CompTIA Network+ Network+ OSI Model and Data Encapsulation 3 — Questions and Answers
Question 1: Which OSI layer is responsible for flow control and error recovery using mechanisms like windowing and acknowledgments?
- Network layer
- Data Link layer
- Session layer
- Transport layer (Correct answer)
Correct answer: Transport layer
The Transport layer (Layer 4) provides flow control through windowing and ensures reliable delivery via acknowledgments and retransmission.
Question 2: A frame is received with a bad FCS value. At which OSI layer is this error detected?
- Physical layer
- Network layer
- Data Link layer (Correct answer)
- Transport layer
Correct answer: Data Link layer
The Frame Check Sequence (FCS) is a Data Link layer field used to detect transmission errors in received frames.
Question 3: Which of the following best describes the role of the Physical layer in the OSI model?
- Routes packets between networks
- Converts data to electrical, optical, or radio signals (Correct answer)
- Assigns logical IP addresses
- Establishes end-to-end sessions
Correct answer: Converts data to electrical, optical, or radio signals
The Physical layer (Layer 1) defines the transmission of raw bits over a physical medium as electrical, optical, or wireless signals.
Question 4: An application developer needs to ensure data is formatted consistently for exchange between different systems. Which OSI layer addresses this concern?
- Application layer
- Transport layer
- Session layer
- Presentation layer (Correct answer)
Correct answer: Presentation layer
The Presentation layer (Layer 6) handles data syntax and semantics, ensuring data is in a common format regardless of the source system.
Question 5: What does a switch primarily use to make forwarding decisions at OSI Layer 2?
- IP addresses
- Port numbers
- MAC addresses (Correct answer)
- VLAN IDs only
Correct answer: MAC addresses
Switches operate at the Data Link layer and use MAC address tables to forward frames to the correct port.
Question 6: Which protocol data unit (PDU) is associated with the Data Link layer?
- Segment
- Packet
- Frame (Correct answer)
- Bit
Correct answer: Frame
The Data Link layer encapsulates packets into frames, adding source and destination MAC addresses along with error-checking fields.
Question 7: A router receives a packet destined for a remote network. At which OSI layer does the router make its forwarding decision?
- Layer 1
- Layer 2
- Layer 3 (Correct answer)
- Layer 4
Correct answer: Layer 3
Routers operate at Layer 3 (Network layer), using IP addresses and routing tables to determine the best path for packet forwarding.
CompTIA Network+ Network+ OSI Model and Data Encapsulation 3
Which OSI layer is responsible for flow control and error recovery using mechanisms like windowing and acknowledgments?