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OSI Reference Model

Introduction to TCP/IP

LAN Basics

Understanding Switching

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Understanding Routing

What Is Layer 3 Switching?

Understanding VirtualLANs

Understanding Qualityof Service

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The Internet

LAN Basics

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

Contents

- Ethernet

- Ethernet and Fast Ethernet

- Ethernet Reliability

- High-Speed Ethernet Options

- Token Ring

- Token Ring Operation

- FDDI

Common LAN Technologies

The three LAN technologies shown here accountfor virtually all deployed LANs:

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


Token Ring technology is widely used in IBM networks.


FDDI networks are popular for campus LANs – and areusually built to support high bandwidth needs for backboneconnectivity.

Let’s take a look at Ethernet in detail.

Ethernet

Ethernet and IEEE 802.3

Ethernet was initially developed by Xerox. They were laterjoined by Digital Equipment Corporation (DEC) and Intel to define the Ethernet1 specification in 1980. There have been further revisions including the Ethernetstandard (IEEE Standard 802.3) which defines rules for configuring Ethernet aswell as specifying how elements in an Ethernet network interact with one another.
Ethernet is the most popular physical layer LAN technology because it strikesa good balance between speed, cost, and ease of installation. These strong points,combined with wide acceptance in the computer marketplace and the ability to supportvirtually all popular network protocols, make Ethernet an ideal networking technologyfor most computer users today.
The Fast Ethernet standard (IEEE 802.3u) has been established for networks thatneed higher transmission speeds. It raises the Ethernet speed limit from 10 Mbpsto 100 Mbps with only minimal changes to the existing cable structure. IncorporatingFast Ethernet into an existing configuration presents a host of decisions forthe network manager. Each site in the network must determine the number of usersthat really need the higher throughput, decide which segments of the backboneneed to be reconfigured specifically for 100BaseT and then choose the necessaryhardware to connect the 100BaseT segments with existing 10BaseT segments.
Gigabit Ethernet is an extension of the IEEE 802.3 Ethernet standard. It increasesspeed tenfold over Fast Ethernet, to 1000 Mbps, or 1 Gbps.

Benefits and background

- Ethernet is the most popular physical layer LAN technology becauseit 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 speedsto 1000 Mbps, or 1 Gbps

One thing to keep in mind in Ethernet isthat there are several framing variations that exist for thiscommon LAN technology.
These differences do not prohibit manufacturers from developingnetwork interface cards that support the common physical layer,and software that recognizes the differences between the twodata links

Ethernet Protocol Names

Ethernet protocol names follow a fixed scheme.The number at the beginning of the name indicates the wirespeed. If the word “base” appears next, the protocolis for baseband applications. If the word “broad”appears, the protocol is for broadband applications. The alphanumericcode 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 multiplyingthat number by 100 meters. For example 10Base2 is a protocolwith a maximum segment length of approximately 200 meters(2 x 100 meters).

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