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Chapter 4 11

Local Area Network Basics

Chapter 4

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Chapter 4 2

Chapter Objectives

Describe Ethernet standard

Explain Ethernet

Understand the concept of CSMA/CD and CSMA/CA

protocols

Explain different types of Ethernet

Understand about repeaters, bridges and hubs used to

extend computer networks

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Chapter 4 3

Recall

Types of copper wire cables are: Coaxial cables (Also known as Coax)

Twisted pair Cables (TP)

Shielded Twisted pair (STP)

Unshielded Twisted pair (UTP)

Wireless transmission media are:

Radio Waves

Microwave Infrared

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Chapter 4 4

IEEE Standards

An association that promotes engineeringand electronic improvement

IEEE 802 was started in February 1980

IEEE 802 committee defines frames, speed,distances and types of cabling to use for

networking

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Chapter 4 5

Protocols and Procedures

Protocols are set of rules which are used by the nodes ona network to communicate with each other

Protocols are developed by committees, different

companies developed products confirming to those

protocols

StandardProtocols

Ethernet Token Ring ARCnet

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Chapter 4 6

LAN Architecture - I

802.3

Defines a standard for physical layer and data link

layer of the Ethernet architecture that uses wired

connection Ethernet is an architecture that mainly uses bus

topology

Defines various cabling used for different types of

topologies

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Chapter 4 7

LAN Architecture - II

802.4

Defines a standard for Token Bus architecture

Token bus is similar to token ring, but it uses

coaxial cables

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Chapter 4 8

LAN Architecture - III

802.5

Defines a standard for Token ring architecture

Uses the 10 Base T cabling standard

Uses twisted pair cabling to connect devicesinstead of coaxial cable

Passes data from one computer to another like in

a token bus network

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Chapter 4 9

IEEE 802.3 Logical relationship with OSIReference Model

IEEE 802.3 physical layer

corresponds to the OSI

physical layer

OSI data link layer is

divided into two IEEE 802sublayers

The Media Access

Control (MAC)

sublayer

The MAC-client

sublayer

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Chapter 4 10

Ethernet

Defined by IEEE as the 802.3 standard

Most widely adapted LAN technology

Supports data transfer rates of 10 Mbps, 100 Mbps and

1 Gbps

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Chapter 4 11

Introduction to Ethernet

Three data rates currently defined for the operation over

optical fiber and twisted-pair cables

10 Mbps – 10Base-T Ethernet

100 Mbps - Fast Ethernet 1000 Mbps - Gigabit Ethernet

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Chapter 4 12

Working of Ethernet

Ethernet frame is used to transfer data over a

network

Each device in an Ethernet network is

uniquely identified by a 48 bit (6 bytes)address called Ethernet address

Ethernet addresses are represented as six

pairs of hexadecimal digits separated by acolon.

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Chapter 4 13

Elements of Ethernet System

Elements of Ethernet

System

MediumSet of Medium Access

Control RulesEthernet frame

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Chapter 4 14

Ethernet Medium

Transmits information over

the network

Computer D transmits

information for Printer C

Computer B and A also

receives the information All device inspects the

destination address

If the received frame is not

meant for them, they will

reject the frame

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Chapter 4 15

Data Transmission

When a computer wants to transmit, it listens

to the cable (transmission medium)

If two or more devices simultaneously

transmit data on an idle cable, collision mayoccur

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Chapter 4 16

Example of Collision

Each device decides to

broadcast an Ethernet

frame to other device

Devices listens to theEthernet medium and

detects that no carrier

is present

Devices transmitsimultaneously, causing

a collision

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Chapter 4 17

Carrier Sense Multiple Access/ Collision

Detection (CSMA/CD)

Permits one device to access to the network

media at a time to avoid collision

Networks using CSMA/CD technology such

as Ethernet, network devices compete for thenetwork media

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Chapter 4 18

Working of CSMA/CD

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Chapter 4 19

Carrier Sensing Multiple Access /

Collision Avoidance (CSMA/CA) Set of rules that can avoid collisions, unlike

CSMA/CD that handles network transmissions once

collisions are detected

In CSMA/CA, all devices are forced to wait for arandom number of time slots and sense the medium

again

If the medium is sensed to be busy, the device stops

the timer until it becomes free again.

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Chapter 4 20

Types of Ethernet

Cabling Standards

10Base5 10Base2 10Base-T 10Base-F

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Chapter 4 21

10Base-5

Thick coaxial cable is also referred to as thicknet

10Base5 refers to specifications of thick coaxial cablecarrying Ethernet signals

The 5 refers to the maximum segment length being500 meters

RG-8 coaxial cable is used

A 15-pin female DB connector called AUI connector isused to connect the device

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Chapter 4 22

10Base-2

10Base-2 (thin coaxial cable) is also referred to asthinnet

In 10Base-2, “2” refers to approximate maximumsegment length of the cable which is 185 meters

10Base2 uses RG-58 coaxial cable with BNCconnectors

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Chapter 4 23

10Base-T

Allows stations to be attached via twisted pair cable 10 refers to the transmission speed of 10 Mbps

“T” refers to twisted pair cable

In a 10BaseT network, each computer (node) is

connected to a hub

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Chapter 4 24

10 Base-F

Uses fiber optics Possesses excellent noise immunity and is the

method of choice when running between buildings

or widely separated hubs

10 Base-F is expensive as the connectors and

terminators used in 10 Base-F are costly

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Chapter 4 25

Comparing Ethernet Types

Ethernet types 10Base5 10Base2 10BaseT 10BaseF

Media Type Thick coaxial (RG8) Thin coaxial (RG58) UTP Fiber-optic

Max.segment length

(meters)

500 185 100 1000

Frequency(MHZ) 10 10 10 10

Max Nodes/Segment 100 30 1024 1024k

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Chapter 4 26

Extending the network

A computer network can be extended using

repeaters, hubs and bridges

In computer networks, a bridge is an Internetworking

device Repeater regenerates signal

Repeaters remove the unwanted noise in an

incoming signal

A hub is a multi port repeater which provides a

common point for the connection of network devices

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Chapter 4 27

Summary - I

Ethernet is a local-area network (LAN) structuraldesign developed by DEC, Intel and XeroxCorporation.

Ethernet is a very common and widely used method

of networking computers in a LAN environment. All nodes on an Ethernet network are either Data

Terminal Equipment (DTE) or Data CommunicationsEquipment (DCE).

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Chapter 4 28

Summary - II

Protocols are set of rules that the nodes on anetwork use to communicate with each other

Carrier Sense Multiple Access/Collision Detection(CSMA/CD) is a network control protocol which uses

a carrier sensing system Carrier Sense Multiple Access/Collision Avoidance

(CSMA/CA) is a set of rules used to avoid collisions.

10 Base-2, 10 Base-5, 10 Base-T, and 10 Base-F

are different types of cabling for Ethernet

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Chapter 4 29

Summary - III

A repeater is a device that is used on a link to

regenerate the signal to extend the physical

length of a network.

Bridges are usually used to divide a busynetwork into separate segments and to connect

multiple LANs.

Hub is a Repeater with multiple ports and

operates at the physical layer.

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