NCTI Test Questions Review Flashcards

Bel Division: The bel was divided into 10 equal units called decibels (dB).
Comparing Amounts: A number representing an amount less than the whole compared to the whole is called a fraction.
Fraction to Percent Conversion: To convert a fraction to a percent, divide the numerator by the denominator and multiply by 100.
Ration Equivalent: A 1:5 ratio equals 20%.
Decibel Measurement: The base power ratio in decibels starts with the bel defined as a 10:1 power ratio.
1 dB Explanation: This is defined as one-tenth of a bel or the 10th root of the 1 bel ratio, indicating a small level change in power.
Coaxial Cable Attenuation: If a coaxial cable has 1 dB attenuation, the input-to-output power ratio is approximately $(1.2589:1)$ .
Voltage Ratio: An input-to-output power ratio of 10:1 corresponds to a voltage ratio of $(3.162:1)$ , calculated as the square root of the power ratio.
Power Ratio Calculation: The input-to-output power ratio for 2 bels is $(100:1)$ , and for 2 dB is $(1.585:1)$ .

CBR Telephony: Circuit-switching technology converts analog audio signals into digital DS0 circuits switched to customers or networks.
DOCSIS 1.1: The addition of Service Flow in its MAC protocol aimed to provide a mechanism for Quality of Service (QoS) for upstream and downstream flows.
PacketCable 1.0 Networks: Consist of three networks:
- DOCSIS Data Over Cable Service Interface Specification (HFC)
- Managed IP Network
- PSTN (Public Switched Telephone Network)
Effective Troubleshooting: Requires a technician to be diligent, detail-oriented, and skilled in using diagnostic tools.
Identifying Issues: Understanding how many customers are affected is crucial in diagnosing problems.
Cable Types: UTP (Unshielded Twisted Pair) is preferred in low interference areas, whereas coaxial cable’s shield dissipates EMI and RFI.
Function of Cladding: In fiber-optic cables, cladding refracts light within the fiber.

Media Access Control Layer: This layer differentiates between cable modems in the CMTS (Cable Modem Termination System).
Bandwidth Increase in DOCSIS 3.0: Technologies were adopted to allow upstream frequencies up to 85 MHz to meet demands.
Asymmetrical Throughput: Data throughput over the upstream path is typically less than over the downstream path due to narrower bandwidth and modulation used in the return path.
Channel Bonding: If two QAM channels with each 38 Mbps are bonded, the resulting downstream throughput will be 76 Mbps.
DOCSIS 3.1 Features: Introduced Orthogonal Frequency Division Multiplexing (OFDM) and Low-Density Parity-Check (LDPC) to enhance network performance.
IP Multicast vs Broadcast: Multicast sends data to specific modem addresses, while broadcast sends to all modems.

Initial Problem Identification: A discussion with customers to gather details is essential at the start of troubleshooting.
Use of Digital Signal Analyzer: A minimum MER (Modulation Error Ratio) of $(32 dB)$ is required into the cable modem for a 256-QAM carrier.
OSI Layers in Cable Networks: Layers 1 to 4 (Physical to Transport) are involved specifically between DOCSIS modems and CMTS.

Signal Leakage Limits: The FCC has set specific requirements for signal leakage measurement, including limits for leakage at certain frequencies and distances.
Leakage Detector Calibration: Calibration can be validated using a leakage carrier, SLM, and a variable attenuator.
GPS-assisted Instruments: These tools capture exact leakage locations down to street addresses for effective repairs.
RF Continuity Checks: Instruments like signal generators are used to ensure continuity in drop systems across specified frequency spectrums.
Electrical Interference Reporting: Must notify relevant authorities as soon as an electrical interference source is identified.