Podcast
Questions and Answers
What does the Frame Check Sequence (FCS) in an Ethernet frame primarily provide?
What does the Frame Check Sequence (FCS) in an Ethernet frame primarily provide?
Which statement accurately describes the MAC layer's responsibilities in Ethernet?
Which statement accurately describes the MAC layer's responsibilities in Ethernet?
When dealing with Ethernet frames, what does a value of ≤ 1500 in the Type/Length field indicate?
When dealing with Ethernet frames, what does a value of ≤ 1500 in the Type/Length field indicate?
What is the minimum valid frame size for Ethernet as specified?
What is the minimum valid frame size for Ethernet as specified?
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In Ethernet, which addressing scheme is used to uniquely identify network interface cards (NICs)?
In Ethernet, which addressing scheme is used to uniquely identify network interface cards (NICs)?
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What purpose does the Preamble and Start Frame Delimiter (SFD) serve in an Ethernet frame?
What purpose does the Preamble and Start Frame Delimiter (SFD) serve in an Ethernet frame?
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What mechanism does half-duplex Ethernet use to avoid collisions?
What mechanism does half-duplex Ethernet use to avoid collisions?
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Which of the following is NOT a field in an Ethernet frame?
Which of the following is NOT a field in an Ethernet frame?
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Study Notes
Ethernet Encapsulation and OSI Layer 2 Operation
- Ethernet operates at both Layer 2 (Data Link) and Layer 1 (Physical) of the OSI model.
- It's defined by IEEE 802.2 (LLC) and IEEE 802.3 (MAC + physical).
Data Link Sublayers
- LLC (Logical Link Control): IEEE 802.2, communicates with upper-layer protocols (like IPv4, IPv6). Identifies the protocol enclosed in the frame.
- MAC (Media Access Control): IEEE 802.3, handles Ethernet framing, addressing (source/destination MAC addresses), and error detection (FCS). Provides media access methods (e.g., CSMA/CD for half-duplex).
MAC Sublayer Functions
- Data Encapsulation: Creates the Ethernet frame structure (header + trailer).
- MAC Addressing: Uses unique 48-bit source and destination addresses for each network interface card (NIC).
- Error Detection: Includes a Frame Check Sequence (FCS) to detect corrupted data using cyclic redundancy checks (CRC).
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Media Access Control:
- Half-Duplex: Uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to prevent collisions on shared media (e.g., legacy hubs).
- Full-Duplex: Modern switches typically operate full-duplex, not using CSMA/CD.
Ethernet Frame Fields
- Preamble & SFD (Start Frame Delimiter): 8 bytes for synchronization (not part of the frame size).
- Destination MAC Address: 6 bytes.
- Source MAC Address: 6 bytes.
- Type/Length: 2 bytes. Indicates the protocol type (≥ 1536, e.g., 0x0800 for IPv4) or the payload length (≤ 1500).
- Data (Payload): 46 to 1500 bytes.
- Frame Check Sequence (FCS): 4 bytes for error detection (CRC).
- Minimum Frame Size: 64 bytes (from destination MAC to FCS).
- Maximum Frame Size: 1518 bytes (from destination MAC to FCS).
- Smaller Frames: Frames below 64 bytes are "runt" frames and considered invalid.
- Larger Frames: Frames above 1518 bytes are "giant" frames (unless jumbo frames are supported).
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Description
This quiz explores the operation of Ethernet at Layer 2 of the OSI model, focusing on its encapsulation methods and the functions of the Data Link sublayers. Learn about the LLC and MAC layers, Ethernet framing, MAC addressing, and error detection mechanisms.
