Computer Network Ch-4

7/29/2019 Computer Network Ch-4

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OSIReferencemodel

Interlayercommunication

Dataencapsulation

Horizontalcommunication,verticalcommunication

physicallayer;datalinklayer;networklayer;transport

layer; sessionlayer;presentationlayer; applicationlayer.

TCP/IP

Reference

model

Link;

Internet;

Transport;

Application

layer.

ComparisonoftheOSIandTCP/IPreferencemodels


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OSIReferencemodel


Dataencapsulation




TCP/IP

Reference

model

Link;

Internet;

Transport;

Application

layer.



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OSIReferenceModel

The

OSI

Model

is

a

model

for

understanding

and

designing

a

network

architecture

that

isflexible,robust&interoperable.

he OSI model is a layered framework for the design of network systems that allows

ommunicationbetweenalltypesofcomputersystems.

Application

Presentation

Session

Transport

Network

DataLink

Physical

7

6

5

4

3

2

1


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OSIReferencemodelOSIReferencemodel


Dataencapsulation

Horizontalcommunication,

vertical

communication



TCP/IPReference

model

Link;

Internet;

Transport;

Application

layer.


Takeaexample

of

Army

communication


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kk

kk

kk

DataLink

DataLink

DataLink

DataLink

DataLink

DataLink

DataLink

Application

Presentation

Session

Transport

Network

DataLink

Physical

7

6

5

4

3

2

1

21interface

32interface

43interface

54interface

65interface

76interface

DataLink

DataLink

DataLink

DataLink

DataLink

DataLink

DataLink

Application

Presentation

Session

Transport

Network

DataLink

Physical

7

6

5

4

3

2

1

21interface

32interface

43interface

54interface

65interface

76interface

N/W N/W

DLL DLL

Phy Phy

Peerto

peer

protocol

(7

th

layer)

Peertopeerprotocol(6thlayer)

Peerto

peer

protocol

(5th

layer)

Peertopeerprotocol(4thlayer)

3rd 3rd 3rd

2nd

2nd

2nd

1st 1st 1st

Device

A

Device

B

Interactionbetweenlayers


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Interlayer

communication

Dataencapsulation

Horizontal

communication,

vertical

communication

Horizontal

communication,

vertical

communication



TCP/IP

Reference

model

Link;

Internet;

Transport;

Application

layer.



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DataEncapsulationApplication

Data

Application

Data

Transport

header

Application

Data

Transport

header

Network

header

ApplicationData

Transportheader

Network

header

DataLink

header

DataLink

footer


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Interlayer

communication

DataencapsulationDataencapsulation




TCP/IP

Reference

model

Link;

Internet;

Transport;

Application

layer.



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Application

Presentation

Session

Transport

Network

DataLink

Physical

7

6

5

4

3

2

1

Application

Presentation

Session

Transport

Network

DataLink

Physical

7

6

5

4

3

2

1

Horizontal andVerticalcommunication


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D7

D6H6

D5

D4

H4

D3H3

H7

D2H2

0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 0 0 0 0 1 0 0 0 0 010

T2

H5

Transmissionmedium


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D7

D6H6

D5

D4

H4

D3H3

H7

D2H2

0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 0 0 0 0 1 0 0 0 0 010

T2

H5

As each block of

data

reaches

the

next higher layer,

the headers and

trailersattached

to

it

atthecorresponding

sending layer are

removed


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Interlayer

communication

DataencapsulationDataencapsulation

Horizontalcommunication,verticalcommunicationHorizontalcommunication,verticalcommunication



TCP/IP

Reference

model

Link;

Internet;

Transport;

Application

layer.



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Physical L ayer

PhysicalTransmission

Medium

101010000001

L2data

Physical Layer

101010000001

L2data

Thislayertransmitstheunstructured,rawbitstreamoveraphysicalmedium

PhysicalLayer

It

deals

with

the

mechanical

and

electrical

specifications

of

the

interface

and

transmissionmedium.FromDLL ToDLL

Thephysicallayerisconcernwith:

Physicalcharacteristicsofinterfacesandmedium

Representationof

bits

Line

configuration

Transmissionmode Synchronizationofbits

Physicaltopology


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L3data

101010000000010

T2 Data H2

Sendsdataframesfromthenetworklayertothephysicallayer

DataLinkLayer

Thedata

link

layer

is

responsible

for

providing

error

free

transfer

of

these

frames

fromonecomputertoanotherthroughthephysicallayer.

FromN/Wlayer ToN/Wlayer

Specificresponsibilities

of

the

data

link

layer

:

1.Framing 2.Physicaladdressing 3.Flowcontrol

4.Errorcontrol

L3data

101010000000010

T2 Data H2

Tophysicallayer Fromphysicallayer


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1.Itisresponsibleforaddressingmessagesandtranslatinglogicaladdressesand

namesinto

physical

addresses.

NetworkLayer

2.Thislayeralsodeterminestheroutefromthesourcetothedestinationcomputer.

FromTransportlayer ToTransportlayer

SpecificresponsibilitiesoftheNetworklayer:

1.Logical

addressing

2.

Routing

ToDataLinklayer FromDataLinklayer

L4 data

H3

L3 data

L4 data

H3

L3 data

4.Italsomanagestrafficproblemsonthenetwork,suchasswitchingandroutingof

packetsandcontrollingthecongestionofdata.

3.Itdetermineswhichpaththedatashouldtakebasedonnetworkconditions,priorityof

service,andotherfactors.


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1.providesanadditionalconnectionlevelbeneaththesessionlayer

TransportLayer

2.It

ensures

that

packets

are

delivered

error

free,

in

sequence,

and

without

losses

or

duplications..FromSessionlayer ToSessionlayer

SpecificresponsibilitiesoftheTransportlayer:

1.Segmentationandreassembly 2.Connectioncontrol

ToN/Wlayer FromN/Wlayer

L5 data

H4 H4 H4

L4dataL4dataL4data

L5 data

H4 H4 H4

L4dataL4dataL4data

3.Flow

control

4.

Error

control


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1. allows two applications on different computers to open, use, and close a

connectioncalled

asession.

SessionLayer

2. It performs namerecognition and other functions, such as security, that are

neededtoallowtwoapplicationstocommunicateoverthenetwork.

FromPresentation

layer

To

Session

layer

ToTransportlayer FromTransportlayer

3. It performs namerecognition and other functions, such as security, that are

needed

to

allow

two

applications

to

communicate

over

the

network.

4.Thesessionlayersynchronizesusertasksbyplacingcheckpointsinthedatastream.

5.Thislayeralsoimplementsdialogcontrolbetweencommunicatingprocesses,such

asregulatingwhichsidetransmits,when,andforhowlong

H5

syn syn syn

H5

syn syn syn


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SpecificresponsibilitiesoftheSessionlayer:

1.DialogControl

2.Synchronization


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1. It defines the format used to exchange data among networked

computers.

PresentationLayer

2. It is concerned with the syntax and semantics of the information

exchangedbetweentwocomputers.

FromApplicationlayer ToApplicationlayer

Tosession

layer

From

session

layer

3. The presentation layer is responsible for converting protocols,

translatingthedata,encryptingthedata,changingorconvertingthecharacterset,andexpandinggraphicscommands

4.Italsomanagesdatacompressiontoreducethenumberofbitsthat

needto

be

transmitted.

H6 Data H6 Data


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SpecificresponsibilitiesofthePresentationlayer:

1.Translation

2.Encryption

3.Compression

Conversion from sender dependant format into a common format at sender and at

receiver change of common format into its receiver format takes place by

presentationlayer.

Thesendertransformstheoriginalinformationtoanotherandsendstheresulting

messageoutoverthenetwork,whichhandlesbypresentationlayer.

Itreducesthenumberofbitstobetransmitted.


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1. This layer relates to the services that directly support user

applications,

such

as

software

for

file

transfers,

database

access,

andemail.

ApplicationLayer

User User

ToPresentationlayer FromPresentationlayer

2. Applicationlayer protocols can be programs in themselves, such

as

File

Transfer

Protocol

(FTP),

or

they

can

be

used

by

otherprograms, such as Simple Mail Transfer Protocol (SMTP), used by

mostemailprograms,toredirectdatatothenetwork.

H7 Data

X.500 FTAM X.400...

Message H7 Data

X.500 FTAM X.400...

Message


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SpecificresponsibilitiesoftheApplicationlayer:

1.NetworkvirtualTerminal

2.Filetransfer,accessandmanagement(FTAM)

3.Mail

services

Itallowsausertologontoaremotehost.

Itallowsausertoaccessfiles inaremotecomputer,toreceivefilesfroma

remotecomputerandtomanageandcontrolfilesinaremotecomputer.

Itprovidesthebasisforemailforwardingandstorage.

4.Directoryservices

It provides distributed data sources and access for global informationaboutvariousobjectsandservices.


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Summaryofdutiesforeachlayer

Application

Presentation

Session

Transport

Network

DataLink

Physical

ToAllow

access

to

networkresourcesToTranslate,encrypt,

andcompressdata

Toestablish,

manage

andterminatesessionsToprovidereliableprocessto

processmessagedelivery&error

recoveryTomovepacketsfrom

sourcetodestinationToorganizebitsinto

framesTotransmitbitsovera

medium


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OSIReferencemodel


Dataencapsulation




TCP/IPReferencemodelLink;Internet;Transport;Application

layer.



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Application

Presentation

Session

Transport

Network

DataLink

Physical

Application

Transport

Internetlayer

N/Waccesslayer

N/W

interface

OR

Link

TCP/IPTransmissionControlProtocolInternetProtocol

It is an industrystandard suite of protocols that provide

communicationsinaheterogeneousenvironment.

TCP/IPalsosupports routingand iscommonlyusedasan

internetworkingprotocol.

TCP/IP is broken

intothefourlayers


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SMTP FTP DNS HTTP TELNET

Application

Applications

Presentation

Session

TCP

UDP

Transport

Internet ICMP IP ARP RARP

Protocolsspecifictotheunderlyingphysicalmedia

usedfordatacommunicationatthehardwarelevel

DataLink

Physical

LinkLayer

TCP/IPTransmissionControlProtocolInternetProtocol


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N/WaccesslayerorN/Winterface

Thenetwork interface layer, corresponding to the physical anddatalink layersoftheOSIreferencemodel,communicatesdirectly

withthenetwork.

It provides the interface between the network architecture (such

astoken

ring,

Ethernet)

and

the

Internet

layer.

Internetlayer

TheInternet layer, corresponding to the network layer of the OSI

reference model, uses several protocols for routing and delivering

packets.

Several

protocols

work

within

the

Internet

layer.

Internet ICMP IP ARP RARP


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1.InternetProtocol(IP)

InternetProtocol(IP) isapacketswitchedprotocolthatperformsaddressing

and

route

selection.

IP is a connectionless protocol and sends packets without

expectingthereceivinghosttoacknowledgereceipt.

IPisresponsibleforpacketassemblyanddisassembly

2. AddressResolutionProtocol(ARP)

Before an IP packet can be forwarded to another host, the

hardwareaddressofthereceivingmachinemustbeknown.

TheARP

determines

hardware

address

(MAC

addresses)

that

correspondtoanIPaddress.

3. ReverseAddressResolutionProtocol(RARP)

A

RARP

server

maintains

a

database

of

machine

numbers

in

theform of an ARP table (or cache) which is created by the system

administrator.

The RARP protocol provides an IP number to a requesting

hardwareaddress.


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4. InternetControlMessageProtocol(ICMP)

TheICMP

is

used

by

IP

and

higher

level

protocols

to

send

and

receivestatusreportsaboutinformationbeingtransmitted.

TransportLayer

It

is

responsible

for

establishing

and

maintaining

endto

end

communicationbetweentwohosts.

The transport layer provides acknowledgment of receipt, flow

control,and

sequencing

of

packets.

Italsohandlesretransmissionsofpackets.

The transport layer can use either TCP or User Datagram Protocol (UDP)

protocolsdepending

on

the

requirements

of

the

transmission.

TCP UDPTransport


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1.TransmissionControlProtocol(TCP)

The TCP is responsible for the reliable transmission of data from

onenode

to

another.

It is a connectionbased protocol and establishes a connection,

betweentwomachinesbeforeanydataistransferred.

2.User

Datagram

Protocol

(UDP)

Aconnectionlessprotocol,theUDP,isresponsibleforendtoend

transmissionofdata.

UDP does not establish a connection, it attempts to send the

dataand

to

verify

that

the

destination

host

actually

receives

the

data.

UDP is best used to send small amounts of data for which

guaranteeddelivery

is

not

required.

ApplicationLayer

Correspondingtothesession,presentation,andapplicationlayers

of the OSI reference model, the application layer connectsapplications

to

the

network.

SMTP FTP DNS HTTP TELNET


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OSIReferencemodel


Dataencapsulation




TCP/IPReferencemodelLink;Internet;Transport;Application

layer.


i b & /


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ComparisonbetweenOSI&TCP/IP

TCP/IP

also

supports

routing

and

is

commonly

used

as

an

internetworkingprotocol.

Application

Presentation

Session

Transport

Network

DataLink

Physical

7

6

5

4

3

2

1

Application

Transport

Internetlayer

N/Waccesslayer

N/Winterface

TCP/IPOSIReferenceModel

4

3

2

1

TCP/IP OSI Reference Model


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TCP/IP OSIReferenceModel

Defined after the

adventof

Internet

Defined before the

adventof

Internet

1. 1.

Service interface &

protocols were not

clearlydistinguished

Service interface &

protocolswereclearly

distinguished

2. 2.

TCP/IPsupports

internetworking

OSIdoesnotsupports

internetworking3. 3.

Looselylayered

Strict

layering

4. 4.Protocol dependent

standard

Protocolindependent

standard

5. 5.

Morecredible

Less

credible

6. 6.TCP reliably delivers

packets, IP does not

reliablydeliver packets

All packets are

reliably

delivered

7. 7.

Comparison between TCP & UDP


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ComparisonbetweenTCP&UDP

TCP UDP

Itisconnectionoriented,

nodatacorruptionwhile

datatransfer

It is connectionless, may

be data corruption while

datatransfer

Factor

Reliability

Messagearrives

in

order

No

order

message

Order

If order miss then it

requirestobebutback

No ordering of message,

notrackingconnection

Heavy/light

weight

Dataisreadasastream.

There may be multiple

packetperreadcall

Packets are individually,

onepacketpercall

Streaming/

datagram

www, email, FTP, HTTP,

TELNET,SMTPetc.

DNS,VOIP,DHCP,NFSExample

Computer Network Ch-4

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