47639281 Network Fundamentals Chapter 3

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2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1

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Appliction !yer

"unctionlity ndProtocols

Network Fundamentals Chapter 3


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2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Application Layer

#he $pen Systems Interconnection%$SI& re'erence model is lyered,bstrct representtion creted s guideline 'or net(or) protocol design.

#he $SI model divides the net(or)ingprocess into seven logicl lyers, echo' (hich hs uni*ue 'unctionlity ndto (hich re ssigned speci'icservices nd protocols.


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Application Layer

#he Presenttionlyer hs three primry'unctions

Coding nd conversion o' dt.

Compression o' dt.

-ncryption nd decryption o' dt.

Stndrds, used in the ppliction lyer suchs P-/ nd uic)#ime, re not typicllyssocited (ith prticulr protocol stc).

#he Sessionlyer cretes nd mintins

dilogs bet(een source nd destintionpplictions.


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Application Layer#(o 'orms o' so't(re progrms or

processes provide ccess to thenet(or) pplictionsnd services.

Applictionsre the so't(reprogrms used by people tocommunicte over the net(or).

Some pplictions re net(or)(re, they implement the

Appliction lyer protocols ndre ble to communicte directly(ith the lo(er lyers o' the

protocol stc).

Servicesre the progrms thtinter'ce (ith the net(or) ndprepre the dt 'or trns'er.

Applictions or net(or) servicesuses protocolss thestndrds nd dt 'ormts.


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The ClientSer!er model

In the clientser!er model, the device re*uesting thein'ormtion is clled clientnd the device respondingto the re*uest is clled ser!er.


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"eer#to#"eer

In peertopeernet(or), t(o or more computers reconnected vi net(or) nd cn shre resources (ithout dedicted server. -very connected end device %)no(ns peer& cn 'unction s either server or client.


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"eer#to#"eer

A peertopeer ppliction %P2P&, llo(s device to ct sboth client nd server (ithin the sme communiction.

5oth cn initite communiction nd re considered e*ulin the communiction process.

Peertopeer pplictions re*uire tht ech end deviceprovide user inter'ce nd run bc)ground service.



"ort Numbers#he #rnsport lyer uses port numbers to identi'y

pplictions nd services tht re the source nddestintion o' dt, common prede'ined port numbers re

omin 8me System %$NS& #CP9:P Port %3

;yperte


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$omain Name System#he omin 8me

System %8S& uses

hierrchicl system to

crete nme

dtbse to provide

nme resolution.

#he hierrchy loo)s

li)e n inverted tree

(ith the root t the top

nd brnches belo(.



$omain Name SystemA 8S server provides nme

resolution using the nme demon,nmed, %pronounced nmedee&, itstores di''erent types o' resourcerecords (hich contin the nme,ddress, nd type o' record

A n end device ddress8S n uthorittive nme serverC8A-> the "ully uli'iedomin 8me 'or n lis? used(hen multiple services hve thesingle net(or) ddress but ech

service hs its o(n entry in 8S@ mil e



&yperte.t Trans/er "rotocol 0&TT"1hen (eb ddress %or :B!&

is typed into (eb bro(ser, itconnects to the (eb servicerunning on the server using the;##P protocol.

:B!s %:ni'orm Besource!octor& nd :BIs %:ni'ormBesource Identi'ier& re thenmes most people ssocite(ith (eb ddresses tht re'ersto speci'ic resource (ebpge nmed inde



&yperte.t Trans/er "rotocol 0&TT"1

;##P speci'ies re*uest9response protocol. #hree commonmessge types in this protocol re /-#, P$S#, nd P:#.

/-#is client re*uest 'or dt.

P$S#includes the dt %unencrypted& in the messge sent to theserver.

P:#uplods resources or content to the (eb server.

;##P Secure %;##PS& is used 'or secure ccessing or posting o'(eb server in'ormtion, it uses uthentiction nd encryption to

secure dt s it trvels bet(een the client nd server.


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Email-mil re*uires severl pplictions nd services, t(o

ppliction lyer protocols re Post $''ice Protocol%P$P& nd Simple il #rns'er Protocol %S#P&.

An emil client or il :ser Agent %:A& is used tocompose emil messges, it llo(s messges to besent nd plces received messges into the clientsmilbo



EmailP$P nd P$P+ %Post $''ice Protocol,

version +& re inboundmil deliveryclient9server protocols, (hich deliveremil 'rom the emil server to theclient %:A&.

$nce the client connects to the server

the A delivers emil to the client.

#he Simple il #rns'er Protocol%S#P& hndles outboundemil'rom the sending client to the emilserver %A&, nd the trnsport

bet(een emil servers %#A& m)ingemil e



FT"2 $&C"2 and Telnet"ile #rns'er Protocol %"#P& llo(s 'or 'ile

trns'ers bet(een client nd server, n"#P client ppliction runs on computernd is used to push nd pull 'iles 'rom server running the "#P demon %"#Pd&.

#he ynmic ;ost Con'igurtion Protocol

%;CP& service enbles devices on net(or) to obtin IP ddresses, subnetms)s, gte(y nd other IP net(or)ingprmeters 'rom ;CP server.

#elnet, terminl emultion protocol, is used

to provide remote ccess to servers ndnet(or)ing devices.

8et(or)Connection

8et(or)Connection

Physicl

Connection

Bther thn using physicl device to connect to the server ,

#elnet uses so't(re to crete virtul device to provide

terminl session (ith ccess to the server commnd lineinter'ce %C!I&.

A connection using #elnet is clled Dirtul #erminl %D#E& session

Server



Ser!er Messae 4lock#he Server essge 5loc) %S5& is client9server 'ile shring

protocol.

$nce connection is estblished, the user o' the client cn ccessthe resources on the server s i' the resource is locl to the clienthost.

S5 'ileshring nd print services hve become the minsty o'

icroso't net(or)ing, (hich uses 8S nming, llo(ing #CP9IPprotocols to directly support S5 resource shring


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47639281 Network Fundamentals Chapter 3

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