Ethernet Technologies

Key Concepts

• Ethernet Frame Structure
• Ethernet Switching
• Ethernet Standards and Speeds

Ethernet Frame Structure

The Ethernet frame is the basic unit of data transmission in Ethernet networks. It consists of several fields that ensure reliable and efficient data transfer. The key fields include:

• Preamble: A 7-byte field that synchronizes the receiver's clock with the sender's.
• Start Frame Delimiter (SFD): A 1-byte field that indicates the start of the frame.
• Destination and Source MAC Addresses: 6-byte fields that identify the recipient and sender of the frame.
• EtherType: A 2-byte field that specifies the protocol of the payload (e.g., IPv4, IPv6).
• Payload: The actual data being transmitted, ranging from 46 to 1500 bytes.
• Frame Check Sequence (FCS): A 4-byte field that contains a cyclic redundancy check (CRC) value used to detect errors in the frame.

Example: Think of an Ethernet frame as an envelope containing a letter. The preamble and SFD are like the envelope's flap, ensuring it's properly sealed. The MAC addresses are the sender's and recipient's names on the envelope. The EtherType is the type of letter (e.g., business, personal), and the payload is the letter's content. The FCS is like a checksum to ensure the letter hasn't been tampered with.

Ethernet Switching

Ethernet switching is the process of forwarding Ethernet frames between network devices. Switches use MAC addresses to determine the appropriate destination port for each frame. Key concepts in Ethernet switching include:

• MAC Address Table: A table maintained by the switch that maps MAC addresses to switch ports.
• Learning: The process by which a switch learns the MAC addresses of devices connected to its ports.
• Forwarding: The process of sending a frame out the appropriate port based on the MAC address table.
• Flooding: The process of sending a frame out all ports except the incoming port if the destination MAC address is unknown.
• Aging: The process of removing entries from the MAC address table after a certain period of inactivity.

Example: Consider a mailroom (switch) in an office building. The mailroom staff (switch) keeps a log (MAC address table) of which employee (device) is located in which office (port). When a letter (frame) arrives, the staff checks the log to determine the correct office (forwarding). If the recipient is unknown, the staff distributes the letter to all offices (flooding). The log entries are periodically updated to reflect changes (aging).

Ethernet Standards and Speeds

Ethernet standards define the specifications for Ethernet networks, including cable types, connector types, and data transfer speeds. Key Ethernet standards and speeds include:

• 10BASE-T: 10 Mbps over twisted-pair copper cables.
• 100BASE-TX: 100 Mbps over twisted-pair copper cables (Fast Ethernet).
• 1000BASE-T: 1 Gbps over twisted-pair copper cables (Gigabit Ethernet).
• 10GBASE-T: 10 Gbps over twisted-pair copper cables (10 Gigabit Ethernet).
• 100GBASE-T: 100 Gbps over twisted-pair copper cables (100 Gigabit Ethernet).

Example: Think of Ethernet standards as different types of roads. 10BASE-T is like a local street (10 Mbps), 100BASE-TX is like a highway (100 Mbps), 1000BASE-T is like an expressway (1 Gbps), 10GBASE-T is like a superhighway (10 Gbps), and 100GBASE-T is like a hyperloop (100 Gbps). Each road type (standard) supports different speeds (data transfer rates) and is suitable for different types of traffic (network usage).