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