osi 7layermodel[1]

7/23/2019 OSI 7LayerModel[1]

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Principles of NetworkingPrinciples of Networking

7 Layer OSI Model7 Layer OSI Model


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StandardsStandards

Activity - What is a standardActivity - What is a standard

!!A principle co""only agreed to #y e$pertsA principle co""only agreed to #y e$pertsin the cond%ct and %se of eval%ation forin the cond%ct and %se of eval%ation for

the "eas%re of the val%e or &%ality of anthe "eas%re of the val%e or &%ality of an

eval%ation'(eval%ation'(

ec'w"ich'ed%)glossary)prog-glossary'htfec'w"ich'ed%)glossary)prog-glossary'htf
http://www.google.co.uk/url?sa=X&start=40&oi=define&q=http://ec.wmich.edu/glossary/prog-glossary.htf&usg=AFQjCNF6JwNO6bPJvz2IiFS_Hxgi06CVOQhttp://www.google.co.uk/url?sa=X&start=40&oi=define&q=http://ec.wmich.edu/glossary/prog-glossary.htf&usg=AFQjCNF6JwNO6bPJvz2IiFS_Hxgi06CVOQhttp://www.google.co.uk/url?sa=X&start=40&oi=define&q=http://ec.wmich.edu/glossary/prog-glossary.htf&usg=AFQjCNF6JwNO6bPJvz2IiFS_Hxgi06CVOQ


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ProtocolProtocol

Activity - What is a ProtocolActivity - What is a Protocol

A protocol is a set of r%les that governs theA protocol is a set of r%les that governs theco""%nications #etween co"p%ters on aco""%nications #etween co"p%ters on a

network' In order for two co"p%ters to talknetwork' In order for two co"p%ters to talk

to each other* they "%st #e speaking theto each other* they "%st #e speaking the

sa"e lang%age'sa"e lang%age'


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Standards + ProtocolsStandards + Protocols

Many different types of network protocols and standards areMany different types of network protocols and standards are

re&%ired to ens%re that yo%r co"p%ter ,no "atter whichre&%ired to ens%re that yo%r co"p%ter ,no "atter which

operating syste"* network card* or application yo% areoperating syste"* network card* or application yo% are

%sing can%sing can communicatecommunicatewith another co"p%ter locatedwith another co"p%ter located

on the ne$t desk or half-way aro%nd the world'on the ne$t desk or half-way aro%nd the world'

.he.he OSI (Open Systems Interconnection) ReferenceOSI (Open Systems Interconnection) Reference

ModelModel definesdefines seven layers of networking protocols.seven layers of networking protocols.


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StandardsStandards

.he I/// ,Instit%te of /lectrical and.he I/// ,Instit%te of /lectrical and

/lectronics /ngineers reg%late the/lectronics /ngineers reg%late the

standards agreed for differentstandards agreed for different

co""%nications syste"s to operate'co""%nications syste"s to operate'

0y acting as the reg%lator* they ens%re that0y acting as the reg%lator* they ens%re that

everyone creates a syste" that willeveryone creates a syste" that will

co""%nicate with other syste"s'co""%nicate with other syste"s'


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.1/ OSI 7 LA2/3 MO4/L.1/ OSI 7 LA2/3 MO4/L

Open Syste"s InterconnectionOpen Syste"s Interconnection

A standard description or !reference "odel(A standard description or !reference "odel(

for how "essages sho%ld #e trans"ittedfor how "essages sho%ld #e trans"itted#etween any two points in a#etween any two points in ateleco""%nication networkteleco""%nication network

Any two co"p%ters can co""%nicate whenAny two co"p%ters can co""%nicate whenconnected regardless of %nderlyingconnected regardless of %nderlyingarchitect%rearchitect%re


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OSI Model LayersOSI Model Layers

.he OSI "odel is represented #y seven.he OSI "odel is represented #y seven

layers'layers'

.he seventh layer #eing the top which is.he seventh layer #eing the top which isnearest the %ser'nearest the %ser'

One #eing the #otto" for theOne #eing the #otto" for the

co""%nication "edi%" ,the data leavingco""%nication "edi%" ,the data leaving

the co"p%ter'the co"p%ter'


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The OSI !ayer Model

7 - Application layer

5 - Presentation layer

6 - Session layer

- .ransport layer

8 - Network layer

9 - 4ata Link layer

: - Physical layer

;ser services*

application*

activities

Act%al datatrans"ission

communications

subnet


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!ayer OSI Role Related to a "etwork

7 Application /"ail and we# #rowsers < "any protocols associated to it'

5 Presentation Organisation of data into a for"at that can #e %sed #yh%"ansAS=II - Plain te$t for we# pages4oc < Word doc%"ents

6 Session .his allows yo% to have "%ltiple #rowsers and reso%rces

open si"%ltaneo%sly witho%t data conflicts in trans"ission'

.ransport >irewalls* layer switches operate at this level?

8 Network Logical address for a server or workstation is "anagedhere < co""on protocol is .=P)IP'

3o%ting takes place at this level

9 4ata Link Physical address ,Media access control ,MA= ;sed toidentify the device'>ra"e relay

: Physical =a#les)wireless encoding of #its of data @@@::::@:@:@:*

1%#s


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.1/ OSI S//N LA2/3 MO4/L.1/ OSI S//N LA2/3 MO4/L

;PP/3 L//LS;PP/3 L//LS

"essage passing < fro" co"p%ter to"essage passing < fro" co"p%ter to

co"p%terco"p%ter

LOW/3 8 L//LSLOW/3 8 L//LS

"essage passing < thro%gh host"essage passing < thro%gh host

co"p%ter to anotherco"p%ter to another

P;3POS/P;3POS/

to separate specific f%nctionsto separate specific f%nctions


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OSI Model and TCP/IP ModelOSI Model and TCP/IP ModelA good way of helping students to memorise the layers in the OSI model is by using a simple rhyme or mnemonic. Suggested mnemonicsA good way of helping students to memorise the layers in the OSI model is by using a simple rhyme or mnemonic. Suggested mnemonics

for remembering the layers arefor remembering the layers are

All Printers Seem To !eed "aily ProddingAll Printers Seem To !eed "aily Prodding

Ancho#y Pi$$a Seems To !eed "ouble PepperoniAncho#y Pi$$a Seems To !eed "ouble Pepperoni..


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APPLI=A.ION LA2/3 7APPLI=A.ION LA2/3 7

Interacts with applications for co""%nicationInteracts with applications for co""%nicationp%rposesp%rposes

4eter"ines identity + availa#ility of4eter"ines identity + availa#ility of

co""%nications partnersco""%nications partners

4eter"ines s%fficient reso%rces availa#le4eter"ines s%fficient reso%rces availa#le

=ontrols the co""%nication -=ontrols the co""%nication -

co-operation #etween applicationsco-operation #etween applications

=losest to %ser < #oth ;ser and Layer 7=losest to %ser < #oth ;ser and Layer 7

software interact with applicationssoftware interact with applications

/'g' We# 0rowser/'g' We# 0rowser


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P3/S/N.A.ION LA2/3 5P3/S/N.A.ION LA2/3 5

Presents data to the %ser in %nderstanda#le for"atPresents data to the %ser in %nderstanda#le for"at

Provides conversion f%nctions for application layer dataProvides conversion f%nctions for application layer data

4ata representation < graphic for"ats4ata representation < graphic for"ats

=haracter representation < te$t ) AS=II=haracter representation < te$t ) AS=II

4ata co"pression4ata co"pression 4ata encryption4ata encryption


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S/SSION LA2/3 6S/SSION LA2/3 6

Manages connections #etween "achinesManages connections #etween "achines4eter"ines whether all data trans"itted ) received4eter"ines whether all data trans"itted ) received

It provides for f%ll-d%ple$* half-d%ple$* or si"ple$It provides for f%ll-d%ple$* half-d%ple$* or si"ple$

operationoperation

/sta#lishes logical connection for co""%nication/sta#lishes logical connection for co""%nication

=hecks data received < retrans"its if necessary=hecks data received < retrans"its if necessary

3econnects on pre"at%re ter"ination3econnects on pre"at%re ter"ination

3eleases logical connection on co"pletion3eleases logical connection on co"pletion


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.3ANSPO3. LA2/3 .3ANSPO3. LA2/3

4ecides %pon network to %se depending on data type4ecides %pon network to %se depending on data typeProvides relia#le data transfer services to the %pperProvides relia#le data transfer services to the %pper

layerslayers

>low control < eno%gh space to send)receive>low control < eno%gh space to send)receive

"essages"essages

M%ltiple$ing < co"#ines "essages to sa"eM%ltiple$ing < co"#ines "essages to sa"e

connectionconnection

Packeting < #reaks larger into s"aller piecesPacketing < #reaks larger into s"aller pieces

/rror checking and recovery/rror checking and recovery


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N/.WO3B LA2/3 8N/.WO3B LA2/3 8

3o%ting and addressing f%nctions < correct3o%ting and addressing f%nctions < correctdestinationsdestinations

3eceives inco"ing packets of data3eceives inco"ing packets of data

3o%ting < decides what ro%te to %se3o%ting < decides what ro%te to %se

>orwarding < sends on packets to other hosts>orwarding < sends on packets to other hosts

=ontrols co""%nication s%#net < layers :-8=ontrols co""%nication s%#net < layers :-8


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4A.A LINB LA2/3 94A.A LINB LA2/3 9

Organisation of data #its into fra"e str%ct%reOrganisation of data #its into fra"e str%ct%re

.he #eginning and end of the data fra"e.he #eginning and end of the data fra"e

.he address of the sender.he address of the sender

.he address of the receiver.he address of the receiver

/rror checking of the data fra"e/rror checking of the data fra"e


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P12SI=AL LA2/3 :P12SI=AL LA2/3 :

.rans"its ) receives data #its as electrical.rans"its ) receives data #its as electrical

p%lsesp%lses

=ontrols physical link #etween co""%nicating=ontrols physical link #etween co""%nicating

syste"ssyste"s

4escri#es network topology4escri#es network topology

.rans"ission "edia < ca#ling ) #roadcasting.rans"ission "edia < ca#ling ) #roadcasting .rans"ission devices < NI=s ) "ode"s.rans"ission devices < NI=s ) "ode"s

/lectrical or optical ,fi#re optic signalling/lectrical or optical ,fi#re optic signalling


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.1/ IN./3N/. APPLI=A.ION L//L.1/ IN./3N/. APPLI=A.ION L//L

.he application layer is "ade %p of other.he application layer is "ade %p of otherprotocolsprotocols

:':' 1.ML ) 1..P1.ML ) 1..P9'9' POP ) SM.PPOP ) SM.P

8'8' >.P>.P

''

./LN/. < re"ote sessions

./LN/. < re"ote sessions

6'6' 4NS < 4o"ain na"e server < IP addresses4NS < 4o"ain na"e server < IP addresses

=orresponds to layers 6-7 of OSI "odel=orresponds to layers 6-7 of OSI "odel


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.=P ) IP.=P ) IP

0asic co""%nication protocol of the Internet0asic co""%nication protocol of the Internet

.3ANSMISSION =ON.3OL P3O.O=OL.3ANSMISSION =ON.3OL P3O.O=OL

Manages asse"#ly of "essages ) files into s"allerManages asse"#ly of "essages ) files into s"allerpackets' 3easse"#les packets when receivedpackets' 3easse"#les packets when received

,OSI layer ,OSI layer

IN./3N/. P3O.O=OLIN./3N/. P3O.O=OL

1andles the address part of the packet1andles the address part of the packet

/ns%res reaches correct destination ,OSI layer 8/ns%res reaches correct destination ,OSI layer 8

osi 7layermodel[1]

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