SCTE DOCSIS Engineering Professional (DEP)
Certification Exam | High-Yield Practice
Questions & Detailed Rationales (2026/2027)
QUESTION 1
In a DOCSIS 3.1 downstream OFDM channel, what are the two
standardized subcarrier spacing options available for system
configuration?
A. 25 kHz and 50 kHz
B. 10 kHz and 100 kHz
C. 1.25 MHz and 6 MHz
D. 50 kHz and 200 kHz
Correct Answer: A. 25 kHz and 50 kHz
,Detailed Rationale: DOCSIS 3.1 specifies OFDM subcarrier spacing of
either 25 kHz (yielding a maximum of 4000 active subcarriers in a 192
MHz block) or 50 kHz (yielding 2000 active subcarriers), chosen based
on network phase noise and Doppler shift characteristics.
QUESTION 2
What is the primary purpose of the cyclic prefix in DOCSIS 3.1 OFDM
downstream transmissions?
A. To guard against inter-symbol interference (ISI) caused by micro-
reflections and multi-path echoes in the coaxial cable plant.
B. To encrypt subscriber data packets using AES-128.
C. To provide forward error correction parity bytes for upstream ranging
bursts.
D. To carry MAC management overhead messages like the MAP.
Correct Answer: A. To guard against inter-symbol interference (ISI)
caused by micro-reflections and multi-path echoes in the coaxial cable
plant.
,Detailed Rationale: The cyclic prefix prepends a copy of the end of an
OFDM symbol to the beginning, absorbing delay spread and micro-
reflections so they do not corrupt adjacent symbols.
QUESTION 3
What is the upper frequency boundary for traditional DOCSIS 3.1
downstream channel operation compared to expanded frequency
architectures?
A. DOCSIS 3.1 downstream typically operates up to 1002 MHz or 1218
MHz (extendable in DOCSIS 4.0 up to 1.8 GHz or higher).
B. DOCSIS 3.1 is strictly limited to a maximum frequency of 550 MHz.
C. DOCSIS 3.1 operates exclusively in the 2.4 GHz and 5 GHz Wi-Fi
bands.
D. DOCSIS 3.1 downstream cannot exceed the 42 MHz return path
boundary.
Correct Answer: A. DOCSIS 3.1 downstream typically operates up to
1002 MHz or 1218 MHz (extendable in DOCSIS 4.0 up to 1.8 GHz or
higher).
, Detailed Rationale: While DOCSIS 3.1 was originally deployed within
traditional 1.0/1.2 GHz spectrum limits, its OFDM physical layer is
designed to scale across higher frequencies implemented in modern
plant upgrades.
QUESTION 4
How does OFDMA improve upstream transmission performance in
DOCSIS 3.1 and DOCSIS 4.0 networks compared to traditional single-
carrier QAM (SC-QAM)?
A. By utilizing orthogonal subcarriers that allow dynamic frequency
assignment, resource block allocation, and avoidance of narrow-band
ingress.
B. By transmitting all upstream data over a single fixed 6 MHz analog
carrier.
C. By doubling the commercial AC power voltage on the coaxial shield.
D. By eliminating the need for any cable modem ranging processes.
Certification Exam | High-Yield Practice
Questions & Detailed Rationales (2026/2027)
QUESTION 1
In a DOCSIS 3.1 downstream OFDM channel, what are the two
standardized subcarrier spacing options available for system
configuration?
A. 25 kHz and 50 kHz
B. 10 kHz and 100 kHz
C. 1.25 MHz and 6 MHz
D. 50 kHz and 200 kHz
Correct Answer: A. 25 kHz and 50 kHz
,Detailed Rationale: DOCSIS 3.1 specifies OFDM subcarrier spacing of
either 25 kHz (yielding a maximum of 4000 active subcarriers in a 192
MHz block) or 50 kHz (yielding 2000 active subcarriers), chosen based
on network phase noise and Doppler shift characteristics.
QUESTION 2
What is the primary purpose of the cyclic prefix in DOCSIS 3.1 OFDM
downstream transmissions?
A. To guard against inter-symbol interference (ISI) caused by micro-
reflections and multi-path echoes in the coaxial cable plant.
B. To encrypt subscriber data packets using AES-128.
C. To provide forward error correction parity bytes for upstream ranging
bursts.
D. To carry MAC management overhead messages like the MAP.
Correct Answer: A. To guard against inter-symbol interference (ISI)
caused by micro-reflections and multi-path echoes in the coaxial cable
plant.
,Detailed Rationale: The cyclic prefix prepends a copy of the end of an
OFDM symbol to the beginning, absorbing delay spread and micro-
reflections so they do not corrupt adjacent symbols.
QUESTION 3
What is the upper frequency boundary for traditional DOCSIS 3.1
downstream channel operation compared to expanded frequency
architectures?
A. DOCSIS 3.1 downstream typically operates up to 1002 MHz or 1218
MHz (extendable in DOCSIS 4.0 up to 1.8 GHz or higher).
B. DOCSIS 3.1 is strictly limited to a maximum frequency of 550 MHz.
C. DOCSIS 3.1 operates exclusively in the 2.4 GHz and 5 GHz Wi-Fi
bands.
D. DOCSIS 3.1 downstream cannot exceed the 42 MHz return path
boundary.
Correct Answer: A. DOCSIS 3.1 downstream typically operates up to
1002 MHz or 1218 MHz (extendable in DOCSIS 4.0 up to 1.8 GHz or
higher).
, Detailed Rationale: While DOCSIS 3.1 was originally deployed within
traditional 1.0/1.2 GHz spectrum limits, its OFDM physical layer is
designed to scale across higher frequencies implemented in modern
plant upgrades.
QUESTION 4
How does OFDMA improve upstream transmission performance in
DOCSIS 3.1 and DOCSIS 4.0 networks compared to traditional single-
carrier QAM (SC-QAM)?
A. By utilizing orthogonal subcarriers that allow dynamic frequency
assignment, resource block allocation, and avoidance of narrow-band
ingress.
B. By transmitting all upstream data over a single fixed 6 MHz analog
carrier.
C. By doubling the commercial AC power voltage on the coaxial shield.
D. By eliminating the need for any cable modem ranging processes.
