ISO-OSI

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© N. Ganesan, Ph.D. , All rights reserved.

Chapter

ISO-OSI Reference Model andIEEE Standards

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Chapter Objectives

• Discuss the most popular ISO-OSI 7-layer communication reference

model• Explain the reference model and

standards relevant to networcommunications

• Descri!e the di"erent IEEEstandards that apply to di"erenttypes of networs

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Module 1

#n Overview of ISO and its

7-$ayer OSI Model

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Models and Standards in

Communication• %ommunication

& Esta!lished standards

& Standards are nown as protocols

• Implementation& # framewor is helpful in the desi'n of

hardware and software forcommunication

& ISO-OSI Model serves this purpose

& ISO-OSI supersedes the (%)*I) model

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ISO and OSI Defned

• ISO

& International Standards Or'ani+ation

• OSI

& Open Systems Interconnect

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OSI Model Background

• Introduced in ,7. and revised in ,./

• 0ormulates the communication process

into structured layers• (here are seven layers in the model1

hence the name the 7-$ayer model

• (he model acts as a frame of referencein the desi'n of communications andnetworin' products

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The a!ered "pproach to

Communication72 #pplication

32 )resentation

42 Session

/2 (ransport

52 6etwor

2 Data $in

,2 )hysical

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Division o# a!ers

8pper $ayers

$ower $ayers

Middle $ayer

72 #pplication

32 )resentation

42 Session

/2 (ransport

52 6etwor

2 Data $in

,2 )hysical

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%ole o# a!ers

72 #pplication

32 )resentation

,2 )hysical

6ode #

Data Out

Data In

(o*from 6ode ;

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Communication Bet&een

a!ers72 #pplication

32 )resentation

42 Session

Data

Encapsulation

DataStrippin'

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The %ole o# a!ers in

'oint(to(pointCommunication

72 #pplication

,2 )hysical

72 #pplication

,2)hysical

6ode a 6ode !

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)irtual Communication

Bet&een a!ers

72 #pplication

52 6etwor

72 #pplication

52 6etwor

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*nd o# Module 1

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Module +

(he ISO 8pper $ayers

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Module Objectives

• #pplication $ayer

• )resentation $ayer

• Session $ayer

• (ransport $ayer

• 6etwor $ayer

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,- "pplication a!er

• )urpose

& 8ser application to networ service

interface

• Examples

& 0ile re

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"pplication a!er $unction

• =eneral networ access

• 0low control

• Error recovery

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.- 'resentation a!er

• )urpose

& 0ormats data for exchan'e !etween

points of communication• Ex: ;etween nodes in a networ

• Example:

& Redirector software• 0ormats for transmission to the server

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'resentation a!er

$unction• )rotocol conversion

• Data translation

• Encryption

• %haracter set conversion

• Expansion of 'raphics command

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%edirector */ample

REDIRE%(OR

0:*)8R*ORDER%:*%ORRES*8SD#

(O SER>ER (O $O%#$DIS?

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0- Session a!er

• )urpose

& Oversee a communication session

• Esta!lish

• Maintain

• (erminate

• Example

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Session a!er $unction

• )erforms name reco'nition andrelated security

• Synchroni+ation !etween senderand receiver

• #ssi'nment of time for transmission

& Start time

& End time etc2

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- Transport a!er

• )urpose

& Repaca'e proper and e@cient

delivery of paca'es• Error free

• In se

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Transport a!er $unction

• 0or sendin' data

& Repaca'e the messa'e to Bt into pacets

• Split lon' messa'es• #ssem!le small messa'es

• On receivin' data

& )erform the reverse

& Send an acnowled'ment to the sender

• Solve pacet pro!lems

& Durin' transmission and reception

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2- 3et&ork a!er

• )urpose

& #ddressin' and routin' the pacets

• Example application at the router

& If the pacet si+e is lar'e1 splits intosmall pacets

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3et&ork a!er $unction

• #ddress messa'es

• #ddress translation from lo'ical to

physical& Ex: n'anesa ----------C ,2,525/424

• Routin' of data

& ;ased on priority& ;est path at the time of transmission

• %on'estion control

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*nd o# Module +

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Module 2

(he ISO $ower $ayers

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+- Data ink a!er

• )urpose

& Mana'es the ow of data over the

physical media

• Responsi!le for error-freetransmission over the physical

media• #ssures error-free data su!mission

to the 6etwor $ayer

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Data ink a!er $unction

• )oint of ori'in

& )aca'es data for transmission over

physical line• Receivin' end

& )aca'es data for su!mission to thenetwor layer

• Deals with networ transmissionprotocols

& IEEE .2 protocols

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Data ink a!er

Subdivision• Improvement to ISO Model

• $o'ical $in %ontrol F$$%G su!-layer

& Mana'es service access points Flo'icallinG

& Error and ow control

• Media #ccess %ontrol FM#%G su!-layer& #pplies directly to networ card

communication

& #ccess control

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ogical ink Control

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Media "ccess Control

"pplication• 6etwor Interface %ard driver

6E(AOR? SO0(A#RE

6E(AOR? %#RD

6I% Driverfacilitates data

transfer

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'h!sical a!er $unction

• Encode !its into si'nals

& %arry data from the h hi'her layers

• DeBne the interface to the card

& Electrical

& Mechanical

& 0unctional

& Example: )in count on the connector

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o&er a!ers "pplication

"reas• Special si'niBcance to networ card

desi'n

• #pplies to 'eneral $#6 hardware desi'n& Exceptions

• Routers etc2

• .2 standards

& %entered around the lower layers

& #pplies to networs

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*nd o# Module 2

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Module

Summary of ISO-OSI0unctional $ayers

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a!er Operations

• #t each layer1 additionalinformation is added to the data

pacet• #n example would !e information

related to the I) protocol that is

added at $ayer 5

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$ormatting o# Data

Through the a!ers

Application Header Presentation HeaderSession Header

Transport HeaderNetwork Header

Data Link Header and Trailer Physical Frame Prea

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'acket 4 5eneral $ormat

Header (railer

Data

# 'eneral concept of pacets serves as a prere

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Some 6eader In#ormation "dded at )arious a!ers

• )acet arrival information

• Receivers address

• Senders address

• Synchroni+ation character

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Data

• #ctual data

• May contain error correction code

& )erformed on individual characters of thedata

& Example: )arity

• Si+e may vary

& Dependin' on the protocol

& Example• .25 speciBes ran'e of data pacet len'th

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Some Trailer In#ormation "dded at )arious a!ers

• Error correction code

& %haracter oriented

& >R% F)arity %hecin'G

• )acet oriented error correctioncodes

& $R%

& %R%

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" 3ote on C%C

• 8sed widely

• Sophisticated

& )olynomial of deferent de'rees areused for error correction

& Example: De'rees ,31 5 etc2

• %R%-5 is a more strin'ent errorchecin' procedure than %R%-,3

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Some o# the MajorComponents o# the Data

'acket

Senders

#ddress

Receivers#ddress

%ontrolData

Data

Error%orrection)rotocol

Start*synchInformation

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Standardi7ing 'acket

$ormatting• )acets must conform to a standard in

order for the nodes in a networ to !e

a!le to communicate with one another• (he International Standards

Or'ani+ation FISOG has provided areference model

• Standards are esta!lished for operationsat each layer of the ISO*OSI model inthe form of protocols

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*nd o# Module

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Module 0

(he IEEE . =roup and theStandards

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I*** Background

• Institution of Electrical andElectronic En'ineers FIEEEG

& # professional non-proBt or'ani+ation

• )ro9ect 'roup .

& Responsi!le for settin' standards

relatin' to the physical lin of thenetwor

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I*** 89+ $ocus

• OSI Reference

& Data $in layer

& )hysical layer• #reas

& 6etwor cards and ca!les

& 6etwor electronic*optical* wireless

communication standard as they apply tothe lower two layers mentioned a!ove

& A#6 connectivity

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:pper a!er $ocus

• IE(0

• A5%

• ISO*IE%

• (he a!ove a'encies focus onsettin' standards on hi'her levelprotocol

& (%)1 I) etc2

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I*** 89+ Committees "nd

%esponsibilities• .2,

& Internetworin'

• .2& $o'ical $in %ontrol F$$%G

• .25

& %SM#*%D• .2/

& (oen ;us $#6

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I*** 89+ Committees and%esponsibilities ;Cont-<

• .24& (oen Rin' $#6

• .23& Metropolitan #rea 6etwor

• .27

& ;road!and (echnical #dvisory =roup• .2.

& 0i!er-Optic (echnical #dvisory =roup

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I*** 89+ ;Cont-<

• .2& Inte'rated >oice*Data 6etwors

• .2,& 6etwor Security

• .2,,& Aireless 6etwors

• .2,& Demand )riority #ccess $#6s

& Ex: ,;ase>=-#ny$#6

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OSI Sub(a!er %e#erence

to I*** 89+ Standards$o'ical$in

%ontrol

F$$%G

Media

#ccess%ontrolFM#%G

.2

.25

.2/

.24

.2,

.2, for!oth2

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*nd o# Module 0

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*3D O$ MOD:**3D O$ MOD:*

*3D O$ C6"'T*%*3D O$ C6"'T*%

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ISO-OSI