WGU D413 OA Hard Hitters questions and answers with 100% accuracy (2026-2027 latest update)

What is OFDM?

Orthogonal Frequency-Division Multiplexing

What is TDM?

Time-Division Multiplexing

What is WDM?

Wavelength Division Multiplexing

What is DWDM?

Dense Wavelength Division Multiplexing

What is FDM?

Frequency Division Multiplexing

What is ATDM?

Asynchronous Time Division Multiplexing

What is STDM?

Statistical Time Division Multiplexing

What is CDM?

Code Division Multiplexing

What type of multiplexing is OFDM?

Digital

What type of multiplexing is TDM?

Digital

What type of multiplexing is WDM?

Optical

What type of multiplexing is DWDM?

Optical

What type of multiplexing is FDM?

Analog/Digital

What type of multiplexing is ATDM?

Digital

What type of multiplexing is STDM?

Digital

What type of multiplexing is CDM?

Digital

What makes OFDM unique?

Orthogonal Subchannels

What makes TDM unique?

Time Slots

What makes WDM unique?

Different Wavelengths of Light

What makes DWDM unique?

Dense Set of Wavelengths

What makes FDM unique?

Frequency Bands (Analog)

What makes ATDM unique?

Variable Time Intervals

What makes STDM unique?

Fixed and Synchronized Time Intervals

What makes CDM unique?

Unique Codes for Each Channel

Baseband Transmission

Uses the entire bandwidth of the medium to carry a single data signal, common in Ethernet networks.

Broadband Transmission

Carries multiple signals simultaneously by dividing the bandwidth into channels, Example: Cable TV.

CSMA/CD

Used in wired Ethernet (IEEE 802.3) to detect collisions after they occur and retransmit data

CSMA/CA

sed in wireless networks (IEEE 802.11) to avoid collisions before they happen using mechanisms like RTS/CTS

RTS/CTS

Hardware flow control signals in serial communications (RS-232) that prevent data loss by managing transmission between devices, Request to Send/Clear to Send

802.11

Max Speed: 2Mb/s

Frequency: 2.4 GHz

802.11a

Max Speed: 54 Mb/s

Frequency: 5GHz

802.11b

Max Speed: 11 Mb/s

Frequency: 2.4 GHz

802.11g

Max Speed: 54 Mb/s

Frequency: 2.4 GHz

802.11n

Max Speed: 600 Mb/s

Frequency: 2.4 GHz and 5 GHz

802.11ac

Max Speed: 1.3 Gb/s

Frequency: 5 GHz

802.11ad

Max Speed: 7 Gb/s

Frequency: 2.4 GHz, 5 GHz and 60 GHz

802.11ax

Max Speed: 9.6 Gb/s

Frequency: 2.4 GHz and 5 GHz

Parity

A single bit added to a binary string to ensure the total number of 1s is even or odd

For single-bit errors, no correction

Checksum

Calculating a sum (or hash) of data blocks, detects multiple-bit errors, no correction

CRC

Highly reliable for detecting burst errors (multiple consecutive corrupted bits), single-bit errors, and odd numbers of errors, no correction

Layer 7 Application

interaction point between the end-user application (like a web browser or email client) and the network

Layer 6 Presentation

Formats, translates, encrypts, and compresses data to ensure it is readable by the receiving application.

Layer 5 Session

Establishes, manages, maintains, and terminates connections (sessions) between local and remote applications.

Layer 4 Transport

Responsible for end-to-end communication, flow control, segmentation, and error correction

Layer 3 Network

Manages packet forwarding, routing, and logical addressing (IP addresses) to send data across different networks.

Layer 2 Data Link

Provides node-to-node data transfer, framing packets into bits and handling physical addressing (MAC addresses) to move data between devices on the same network.

Layer 1 Physical

Deals with the physical, raw transmission of unstructured data bits (s and s) over a physical medium (cables, radio waves, electrical signals).

CSU (Channel Service Unit)

terminates the digital circuit at the customer premises, provides framing, and ensures compatibility with the telephone company network

DSU (Data Service Unit

manages the timing, buffers data, and translates digital signals between the LAN and WAN formats

CSU/DSU (Channel Service Unit/Data Service Unit)

bridges (LANs) and (WANs), acting as a digital modem to connect routers to dedicated digital circuits like T1 or T3 lines, fully digital

ISDN (Integrated Services Digital Network) BRI/PRI

legacy digital telephony standards enabling voice and data transmission over traditional phone lines

ADSL (Asymmetric Digital Subscriber Line)

residential use, providing much faster download speeds than upload speeds, ideal for streaming and browsing.

VDSL (Very-high-bit-rate Digital Subscriber Line

extremely high speeds (up to 100+ Mbps) over short distances (typically under 1,200 meters)

SDSL (Symmetric Digital Subscriber Line)

equal download and upload speeds, generally preferred by businesses for services like video conferencing and VOIP

HDSL (High-bit-rate Digital Subscriber Line)

symmetric, high-speed connection that often requires multiple twisted-pair copper wires, ideal for corporate applications

SHDSL (Single-pair High-speed Digital Subscriber Line)

standardized version of symmetric DSL that allows for superior data rates over a single pair of copper wires, often used in business environments

RADSL (Rate-Adaptive Digital Subscriber Line)

A variant of ADSL that adjusts the connection speed based on the quality and length of the copper line

DOCSIS (Data Over Cable Service Interface Specification)

international standard for transferring high-speed data over existing coaxial cable TV networks, 10 Gbps downstream and 6 Gbps upstream

SONET (Synchronous Optical Networking)

standardized protocol for transmitting large volumes of digital data over fiber optic networks at high speeds (up to 40 Gbps+) using synchronized frames

T1/T3

dedicated digital transmission lines used for telecommunications

T1

1.544 Mbps, used for smaller business internet or voice connectivity

T3

44.736 Mbps, used by ISPs or large enterprises requiring high bandwidth

Cat 1

1 Mbs, 0.4MHz, Telephone and modem lines

Cat 2

4Mbps, 4MHz, LocalTalk & Telephone

Cat 3

10Mbps, 16MHz, 100 m(328 ft), 10BaseT Ethernet

Cat 4

16Mbps, 20MHz, 100 m (328 ft), Token Ring

Cat 5

100 Mbps, 100MHz, 100 m (328 ft), 100BaseT Ethernet

Cat 5e

1Gbps, 100MHz, 100 m (328 ft), 100BaseT Ethernet, Residential homes

Cat 6

1Gbps, 100MHz, 100 m (328 ft), 100BaseT Ethernet, Residential homes

Cat 6a

10Gbps, 500MHz, 100 m (328ft), Gigabit Ethernet in data centers and commercial buildings

Cat 7

10Gbps, 600MHz, 100 m (328 ft), 10Gbps Core Infrastructure

Cat 7a

10Gbps, 1000MHz, 100 M (328 ft) or 40Gbos at 50 m (164 ft), 10Gbps core infrastructure

Cat 8

25Gbps (cat 8.1), 40Gbps (cat 8.2), 200MHz, 30m (98 ft), 25Gbps/ 40Gbps core infrastructure

RG-6

coax, standard for high-bandwidth, high-frequency applications like satellite TV, cable internet, and digital HDTV, 75ohm impedance, 100ft

RG-58

coax, thin, temporary, mobile, or low-power setups, connecting CB/ham radios, antennas, and test equipment, 50ohm impedance, 50-100ft, high loss

RG-8

coax, thick, permanent, low-loss, 50-ohm cable suited for high-power or long-run base station antennas

MMF (1Gbps)

~550m to 1 km, further at lower speeds

MMF (10Gbps)

300m to 550m

MMF (40/100 Gbps)

100m to 150m

SMF (1Gbps)

10 km to 100+ km

SMF (10/40/100 Gbps)

10 km to 40+ km