Ethernet Layer 1/Layer 2 Quiz

Ethernet (Layer 1/Layer 2)

• Ethernet is a common local area network (LAN) technology for wired communication.
• It's standardized by the Institute of Electrical and Electronics Engineers (IEEE) under the 802.3 protocol.
• Ethernet typically uses twisted-pair cables (like Cat5e, Cat6) or fiber optic cables for data transmission.
• Data is transmitted in packets with headers containing source and destination MAC addresses.
• Speeds have increased from 10 Mbps to 100 Gbps (e.g., 100 Mbps, 1 Gbps, 10 Gbps).
• Ethernet supports various network topologies (e.g., star, bus, ring).
• Early Ethernet used CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to manage transmissions, but modern Ethernet largely eliminates collisions with switches.
• Switches direct data packets to specific devices, improving efficiency.
• Ethernet is compatible with diverse network protocols.
• Ethernet is used in home, corporate, data center, and industrial networks due to its reliability and scalability.

OSI Model

• The OSI (Open Systems Interconnection) model is a conceptual framework for understanding network communication.
• It structures communications into seven layers with specific functions.
• The Physical Layer (Layer 1) is responsible for transmitting raw binary data over a physical medium (e.g., cables, radio frequencies).
• The Data Link Layer (Layer 2) handles node-to-node data transfer and error correction.
• The Network Layer (Layer 3) manages routing data packets between different networks.
• The Transport Layer (Layer 4) ensures reliable data transfer with error checking and flow control.
• The Session Layer (Layer 5) manages and controls connections between two computers.
• The Presentation Layer (Layer 6) handles data encryption, compression, and conversion.
• The Application Layer (Layer 7) provides end-user services and interfaces with application software.

Ethernet Frame

• Ethernet frames have a standardized structure for organizing and transmitting data over Ethernet networks.
• The frame consists of preamble, start frame delimiter, destination MAC address, source MAC address, EtherType/Length, payload/data, and FCS (Frame Check Sequence).
• Preamble (7 bytes): Alternating 1s and 0s for synchronization.
• Start Frame Delimiter (SFD): Marks the start of the frame.
• MAC addresses (6 bytes each): Unique identifiers for sending and receiving devices.
• EtherType/Length (2 bytes): Specifies the protocol type or the length of the payload.
• Payload/Data (46-1500 bytes): Contains the actual data being transmitted.
• FCS (4 bytes): Error-checking mechanism using Cyclic Redundancy Check (CRC).

Error Detection

• Cyclic Redundancy Check (CRC) is a vital method for error detection in digital communications.
• CRC involves treating data as a large binary number and dividing it by a fixed binary "divisor" (generator polynomial).
• The remainder (CRC code) is appended to the original data to form a transmitted frame.
• On the receiving end, the received data is divided by the same generator polynomial. If the result is zero, the data is deemed error-free.
• Error detection techniques use polynomial division on transmitted data to ensure reliability.

Ethernet Encoding

• Encoding techniques convert binary data into electrical signals that can be transmitted over a physical medium.
• 10BASE-T uses Manchester encoding with two voltage levels to represent data bits.
• 100BASE-TX uses 4B/5B encoding and MLT-3 signaling for slightly higher speed.
• 1000BASE-T (Gigabit Ethernet) uses PAM-5 (Pulse Amplitude Modulation with 5 levels) to increase speed while maintaining the medium.
• 10GBASE-T (10 Gigabit Ethernet) uses PAM-16 and advanced signal processing to achieve higher transmission rates.