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COMPUTER NETWORKS
INTRODUCTION
Shanika Ekanayake
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Aim and objective of the lecture
Aim
To develop an understanding of the odern net!or"te#hnologies in #oon use toda$
Objective
To %e a%le to deonstrate an understanding of the iportan#eof #ouni#ation standards& in#luding an appre#iation of
proto#ol la$er odels and enhan#eents to those standards
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Introdu#tion
'i and o%(e#tive of the le#ture Models of net!or" ar#hite#ture ISO ) ISO Model
The ISO ) ISO Model What is ISO ) ISO odel What is ISO ) ISO odel
Inforation e*#hange using the OSI odel ISO+OSI Seven ,a$ers
Ph$si#al ,a$er Data ,in" ,a$er Net!or" ,a$er Transport ,a$er
Session ,a$er Presentation ,a$er 'ppli#ation ,a$er
Introdu#tion to TCP-IP odel The TCP-IP Model TCP-IP Model
Suar$
Introduction to the Lecture Slide
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Models of network architecture
Network
' #on#eptual frae!or" that des#ri%es ho! data andnet!or" inforation are #ouni#ated fro an appli#ationon one #oputer through net!or" edia to an appli#ationon other #oputers in ters of di.erent la$ers/
Net!or" ar#hite#ture is a design of a #ouni#ationsnet!or" and also "no!n as a Referen#e odel/
T!o t$pes of Referen#e odels &
Open Referen#e odels ) 'r#hite#ture is pu%li#all$availa%le 0e/g/ OSI odel 1
Closed Referen#e odels 0proprietar$ s$stes1 )
'r#hite#ture is un"no!n 0e/g/ I2M3s SN' 4 la$er odel1
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ISO ) International Organi5ation for Standardi5ation/
OSI ) Open S$stes Inter#onne#tion/
ISO is esta%lished in 6784 and it is a ultinational %od$
dedi#ated to !orld!ide agreeent on internationalstandards/
ISO standard that #overs all aspe#ts of net!or"#ouni#ations is the OSI odel !hi#h introdu#ed in late
6749s/
Note ISO + organi5ation/ OSI + odel/
The ISO OSI Model
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!hat is ISO OSI model""# De:nes data
#ouni#ation fun#tionsusing 4 la$ers !hi#h areorgani5ed in the se;uentialorder of events o##urringduring a #ouni#ationssession/
Top < la$ers + =o!appli#ations !ithin endstations #ouni#ate ea#hother and also !ith users/
2otto 8 la$ers + End toend data transission/
M$ths a%out ISO OSI odel& The OSI Model is not a
te#hnolog$/ The OSI Model is not a proto#ol/
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Information e$chan%e usin% the OSI
model
Proto#ol Data Unit0PDU1 + Inforation delivered as a unit aongpeer entities of net!or"s #ontaining #ontrol inforation and user
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!hy ISO OSI model""#
Advanta%es of ISO OSI model
Interopera%ilit$ %et!een devi#es fro variousvendors/
=igh aintaina%ilit$/
Cost redu#tion/
'ssists in proto#ol design& %e#ause proto#ols thatoperate at a spe#i:# la$er have de:ned
inforation and interfa#es/
'n edu#ational tool + ISO-OSI odel not (uste*plains the operation of the OSI proto#ols& ite*plains net!or"ing in general ters/
Prevents te#hnolog$ or #apa%ilit$ #hanges in one
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,a$er 6 of the OSI odel/
Responsi%le for the oveent of individual %its froone node 0hop1 to the ne*t/
&hysicalLayer
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&hysicalLayer 'ont"(o)*to*(o)+elivery
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&hysicalLayer 'ont"
Ph$si#al la$er de:nes standards for DTE+DCEinterfa#e !/r/t/
Me#hani#al Spe#i:#ations
Ele#tri#al Spe#i:#ations >un#tional Spe#i:#ations
Pro#edural Spe#i:#ations
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&hysicalLayer 'ont"
Mechanical Specifcations
Shape of the #onne#tor/
Nu%er of pins/
Diaeter of a pin/
Distan#e %et!een t!o pins Et#/
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&hysicalLayer 'ont"
Electrical Specifcations
Use ?oltage levels/
E/g/@ A6B + ?A9B + 9 ?
DTE and DCE should use sae ele#tri#al signallevels
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&hysical Layer 'ont"
Procedural Specifcations
Pro#edure 0or steps1 of #ouni#ation %et!een DTE
and DCE/
E/g/@ DTE re;uests fro DCE to send data 0DTEa#tivates RTS pin1DCE sa$s OK 0DCE a#tivates CTS pin1
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&hysical Layer 'ont"
Standard bodies o Physical Layer Specifcations
EI' ) Ele#troni# Industries 'llian#e/
ITU+T)International Tele#ouni#ation UnionTele#ouni#ation Standardi5ation Se#tor/
'NSI ) 'eri#an National Standards Institute /
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+ataLinkLayer
,a$er of the OSI odel/ Responsi%le for oving fraes fro one node 0hop1
to the ne*t/
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Data Link Layer Frame (E! Ethernet rame"
Ethernet frae is one of the ost !idel$ used fraeat the data lin" la$er/
+ataLinkLayer 'ont"
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+ata Link Layer 'ont"
(o)*to*(o)+elivery
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+ataLink Layer 'ont"
Data Link Layer Functionalities
Iportant fun#tionalities to guarantee thesu##essful transission of fraes fro one hop tothe ne*t/
>raing ) We have alread$ dis#ussed this/
Ph$si#al addressing/
>lo! #ontrol/
Error #ontrol/
'##ess #ontrol/
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+ataLinkLayer 'ont"
Sub#layers
Contains t!o su%+la$ers
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+ata Link Layer 'ont"
Physical $ddressin!
Ea#h devi#e is universall$uni;uel$ identi:ed %$ theph$si#al address 0M'C
address1/
8G %its long/
8G %its H 8G total addresses
HG6&848&74&469&
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+ata Link Layer 'ont"Flow %ontrol
Spe#i:es ho! u#h data the Sender #an transit%efore re#eiving perission to #ontinue fro theRe#eiver/
The Re#eiver !ill %e for#ed to drop the pa#"ets
!hen the sender transits faster than theRe#eiver #an pro#ess the/
Solution@
Signal the Sender to slo! do!n to a ratea##epta%le to the Re#eiver/
This signal #an %e e*pli#it or ipli#it
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+ata Link Layer 'ont"Flow %ontrol
Methods
Stop+and+WaitJo!#ontrol
Sliding!indo!Jo!#ontrol
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+ata Link Layer 'ont"Error %ontrol
'llo!s the Re#eiver to tell the Sender a%out fraesdaaged or lost during transission& and #oordinatesthe re+transission of those fraes %$ the Sender/
Sin#e Jo! #ontrol provides the Re#eiverBsa#"no!ledgeent 0'CK1 of #orre#tl$+re#eivedfraes& it is #losel$ lin"ed to error #ontrol/
2asi# idea of error #ontrol
'CK ever$ #orre#tl$+re#eived frae and negativel$a#"no!ledge 0N'CK1 ea#h in#orre#tl$+re#eivedfrae/
Sender "eeps #opies of un+'CKed >raes to re+
transit if re;uired/
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+ata Link Layer 'ont"&wo steps o Error %ontrol
Error Detection
Me#hanis of dete#ting errors in fraes&
Parit$ #he#" 0Odd parit$& Even parit$1 CRC ) #oon et#/
Error %orrection
'utoati# Repeat reuest 0'R1 is use to #orre#t errors/
'R retransits fraes in three #ases&
Daaged fraes ,ost fraes ,ost a#"no!ledgeents
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+ata Link Layer 'ont"
$ccess %ontrol
When ore than a single #oputer is #onne#ted to the saelin"& !ho gets the turn to transit data and ho! to a#;uire thisturn/
The ost popular edia a##ess #ontrol e#hanis is CSM'-CDand it is ipleented in the Media '##ess Control su%+la$er ofthe Data ,in" ,a$er/
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,etworkLayer
,a$er < of the OSI ode/
The net!or" la$er is responsi%le for the deliver$ ofindividual pa#"ets fro the sour#e host to thedestination host/
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,etworkLayer
Source
to
+estination
+elivery
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,etworkLayer'ont"
T!o a(or fun#tionalities&
'outin!
Independent lo#al net!or"s are inter#onne#ted !ith ea#hother& therefore need a e#hanis to route the pa#"ets
fro one net!or" to another/
Lo!ical addressin!
To route a pa#"et %e$ond the %oundar$ of a lo#alnet!or"0 i/e/ to a di.erent lo#al net!or"1 ph$si#al address
alone is not enough/
Net!or" la$er eplo$s address t$pe #all logi#aladdresses to #ouni#ate aong net!or"s+IP addresses/
The logi#al addresses are in#luded in the net!or" la$er
header/
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Trans)ort Layer
,a$er 8 of the OSI odel/
The transport la$er is responsi%le for the deliver$ of aessage fro one pro#ess to another/
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Trans)ort Layer 'ont"
Process to Process Deliery
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Trans)ort Layer'ont"
Transport la$er eplo$s several iportant fun#tionalities&
Servi#e+point addressing
Segentation and reasse%l$
Conne#tion #ontrol
>lo! #ontrol
Error #ontrol
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Trans)ort Layer 'ont"
Serice#point $ddressin! Process(Port addressin!"
To transfer a essage fro a sour#e pro#ess 0i/e/ the sour#eappli#ation1 to a destination pro#ess 0i/e/ the destinationappli#ation1 HL need a e#hanis to uni;uel$ identif$ ea#hpro#ess/
'ssigned a uni;ue nu%er !hi#h is #oonl$ "no!n as the portnu%er/
Port nu%er is a 6 %it integer nu%er and #an range fro 9 toile Transfer Proto#ol 0>TP1
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Trans)ort Layer 'ont"
Se!mentation and 'eassembly
The data passed to the transport la$er fro the la$er a%ove0i/e/ session la$er1 is too large to transfer at on#e/
Therefore& transport la$er %rea"s the data into sall #hun"s"no!n as segents %efore passing to the net!or" la$er/
't the re#eiver& the segents need to %e reasse%led to getthe full essage %efore passing to the upper la$er 0i/e/
session la$er1 at the re#eiver/
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Trans)ort Layer 'ont"
To ea#h segent a transport la$er header is added/
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Trans)ort Layer 'ont"Transport la$er #an operate in t!o odes&
%onnection oriented
>irst a #onne#tion is esta%lished %et!een the sour#e andthe destination pro#esses/
'll segents are transported using this #onne#tion/
On#e the transport of segents is #oplete& the#onne#tion is terinated/
uarantees the deliver$ of segents/ To fa#ilitate this ode& transport la$er uses Transport
Control Proto#ol 0TCP1/
%onnectionless
Ea#h segent is treated as a single pa#"et and delivered tothe destination pro#ess !ithout an$ #onne#tions/
No guarantee on the deliver$ of the segents/ To fa#ilitate this ode& transport la$er uses User Datagra
Proto#ol 0UDP1/
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Trans)ort Layer 'ont"
Sae as the Data ,in" ,a$er& the Transport ,a$er also e;uipsJo! #ontrol and error #ontrol of segents/
The a(or di.eren#e in the t!o la$ers !/r/t Jo! and error
#ontrol is that&
Data ,in" ,a$er is #on#erned a%out the hop+to+hop Jo! anderror #ontrol %et!een t!o ad(a#ent hops/
Transport ,a$er is #on#erned a%out the end+to+end Jo! anderror #ontrol %et!een the sour#e and the destination 0!hi#h #an%e several hops apart fro ea#h other1/
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SessionLayer
,a$er of the OSI odel/
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SessionLayer'ont"Session ,a$er perfors t!o a(or fun#tionalities&
Dialo! %ontrol
'llo!s the t!o #ouni#ating pro#esses to enter into adialog 0i/e/ a t!o !a$ #ouni#ation1/
This dialog #an %e either half duple* or full duple*/ Therefore& session la$er is a dialog #ontroller/ Coon session+la$er servi#es in appli#ation
environents use reote pro#edure #alls 0RPCs1/
Synchroni)ation
Session la$er adds #he#"points in %et!een the long datastrea passed %$ the la$er a%ove 0i/e/ presentationla$er1/
These #he#"points adds an additional level of veri:#ationof the re#eived data for the re#eiver/
It allo!s inforation of di.erent streas& perhaps
originating fro di.erent sour#es& to %e properl$#o%ined or s$n#hroni5ed/
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&resentationLayer
,a$er of the OSI odel/
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&resentationLayer'ont"There are three a(or fun#tions perfored %$ the Presentation
,a$er&
&ranslation Sender and Re#eiver a$ %e using t!o di.erent
forats to represent data 0e/g/ 'SCII vs/ UNICODE1/ Translation is the pro#ess of #onverting data&
>ro sender+dependent forat to a #oonforat at the sender/
>ro #oon forat to the re#eiver+dependentforat at the re#eiver/
Encryption To prevent unauthori5ed people fro vie!ing the
data/
%ompression To redu#e the nu%er of %its to %e transitted/ Iportant !hen sending ultiedia #ontent su#h as
audio and video/
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,a$er 4 of the OSI odel/
A))lication Layer
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A))licationLayercont"
'ppli#ation la$er is user interfa#e to the net!or"/
Provides an$ useful appli#ations to fa#ilitate our da$+to+da$ tas"s&
Eail servi#es/ >ile transferring/ Reote terinal/ et#/
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E*ample Scenario+ %onnection to a website ia a ,i#fconnection
(-"Ph$si#al la$er + Wi+>i #ard of the #oputer !hi#h transitsdata using the IEEE G9/66n standard/
(."Data lin" la$er + Conne#ting to a router via D=CP/
(/"Net!or" la$er + D=CP provides an IP address to the s$ste/
(0"Transport la$er + On#e the #oputer o%tains an IP address& it#an #onne#t to the Internet via the TCP proto#ol/
(1"Session la$er + The s$ste a$ then esta%lish a Net!or"2asi# Input-Output S$ste0Net2IOS1 session/
(2"Presentation la$er+ If a se#ure #onne#tion is esta%lishedonne#tion a$ involve an SS, #onne#tion/
>inall$& (3"'ppli#ation la$er + Consists of the =TTP #onne#tionto the !e%site/
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,etworks fits to ISO-OSI layered
architecture
Mo%ileNet!or"
G9/66 !irelessNet!or"
'TM Net!or"
>rae Rela$Net!or"
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The T'&-I& Model TCP-IP 0 Transission Control Proto#ol-Internet Proto#ol1 is a
proto#ol !hi#h developed using the Departent of Defense0DoD1 referen#e odel to de:ne a large #olle#tion of proto#olsthat allo! #oputers to #ouni#ate/
It has a 8 la$er ar#hite#ture/
TCP- IP de:nes ea#h of these proto#ols inside do#uent #alledRe;uests >or Coents 0R>Cs1/
2$ ipleenting the re;uired proto#ols in TCP-IP R>Cs& a#oputer #an %e relativel$ #on:dent that it #an #ouni#ate
!ith other #oputers that also ipleent TCP-IP/
The TCP-IP proto#ol suite !as developed %efore the OSI odel!as pu%lished/ 's a result& it does not use the OSI odel as areferen#e/
It is iportant to %e failiar !ith the OSI odel& though&%e#ause OSI is used to #opare the TCP-IP Suite !ith other
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T'&-I&Model
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Summary
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Summaryof the ISO OSI Layers
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,ames used for +ata at each layer
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Addresses used at different layers
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'onnectionsused at different layers
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&rotocolsused at each layer
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OSILayersin O)erations
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Thank .ou