Chapter 13 Wired LANs: Ethernet

Chapter 13 of Data Communications and Networking by Behrouz A. Forouzan, titled "Wired LANs: Ethernet", focuses on Ethernet technology, the most widely used LAN (Local Area Network) protocol. Below are detailed notes from the chapter:

1. Introduction to Ethernet

• Ethernet is the dominant technology used in LANs.

• LANs are designed for small geographic areas like buildings or campuses, primarily used for connecting computers to share resources.

• While several LAN technologies have existed (e.g., Token Ring, FDDI, ATM LAN), Ethernet has persisted and evolved through four generations: Standard Ethernet, Fast Ethernet, Gigabit Ethernet, and Ten-Gigabit Ethernet.

2. IEEE Standards

• Project 802: Established by the IEEE in 1985 to set standards for LAN communication, focusing on the physical and data link layers.

• The IEEE data link layer is divided into two sublayers:

  1. Logical Link Control (LLC): Provides flow and error control.

  2. Media Access Control (MAC): Defines protocols for accessing the physical medium.

• The physical layer defines detailed specifications for each LAN implementation.

3. Standard Ethernet (10 Mbps)

• The first generation of Ethernet operates at 10 Mbps.

• MAC Sublayer:

  • Governs the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method, where stations sense the medium before transmitting.

• Frame Format: The Ethernet frame consists of seven fields: Preamble, SFD, Destination Address (DA), Source Address (SA), Length/Type, Data, and CRC.

• Frame Length:

  • Minimum: 64 bytes (512 bits).

  • Maximum: 1518 bytes (12,144 bits), including the header and trailer.

• Addressing: Each Ethernet device has a 48-bit MAC address, which can be:

  • Unicast: Single destination.

  • Multicast: Group of devices.

  • Broadcast: All devices on the LAN.

4. Bridged and Switched Ethernet

• Bridged Ethernet:

  • Bridges divide a network into segments to increase bandwidth and reduce the size of the collision domain.

• Switched Ethernet:

  • Switches replace hubs and allow each device to have its own dedicated bandwidth, eliminating collisions in full-duplex mode.

5. Fast Ethernet (100 Mbps)

• Goal: To increase data rates from 10 Mbps to 100 Mbps while maintaining backward compatibility with standard Ethernet.

• Autonegotiation: Introduced to allow devices to automatically select the best mode of operation (10 Mbps or 100 Mbps).

• Physical Layer: Supports two-wire and four-wire implementations, using either twisted-pair cables (100Base-TX) or fiber-optic cables (100Base-FX).

6. Gigabit Ethernet (1 Gbps)

• Goal: To increase the data rate to 1 Gbps, maintaining compatibility with previous generations.

• Frame Format: Remains the same as in standard Ethernet.

• Implementations:

  • 1000Base-SX: Short-wave fiber.

  • 1000Base-LX: Long-wave fiber.

  • 1000Base-T: Twisted-pair cables.

7. Ten-Gigabit Ethernet (10 Gbps)

• Goal: To support data rates of 10 Gbps, designed for backbone and wide-area networks (WANs).

• Physical Layer: Uses fiber-optic cables, with implementations such as 10GBase-S, 10GBase-L, and 10GBase-E for different distances.

• Full-Duplex Only: Ten-Gigabit Ethernet operates only in full-duplex mode, removing the need for CSMA/CD.

8. Summary

• Ethernet has evolved through four generations while maintaining its core frame structure and MAC protocol.

• Bridges and switches have improved bandwidth and network efficiency.

• Fast, Gigabit, and Ten-Gigabit Ethernet offer increasingly higher data rates while supporting the same foundational Ethernet technologies.

This chapter provides an in-depth look at Ethernet’s development and its continuing importance in LAN networking【7:0†source】【7:2†source】【7:11†source】.