Lesson 4: LAN Basics

In this lesson, we will cover the fundamentals of LAN technologies. We’ll look at Ethernet, Token Ring, and FDDI. For each one, we’ll look at the technology as well as its operations.

      The Agenda

 - Ethernet

 - Token Ring

 - FDDI

Common LAN Technologies

The three LAN technologies shown here account for virtually all deployed LANs:

The most popular local area networking protocol today is Ethernet. Most network administrators building a network from scratch use Ethernet as a fundamental technology.

Token Ring technology is widely used in IBM networks.

FDDI networks are popular for campus LANs – and are usually built to support high bandwidth needs for backbone connectivity.

Let’s take a look at Ethernet in detail.

Ethernet

Ethernet and IEEE 802.3

Ethernet was initially developed by Xerox. They were later joined by Digital Equipment Corporation (DEC) and Intel to define the Ethernet 1 specification in 1980. There have been further revisions including the Ethernet standard (IEEE Standard 802.3) which defines rules for configuring Ethernet as well as specifying how elements in an Ethernet network interact with one another.
Ethernet is the most popular physical layer LAN technology because it strikes a good balance between speed, cost, and ease of installation. These strong points, combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today.
The Fast Ethernet standard (IEEE 802.3u) has been established for networks that need higher transmission speeds. It raises the Ethernet speed limit from 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure. Incorporating Fast Ethernet into an existing configuration presents a host of decisions for the network manager. Each site in the network must determine the number of users that really need the higher throughput, decide which segments of the backbone need to be reconfigured specifically for 100BaseT and then choose the necessary hardware to connect the 100BaseT segments with existing 10BaseT segments.
Gigabit Ethernet is an extension of the IEEE 802.3 Ethernet standard. It increases speed tenfold over Fast Ethernet, to 1000 Mbps, or 1 Gbps.

    Benefits and background

 - Ethernet is the most popular physical layer LAN technology because it strikes a good balance    between speed, cost, and ease of installation
 - Supports virtually all network protocols
 - Xerox initiated, then joined by DEC & Intel in 1980

   Revisions of Ethernet specification

 - Fast Ethernet (IEEE 802.3u) raises speed from 10 Mbps to 100 Mbps
 - Gigabit Ethernet is an extension of IEEE 802.3 which increases speeds to 1000 Mbps, or 1 Gbps

One thing to keep in mind in Ethernet is that there are several framing variations that exist for this common LAN technology.
These differences do not prohibit manufacturers from developing network interface cards that support the common physical layer, and software that recognizes the differences between the two data links

Ethernet Protocol Names

Ethernet protocol names follow a fixed scheme. The number at the beginning of the name indicates the wire speed. If the word “base” appears next, the protocol is for baseband applications. If the word “broad” appears, the protocol is for broadband applications. The alphanumeric code at the end of the name indicates the type of cable and, in some cases, the cable length. If a number appears alone, you can determine the maximum segment length by multiplying that number by 100 meters. For example 10Base2 is a protocol with a maximum segment length of approximately 200 meters (2 x 100 meters).

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