chapter 4 vn.2
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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.