable modems?
The DOCSIS Media Access Control (MAC) layer.
To resolve where the source of a digital video problem lies, a technician uses...
The divide-and-conquer method for troubleshooting, which can begin with measurements on customer premise equipment that offer easier access for testing
What is the difference between the wiring configurations for a residential, 8-position, 8-contact (8P8C) modular plug and jack in the Universal Service Order Codes (USOC) and ANSI/TIA/EIA 570-B?
The placement of pair numbers 3 and 4.
When analyzing a problem, what can the technician learn by asking the customer to show or demonstrate the problem?
The symptoms of the problem can be viewed and any unusual screens or customer entries can be identified.
If a digital video service customer calls with an issue related to not being able to delete a recorded program, it could be caused by...
the program is being played on a second set-top-box on a whole house or multi-room digital video recording (DVR) configuration.
You have a cable modem analyzer and you want to replace the cable modem to determine whether the modem is bad. How should the modem analyzer be connected to replace the modem?
An Ethernet cable is connected from the cable modem analyzer to the customer's computer, and the RF drop input cable is connected to the cable modem analyzer.
To determine if objective network data measured by quality of service (QOS) parameters match a customer's overall satisfaction level...
Cable operators use a quality of experience (QOE) measurement based on mean opinion score (MOS) and perceptual quality metrics (PQM).
When troubleshooting telephone service in the customer premises, what is the next step if there is no dial-tone voltage at the telephone outlet?
Check for voltage at the embedded multimedia terminal adapter (EMTA); if no voltage is present, the problem is either the network signal entering the EMTA or the EMTA is bad.
If a customer reports that a program's audio plays but there is no video display, the recommended actions are...
Check if any cables are disconnected, make sure the TV set is properly configured, and check to see if the TV in on (if audio runs through a different system such as surround sound).
