Ch.3 - Ethernet Basics (Network+)

Ethernet Basics

• Ethernet is the fundamental infrastructure for all wired LANs.
• IEEE 802.3 standards define key Ethernet features, including data frame creation, media access, and data transmission.
• While Ethernet speeds have significantly increased, the core technology remains the same: MAC addresses identify nodes, and data transfer happens using Ethernet frames.

IEEE 802.3

• Ethernet originated at Xerox PARC in the early 1970s.
• Xerox, DEC, and Intel collaborated on the initial standard in 1979-1980.
• Ethernet II (version 2.0) was published in 1982.
• IEEE 802.3 standardized Ethernet in 1983.
• The IEEE 802.3 standard remains relevant.
• The Ethernet II frame format (using a Type field) is still used for data frames today while the IEEE 802.3 format that replaces a Type field with a Length field is used for special-type control traffic.

CSMA/CD

• In early Ethernet (half-duplex), only one node could transmit at a time.
• CSMA/CD (carrier sense multiple access/collision detection) managed media access to prevent collisions.
• The CSMA part determined if another node was transmitting.
• The CD part handled collisions.
• Modern Ethernet (full-duplex) no longer uses CSMA/CD.

Origins of Ethernet

• Ethernet was invented at Xerox PARC.
• The creation of Ethernet was motivated by the need for a data exchange standard between computers.
• Xerox created PARC to research and develop new technologies.
• Robert Metcalfe is considered the primary inventor of Ethernet.
• The original Ethernet used a bus topology and coaxial cable.
• Ethernet's original speed was 2.94 Mbps.
• An earlier network, the ALOHAnet, provided a template. ALOHAnet was fundamentally different, as ALOHAnet allowed multiple devices to transmit on the same network at the same time, whereas Ethernet was designed for single-node transmission at a time to avoid collisions.
• Ethernet got its name from the "luminiferous ether," an outdated concept in physics.
• Ethernet was commercialized by 3Com, which was developed by Robert Metcalfe.
• 3Com's first products were Ethernet network interface cards (NICs).
• Ethernet's standards were developed by Xerox, DEC, and Intel.
• Other networks (e.g., token ring) attempted to compete with Ethernet, but Ethernet eventually became dominant.

Lab Analysis

• Half-duplex: Only one device can transmit data at a time.
• Full-duplex: Two devices can transmit simultaneously preventing collisions -FCS: The FCS (frame check sequence) is used to ensure that data frames received are correct. It does this by creating a checksum of the frame contents and checking it against a calculated checksum during transmission. Specific algorithms are used to generate and verify the FCS check.
• Ethernet frames contain destination and source MAC addresses.

Key Term Quiz

• Half-duplex mode: When devices are operating in half-duplex mode, CSMA/CD is active.
• Full-duplex mode: Switches and NICs today operate in full-duplex mode.