Introduction to 7 Layer OSI Model

7/25/2019 Introduction to 7 Layer OSI Model

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7 Layer OSI Model

CS4390


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Network Architecture

How should we o a!out !uildi" the "etworkthat will reali#e our wish$list o% re&uire'e"ts(

)Ma"y re&uire'e"ts* i"cludi" e"eral* relia!le*

secure* e%%icie"t* %air* hih +er%or'a"ce

)Co""ecti,ity a'o" a lare "u'!er o% co'+uters

)-ech"oloy a"d a++licatio" de'a"ds co"sta"tly

cha"i"

)Hardware is heteroe"eous

Need a flexiblearchitecture to 'a"ae this

co'+le.ity/

2


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History

a+id rowth o% co'+uter "etworks caused co'+ati!ility+ro!le's

ISO reco"i#ed the +ro!le' a"d released the OSI 'odel i"

1924

OSI sta"ds %or O+e" Syste's I"terco""ectio" a"d co"sistso% 7 Layers

-he use o% layers is desi"ed to reduce co'+le.ity a"d

'ake sta"dardi#atio" easier Layered structure 'akes a co'+le. syste' easy to

Co"struct* u"dersta"d* a"d 'a"ae


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A!stractio" throuh Layeri"

eco'+ose the +ro!le' o% !uildi" a "etwork i"to'a"aea!le co'+o"e"ts* o"e layer +er +ro!le'/

) ach layer +ro,ides so'e %u"ctio"ality to the layer a!o,e/

Modular desi" +ro,ides %le.i!ility

) Modi%y5re+lace each layer i"de+e"de"tly) Allows alter"ati,e a!stractio"s

4

Request/replychannel Message streamchannel

Application programs

Hardware

Host-to-host connectivity

Application programs

Hardware

Host-to-host connectivity

Process-to-process channels


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-asks $ eli,ery o% a letter


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7 Layers o% the OSI Model

Layer es+o"si!le 6or

7/8 A++licatio" ro,ides Ser,ices to :ser A++s

;/8 rese"tatio" ata e+rese"tatio"


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.a'+les

Layer .a'+le

7/8 A++licatio" H--* 6-* SM-

;/8 rese"tatio" ASCII* ?@* @

/8 ata Li"k ther"et* -oke" i"* 6ra'e elay

1/8 hysical =its* I"ter%aces* Hu!s


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The interaction between layers in the OSI model

router

Ethernet


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Layeri" Co"ce+ts "ca+sulatio"

) ach hihest layer +rotocol creates 'essaes a"d se"ds the'

,ia its lower layer +rotocol/

) -hese 'essaes are treated as data !y the lower le,el

+rotocols

) ach +rotocol adds its ow" co"trol i"%or'atio" i" the %or' o%headers or trailers

Multi+le.i" a"d e$'ulti+le.i"

) :se +rotocol keys B+rotocol "u'!ers8 i" the header to

deter'i"e correct u++er$layer +rotocol

9

header data trailer

Message


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"ca+sulatio"

ata e.ists at each layer co"tai"ed withi" au"it called a rotocol ata :"it B:8/

-he +rocess !y which data 'o,es !etwee": ty+es is called "ca+sulatio"

: 'o,e throuh i"ter%aces !etwee"

layers usi" Ser,ice Access oi"ts BSA8


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An exchange using the OSI model (encapsulation)


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:s A"d the OSI Model

Layer : Na'e

7/8 A++licatio" ata

;/8 rese"tatio" ata


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Layer 1 -he hysical Layer

) hysical characteristics o% i"ter%aces a"d 'ediu'/

) : =its

) e+rese"tatio" o% !its B'a"y di%%ere"t codi"8/) ata rate/

) Sy"chro"i#atio" o% !its/

) Li"e co"%iuratio" B+oi"t$to$+oi"t or 'ulti+oi"t8/

) hysical to+oloy B!us* star* ri"8/

) -ra"s'issio" 'ode si'+le.* hal%5%ull du+le.


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Physical layer

Physical medium:

direct digital signals (e.g., Ethernet, optical fimodulated signals (e.g., WiFi, 3)


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!he physical layer is responsible for mo"ements ofindividual bits from one hop (node) to the next.

Note


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ata lin! layer


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2.

!he data lin# layer is responsible for mo"ing"ramesfrom one hop (node) to the next.

Note


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#op$to$hop delivery "or data lin! layer

Example de"ice:

Ethernet s$itch%hubWiFi access point


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Layer 3 -he Network Layer

: acket

"d to e"d deli,ery o% +ackets

Creates loical +aths

ath deter'i"atio" Brouti"8

Hides the lower layers 'aki" thi"shardware i"de+e"de"t

:ses loical hierarchical addresses


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-he Network Layer Bco"t/8

Loical hierarchical addresses do cha"e

whe" a "ode is 'o,ed to a "ew su!"et

e,ices routers* %irewalls


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Networ! layer


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!he net$or# layer is responsible for the

deli"ery of indi"idual pac#ets from

the source host to the destination host.

Note

!he data lin# layer is responsible for mo"ing"ramesfrom one hop (node) to the next.

!he t$o hosts can be many hops a$ay

&ingle hop deli"ery


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Source$to$destination delivery

Example de"ice:

'outers


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Layer 4 -he -ra"s+ort Layer

: Se'e"t

Ser,ice oi"t Address B'ore o%te" called a +ort8

used to track 'ulti+le sessio"s !etwee" the sa'esyste's/ SAs are used to allow a "ode to o%%er

'ore tha" o"e ser,ice Bi/e/ it could o%%er !oth 'ail

a"d we! ser,ices8

-his layer is why you ha,e to s+eci%y -C or :

whe" deali" with -C5I


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-he -ra"s+ort Layer Bco"t/8

Co""ectio" orie"ted sessio"s re&uire the se"der to

%irst re&uest a co""ectio"* the recei,er to

ack"owlede the co""ectio"* a"d that they"eotiate how 'uch data ca" !e se"t5recei,ed

!e%ore its rece+tio" is ack"owleded

:ses ack"owlede'e"ts D retra"s'issio" %or

error correctio"

.a'+le -C Bused !y thi"s like tel"et* htt+8


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Transport layer


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!he transport layer is responsible for the deli"ery

of a message from oneprocessto another.

Note


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Transport Layer

-ra"s+ort ,s/ "etwork layer

network layer:loical co''u"icatio" !etwee" hosts

transport layer:loical co''u"icatio" !etwee"+rocesses

A

B

C

DSport:4625Dport: 80

Sport:8050Dport: 25


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Layer


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Layer ; -he rese"tatio" Layer

ata %or'atti"* tra"slatio"* e"cry+tio"*

a"d co'+ressio"

. ASCII* =CIC* H-ML* ?@


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Layer 7 -he A++licatio" Layer

ro,ides co''u"icatio" ser,ices to

a++licatio"s

. H--* 6-* SM-


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OSI 'odel ) I Stack

!"

Introduction to 7 Layer OSI Model

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